172Chapter 20

The Strip Plank Method for Laminating andStrip Composite Construction

The strip plank method for laminating hulls is a crossbetween the mold method and traditional strip plank-ing techniques. Mold frames are set up and solidlyplanked, usually with edge-glued' strips of softwood.The set-up is then covered with layers of veneer. Thestrip planks become the interior lamination of thefinished hull. When construction is finished, temporaryframes are removed. The rigid, monococque structureswhich can be built with this method require substan-tially less interior framing than other types of woodenboats.

Because the type and number of layers of materialwhich can be laminated over the first layer of stripplanking can be infinitely manipulated, this method ofconstruction has endless variations and may be used toconstruct boat components as well as entire hulls. Inthis edition of The Gougeon Brothers on Boat Con-struction, we have expanded our discussion of stripplanking to include strip plank composite construction,one of the more popular and versatile of thesevariations.

Strip composite construction is probably mostwidely used in building stripper canoes. It differs fromstandard strip plank laminating in only one major re-spect: softwood strips are bent over temporary moldframes, but are covered with fiberglass cloth, insideand out, rather 'than veneer. Although strip compositeconstruction is a quick and relatively easy way to buildstrong, light hulls, its use has been restricted to smallcraft and to parts such as spars and cabin tops. This islargely because no scantling rules have been set forstrip composite hulls.

Setting Up for Strip Planking

With the strip plank method, just as with the moldmethod, we use % inch thick particle board temporarymold frames to define the shape of the hull. Set up theframes as described for the mold method, and thencover them with strip planking. The only difference isthat extra care must be taken to be sure that the bevelson the frames are correct. Hard spots may dent theplanking as it is bent over the frames, and this damagecan be visible in the interior. . ,

Decide temporary mold frame positioning and spac-ing during lofting, taking into account the locations of

stationary bulkheads, framework and any other inter-nal items which might interfere with a chosen tempo-rary frame location. Usually, setting up a permanentbulkhead means that you can eliminate a temporaryframe, but sometimes a bulkhead is situated betweentwo temporary frames and too large a gap would beleft if either were removed. Therefore, early on, coor-dinate the locations of the permanent structural mem-bers which can act as mold frames with the locations ofthe temporary mold frames so that you can provideproper support for the strip planking process with theleast amount of set-up.

Planking thickness and the shape of the hull deter-mine the standard spacing between mold stations. ForVzinch thick planking, a 16 inch span between stationsis about maximum. Frames which will be covered with1 inch thick planking might be as far as 30 inches apart.Average spacing for % inch to 18 inch planking is 18 to24 inches. With any hull, there may be areas of tight,sharp curves which cannot be properly defined by thegeneral station spacing. We usually insert half framesbetween two normally positioned frames in theseareas. If there aren't too many sharp curves, this ismuch quicker than decreasing the standard framespacing throughout the hull to accommodate one areaof sharp curves.

With the strip plank method, the keel, stem andtransom are always included in the set-up to becomepart of the permanent hull. This means that you willhave to make provisions for notching the keel andstem into the temporary mold frames as well as intobulkheads and laminated frames which may also be inthe set-up. Hold the keel and stem temporarily in place .to each temporary mold frame by inserting a screwthrough a small block that is attached to the side of thetemporary mold frame just underneath the keel orstem area. The screw holds the keel or stem snugagainst the temporary mold frame until the laminationprocess is complete. You can then remove thesescrews easily when it is time to remove the temporarymold frames. Permanently position and attach the keeland stem to bulkheads, frames or any other permanentinterior items using alloy wood screws of proper length.

A permanent or temporary sheer clamp must beincluded in the set-up so that the planks near the sheercan attach to it, especially if the planking will run out,or cross the sheer at an angle. Without hand spiling, it's

very difficult to finish planking with strips runningexactly parallel to the sheer line. We usually installpermanent sheer clamps, although doing this meansthat we often have to saw temporary frames in order toremove them. This is only a problem if we want to usethe frames for another boat.

Precoat and sand exposed interior areas of the per-manent sheer clamp, keel, stem, transom, bulkheadsand other permanent interior items before installingthem in the set-up. Protect all prefinished permanentmembers by covering them with duct tape or otherheavy duty tape which will prevent damage from bothdripping epoxy and sanding.

When you have installed all of the permanent mem-bers in the set-up and completed final fairing of bothtemporary frames and permanent members, the set-upis ready for strip planking. During this procedure, youshould attach the planking permanently to all perma-nent members, but avoid any possibility of accidentallybonding the planking to the temporary mold frames.Cover the edges of all temporary frames carefully withstrips of 4 mil or 6 mil polyethylene sheet, stapling theplastic several inches back from the edges on bothsides of the frame. When you have completed this, youare ready to begin strip planking.

Stock for Strip Planking

Choose the most practical planking size for yourproject. Most boats will require strip planks between Yzinch and 1 inch thick. Determine the planking size foryour hull after considering the following:

(1) the size and width of the boat,(2) the spacing between permanent or temporary

frames in the set-up,(3) whether the chosen thickness of planking can

bend around the most severe curves in the hull,and

(4) the most efficient use of available dimensionallumber.

. Planking width is governed by two factors. There is,first, the need to attach one plank to the next withdowels or nails in the process of edge nailing. This issomewhat impractical with anything wider than 1Yzinch strips: the widest we've ever used was 1% inches.The flexibility of the planking in the edgewise directionis the second factor and is an important considerationfor rapid application of strip planking.

If you can select the base stock from which to sawstrips, we suggest that you choose slab sawn plankswhich, when ripped, will show edge grain on interiorand exterior surfaces. Edge grain planks are usuallymore attractive for naturally finished interiors. There

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are two better reasons for using them, however: edgegrain planks are more stable than other planks andthey sand and machine more consistently than flatgrain. Fairing up surfaces for final finishing and laminat-ing therefore goes a bit more quickly.

Dimensional accuracy is important when you aresawing and milling the stock for planking. Accuracy isparticularly important in the thickness dimension. Aplank that is even 1/32 inch smaller than its neighborswill create a depression along its entire length that youwill need to fill prior to further laminating. Sawingenough planking for an entire hull is a large undertak-ing. We always take the time to set up a proper sawingoperation by making sure that we have a good feedramp for easily moving the stock into the saw and agood exit ramp for the stock to lie on as it is exitingfrom the back of the saw. Whenever possible, we setup spring tensioning to hold the stock down on the sawtable and up against the saw guide so that we don'thave to rely entirely on hand pressure to guide thestock through the saw blade.

You probably won't be able to buy planks longenough to cover your entire hull. Usually, you have tocut at least one scarf and perhaps as many as four tomake up a plank to span all of the hull stations. It ismuch easier to scarf strips before you apply them, andit can be quite difficult to scarf strip planking in placewhile bending it over frames, especially in short, wideboats. Do all scarfing carefully and accurately, follow-ing instructions in Chapter 10, so that there will be nodog legs or kinks at the scarf or overlaps to increaseplanking thickness at the joints.

Spiling and Beveling Strip Planks

The concept of planking a hull is at least severalthousand years old. The traditional carvel built hull hasplanks lying edge to edge, and the techniques devel-oped for carvel planking are well known. Traditionally,because boats are fatter in the middle and smaller outat the bow and stern, planking has always been ta-pered at its ends to adjust for this change in dimen-sions. Because planks are joined one by one around acurved surface, it's also common to bevel their edgesso that they meet flush where they join. Both the spil-ing and beveling operations are very tedious andtime-consuming, and both require a good deal of skill.

With traditional procedures, two workers might belucky to apply five or six planks a day on a 40 foot hull.To speed up the planking process and make this con-struction method more practical, we have eliminatedspiling and beveling. When these two jobs are un-necessary, two well-organized people can apply up to25 planks in eight hours.

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Instead of spiling, we adjust for dimensional de-creases as planks approach the ends of the hull byallowing them to run out at the keel and the sheer asthey do when building a mold. Unless the hull is par-ticularly fat for its length, this technique presents nodifficulties, provided that the planking is thin enough tobend easily edgewise as it arcs toward the sheer orkeel. With a thick WEST SYSTEM* Brand resin mix-ture, beveling is usually unnecessary for structural rea-sons. Eliminating it saves a great deal of time. Whenviewed from the interior, the planking on most hullsalways fits tight and looks the same whether it has beenbeveled or not.

Applying Strip Planking

As might be imagined, locating the first plank on theset-up is of paramount importance because the loca-tion of this master plank determines the direction andamount of curve that all succeeding planking will fol-low as it approaches either the keel or sheer. Improperlocation of this first plank might cause the plankingapproaching the sheer to become overly curved to thepoint where it would be difficult to bend the planks inplace, while the planking on the other side of the mas-ter plank that is approaching the keel might hardlycurve at all. The goal is to locate the master plankabout midpoint along the hull, and in an arc that willallow the planking installed on either side of it to bendabout the same amount as it approaches the keel orsheer. The simplest method of determining the loca-tion of the master plank is to determine mid-framelocations at various points along the hull. Establishthese positions by measuring along the perimeter ofthe frames between the keel and the sheer, starting inthe middle of the hull and working out towards theends. Temporarily exclude the first few stations at thebow and the transom because the shape of the boat ischanging abruptly at these points and will not give youa true overall reading of what is happening with themajority of the hull. When you have located a point onthe frame at each station which is equidistant fromboth the keel and the sheer, position a batten alongthese marks and temporarily nail it in position. Usingyour eye as the guide, move the batten whereverneeded to achieve a fair curve that still intersects themid-frame marks as closely as possible. You can ex-tend the batten arc to achieve a fair curve over theunmarked fore and aft frames.

With this batten installed, you can get a better ideaabout how the planking will lie on the rest of the hull.Measure either up or down from the batten at various

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points on all the frames to try to get a sense of what theplanking will look like as it approaches the sheerand/or keel. As you work out the planking direction,try to determine which are the most severe curves inthe hull and establish the best angle for negotiatingthem. Then compare this with the angle of the masterveneer. Another factor which might affect placement ofthe master plank is the amount of compound curvetoward the sheer compared with the compound curvetoward the keel. The bottoms of boats are usuallycompounded more than the topsides, and this mayindicate that the master plank should be curved moretoward the sheer, where the planks might be moreeasily bent edgewise due to the lack of compoundcurvature.

When you have lined up the batten and adjusted itto suit your desire for positioning the master plank,carefully mark its position on each station so that youcan install the master plank using these marks as refer-ence. Although it is normally done, it is not necessarythat the master plank be located right at this markedmid-point position. You could position the masterplank at any point above or below the mid-point marksthat you established with the batten, but it must runparallel to and at the same distance from each mark ateach station point so that as the hull is fully planked,the planks in the area of the original marks will run trueto them.

If you decide that the shape of your hull is not wellsuited to this type of planking procedure (for example,if the hull is too fat), you can use the double run plank-ing system. With this method, you apply the plankingparallel with 'the sheer line up to a point on the hullwhere it begins to curve excessively. Then apply the

next group of planking parallel with the keel, joining itwith the planking that has been run parallel with thesheer at a central joining plank. Joining the two direc-tions of planking as they run out into each other atsome point in the central hull area is difficult withoutcausing a hard spot. This difficulty is not insurmounta-ble, but the double run planking system takes a gooddeal of extra time in comparison to the run outmethod, where you have to do little or no fitting at all.

Figure 2-Strip planking a mold.

Applying WEST SYSTEM Epoxy

Assume that you are going to run bottom plankingparallel to the keel and topsides planking parallel to thesheer in a double run planking system and that youhave accurately marked the set-up to receive the mas-ter plank. Instali this plank, using screws which areabout twice as long as the thickness of the planking tohold it temporarily to the mold frames. We use inex-pensive roundhead sheet metal screws with largewashers which make it possible to apply more pressurewithout damage to the wood fiber. Chipboard framesrequire longer screws than wood frames because chip-board's holding power is not as good as wood's. Inareas where you need extra holding power, screw orstaple and bond a piece of wood to the side of a chip-board frame and screw the planking into this. Step drillbits, which can cut a pilot hole in the temporary frameand a shank-sized hole in the plank in one operation,save the added step of switching between two differentdrills or changing bits.

Use alloy screws and epoxy thickened with highdensity filler to attach planking to all permanent partsof the boat. These screws will be left inthe hull. Coun-tersink them enough so they won't interfere with fair-ing. You will be using two different types and perhaps

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sizes of screws, one to attach planking to temporaryframes and the other to attach it to permanent mem-bers. Two electric drill motors set up with two differentsize bits will save time.

When you have installed the master plank, set up aprocedure to easily and efficiently apply the rest of theplanking to the frames. Mark the planks with surmarkswhich line up with a station in the middle of the hull sothat you can accurately position them without havingto guess if they are centered.

If you are using a softwood such as cedar, use lowdensity additive with epoxy to make a thick syrup. Thiscombination far exceeds the grain strength of mostsoftwoods. If you are working with high density woodswith higher grain strength, like mahogany, use the highdensity filler for a stronger resin mixture.

Support jigs will hold planking upright for conven-ient epoxy application. We make them of Yz inchplywood, with slots in the tops just large enough for theplank to sit in. We nail these to saw horses and set upas many as are needed to support the plank. About 3feet off the floor seems to be a comfortable workingheight.

Applying epoxy to the edges of several hundredplanks is a Significant part of the work of strip plankinga hull. You need a quick, efficient and clean methodfor mixing and applying the adhesive to plank edges.In the long run, we've found it best to spread the resinmixture with an inch-wide stick. We mix epoxy in atub, such as the WEST SYSTEM 805 Mixing Pot, mak-ing up only enough at one time to fill one third of thetub's volume. Then we stroke it along the edge of theplank with the stick, applying a controlled amount ofresin to the surface. If the resin is so thin that it runseasily off the stick, and perhaps off the edge of theplank, thicken it up with more filler.

After you have applied the thickened resin to oneedge of a plank, wet out the edge of the strip which hasalready been installed with a thin coat of standardepoxy. You can do this quickly with a foam roller cut toa good working length. Use the surmark you madeearlier to line up the center of the new plank and themiddle station. If the hull is very large, it's difficult forone person to install a plank without getting messy.Ideally, two or three people can work together, but ifyou are shorthanded, make some adjustable stands tohold the edges of the plank at the right height whileyou fasten its middle to the frames. As fastening prog-resses out towards the ends of the hull, move thestands inward, and then remove them.

Think of the plank which is being installed as theglue plank, and the plank which has already been in-stalled as the permanent plank. Begin by fastening the

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glue plank tight against the permanent plank aboutmidway along the hull. Insert a screw through the newstrip into the mold frame. Then skip one or two sta-tions, depending on the size and curvature of the hull,and insert another screw into a mold frame. Hold theglue plank tight against the permanent plank so thatthere is the best possible fit between them as you insertthe screw. After you have fastened it at several moldframes on either side of the mid-hull frame, the glueplank will be under reasonable control and you canfasten it easily to each frame in the set-up. If you haveapplied sufficient epoxy to the new plank, some shouldsqueeze out. Most of this will be on the exterior of thehull because of the tapered gap between the planks,but some will invariably end up on the interior. Re-move excess adhesive from both surfaces before itcures.

Edge Fastening

It is common to have some misalignment betweenplanks in the areas between the mold frames. To keepthis misalignment to a minimum, you should alloweach plank to take a natural curve as you bend itaround the hull. You can correct plank misalignmenteasily by edge nailing with the use of Va inch diameterwooden dowels. While you could use nails instead ofwooden dowels, dowels are preferable for several rea-sons. Because the hull will be laminated over anyway,the extra cross grain strength that nails might provideisn't needed. (Wooden dowels could also provide ex-

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Figure 4-Strip planking a 42 foot hull. These strips are beinglaid from a master plank at the bilge up to the keel.

cellent cross grain strength if they were bonded inplace.) Of the hundreds of nails that might be used in ahull, a small percentage will inadvertently breakthrough the sides of a plank. This is a particular prob-lem on the interior of the hull, because the nails are notonly unsightly, but difficult to sand smooth or remove.If a wooden dowel happens to run out in the planking,it is easily sanded smooth and is not particularlyunattractive.

To align the planking between frames, hold the glueplank and permanent plank between your thumb andforefinger so that they are in exact alignment. Thendrill a Va inch diameter hole through the edge of oneplank into the next, moving down the plank betweeneach station until you have drilled all of the holes whileholding the planking in perfect alignment. The holedrilling depth should be 1 Vztimes the planking width.Depending on the distance between frames, you mayneed from one to four dowels to hold the planks inproper alignment between stations until the adhesivecures. Drill the hole for the dowel slightly undersize, sothat the dowel fits snugly and helps draw the plankstogether. If available, a second person can follow downthe planks as the holes are being drilled, and insert andtap in place the Va inch dowels, while at the same timerealigning the planks with his hands to make sure thatthe predrilled holes line up.

Occasionally the dowels won't have sufficient hold-ing power to hold an errant glue plank snug against thepermanent plank. Besides causing an unsightly gap,this problem will cause the planking to get out of fair.To solve this, staple a strip of plywood to the glueplank and then hold it in proper position to close thegap. Staple the other end of the plywood strip to theadjacent two or three planks that you have alreadypositioned ....

After installing three or four planks, take the time to

Figure 5- The keel joint on 42 foot hull shown in Figure 4. Notescrew holes where strips are secured to mold.

remove any excess adhesive that has oozed out of thejoints from both the exterior and interior surfaces, tak-ing particular care on the interior to keep this surface asclean as possible, saving work later on. After thecleanup operation, check the edge joints to make surethat the alignment is good and that the planking isgoing on in nice, fair curves with no humps or bumpsdeveloping. You will also want to check the edge of thelast plank that you have installed to make sure that nobumps or unusual curves are developing along theedge that may cause difficulties when you try to fit thenext plank. If a bump does develop, it is best to fair itout before installing the next plank.

Difficulty may develop toward the end of the plank-ing job if the planks begin bending excessively in thewidth dimension, making it difficult to secure them inplace. If this problem becomes severe enough, you can

Figure 6-Laminating first layer of veneer over faired strips.Note planking bench to right.

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rectify it easily by installing one or two maximum ta-pered planks to reduce the amount of curve in thewidth direction. Do this by marking the maximumamount of taper available in the width dimension,using a heavy lofting batten to mark a nice, even curvewhich extends from' the middle of the plank out to atapered point at each end.

Although the planking will simply run out at mostareas of the hull and require no fitting, at some pointalong the keel the planking from one side of the hullwill begin to butt into the planking from the other side.Carefully cut the planking of the side done first to anice, straight edge that runs parallel to the centerline ofthe keel, so that an easily defined plane is availableagainst which you can fit the planking that runs in fromthe other side of the hull.

Figure 7-Laminating second layer of veneer onto hull.

Veneer Laminations

After you have installed all the planking, begin pre-paring it just as you would a mold for further veneerlamination. First check to make sure that you haveremoved all temporary metal screws and properly re-cessed all permanent screws. Next, rough trim all of theplanks which might run out at the sheer, the stem orthe transom, so that you have a roughly defined sur-face on which to laminate veneers. Rather than trimthe planking flush with these surfaces, allow them toextend an inch or two to provide a little extra area inwhich to extend laminating pressure. Later, after youhave completed laminating, you can trim the plankingflush with the desired surface.

Before you sand or fair, carefully check the entirestrip plank surface for voids and crevices in the plank-ing and in the joints between planks. Fill these voids,and holes in the planking at mold frame intersectionswhere you have removed temporary screws, with a

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thick mixture of epoxy and low density filler. Roughfair the hull, and then begin laminating veneer. .

You can laminate veneer to a strip plank hull exactlyas described for the mold method in Chapter 19, ex-cept that with strip planking you can install the first andsecond layers of veneer with alloy staples which do nothave to be removed. Leaving the staples in saves timeand helps make the strip plank method a practical con-struction technique.

Figure 8-Forty-two foot hull with temporary molds removed.Hull is supported by permanent bulkheads installed duringset-up. Note clean interior in which work can progress as ex-terior finishing is completed.

Begin the first layer of veneer about midpoint on thehull, using a thick low density adhesive mixture tobond it to the strip planking. Recess staples so that theywill not be in the way of rough fairing in preparation forthe second lamination. You can use the mechanicalspiling system with this and succeeding layers, andgreatly speed up the process. The strip plank hull is anideal solid mold for laminating: you will find that youcan laminate all layers of veneer quickly and efficiently,and probably in less time than it took to strip plank thehull. The quality mold surface also helps the hull sur-face remain very fair, with little work required betweenlayers, up through four or five laminations of veneer.

You can remove the temporary frames from the in-terior of the hull at a point during construction whenyou have applied enough veneer so that the hull isrigidly self-supporting. It's possible to disassembleframes, but probably faster to saw them out, beingcareful not to damage the hull. You may have enoughbulkheads and permanent frames in the set-up to sup-port the hull, but it's more likely that you'll need toprop up the sheer, bow and transom with blocking tohelp distribute its weight. Do not, of course, cut the legsoff permanent frames at this stage.

Figure 9-Launching 42 foot yacht. The natural finish high-lights final layer of veneer laid fore and aft.

Final Finishing

With the temporary frames removed, you can worksimultaneously on the interior and exterior surfaces.It's usually easiest to sand interior planking smoothwhile the hull is upside down, so that dust settles to thefloor rather than to the bottom of the boat. Install goodlighting in the interior, provide ventilation with fans,and wear a dust mask. If you have not done so al-ready, cover all prefinished items with tape to protectthem from damage from dripping resin and duringsanding.

We use a polisher with 80 grit paper on a soft foampad to rough sand and fair interior planking. When thesurface is generally smooth and fair, we finish sandwith orbital sanders and 100 grit paper until the surfaceis smooth enough to receive an initial coat of WESTSYSTEM resin.

Although it is not absolutely necessary, you mayprefinish the entire interior while the hull is still upsidedown. It's our experience that all sanding and coatingoperations are much easier with the hull in this positionthan when it's upright. A good portion of the interiorcan be easily installed in an upside-down hull, as willbe explained in more detail in Chapter 24. Just as withmold method hulls, it is more efficient to do a lot ofexterior final finishing, including all fiberglassing, coat-ing and sanding, before turning the boat over.

Build a cradle, as described in Chapter 19, in prepa-ration for rolling. Unlike a molded hull, which you mustlift up and off the mold and then turn over, a strip

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Figure IO-Stripper canoes built by Herschel Payne. Western red cedar and WEST SYSTEMepoxywere used for both boats.The 15 foot model weighs 32 Ibs. and the I8-footer weighs 48 Ibs.

plank hull is simply pushed over, using mattresses andtires covered with carpet to absorb the load. Beginrolling by lifting one sheer continually upward, block-ing the hull as you go. When you have raised the sheerto about a 60° angle, attach lines to it, some going inthe direction in which the hull will be rolled and someleading in the opposite direction, so that people hold-ing them on both sides of the hull can control it. Unlessthe boat is unusually large, a few people can pull itover, while others hanging onto the ropes on the op-posite side snub their lines around a post or heavymachinery to slow the rate of fall until it sits gently onits bottom. Set the cradle under the hull and level itaccording to the waterlines so that you can completethe interior and install the deck.

Strip Composite Construction

The use of strip composite construction has beenlimited to stripper canoes, rowing shells, prams anddinghies. Although the strength and stiffness of strippercanoes have been proven through use for years, stripcomposites have never been subjected to controlledtesting. There is no body of data from which to drawideas for using stripper methods on other types of smallcraft.

We hope that this situation will change. Strip com-posite construction has some very attractive features.Veneer spiling and fitting are unnecessary and onlymold frames are used, so the method is very quick.You can use lumber from your local dealer rather thanveneers, which can be hard to find. The techniqueworks well on compounded hulls and results in verystrong and stiff small craft with little or no interiorframework.

In an effort to expand its applications, we haveexamined several aspects of strip composite construc-tion. Our approach has been to evaluate the relativeeffects of various weights and numbers of layers ofglass cloth and to explore the relationships betweenthese and wood core thickness in terms of stiffness,ultimate strength and weight. Our results provide pre-liminary suggestions on the best ways to build strength

. and stiffness into stripper hulls.Glass fabric is used in strip composition construction

to supply cross grain strength to wood planking. Inmore traditional methods, closely spaced ribs serve thisfunction. While two layers of cloth and 1f4 inch plankingare sufficient to support a canoe, this schedule is in-adequate for larger hulls. Two approaches to increas-ing strength and stiffness are adding extra layers of

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cloth and increasing planking thickness. Our testingindicates that, up to a certain point, adding more fi-berglass to a hull justifies itself by increasing strengthand stiffness disproportionately to the increase inweight.

Our data are intended to be used for the purpose ofranking materials and cannot be used to predictwhether a material will prove satisfactory in service.Figure 11 shows the effects of increasing plankingthickness while maintaining a typical stripper canoefiberglass schedule. Data on ~ inch okoume plywoodwith no cloth are provided as a control. Other testinghas demonstrated that the impact resistance of a com-posite can be substantially increased. by balancingpanels with layers of fiberglass or aramid cloth on bothinterior and exterior surfaces.

Building a Stripper Canoe

Excellent detailed instructions for building strippercanoes with WEST SYSTEM epoxy have been pub-lished. If you have any problems finding a book on thesubject, please call us for sources. The following briefoutline presents but one of the many variations on thetechnique.

Setting up for a stripper canoe is not much differentfrom setting up for a strip plank hull. You can use astandard four-sided strongback, but a three-sided,U-shaped foundation made of two 2 x 4' s and one 2 x6 is strong enough for a 17 foot canoe. Set up moldframes and stems to define the hull shape and boltthem to the strong back. Fair the set-up, and then tapethe edges of the frames or cover them with plastic strips

so that they will not be bonded to the hull.Many strippers are planked with western red cedar

and sheathed, inside and out, with 4 oz. or 6 oz. fi-berglass cloth. One of the most efficient ways to pre-pare stock for planking is to buy nominally 3,4 inch thickflat grain boards, rip them to ~ by % inch edge grainstrips, and then scarf them to length. Depending uponthe design, only about 30% of the strips will need to bethe full length of the craft.

Begin by planking the bottom of the canoe fore andaft, starting at the centerline and working out on eachside. Edge glue the planks with a thickened low densityepoxy mixture and use staples for temporary pressureuntil the epoxy cures. Wire brads or finish nails can beused at the stations. The flat bottom section of a canoeresembles a football.

When the bottom is planked, begin on the topsides.In most canoes, this and the bottom planking run atdifferent angles so the strip which joins the two requiresspecial fitting. Begin midway down the boat and workup and down from there. The strips should lie higherabove the waterline at the bow than at the mid-section.Scribe and fit the final plank to the bottom.

Remove staples and nails when the epoxy hascured. Fair the canoe, first with a block plane and thenwith an 11 inch long sanding block. When you aresatisfied, clean the surface and apply an initial coatingof WEST SYSTEM resin. Allow this to cure, lightlysand and clean the surface again, and apply 4 oz. or 6oz. woven fiberglass cloth.

Use the dry method for applying cloth described inChapter 12 to apply the fabric. Fit and cut it and place

Figure ll-Preliminary results of testing of strip composite samples.

Twelve inch square samples of a variety of combina- additional layers of fiberglass and epoxy, but up to ations of western red cedar and fiberglass cloth were point strength and stiffness increased dispropor-weighed and subjected to increasing loads to failure. In tionately to weight. In order to compare these resultsall cases, 6 oz. glass cloth was applied to both sides of with conventional materials, we also tested a sample ofthe samples. The goal of this experiment was to gauge ~ inch okoume plywood which was not covered withthe relative effects of wood core thickness and quantity fiberglass cloth. The plywood sample failed at 225 lbs.,of fiberglass cloth on strength, stiffness and weight in weighed 10.7 oz. and deflected .63 inch.stripper construction. Samples became heavier with

Cedar Planking Average Pounds Average Weight Average DeflectionThickness to Failure per Square Foot at Failure

3/16 in. 214 8.0 oz. .73 in.1/4 in. 221 9.8 oz. .49 in.

5/16 in. 300 11.6 oz. .48 in.3/8 in. 298 13.1'oz. .32 in.

it over the entire hull exterior. Pour mixed resin ontothe cloth and spread it out with a plastic spreader. Theglass should be clear but slightly dull.

When the first layer of cloth has cured, apply a sec-ond layer to the bottom, allow it to cure, and lightlysand it, feathering the edges of the fiberglass. Coat thehull as many times as necessary to fill the cloth's weaveentirely. After the resin has cured, sand again, first with80 grit paper and then with 120 grit paper until thesurface is smooth and dull.

At this point, build a cradle. Unbolt the mold framesand turn them sideways to free the canoe. Turn theboat over, and place it in its cradle. Sand the interiorwith a disc sander and soft foam pad as well as with ablock where necessary. Apply fiberglass on the insideexactly as you did the outside, with one overall layerand a second layer in the flat bottom section.

Layout the sheer clamp and trim it to shape. Lami-nate gunwales and breasthooks. Double check thewidth of the hull, and install thwarts. These are usuallyhung from screws which fasten up into the gunwales.Build or buy seats to your liking, install them, and finishthe canoe as you would a strip plank hull.

Strip Composite Components

Strip composite construction methods can be usedto build many boat parts. One of the more interestingapplications is in building spars up to about 30 feetlong. The same technique may be used to build cabintops and other panels and components where designconsiderations favor low weight and minimal interiorframing or where heavy compound curvature pre-cludes the use of plywood.

In the past, solid masts were built by shaping arectangular piece of wood into an airfoil and then, ifweight was a problem, hollowing out the center. Wesuggest that instead of building spars this way, youbegin with a male form which describes the shape ofone half of the mast, strip plank it, sheath it with glass,make a second half, and then bond the two together.The resulting spar is lightweight and can be designed toreceive specific loads.

181

)4: )(~. o<rch 9trip

Figure 12-Building a strip composite spar.

Because this type of construction has not beenwidely used, we cannot recommend strip dimensionsand fiberglass schedules. Smaller spars will probablyrequire both high density wood strips and softwood. Itis possible to taper the wall thickness and section of afreestanding mast, but as with all other aspects of stripcomposite spars, careful study must be made to cor-rectly address anticipated loading.

A strip composite mast is built in two halves whichare later joined. Set up a mold much as you would fora stripper canoe, except that it will only define half thespar. We suggest using Vz inch plywood for the for-mers' and that they be placed about a foot apart alonga strongback as in Figure 12. Prepare desired stock forstrip planking as described earlier in this chapter.

There are several ways to plank a strip spar. You canlay strips over your frames, spot bonding as you go,and then, when they are all in place, fill all the gapswith an epoxy/high density filler mixture in one opera-tion. One builder reported that he was able to hold thestrips in position with tape until he was ready to bondthem. If you are reluctant to try one of these ap-proaches, edge glue and staple the planking as youwould on a stripper canoe.

When the resin between the strips has cured, re-move the first mast half from the mold, and applyfiberglass to its inside. Make a second strip half, applyfiberglass inside, and then bond the two together. Fairthe exterior surface and cover it with fiberglass cloth.