MULTI-HULL VESSELS

ADVANCEMENTS & BACKDROPS

SCOPE• Introduction•Origin & History•Today’s scenario•Features•New advancements•Future prospects•Backdrops

INTRODUCTION•A multihull is a ship, vessel, craft or boat with more than one hull.•Comprise a great variety of types, sizes and applications.•Consist of various numbers of hulls and of hulls of various common or uncommon shapes and/or hulls with a SWA.

INTRODUCTION•Different types of multi-hull ships differ from each other and from mono-hull ships due to their own specific features•Firstly, it must be noted, that variously shaped hulls can be applied as parts of multi-hull ships, including SWA hulls, which have no transverse stability, unlike single hulls.•These hulls can be asymmetric relative to their own longitudinal axes.

ORIGIN & HISTORY•Prior to about 1850, the principal requirement maximum stowage space.•Speed - never an issue.•Only since the introduction of mechanical propulsion and the socio-economically-driven development of international trade.

ORIGIN & HISTORY•Today, greater speed can provide a commercial edge in getting the product to the market as well as suiting the modern rapid lifestyle.•Greater speed might be achieved by greater installed propulsion power, but usually it is more efficiently obtained by the minimization of resistance.

Hull form determines the resistance of the craft

ORIGIN & HISTORY•Solution for a mono-hull to achieve low resistance:

•Minimum displacement•Minimum beam•Greatest practical length.

ORIGIN & HISTORY•Unfortunately these three hull characteristics not only affect the resistance, but the stability characteristics and the payload capacity. A long thin lightweight mono-hull may have the minimum of resistance, but would exhibit poor and probably inadequate stability.

THE NEED

•An obvious solution to this dilemma of poor stability is to add one or more stabilizing hulls to the main hull, and this is the basic reason for the success of the multi-hull as a high-speed craft.

THE NEED

•The advantages of a high L/B ratio in minimizing resistance, are such that a catamaran (L/b = 15) will have considerably less resistance than a mono-hull (L/b = say 6) of equal Δ and L, despite having two hulls.

TODAY’S SCENARIO•A wide development of various multi-hull ships began in the second half of the twentieth century.• small sized twin-hull boats for fishing, tourism, pleasure, working• twin-hull ships function as fast ferries (today about half of fast ferries are catamarans)

TODAY’S SCENARIO•Semi-submersible structures for drilling and auxiliary services at sea.•About 70 twin-hull ships with small water-plane area.•Some triple-hull ships and boats (the main hull and two small side hulls – “outriggers”).•Twin-hull ships with a main hull and one small side hull (outrigger), known as “proas”.

Multi-hull ships with traditional hull shapes: 1, 2 – catamarans, symmetrical and asymmetric hulls;

3,4 – trimarans, symmetrical and asymmetric hulls;

5 – catamaran with staggered hulls;

6 – proa;

7 – ship with (two) outriggers

FEATURES•A great number of type and shape options with various characteristics.•Larger relative deck area.•More or less higher seaworthiness.•Any needed initial stability without any restriction of the hull aspect ratio.•Large above-water watertight volume.

FEATURES•Possibility of wet deck slamming.•A sufficient influence of transverse external loads on strength.•Deck area:• 2.4 – 4 times larger for a catamaran; • 1.9 – 2.3 times larger for a twin-hull SWA ship; • 1.6 – 2.3 times larger for proa; • 1.3 – 2.3 times larger for an outrigger ship with an

SWA main hull.

NEW ADVANCEMENTS

WAVE-PIERCING’ TRIMARANS

WAVE-PIERCING’ TRIMARANS

•Doubled speeds (in comparison with contemporary level).•Increased seaworthiness and minimal wash.•Sufficient air-borne unloading capacity.

WAVE-PIERCING’ TRIMARANS

•Restricted at the top speeds only by the power capacity of existing gas turbines.•No mono-hulls can ensure such speeds together at the required level of sea keeping.

SEMI-PLANING SWA MONO-HULLS WITH FOILS

SEMI-PLANING SWA MONO-HULLS WITH FOILS

• A higher level of sea keeping.

• greater speeds in waves.

• suitable for fast battleships.

• SWA corvettes.

CONTAINER-CARRIERS

CONTAINER-CARRIERS

•Small design draught.•High degree of seaworthiness can be ensured by an outrigger SWA ship-platform as a feeder carrier of containers.

CHINA DEVELOPING 180,000-TON CATAMARAN AIRCRAFT CARRIER

BACKDROPS•The wider overall beam of a multihull vessel is often a problem for conventional docking.•Relatively greater total wetted area increases the frictional component of water resistance of the vessel, and thus the total resistance at low speeds.

BACKDROPS•Weight of hull structures per ton of displacement is greater than that of monohulls.•Assembly of a multi-hull vessel in a shipyard takes a wider area; as a result, the construction cost and maintenance (in dry dock) can be greater.

BACKDROPS

•All multihulls are less applicable ships in ice than monohulls.•The main problem of designing is the restriction of all disadvantage results and full application of advantages.

REFERENCE

•Multihull Vessels, Dubrovsky (2000).•Google.com•Sailyachts.com•Wikipedia.org

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