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A Systematic Study of Wave Phasing on Righting Arm Curves for Fishing Vessels - Paper #D15 - 07-11-05 John Womack, Member, Mid-Atlantic Shipwrights Bruce Johnson, Fellow, U. S. Naval Academy

ABSTRACT This paper summarizes the results from the SNAME funded T&R grant titled Preliminary Development of the Next Generation of Stability Criteria for Small Fishing Boats. The principal goal of this project was to take a broad look at effects of head and following waves on the current still water based stability evaluation methods to focus the needs for future research in the development of new performance based stability criteria. The wave effects were calculated using an off the shelf naval architect software package of the type typically used in small fishing vessel stability evaluations to explore the ability of these software packages to perform cost effective meaningful stability research. The use of the off the shelf naval architect software package also allowed the authors to explore new performance based stability criteria formats that utilized software and basic concepts already available to the naval architect.

NOMENCLATURE (ITTC symbols when applicable including computer compatible symbols for graphics) AM - Amidships AP - After Perpendicular cG – Wave Group velocity or celerity cW – Wave Phase velocity or celerity FP - Forward Perpendicular GHS – General Hydrostatics Program GM – Metacentric Height HW, HW – Wave height KG - Center of Gravity Above Baseline LPP - Length Between Perpendiculars λ, Lw, LW - Wave Length LWL – Waterline Length of vessel TW – Basic wave period US - United States USCG - United States Coast Guard Vs – Speed of vessel (ship) WC – Wave Crest (graphs) WT - Watertight, Wave Trough (graphs)

σ - Wave Encounter Angle - Relative to the Bow λM – Linear Scale of ship model INTRODUCTION AND PROJECT GOALS This SNAME T&R supported project was developed to achieve the following goals. 1. Investigate the relative effects of head/following seas on the

intact righting arm curve evaluated at various ratios of wave length to ship length, wave steepness and position on the wave. Discuss the significance of the results on current still water based stability evaluation criteria methods.

2. Investigate the relative effect on the area under the righting arm curve up to watertight openings which are not evaluated in current stability criteria.

With the recent availability of affordable software packages that have been developed for the efficient analysis of the static stability of small working vessels operating in various regular wave conditions, these goals are now readily obtainable. From the results that were obtained from these goals, it is also now time to consider proposing affordable new fishing vessel stability evaluation methods and criteria. To do so will require considerable additional research and development efforts, but this can be divided into short and long term goals to speed up this process and introduce the needed safety benefits as soon as is practical. The short term goals of such an effort should be to explore ways to improve on the current static stillwater righting arm curve approach. The basic goals are two fold. One; provide some level of capsizing risks as opposed to the current strictly pass/fail approach. And two; take into account a vessel’s unique characteristics, operating conditions, and stability “Achilles Heels” such as downflooding through watertight openings and large enclosed deck house spaces. The long term goals are to develop prediction methods for a vessel’s response to given sea conditions to allow the; - Determination of the maximum expected roll/pitch/etc.

This is useful for both vessel survivability and crew working safety.

- Determination of the risk of capsize from broaching, breaking waves, and other similar capsize events.

- Determination of the likelihood of boarding seas on decks, pilothouse, etc.

- Determination of the likelihood of watertight openings being submerged and the risks from any resulting potential internal flooding

The process required to achieve the short and long term goals will be a multifaceted project using the following four principal investigation techniques. - Analytical investigations using existing naval architecture

software packages. This would principally be for short

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term improvements to the current static still-water righting arm curve stability evaluation methods.

- Theoretical research using advanced computational fluid dynamics (CFD) methods. (Beck and Reed 2001)

- Model tests to confirm theoretical research and to develop data when theoretical methods will not work or are impractical.

- Realistic experimentation by outfitting research vessels with motion and sea state monitoring systems such as Ship Motion Control’s SMCFish and Ocean Wave’s WaMos II. This is also to confirm theoretical research and to develop data when theoretical methods will not work or are impractical.

BACKGROUND AND STATE OF THE ART Model Tests and Analysis of Vessel Stability in Following and Quartering Waves The effect of the seaway on vessel stability has been researched for many years, albeit with limited computational tools until recently. Paulling (1961) and Du Cane (1962) review the history at their time of writing of attempts to analyze the effects of ahead and following seas on the overall stability of various classes of vessels. In the pre-personal computer age, Kempf (1938), Graff (1941), Grim (1952) and Wendel (1954) performed experimental investigations in Germany on the subject. The first systematic look at the “Transverse Stability of a Ship in a Longitudinal Seaway” was done by Paulling (1961). He used a DTMB Series 60 parent with three beams and three freeboards of ± 25% to the parent hull which was towed at a fixed angle of heel in various overtaking constant steepness waves. At this wave steepness, little change in inclined GZ with wavelength was noted for the parent hull form, so the standard wavelength equal waterline ship length in λ/20 waves was used for the rest of the tests. (It is possible that λ/20 waves represented the practical steepness limit for nearly sinusoidal wave generation using wavemakers installed before the mid 70s. That was the case at the Naval Academy before the powerful, low harmonic distortion hydraulic wavemakers were installed in 1975 in the new Hydromechanics Lab.) Paulling performed a number of model experiments in following seas and experimentally measured the righting moment at various heel angles. The model was fixed at various heel angles and allowed to heave but was not free to surge. His results confirmed that “relatively narrow, high freeboard vessels suffer substantially smaller stability changes in a seaway.” However, beamy, low freeboard vessels suffer dramatic reductions in their righting arm curves when “perched on a wave”. The concluding statement from Paulling (1961) is "The effect of the seaway should be taken into consideration in judging the stability of vessels, particularly those of large beam-to-draft and low freeboard-to-beam ratios, if a more concise representation of the vessel's ultimate performance at sea is to be obtained."

The systematic model tests on the series 60 hull form followed Paulling’s “Transverse Stability of Tuna Clippers” (Paulling 1960) in which he confirmed that for vessels with high freeboard and watertight buoyancy forward and low freeboard and watertight buoyancy aft (as is the case for many types of working vessels) “the basic assumption of the usual cross-curve computation, i.e. no heel induced trim, is violated and the results so calculated will not accurately represent the actual behavior of the vessel.” This comment is true for many types of fishing vessels “which exhibit a strong tendency to trim by the stern at angles of heel greater than that at which the deck edge is submerged.” Thus Paulling concluded that “the initial metacentric height is even less valid as a criterion of stability than in the case of most other vessel types.” Paulling (1960) also stated the following with reference to using static ship-wave orientation: “Preliminary tests showed that the measured righting moments are independent of model speed for a range of zero speed up to a model speed equal to the wave speed. From the agreement between computed and measured values, it is therefore concluded that the assumption of static equilibrium and hydrostatic pressure distribution leads to results which are of acceptable accuracy in representing the following sea situation. Since the most dangerous situation occurs when a wave crest is amidships (in that investigation) Paulling also concluded that “it may be possible to serve the needs of the fishing method by keeping freeboard to a minimum aft and, at the same time, materially improve the seagoing stability of the vessel by raising the freeboard amidships.” Du Cane and Goodrich (1962) examined the broaching problem, including loss of stability on waves using a free to surge sub-carriage arrangement. A major focus is on directional stability and the ratio of ship speed to wave speed has a large influence on whether or not the wave can accelerate a slower moving vessel up to or slightly more that the wave speed. To quote from the paper “The instability of surge velocity at what has been called the critical wave speed (Vs/ cW > 0.7) can result in a very large change in speed due to a slight increase in wavelength. The most interesting fact illustrated by these experiments was the large range of wavelengths over which the model was carried along at the wave crest speed.” One of the discussers (H. Lackenby) of the paper pointed out that the critical wave speed is probably a function of the wave height (held constant during these experiments) and slope. The authors also did not discuss the influence of vessel inertia on the critical wave slope for the surge acceleration to take place. Later investigations on capsizing in following and quartering seas determined that breaking waves can accelerate the vessel quickly to the crest velocity, especially in the light loaded condition with a critical vessel speed as low as 0.5 of the wave speed (Grochowalski, 1989). These investigations also showed that accelerating to a surf-riding situation is important to both pure loss of stability on a wave and broaching when a breaking wave impacts the vessel in a quartering condition.

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Using the development of hydrostatic software for personal computers, Storch (1978a and b) analyzed crab vessel losses including loss of stability on waves properly corrected for heel and trim. He analyzed 13 specific vessels for waves of λ/LWL = 1, height equal to 1.1 √LWL and crest at amidships. Although this condition was considered by many a worst case scenario at the time, it is not the most dangerous or common scenario for small working vessels encountering gales of significant wave height considerably greater than 1.1√LWL, corresponding periods much longer than √LWL*2π/g and wave celerities, cW =λ/T much greater than √LWL*g/2π, the criteria used by Storch. The loss of the 57 m stern trawler Gaul with all 36 crew in very heavy seas north of Norway in February, 1974 spurred a number of investigations which continue to the present. The first of these was published by Morrall in 1980. The investigation included an evaluation of the variation in righting arms in waves equal to the vessel length and wave height equal to LS / 20 (2.85m) with the crest at the FP and AP, 0.25LS from the AP, crest at amidships and crest at 0.25 LS from the FP. The effect of the wave position on the righting arm curve was typical for a “shelter deck” vessel as described later in this paper. The unfortunate use of the LS / 20 rule of thumb was quite inappropriate for the estimated significant wave height of 6.7 m and estimated significant wave period of over 11 seconds. The reported heavy seas could have easily included wave groups of around 11 m high approximately 1 percent of the time. (Kriebel, 1993, Dawson, 1996, 2002). One of the discussers (Gilfillan) gave an example of comparing the results of LS / 20 waves with LS / 7 breaking waves and mentioned that 1.2 LS / 7 waves were even more dramatic in their effect on righting arms. The intact stability of towing and fishing vessels was the subject of a major set of model experiments at Hydronautics in the mid 70s (Amy, Johnson and Miller 1976). These tests involved both free running and towed tests. “In all the free-running tests in following seas, capsizings and extreme rolling were due to either a complete loss of stability with the model poised on the wave crest or to rolling at a period equal to twice the wave encounter period. In no case did the model capsize in stern waves while running free at a low speed–length ratio. It was necessary to have waves which were long enough ( λ/LWL = 1.5) and a high enough model speed (speed/length ratio of approx. 1 corresponding to Fn = 0.3) for the model to surf for some time with the crest amidships. No models capsized by broaching.” Corrections to the vessel righting arm curves for the tugboat

perched on a wave were calculated but the wave conditions were not given. The multiple capsizes during the Fastnet Yacht Race in 1979 brought increased interest in capsize studies and the development of capability to generate large breaking waves in a towing tank for beam sea testing. (Hirayama and Takezawa 1982, Salsich, et al, 1983, Zseleczki, 1988, 1989). Various modes of capsize were discussed by many authors at the Stability 82 conference in Japan including a good summary by Takaishi (1982). Many of the following sea model tests at that time were still towed by a carriage in which surfing is not allowed by the towing rig (Hamamoto and Nomoto 1982). This enables direct measurement of corrections to the righting arm curve at various fixed angles of heel while the model travels at the wave phase velocity (as was done previously by Paulling). However, several self-propelled tests which allowed the free to surge condition were reported. Blume and Hattendorff (1982) reported their initial results of an extensive investigation on the intact stability of free running fast cargo liners in both regular (λ/LWL = 1) and irregular waves. They investigated the effect of Froude Number, initial heel angle, and position on the wave for the λ/LWL = 1 case. Rennilson (1982) reported on his investigation the likelihood of broaching to in following seas with 1 < λ/LWL < 2. His suggested guidelines for avoiding a broaching situation include the following comments “The predominant wave length must be of the order of the ship length or greater, with the wave amplitude the order of the ship draft or greater…Since the critical wave lengths are dependent on the ship length, shorter ships will encounter more severe conditions and, hence, are more likely to broach.” An extensive series of intact stability model tests was performed at the SSPA model tank during the 1980s (Grochowalski, 1989, 1990, 1993, 1994). The fishing vessel used for these tests was based on a 1/14 model of a typical small Canadian, hard-chine stern trawler of 19.8 m length. The model was self-propelled and was tested at three different model speeds in following and quartering seas using four loading conditions, two of which met the IMO criteria and two which did not. Six breaking (spilling) regular wave conditions at H/λ = 1/7 and two irregular wave conditions with numerous breaking waves were used for the testing. The regular wave conditions are summarized in Table 1 (Table 4 from Johnson and Grochowalski 2002). .

Table 1. Regular Wave Conditions for Scale Ratio of 14 Ratio of Vessel Speed to Wave Celerity

Regular Wave Wave Wave Wave Wave Wave Vessel Speed Wave Height Period Length λ/LWL Steep. Celerity Celerity 5.1 8.0 10.2

# m Sec m m/sec Knots Knots Knots Knots #1 2.52 3.37 17.7 .95 0.142 5.26 10.2 0.50 0.78 1.00 #2 3.78 4.12 26.4 1.42 0.143 6.43 12.5 0.41 0.64 0.81 #3 5.32 4.86 36.9 1.99 0.144 7.59 14.8 0.34 0.54 0.69 #4 6.16 5.24 42.8 2.30 0.144 8.16 15.9 0.32 0.50 0.64 #5 7.00 5.61 49.2 2.65 0.142 8.76 17.0 0.30 0.47 0.60 #6 9.10 6.36 63.2 3.40 0.144 9.93 19.3 0.26 0.41 0.53

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No capsizes occurred in wave #1 with a λ/LWL = 0.95, even for model conditions which were below IMO minimums. The model conditions not meeting the IMO criteria generally capsized in 1.42 <= λ/LWL <= 3.4. A significant result occurred while testing the light displacement (port departure) model IA (which satisfied the IMO criteria) in #6 waves of 9m full scale wave height which can occur 1% of the time in 6m significant wave height. While traveling at 8 knots full scale in quartering waves (corresponding to 41% of the linear wave celerity), the model did not capsize in a wave group, but at 10.2 knots full scale (corresponding the 53% of the linear wave celerity), it experienced some breaking wave-riding and capsized on the passage of the second wave. The model condition IIB with an extended range of stability did not capsize in any of the wave conditions. A comprehensive table of the capsize conditions and reasons for capsize is included in Grochowalski 1994. In the response to the discussion of that paper, Grochowalski pointed out that when the energy of extreme wave impact contributes significantly to accelerating the ship, it may stay in the breaking portion for some time, which is not really surf-riding and requires further studies. Note that this condition cannot be analyzed correctly by assuming trochoidal waves acting to reduce the hydrostatic GZ curves for “perched on a wave” By the time of the 1990 STAB conference, many investigations of the effect of waves on transverse stability and surf-riding were reported. Kan (1990) extended Rennilson’s guidelines to avoid surf-riding study from 0.5 < λ/LWL < 3 and determined theoretical critical wave heights as a function of Froude number and thus estimated critical speed for a 124T Stern Trawler as in his Figures 15 and 16. (From Kan 1990)

Figure 1. Fig. 15 from Kan (1990) (Note that the labels “critical wave height” are actually “critical wave steepness”.) Umeda (1990) used Kan’s surf-riding results as data points in a theoretical probabilistic study in irregular following seas. He suggested “that it is possible to escape from surf-riding by lowering propeller RPM when the regular wave steepness H/λ is 1/20 or less, but is not possible to escape when H/λ is 1/10. The criteria are more complex in irregular waves and once a vessel is

captured by a large wave it cannot escape by reducing propeller RPM.”

Figure 2. Fig. 16 from Kan (1990) Blume (1990) tested in irregular waves two extreme models designed to experience small and large variations in righting levers in waves. The loss of righting lever on a wave crest with λ/LWL = 1 and H/λ = 1/15 was calculated for each model. Blume concluded that “stability parameters derived from righting levers on a crest itselves are not suitable for a fair judgment of the safety against capsizing. The hydrostatically calculated values do not reflect the physical phenomena. Stability parameters derived from these curves therefore also can be seen only as comparative values which are not necessarily better than those derived from the calm water righting lever curves.” It should be noted that λ/LWL based on the peak period of the irregular wave spectrum was about 2 rather than 1 used to calculate the righting lever on a crest. At the 1994 STAB conference, Kan, Saruta and Taguchi, (1994) extended Blume’s comparative model tests on capsizing of container ships in following and quartering seas with somewhat smaller models. The only correction to the GZ curve for riding on a crest was again for λ/LWL = 1 and H/λ = 1/15. The regular waves used for the testing ran from 0.5 < λ/LWL < 2.25 with H/λ = 1/20, 1/15, 1/12 and 1/10. The longer wave tests λ/LWL > 1.5 were run only at H/λ=1/20 and naturally fewer capsizes occurred. The irregular wave tests were run at a peak period which gave λp/LWL = 2. Capsizing vanished in the irregular waves at FN <= 0.26. The following quotes from Kan (1994) bear repeating, “It has been said that the most dangerous wave length is λ/LWL = 1. However, it is obvious from these tables that many capsizings were observed in longer waves such as λ/LWL = 1.25 to 1.75” (Note: beyond which the steepness decreased to 1/20 in these tests.) “Therefore, we should recognize that the most dangerous wave length is not restricted to λ/LWL = 1…..”

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In their Risk Analysis applied to Capsize of Fishing Vessels, Dahle and Myrhaug 1995 assumed pure loss of stability only occurs at λ/LWL = 1 and when Vs equals the wave celerity. This constraint reduced the probability of capsizing from pure loss of stability to near zero for the cases considered. On the other hand, Umeda, et al in 1999 carried out free running model experiments in extremely steep regular waves and concluded that capsizing is caused by broaching, loss of stability on a wave crest, or bow diving. Also that a ship capsizes in following and quartering seas more easily than in beam seas. (Previously shown by Grochowalski, 1989). Based on some previous suggestions by Takaishi (1982) that capsizing due to regular excitation is more dangerous than that due to random excitation, Umeda proposes to carry out capsizing model experiments in extremely steep regular waves. “If the model does not capsize, we can presume that the possibility of capsizing from this ship in any irregular waves is negligibly small. Because of wave breaking, the measured wave steepness can be smaller than 1/7 but should be larger than 1/10. The wave length to ship length ratio, λ/LWL , is set at about 1.5, because ship motions become significant in this wave condition.” At the STAB 2000 Conference, Rahim and Khondoker (2000) report on their investigation of the effects of the presence of waves on the stability of 6 inland passenger vessels by showing the variation in GZ correction for 16 equally spaced positions along the hull. “To conform to the “Strathclyde Method”, the length of the wave is taken equal to that of the vessel.” However, it is uncertain what wave steepness was used in the investigation. Thus, in the stability literature, there appears to be no universal agreement on what wave conditions constitute the most dangerous situations. Comments on Existing Intact Stability Criteria The intact stability criteria currently used in the United States for fishing vessels (Cleary 1993, IMO 1995, CFR 46.28 Subpart E), harkens back to the days of the paper drawings, the slide rule, the planimeter, and for those high end shops, an integrator. All of the criteria are based on the static still-water righting arm curve. A typical intact stability criteria would be; - A minimum GM value of at least 0.35m (1.15 ft). - The maximum righting arm occurs at a heel angle of at

least 25 degrees. - A righting arm of at least 0.20m (0.66 ft) at a heel angle of

not less than 30 degrees. - An area under the RA curve of at least 3.15 m-deg (10.3

ft-deg) up to a heel angle of 30 degrees. - An area under the RA curve of at least 5.16 m-deg (16.9

ft-deg) up to the lesser of a heel angle of 40 degrees or the angle of downflooding.

- An area under the RA curve of at least 1.72 m-deg (5.6 ft-deg) from 30 degrees of heel up to the lesser of a heel angle of 40 degrees or the angle of downflooding.

- A minimum range of positive righting arms of at least 60 degrees.

These are purely static criteria based on the original stability criteria developed by Dr. Rahola in his 1939 PhD thesis “The Judging of the Stability of Ships and The Determination of the Minimum Amount of Stability Especially Considering the Vessels Navigating Finnish Waters” (Rahola 1939, Cleary 1993, Johnson and Womack 2001). While ground breaking in its time, two fundamental problems remain using this approach. The first is that the current design of US fishing vessels has deviated significantly from the characteristics of the one fishing vessel used in Dr. Rahola’s analysis. (Womack 2002) Freeboards have become lower, beams have widen, watertight openings have been lowered and moved outboard, and capsizing forces have increased from larger nets and more powerful engines since the 1930’s. When at sea, a fishing vessel is operating in a highly dynamic environment; and the smaller the vessel the higher the dynamic impacts are for a given sea condition. (Johnson and Grochowalski 2002) Attempts have been made to reflect the realistic dynamics in criteria such as the IMO or USCG’s Severe Wind and Roll Criteria. The problem is these criteria are still based on the static still-water RA curve and are applicable only for beam seas and winds. From model tests carried out at the SSPA Maritime Consulting facilities in 1984 to 1985, it was shown that for fishing vessels following and stern quartering seas may be significantly more dangerous that beam seas. All loading conditions, both meeting and failing IMO standards, survived irregular beam seas, but loading conditions that met existing IMO criteria capsized in certain following irregular sea conditions. (Grochowalski, 1989, 1990, 1993, 1998) In addition to the dynamic failings, the “one size fits all vessels and all seas” nature of the criteria also severely limits their effectiveness in analyzing a fishing vessel’s stability. The current criteria; - Do not differentiate between the amount of the hull and

the deckhouse which is included in the buoyant volume used in the calculation.

- Do not adequately account for the locations of watertight openings such as doors or fish hold hatches. These are currently assumed closed for the calculations but in the real world are often used at sea and could be inadvertently opened at the wrong time.

- Do not take into account the internal configuration of the spaces, particularly any large enclosed spaces on the main deck or above that if partially flooded could significantly reduced stability included introducing a large loll angle.

- Do not take into account the actual sea conditions the vessel will operate in such as sea state or wave encounter angle.

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- Are not applicable for vessels under 24 meters (79 feet) in length.

- Are minimum recommended values only; no guidance is provided on when these minimums may not be adequate for certain fisheries.

- The criteria are purely pass/fail and do not provide any level of risk advice.

- The criteria fail to provide adequate stability guidance for near shore “day trip” fisheries such as the Mid-Atlantic Clam Fishery and derby style fisheries such as the Gulf of Mexico Red Snapper of Bearing Sea Opilio (Snow) Crab Fisheries.

Clearly at the least the current criteria are in the need of a significant reassessment (Francescutto, 2002, Cramer and Telkamp, 2002). The following quote from Daniel Parrott in his book, “Tall Ships Down”, sums up that author’s opinions why more has not been done in the United States to rectify this.

“When there is a precedent for a particular activity, human nature is such that people are inclined to perpetuate that activity rather than analyze it afresh: “If it ain’t broke, don’t fix it.” But sometimes things are broken we just don’t know it yet.”

Recent losses such as the Scalloper F/V Northern Edge (2005), the Trawler/Processor F/V Arctic Rose (2001), and the Clammers Beth-Dee-Bob and Adriatic (1999) indicate that operations using the current stability criteria may have some problems. In all of these cases the vessels were lost in moderate sea conditions that they had experienced many times in the past. PROJECT DESCRIPTION Study Vessel Characteristics Two hull and deckhouse configurations were used to reflect the most common fishing vessel configurations. The two configurations are: - The short forecastle is typical of house forward trawlers,

crabbers, scallopers, and ocean clammers that have a large open after working deck. The configuration covers a majority of US fishing vessels. See Figure 3 for a typical example.

- The large shelter deck configuration typical of catcher /processors and longliners. See Figure 4 for typical example.

Figure 3. Short Forecastle

Figure 4. Shelter Deckhouse For this preliminary study only the style of the deckhouse is being varied as this the most prominent difference in a typical fishing vessel’s watertight envelope. Additional research will be needed to investigate the effect of other non-dimensional parameters such as the length to beam ratio. The model configurations used for the study is based on the fishing vessel Arctic Rose (See also Appendix D). The Arctic Rose was a 31 meter (100 foot) catcher/processor trawler working in the Bearing Sea when she was lost in 2001(Borlase, 2002, Johnson and Borlase 2003). This vessel offers the following advantages for use in this study. - The vessel was originally built as a short forecastle vessel and

later converted to a large shelter deck style. The parent vessel’s actual configurations covers both of the model configurations used in this study.

- The vessel’s single hard chine hull shape is typical for most US fishing vessels.

- The vessel’s size is mid-range for most US offshore fishing vessels.

- The reported on-scene weather and sea conditions before the time of the casualty were typical for the Bearing Sea with winds and seas estimated at 20 knots and 2-2.5 meters (6-8 feet). These are not anywhere near extreme conditions for this area. Unfortunately, the closest NOAA data buoy in the Bearing was out of commission at the time. so the Marine Board requested a hindcast from NWSFO, which estimated a maximum significant wave height at 7.3 meters (24 feet) and a wave period between 8 and 12 seconds corresponding to a peak period wave length to vessel length (LW/LPP) of between 3.6 and 8.

- The vessel at the time of the casualty is believed to have met all applicable USCG intact stability criteria.

- The vessel’s loss was likely due to a watertight door being open which compromised the vessels’ stability from flooding. The location of the WT door is not reflected in the current USCG intact stability criteria. - Due to the vessel’s very low main deck freeboard, the

watertight door would become submerged at a heel angle of around 20 degrees in still water conditions. (The vessel’s most recent stability letter required a minimum freeboard at the lowest point of 150mm (6”)).

- The watertight door opened to a large full width main deck processing space. A small amount of water in this space, approximately 150mm (6”) deep, would create a loll angle of 20-25 degrees.

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The lines plan for the study’s two models are shown in Figure 3 and the basic parameters are listed in Table 3. The shelter deckhouse version has a main deck house length approximately 75% of the LPP. For the short forecastle version has a main deck house length approximately 25% of the LPP. Table 2. Study Model General Characteristics Shelter Deckhouse Short Forecastle Length Overall: 31.25m 102.5ft 31.25m 102.5ft Waterline Length: 28.01m 91.90ft 28.01m 91.90ft Hull Beam: 7.42m 24.35ft 7.42m 24.35ft Hull Depth: 3.55m 11.65ft 3.55m 11.65ft Molded Draft: 3.10m 10.17ft 3.10m 10.17ft KG Abv BL 3.25m 10.40ft 2.80m 9.00ft Displacement: 360.7mt 354.9lt 360.7mt 354.9lt The two model versions were developed in MaxSurf’s NURBS based MaxSurf Pro surface modeling software. The hull consists of four separate surfaces; a bottom, side, main deck, and transom. Each deckhouse was modeled with three separate surfaces; a side, 2nd deck, and aft bulkhead. A WT door was also modeled in the after main deck house bulkhead to visually represent the existing WT door on the Arctic Rose. For the short forecastle model the WT door was located the same distance off center and with the same sill height as on the Arctic Rose.

Figure 5. Study Models Lines Plans A fixed displacement of 360.7 mt (354.9 LTs) was used for all calculations, this is the estimated value at the time of the Arctic Rose’s loss. A fixed center of gravity (KG) location was set for

each of the two model versions by incrementally raising the KG until the USCG stability criteria outlined in the Introduction Section were met. This results in a KG value of 3.25 meters (10.4 feet) for the shelter deckhouse model and 2.80 m (9.0 feet) for the short forecastle model. The use of two different KG values reflects the realistic differences that occur between the two versions. For this study, these KG values will give the minimum acceptable still water righting arm curve and any deviations below current stability standards from a wave effect will be clearly evident. Further since this a study in the relative changes in the righting arm curves and each model configuration is being studied independently, the use of two different KG values will not effect this studies conclusions. Selection of Analysis Software Today’s powerful personal computers and integrated naval architecture software packages now allow for more sophisticated evaluation of a fishing vessel’s overall stability at costs feasible for small and large design offices. High end personal computers can be obtained for $1,000 to $2,000 with all the memory, processing power, storage devices, and graphics display power required for today’s software packages. And integrated naval architecture software packages can be obtained for around $4,000 for a basic modeling and intact hydrostatics suite to around $10,000 for advanced modeling capabilities, damaged hydrostatics, and ship motion predictions. These integrated naval architecture software packages allow the naval architect to easily analyze a fishing vessel’s stability with; - The ability to use sophisticated models that include both

exterior watertight hull and deckhouse surfaces and internal boundaries for tanks and compartments.

- The ability to locate watertight openings anywhere on the model.

- The ability to flood hull and deckhouse spaces. - The ability to account for the true free surface effect of

complex compartments and tank spaces. - The ability to calculate the static righting arm curve using

user define wave profiles and crest/trough locations. - The ability to predicate basic vessel motions in response to

user define sea states.

This study used Formation System’s MaxSurf HydroMax Pro hydrostatics software package (Courser, 2003). This package was selected for several reasons. - The software package is an off the shelf package that is priced

at levels that allow it to be affordable for use in small architecture firms that work on fishing vessels.

- The software easily handles varied wave profiles and configurations.

- The software’s output is easily copied into a Microsoft Excel or similar spreadsheet to allow for convenient numerical and graphical comparisons of the results.

- The software is fairly intuitive to use, which will allow infrequent users to effectively use methods similar to this study to evaluate the stability of a fishing vessel..

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Analysis Methodology For each of the wave length to height and wave crest/trough location combinations (see next section), MaxSurf’s HydroMax Pro hydrostatics software was used to calculate the resulting righting arm curve using the software’s built-in trochoidal wave profile. In all calculations no free surface effects are included and the initial trim was set at even keel to remove any potential skewing of the results. The vessel was free to trim and rise or sink during all calculations to be in quasi-static equilibrium at each heel angle. The trochoidal wave assumption used in this study, while not capable of modeling spilling breakers commonly found in extreme steep waves, represents the best affordable compromise for the analytical analysis of small fishing vessel righting arms in steep waves. Even more advanced and costly CFD methods are forced to use similar non-breaking wave approximations. The values for the typical stability criteria applicable to vessels of this type were also calculated using the software’s built-in criteria evaluation features. The criteria used were the same ones listed above that were used to set a KG value for each model version. The area under the righting arm curve to a typical watertight deckhouse door downflooding heel angle was also calculated in this study. Currently the area under the righting arm curve is calculated to 40 degrees or the angle of uncontrollable downflooding. Uncontrollable downflooding is defined by the USCG as any opening in the watertight envelope that cannot be made weathertight. While this definition may be adequate for most vessels, fishing vessels present a unique situation that based on past vessel casualties indicate the definition may be inadequate. For example, on fishing vessels, watertight doors that access working decks are in constant use in all weather conditions. In addition, these watertight doors are often located on decks with relatively low working freeboards and may be located toward the vessel’s sides. For most other vessel types, low working decks simply are either non-existent or not used once underway in heavy seas and thus at sea watertight doors will likely remain closed. Because of this key difference, the area to a typical deckhouse watertight door is an important piece of information in a fishing vessel’s stability analysis. All results from HydroMax Pro were copied into Microsoft Excel spreadsheets. From these spreadsheets the resulting righting arm curves and stability criteria values were grouped by desired common parameters such as wave height and comparative graphs created. Wave Conditions Analyzed The project involved imposing a series of standard trochoidal wave profiles on two sets of vessel hull and deckhouse forms

and calculating the resulting righting arm curves with currently available off the self naval architecture software. The wave length to height ratios and wave crest/trough locations defined below outline the scope of the wave profiles used in this study. For all calculations, a wave encounter angle σ=0/180° (head or following seas) was used. Wave Length to Height Matrix The wave matrix (Table 3) was used to define the various wave height and length combinations. The wave length was varied from a short wave of one times the vessel’s length between perpendiculars (1 X LPP) to a long wave of 8 X LPP. The wave height was varied from a steep wave with a wave height to wave length ratio of 7.5 (LW/HW=7.5) to a shallow sloped wave with a LW/HW=60. A maximum wave height of 15 meters (49 ft) was selected as reasonable extreme for the subject vessel’s 28 meter (98 ft) LPP.

Table 3. Wave Height to Length Study Matrix This range of wave steepness ratios was selected to cover the operating conditions typically seen by small fishing vessels. These vessels generally operate in near coastal waters that see the full range of sea conditions from short steep seas created by shallow waters, land masses, and converging weather systems to long high waves from offshore storms. Wave Crest/Trough Location Matrix The position of the crest and trough was varied along the length of the model’s hull as shown in Appendix A and defined as follows. The following fixed locations were used; Forward Perpendicular (FP), 1/4 LPP aft of FP, Amidships (AM), 3/4 LPP aft of FP, After Perpendicular (AP) and the wave’s Front and Back.

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SHORT FORECASTLE MODEL - Results and Discussions Short Forecastle Model - Effect of the Wave Crest and Trough Location - Figures B1 to B3 and B7 to B12 For the short forecastle model the location of the wave crest and trough along the hull determined the magnitude of the change to the model’s stillwater righting arm curve. Figures B1 to B3 are the righting arm curves for 3.73m (12.25 ft), 7.47m (24.49 ft) and 14.93m (48.98 ft) high waves at the key crest and trough locations along the hull length. Figures B7 to B9 and B10 to B12 are the graphs for the area under righting arm curve to the three key heel angles in this study as a wave passes along the hull for 7.47 m (24.49 ft) and 14.93m (48.98 ft) wave heights.

Figure 6. Figures 6 shows the typical large reductions from the stillwater righting arm curve when the wave crest is located at or near amidships. For the 7.47m (24.49 ft) and 14.93m (48.98 ft) high waves the righting arms were negative throughout and near zero or negative for the 3.73m (12.25 ft) high wave. The location of the wave trough on the other hand had at most only a moderate impact on the stillwater righting arm curve when compared to the location of the wave crest. And in all cases this impact was an increase in the righting arms, particularly in the higher heel angles. (See Figures B1 to B6) And interestingly as the wave length to hull length ratio increases from LW/LPP=1 to LW/LPP = 4 for a given wave steepness (LW/HW constant) the range of the wave crest locations that these righting arm curve reductions occur increases. At LW/LPP=1 the reduction occurs when only when the wave crest is at amidships. But from Figure 7, by the time the wave length has increased to LW/LPP=4 the reductions now occurs when the wave crest is located to between 1/4 and 3/4 of the LPP. This is also seen by the increase in the width of the

dips in the graphs when going from Figures B7 to B10, B8 to B11, or B9 to B12.

Figure 7. Short Forecastle Model - Effect of Wave Steepness - Figures B4 to B6, B13 to B15, and B16 to B18 The steepness of the wave for the short forecastle model also had a significant determination on the size of the impact on the short forecastle model’s stillwater righting arm curve. Figures B4 to B6 are the righting arm curves for a 7.47m (24.49 ft) high wave for varying wave steepnesses at the key crest and trough locations along the hull. The 3.73m (12.25 ft) and 14.93m (48.98 ft) wave heights had similar results.

Figure 8. The primary observation from Figure 8 is that as the wave steepness decreases, i.e. the wave length is increasing for a given wave height, the wave righting arm curves quickly

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converge to the stillwater righting arm curve. The steep wave, LW/HW ratio= 7.5, (Figure B4) had the most effect on the model’s righting arm curve with the impacts then rapidly diminishing as the wave steepness decreased as shown in Figure B5 and then Figure B6. This effect can also be shown in Figures B13 to B15 and B16 to B18. These graphs show the lowest and highest areas under the wave righting arm curves to the study’s three key heel angles as compared to the stillwater value. The lowest and highest values were obtained from area under the righting arm curve graphs as shown in Figures B7 to B12. Figures B13 to B15 use the wave length to wave height ratio (LW/HW) as the comparator. Figures B16 to B18 use the wave length to hull length ratio (LW/LPP) as the comparator. For all three wave heights the steepest waves have the most impact with the curves quickly converging to the stillwater levels. And interestingly the larger waves, 7.47m (24.49 ft) and 14.93m (48.98 ft) high, caused the largest reduction in the areas under the righting arm curve to the three key heel angles. From Figure 9 at a LW/HW = 7.5, both the 7.47m (24.49 ft) and 14.93m (48.98 ft) high waves had a worst case reduction of about 110% to 120% while the 3.73m (12.25 ft) high wave only had a worst case reduction of about 90%.

Figure 9. A similar result also exists when comparing wave length the to hull length (LW/LPP). In this case the wave length equal to hull length condition (LW/LPP=1) also does not cause the worst case reduction in the stillwater areas under the righting arm curve. Both wave lengths two and four times the hull length (LW/LPP = 2 & 4) showed higher potential reductions of about 110% to 120% while the 3.73m (12.25 ft) high wave only had a worst case reduction of about 90%. (See Figures B16 to B18)

The other observation from Figure 9 is that higher waves’ area under the righting arm curve values converge quicker to the stillwater values than the smaller waves. For example from Figure 9, the 7.47m (24.49 ft) wave had the larger reduction in the stillwater area to 40 degrees of heel than the 3.73m (12.25 ft) high wave at a LW/HW=7.5. However, by a LW/HW=12 both wave heights had the same reduction value and for LW/HW values greater than 12 the 3.73m (12.25 ft) had the larger reductions. Short Forecastle Model - Effect on Area Under the Righting Arm Curve - Figures B7 to B9 and B10 to B12 Another observation is that as a wave passes the area under the righting arm curve to the forecastle’s watertight door follows the same trend as the area under the righting arm curve to 30 and 40 degrees. For example when the area under the righting arm curve to 30 and 40 degrees dips (Figures B7, B8 & B10, B11) the area under the righting arm curve to the watertight door also dips (Figures B9 & B12) in roughly the same proportion. This result is logical as the areas under the righting arm curve are all derived from the same righting arm curves. Short Forecastle Model – Summary of Results The following summary of the impact of following or head waves on the short forecastle style fishing vessel are; One, the principal reduction in the stillwater righting arm curve and in the area under the righting arm curve occurs when the wave crest is at or around the amidships position. (Figures B1 to B3) Second , the location of the trough had minimal effects on the stillwater righting arm curve and the area under the righting arm curve. As has been demonstrated in many investigations the area values are slightly above the stillwater values. (Figures B1 to B3) Third, in the steeper wave profiles (LW/HW=7.5) the areas under the righting arm curve dip well below the minimums required by the current stability criteria and is actually negative for the larger wave heights (i.e. the vessel will capsize on its own given enough time while riding in the crest area). (Figures B7 to B9 and B10 to B12) Fourth, as the wave steepness decreases, the wave righting arm curves and the areas under the righting arm curve quickly converge to the stillwater values. (Figures B4 to B6, B7 to B9, and B10 to B12) Five, sharp reductions in stability can occur at waves several times the length of the vessel in addition the currently used standard of wave length equal to ship length (LW=LPP). These reductions at the longer wave lengths and higher steepnesses are larger than when the wave length is equal to ship length. (Figures B16 to B18)

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Six, the larger waves’ areas under the righting arm curve values converged quicker to the stillwater values than the smaller waves. (Figures B13 to B15 and B16 to B18) Seven, the area under the righting arm curve to the forecastle’s watertight door follows the same trend as the area under the righting arm curve to 30 and 40 degrees as a wave passes. When the area under the righting arm curve to 30 and 40 degrees dips the area under the righting arm curve to the watertight door also dips in roughly the same proportion. (Figures B7 to B9 and B10 to B12) Based on the past studies and the above observations, the key areas of concern when evaluating the impact of a wave on a short forecastle fishing vessel’s stability is steep waves (LW/HW=7.5) ranging in heights up to the maximum expected for the area the vessel will operate in. SHELTER DECKHOUSE MODEL - Results and Discussions Shelter Deckhouse Model - Effect of the Wave Crest and Trough Location - Figures C1 to C3 and C7 to C12 As opposed to the short forecastle model, the location of the wave crest had minimal impact on the shelter deckhouse model’s righting arm stillwater curves. In the shelter deckhouse configuration neither the location of the wave crest and trough had any significant impact on the righting arm curve as shown in Figure 10. Figures C1 to C3 are the righting arm curves for 3.73m (12.25 ft), 7.47m (24.49 ft) and 14.93m (48.98 ft) high waves at the key crest and trough locations along the hull. Figures C7 to C9 and C10 to C12 are the graphs for the area under righting arm curve to the three key heel angles in this study as a wave passes along the hull for 7.47 m (24.49 ft) and 14.93m (48.98 ft) wave heights. However, unlike the short forecastle model, the location of the wave trough had no consistent impact on the shelter deckhouse model’s righting arm curve. The righting arm curve was slightly reduced for the 14.93m (48.98 ft) high wave and slightly increased for the 3.73m (12.25 ft) and 7.47m (24.49 ft) high waves. In addition from Figures C1 to C3 the height of the wave appears to only a small impact on the magnitude of the changes in the shelter deckhouse model’s righting arm curve as the wave passes by the model. The 7.47m (24.49 ft) high wave showed the most variation in maximum righting arm value, ranging from 0.455m (1.46 ft) to 0.587m (1.88 ft), a 29% variation. The 14.93m (48.98 ft) high wave followed with maximum righting arm value ranging from 0.475m (1.52 ft) to 0.578m (1.85 ft), a 22% variation. The 3.73m (12.25 ft) high wave had the least variation with a maximum righting arm value ranging from 0.470m (1.51 ft) to 0.550m (1.76 ft), a 17% variation.

Figure 10. These results are similar to the findings by Pauling (1961) in his study using the series 60 cargo ship hull form. Because of the series 60’s wall sidedness and relatively high freeboards, this approximates the general configuration of a shelter deckhouse style fishing vessel. Shelter Deckhouse Model - Effect of Wave Steepness - Figures C4 to C6, C16 to C18, and C19 to C21 As with the short forecastle model, the steepness of the wave for the shelter deckhouse model also had significant determination on the size of the impact on the shelter deckhouse model’s stillwater righting arm curve as shown in Figure 11. Figures C4 to C6 are the righting arm curves for a 7.47m (24.49 ft) high wave for varying wave steepnesses at the key crest and trough locations along the hull. The 3.73m (12.25 ft) and 14.93m (48.98 ft) wave heights had similar results. The primary observation from Figures C4 to C6, the steep waves, LW/HW ratios = 7.5, (Figure C4) had the most impact on the model’s righting arm curve. As the wave length increases, i.e. the waves become less steep, (increasing LW/HW ratio) the impacts rapidly diminish as shown by Figures C5 and then C6. The results for the 3.73m (12.25 ft) and 14.93m (48.98 ft) high waves were similar. This effect can also be shown in Figures C16 to C18 and C19 to C21. These graphs show the lowest and highest areas under the wave righting arm curves to the study’s three key heel angles as compared to the stillwater value. The lowest and highest values were obtained from graphs as shown in Figures C7 to C15. Figures C16 to C18 use the wave length to wave height ratio (LW/HW) as the comparator. Figures C19 to C21 use the wave length to hull length ratio (LW/LPP) as the comparator.

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Figure 11. Shelter Deckhouse Model - Effect on Area Under the Righting Arm Curve - Figures C7 to C22 As shown in Figures C7/C8, C10/C11 and C14/C14 (Example of is Figure 12), the areas to the fixed 30 and 40 degree heel angles has little variation from the stillwater values. And in all cases the calculated areas never dipped below the minimum values required by the current USCG stability criteria. This result is logical as there is little variation in the righting arm curves as a wave passes by the model as discussed above.

Figure 12. Appendix C Figure C8 This is also shown in Figures C16 to C18 and C19 to C21 (Example of is Figure 13) which only show a small, 25% or less, reduction in the “Area to 30 Deg” and “Area to 40 Deg” curves. Therefore for this hull and deckhouse configuration, it could be concluded that little impact on the models stability levels from

following or head waves would become evident when evaluated by the current USCG criteria. This though could give a false indication that the vessels stability was adequate in all aspects. Though the impacts on the stillwater righting curve and the subsequent area under the righting arm curve to 30 and 40 degrees were minimal, there was a significant change in the area to the heel angle at which the shelter deck watertight door submerged. This is shown in Figure 13 for the 3.73m (12.25 ft) waves, particularly in the steeper waves as previously discussed. The 7.47m (24.49 ft) and 14.93m (48.98 ft) high waves showed similar results. (Figures C17 and C18) This is primarily due to the fact that the watertight door is submerged at lower heel angles in the smaller waves because there are minimal changes in the righting arm curves as previously discussed. In fact for the 3.73m (12.25 ft) high wave the watertight door is submerged, i.e. the submergence heel angle is negative, with the vessel upright with the wave crest at the location of the watertight door as shown in Figure C22.

Figure 13. Appendix C Figure C16 For this shelter deckhouse model the worst reductions the area under the righting arm curve to the watertight door submergence occur when the wave crest is at approximately 3/4 of the hull’s length from the forward perpendicular, which is coincidently or not the same location as the WT door. This result will be more apparent in the following discussions. From Figures C9, C12, and C15, when the wave crest was located along the hull at the watertight door there is a much larger dip in the area under the righting arm curve to the watertight door (“Area to WT Door”) than to either the 30 or 40 degree heel angle (Figures C7/C8, C10/C11, and C13/C14). This dip is most evident in the steep waves, with it quickly dissipating as the wave length increases to near nothing as discussed in the previous section.

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This observation means that for this model, which is based on the F/V Arctic Rose, a smaller 3.73m (12.25 ft) high wave can present a higher risk for potential flooding through the shelter deckhouse watertight door than the 7.47m (24.49 ft) or 14.93m (48.98 ft) high wave. From Figure 14 the maximum reduction in the area to the watertight door for the 14.93m (48.98 ft) high wave is 79% and 90% for the 7.47m (24.49 ft) high wave while the corresponding maximum reduction is 102% for the smaller 3.73m (12.25 ft) high wave. The last observation from Figure 14 is that higher waves area under the righting arm curve values converge quicker to the stillwater values than the smaller waves. For example from Figure 9, the 7.47m (24.49 ft) wave had the larger reduction in the stillwater area to 40 degrees of heel than the 3.73m (12.25 ft) high wave at a LW/HW=7.5. However, by a LW/HW=12 both wave heights had the same reduction value and for LW/HW values greater than 12 the 3.73m (12.25 ft) had the larger reductions.

Figure 14. Shelter Deckhouse Model – Summary of Results The following summary of the impact of following or head waves on the shelter deckhouse style fishing vessel are; One, the location of the wave crest or trough had minimal effects on the stillwater righting arm curve and the area under the righting arm curve to 30 or 40 degrees of heel. (Figures C1 to C3) Two, as the wave steepness decreases, the wave righting arm curves and the areas under the righting arm curve to 30 or 40 degrees of heel quickly converge to the stillwater values. (Figures C7 to C9, C10 to C12, and C13 to C15)

Third, in the steeper wave profiles (LW/HW=7.5) when the wave crest is located at the shelter deckhouse’s aft watertight door, there is a larger reduction in the stillwater area under the righting arm curve to the angle of the watertight door submergence. (Figures C16 to C18 and C19 to C21) Four, these sharp reductions in the stillwater area under the righting arm curve to the angle of the watertight door submergence can occur at waves several times the length of the vessel in addition the currently used standard of wave length equal to ship length (LW=LPP). These reductions at the longer wave lengths though are smaller than when the wave length is equal to ship length. (Figures C16 to C18 and C19 to C21) Five, the larger waves’ areas under the righting arm curve values converged quicker to the stillwater values than the smaller waves. (Figures C16 to C18 and C19 to C21) Based on past studies and the above observations, the key area of concern when evaluating the impact of a wave on a shelter deckhouse style fishing vessel’s stability are any watertight openings that if inadvertently opened at the wrong time would lead to the loss of sufficient stability from flooding. The principal concern is while operating in steep waves (LW/HW=7.5) ranging in heights up to the maximum expected for the area the vessel will operate in. GENERAL CONCLUSIONS This study achieved two major results. The first is that existing off the shelf hydrostatics software with good graphical displays can be used to investigate in a systematic approach the general effects of following/head waves on the overall stability of fishing vessels. The second is that the same software can then be used to provide useful stability information from the effect of waves on typical fishing vessels righting arm curves for providing stability guidance to the fishing vessel crews and designers in a cost effective manner. From the discussions above the following conclusions are put forth. As in previous investigations discussed in the Background section for short forecastle style deckhouses, when the wave crest is located around amidships there is a significant reduction in the stillwater righting arm curve. This reduction can occur at wave lengths significantly longer the length of the vessel, and the longer the wave length, the broader the range centered around amidships of the wave crest locations when the reductions occur. The magnitude of the reduction was also highly dependent on the steepness of the wave. The steep waves (LW/HW=7.5) had the most effect which then quickly decreased as the wave steepness dropped and eventually converged on the stillwater righting arm curve values. For the shelter deckhouse arrangement though, the location of the wave crest had little significant impact on the righting arm curves. However the location of the wave crest did have a significant impact on the area under the righting arm curve to the heel angle for submergence of a typical watertight door in

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the aft end of the shelter deckhouse. When the wave crest is located near the watertight door there was a large reduction in the area under the righting arm curve to the watertight door submergence when compared to the stillwater values. As with the short forecastle style, the magnitude of the reduction was highly dependent on the steepness of the wave. The steep waves (LW/HW=7.5) had the largest effect which then quickly decreased as the wave steepness dropped and eventually converged on the stillwater righting arm curve values. For both the short forecastle style deckhouse and the shelter deckhouse arrangement the location of the wave trough has minimal impact on the righting arm curves when compared to the stillwater righting arm curve. Because of this the effect of the wave trough can probably be ignored in any performance based criteria. “Freeboard is the key to stability” has been said since before Rahola’s ground breaking thesis. This is clearly supported by the results from this study as the negative impacts from waves that occur in the low freeboard short forecastle arrangement are not present in the shelter deckhouse arrangement. The shelter deckhouse creates a high effective freeboard as far as stability is concerned even though the after main deck has a low freeboard. In essence, if you were to add freeboard the short forecastle model it basically will become equivalent stability wise to the shelter deckhouse arrangement. This higher effective freeboard in a shelter deckhouse style fishing boat though can create an “Achilles” heel in its stability that is not addressed in the current USCG and IMO stability criteria. As noted previously, the area under the righting arm curve to the submergence of the watertight door on the aft end of the shelter deckhouse was significantly reduced by a passing wave crest. And for the steep small wave the reduction actually created a negative area under the righting arm curve to the watertight door, that is the watertight door was submerged by the passing wave with the model still in the upright position. This can occur because the buoyant volume from the shelter deckhouse will compensate for the loss of buoyant volume from a low freeboard main deck and allow the vessel to still meet current USCG or IMO stability criteria. The watertight doors needed to access the very low aft working main decks typical of shelter deck fishing vessels, if placed outboard will then be submerged at relatively low heel angles. And with the interior spaces of many shelter deckhouses being large and the full width of the vessel, a small amount of water accidentally flooding these spaces will result in large free surface effects. This effect was likely the reason for the loss of the F/V Arctic Rose in moderate sea conditions. See Appendix D for additional discussion on this and water on deck considerations for all types of watertight openings (watertight doors, fish hold hatches, vents). Because of this, this phenomena should be one of the areas of concern for future investigation into performance based stability criteria. One relatively small wave can quickly submerge a low “freeboard” opening. And generally once the water enters the

space it doesn’t come back out due to watertight door sills and can lead to capsizing. (i.e. it takes only a brief moment to get a shelter deckhouse vessel into trouble from which it can not recover) One possible solution would be requiring a minimum area under the righting arm curve to all watertight openings. This would be similar in concept to requiring minimum sill heights for a watertight door. The other area of concern for future investigation into performance based stability criteria is loss of stability in short forecastle style deckhouse fishing vessels when a steep wave’s crest is located near the vessel’s amidships. As this and many other investigations have shown, there is not much that can be done about the loss of stability when the wave crest is near amidships. This is a phenomenon that is mostly a function of freeboard which for many fisheries is dictated by the fishing gear used. This is not to say that additional investigations should not be done. This phenomenon is likely a major contributing factor in many of the recent losses in the US Northeast and needs to be addressed. Some of this can be addressed with operator training. If the wave crest passes by the fishing vessel quickly, it will not remain in the danger zone long. It takes time for the reduction in stability on a wave crest to take effect thus the old seaman’s adage in following seas your speed should be less than 1/2 of the wave speed to prevent surfing and capsizing. And this adage has been confirmed by the many model tests as discussed in the background section. However there probably still should be a maximum reduction allowed from stillwater righting arm curves set by the current USCG and IMO stability criteria. This would force a reasonable minimum freeboard to allow a fishing vessel a chance to survive being inadvertently “perched” on a wave. Based on these conclusions and using the software currently available, significant improvements in creating stability criteria that reflect an individual vessel’s actual characteristics and operating conditions can be done now with simple additions to the existing USCG and IMO stillwater based stability criteria. These additions such as requiring a minimum area to watertight openings or maximum allowable reductions in the righting arm curve from waves are doable now and would address the causes of many fishing vessel losses. ACKNOWLEDGEMENTS The authors wish to thank the SNAME T&R Steering Committee for sponsoring this research and Formation Systems for the kind loan of their MaxSurf Software used in this paper. The authors also wish to thank those who reviewed this paper; their comments were very instrumental in assisting the authors in the development of this paper.

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REFERENCES: Amy, J.R., Johnson, R.E. and Miller, E.R, 1976, Development of Intact Stability Criteria for Towing and Fishing Vessels, SNAME Transactions, Vol xxx, 1976, pp 75-114. Beck R. F., and Reed, A.M., 2001, Modern Computational Methods for Ships in a Seaway, SNAME Transactions, Vol 109, 2001, pp 1-51 Bird, H. and Morrall, A. 1986. Research Towards Realistic Stability Criteria, Proceedings of the International Conference on the Safeship Project: Ship Stability and Safety, RINA, London 9-10 June 1986. Blume, P and Hattendorff, H.G. (1982). An Investigation on Intact Stability of Fast Cargo Liners. Proceedings of the 2nd International Conference on Stability of Ships and Ocean Vehicles, Tokyo, October 1982. Blume, P, 1990, On the Influence of the Variation of Righting Levers in Waves on Stability Requirements, Proceedings of the STAB 1990, Naples, September 1990 Borlase, G., 2002, Research Opportunities Identified during the Casualty Analysis of the Fishing Vessel ARCTIC ROSE, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002 Cleary, W., 1993, The Regulation of Ships Stability Reserve, Proc. of the U. S. coast Guard Vessel Stability Symposium, New London, CT, March 15-17, 1993. Courser, P. 2003. A Software Developer’s Perspective of Stability Criteria, Proceedings of STAB 2003, Madrid, September 2003 Cramer, H., and Tellkamp, J., 2002. Towards the Direct Assessment of a Ship’s Intact Stability, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002 Dahle, E. A., and Myrhaug, D., 1995. Risk Analysis Applied to Capsize of Fishing Vessels. Marine Technology, Vol. 32, No. 4, October 1995, pp. 245-257. Dawson, T.H., Kriebel, D. L., and Wallendorf, L.A. 1996, Markov Description of Wave-Crest Statistics, ASME J. Offshore Mech. Arct. Eng., 118, pp 37-45. Dawson, T. H., 2002 Markov Theory for groups of Very High Waves, International Journal of Offshore and Polar engineering, vol 12, No. 2, June 2002. Du Cane, P., and Goodrich, G.J. 1962, The Following Sea, Broaching and Surging, Quarterly Transactions of the Royal Institution of Naval Architects, Vol. 104, No. 2, April 1962

Francescutto, A., Russo Krauss, G., and Cardo, A., 2001 "Dynamic Stability and Effect of Water on Deck on Small Fishing Vessels", Paper n. 6, Proceedings International Conference on "Small Craft Safety", The Royal Institution of Naval Architects, London, 22-23 May 2001 Francescutto, A., 2002 Intact Stability, The Way Ahead, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002 Grochowalski, S., 1989, Investigation into the Physics of Ship Capsizing by Combined Captive and Free-Running Model Tests. SNAME Transactions, 1989 pp 169-212 Grochowalski, S., 1990, Hydrodynamic Phenomenon Generated by Bulwark Submergence and its Influence on Ship Susceptibility to Capsizing, Proceedings of the STAB 1990, Naples, September 1990 Grochowalski, S., 1993. Effect of Bulwark and Deck Edge Submergence in Dynamics of Ship Capsizing. Proceedings, US Coast Guard Vessel Stability Symposium, New London, Connecticut, USA. March 1993. Grochowalski, S., Archibald, J., Connolly, F, and Lee, C.,1994, Operational Factors in Stability Safety of Ships in Heavy Seas, Proceedings of STAB 94, Melbourne, Fla, November 1994. Grochowalski, S., Hsiung, C. C., and Huang, Z. J., 1997, Development of a Time-Domain Simulation Program for Examination of Stability Safety of Ships in Extreme Waves. Proc., International Conference on Ship and Marine Research, NAV ’97 Naples, Italy, March 1997. Hamamoto, M. and Nomoto, K. 1982, Transverse Stability of Ships in a Following Sea Proceedings of the 2nd International Conference on Stability of Ships and Ocean Vehicles, Tokyo, October 1982. Hirayama, T. and Takezawa, S. 1982. Transient and Irregular Experiments for Predicting the Large Rolling in Beam Irregular Waves, Proceedings of the 2nd International Conference on Stability of Ships and Ocean Vehicles, Tokyo, October 1982. IMO, 1995. 1993 Torremolinos Protocol and Torremolinos International convention for the Safety of Fishing Vessels. Consolidated Edition, 1995 IMO, 2004. Review of the Intact Stability Code, Towards the development of dynamic stability criteria, SLF 47/6/4, submitted by Germany. Johnson, B. 2000, Capsize Resistance and Survivability When Smaller Vessels Encounter Extreme Waves, Proceedings of the Rogue Wave 2000 Conference, Brest France, 29-30 November 2000

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Johnson, B., and Womack, J. 2001, On Developing a Rational and User-Friendly Approach to Fishing Vessel Stability and Operational Guidance, Proceedings of the 5th International Workshop on Stability and Operational Safety of Ships, Trieste, Italy, 12-13 September 2001. Johnson, B., and Grochowalski, S., 2002. Development of a Performance Based Fishing Vessel Stability Criteria, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002 Johnson, B. and Borlase, G., 2003. Time to Flood Analysis for the Fishing Vessel Arctic Rose, Proceedings of the SNAME WMTC Conference, 2003 Kan, M. 1990, A Guideline to Avoid the Dangerous Surf-Riding, Proceedings of the STAB 1990, Naples, September 1990 Kan, M, Saruta, T., and Taguchi, H., 1994 Comparative Model Tests on Capsizing of Ships in Quartering Seas, Proceedings of STAB 94, Melbourne, Fla, November 1994. Kriebel, D. L. and Dawson, T. H., 1993, Nonlinearity in wave crest statistics. Proceedings, 2nd International Symposium on Ocean wave Measurement and Analysis, ASCE, New Orleans, LA, 61-75 MAIB 1999,‘Report on the Underwater Survey of the Stern Trawler GAUL H.423 and the Supporting Model Experiments, August 1998-January 1999,’ MAIB Accident Report No. 4/99. MAIB 2003, “Report of investigation into sinking of fv Tullaghmurry Lass N246 with loss of three lives in the Irish Sea on 14 February 2002 Report No. 4/2003. Morrall, A.,1980 ‘The GAUL Disaster: An Investigation into the Loss of a Large Stern Trawler,’ Naval Architect, Royal Institution of Naval Architects, 1980 Paulling, J. R., 1960, “Transverse Stability of Tuna Clippers,” Fishing Boats of the World, Vol 2, edited by Jan-Olof Traung, published by Fishing News Limited, London, England 1960, pp 489-495. Paulling, J. R.,1961 “The Transverse Stability of a Ship in a Longitudinal Seaway, Journal of Ship Research, Vol. 5 No. 1, March 1961 Rahim, A, Reaz, M., and Khondoker, H., 2000, Effects of the Presence of Waves on the Stability of Passenger Vessels, Proceedings of STAB 2000, Launceston, Australia, February 2000. Rennilson, M. R. 1982. An Investigation into the Factors Affecting the Likelihood of Broaching-To in Following Seas, Proceedings of the 2nd International Conference on Stability of Ships and Ocean Vehicles, Tokyo, October 1982.

Salsich, J. O., Johnson, B., and Holton, C. 1983, A Transient Wave Generation Technique and Some Engineering Applications, Proceedings of the 20th American Towing Tank conference, 1983 Sevast’yanov, N. B. and Nechayev, Yu. I., Studies on Stability of fishing Vessels on a Wave Crest, IMCO, London, Aug. 1966 Storch, R. L., 1978 Alaskan King Crab Boat Casualties, Marine Technology, Vol. 15. No. 1, Jan. 1978,pp 75-83 Takaishi, Y, 1982 Consideration on the Dangerous Situations Leading to Capsize of Ships in Waves, Proceedings of the 2nd International Conference on Stability of Ships and Ocean Vehicles, Tokyo, October 1982. Umeda, N, 1990, Probabilistic Study on Surf-Riding of a Ship in Irregular Following Seas, Proceedings of the STAB 1990, Naples, September 1990 Umeda, N and Yamakoshi.Y., 1994, Probability of Ship capsizing due to Pure Loss of Stability in Quartering Seas, Naval Arch and Ocean eng., Vol 30, pp. 73-85 Umeda, N., Matsuda, A., Hamamoto, M, and Suzuki, S. 1999. Stability Assessment for Intact Ships in the Light of Model Experiments. J. of Marine Science and Technology, SNAJ, Japan, Vol. 4, pp 45-57, 1999. Umeda, N., and Peters, A., 2002. Recent Research Progress on Intact Stability in Following/Quartering Seas. Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002. Umeda, N., Kamo, T and Ikeda, Y., 2002b. Some Remarks on theoretical Modeling of Damage Stability. Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002 Womack, J., 2002, Small Commercial Fishing Vessel Stability Analysis, Where are We Now Where are We going, Proceedings of the 6th International Ship Stability Workshop, Webb Institute, 14-16 October 2002. Womack, J. and Johnson, B., 2003, SNAME Guide to Fishing Vessel Stability Zseleczky, J. J., 1988. Evolving Methods for Estimating Capsize Resistance in Breaking Waves. Proceedings of the SNAME New England Sailing Yacht Symposium, New England, March 1988. Zseleczky, J. J. and Cohen, S. H. 1989, Model Tests to Evaluate the Capsize Resistance of a Motor Lifeboat in Breaking Waves, Proceedings of the 22nd American Towing Tank Conference, St. Johns, Newfoundland, 1989.

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APPENDIX A - Definition of Wave Crest and Trough Locations

Wave Crest @ Fwd Perp

Wave Crest @ 3/4 LPP

Wave Trough @ Fwd Perp

Wave Trough @ 3/4 LPP

Wave Crest @ 1/4 LPP

Wave Crest @ Aft Perp

Wave Trough @ 1/4 LPP

Wave Trough @ Aft Perp

Wave Crest @ Amidships

Wave Front

Wave Trough @ Amidships

Wave Back

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APPENDIX B - Short Forecastle Model Figures

Figure B1

Figure B2

Figure B3

Figure B4

Figure B5

Figure B6

19

Figure B7

Figure B8

Figure B9

Figure B10

Figure B11

Figure B12

20

Figure B13

Figure B14

Figure B15

Figure B16

Figure B17

Figure B18

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APPENDIX C - Shelter Deckhouse Figures

Figure C1

Figure C2

Figures C3

Figure C4

Figure C5

Figure C6

22

Figure C7

Figure C8

Figure C9

Figure C10

Figure C11

Figure C12

23

Figure C13

Figure C14

Figure C15

Figure C16

Figure C17

Figure C18

24

Figure C19

Figure C20

Figure C21

Figure C22

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APPENDIX D Water on Deck considerations. A number of recent investigations concern dynamic simulations of how to handle water on deck for stability calculations. The standard model of the water on deck can be calculated as an asymmetrical heeling arm curve superimposed on the righting arm curve. This is the method the current Code of Federal Regulations, CFR 28.560 specifies and is discussed briefly in Francescutto et al (2001). The corrections to the effect of wave conditions on the righting arm curve are covered in this investigation, but no new criteria are suggested. The various rules incorrectly call the area under the righting and heeling arm curves righting and heeling energy.(Figure 28.565 in CFR 28.560.) They are actually righting and heeling energy per unit displacement since the area under the righting moment curve is the actual righting energy. The Arctic Rose Time to Flood analysis as a motivation for this investigation. The righting arms for the ARCTIC ROSE were calculated from the cross-curves of stability tables using GHS at the estimated at-loss displacement and KG. This curve was used as the baseline for the righting arm calculations at each time step. A second righting arm curve was then calculated from the cross-curves of stability tables based on the displacement and trim of the vessel and the weight of the flooding water using look up tables for all corrections including the trim vs heel correction to the assumed roll axis. The current investigation could have correctly computed the quasi-static GZ curves directly, had it been available. As described in Johnson and Borlase, 2003, the Arctic Rose’s motion in following waves was broken into four distinct motions based on equal time steps equal to one fourth of the encounter period, Te. During the “Vessel in Trough” time step, the vessel was assumed to be traveling in the trough of the wave, and accumulate water on the starboard side aft deck well if the heel angle was less than the angle of bulwark submergence. No righting arm correction was applied because no loss or gain of waterplane area was assumed for such long waves. The estimated 10 second wave period from hindcasts gave a λ/LWL = 5.4. During the “Wave Raises Stern” time step, the wave at the aft deck was assumed to be two feet above the normal waterline and a pitch down correction could be applied to the internal gravity head flooding calculations for sensitivity purposes. Additionally, in the absence of the results of the current investigation, a righting arm correction factor of 0.9 was applied

to all values of GZ. This factor attempted to account for the loss of waterplane area as the vessel travels up the face of the wave. During the “Ride Wave Crest” time step, the water was assumed to have cleared off the deck through the freeing ports and aft stern ramp and a righting arm factor of between 0.7 and 0.9 was applied to estimate the loss of waterplane area at the bow and stern of the vessel at the crest of the wave. The wave was assumed to be up to 2 feet above the normal still waterline. During the “Wave lowers Stern”, the vessel would shed the water on deck, including that which flowed out of the processing space because of the attitude of the vessel on the wave and a pitch up correction could be applied to the internal gravity head flooding calculations. This crude method of estimating the righting arm correction can now be replaced by the methods outlined in this paper. Vessel responses in long quartering or following seas which break but do not induce surf-riding can still involve several seconds in the breaking portion of the wave. If the vessel already has water on deck and possibly downflooding started, serious consequences can result. APPENDIX E Current IMO Review of the Intact Stability Code SLF 47/6/4 June 2004 Quoting from SLF 47/6/4 “This document suggests a structure for these dynamic criteria and within this proposed structure one set of criteria will account for a minimum stability limit required to ensure that these minimum stability standards will provide the ships with sufficient safety.” However in section 28 “The righting levers shall be computed in a wave equal to the wetted length of the ship, wave height according to the 90% quantile (see above) with the vessel trimming freely. The crest shall be located at the half of the wetted length fro the crest condition and at AP for the trough condition.” “For all waveheights above the limiting wave height according to the failure criterion, we assume that the ship will capsize or be exposed to a large rolling angle that leads to a loss. For all waveheights below this limiting wave height, we assume that the ship is safe and the probability is set to zero.” There are two fundamental reasons to reject this proposal as a step backwards to oversimplified pass/fail criteria.

1. The use of λ/LWL = 1 as a worst case criteria ignores the many model tests and the results of this investigation which demonstrate that there are many other wave conditions which can cause a high a probability of capsize. .

2. The use of a 90% quantile wave height ignores that dangerous groups of high waves can occur 1% of the time in severe seas.

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To illustrate this point, Section 17 of SLF47/6/4 has been reworked to show that the table uses critical waveheights and steepnesses that are much too small for the assumed mean periods. The major focus of the proposal is to prevent serious parametric rolling and for large ships, this may be a useful tool. However

for smaller vessels of various shapes not coinciding with the ship type covered in this proposal, the author’s feel that from the results of this investigation, especially Figures B1 to B3, illustrate that the λ/LWL = 1 is not the worst case for alterations between the wave crest and trough.

IMO SLF47/6/4 Modified Table on page 7 Implied Implied Deep Deep

H_1/10 H_1/10 H_1/3 H_1/100 H_1/100 Water Water Wave Wave Wave LW/H Wave Wave LW/H Wave Group Period Length Height Height Height Celerity Velocity

sec m m m m Knots Knots 2.5 9.76 0.49 19.86 0.386 0.644 15.16 7.59 3.793.5 19.13 0.73 26.21 0.573 0.957 20.00 10.62 5.314.5 31.62 1.44 21.96 1.131 1.887 16.76 13.66 6.835.5 47.23 1.98 23.85 1.555 2.594 18.20 16.69 8.356.5 65.97 2.72 24.25 2.137 3.564 18.51 19.73 9.867.5 87.83 3.70 23.74 2.907 4.848 18.12 22.76 11.388.5 112.81 4.36 25.87 3.425 5.713 19.75 25.80 12.909.5 140.91 5.43 25.95 4.266 7.115 19.80 28.83 14.4210.5 172.14 6.53 26.36 5.130 8.556 20.12 31.87 15.9311.5 206.49 7.43 27.79 5.837 9.735 21.21 34.90 17.4512.5 243.96 8.44 28.91 6.630 11.059 22.06 37.94 18.9713.5 284.56 9.37 30.37 7.361 12.277 23.18 40.97 20.4914.5 328.28 10.30 31.87 8.091 13.496 24.32 44.01 22.0015.5 375.12 10.95 34.26 8.602 14.348 26.14 47.04 23.5216.5 425.08 12.06 35.25 9.474 15.802 26.90 50.08 25.0417.5 478.17 13.10 36.50 10.291 17.165 27.86 53.11 26.5618.5 534.37 14.30 37.37 11.233 18.737 28.52 56.15 28.0719.5 593.71 15.28 38.86 12.003 20.021 29.65 59.18 29.5920.5 656.16 16.35 40.13 12.844 21.423 30.63 62.22 31.11