GB2371776A - Trimaran with plate means to reduce drag - Google Patents

Abstract

A trimaran vessel has a pair of outer hulls 2A and 2B arranged symmetrically about a centre line of the vessel and a central hull 1 lying along said centre line and attached to said outer hulls by means of connection beams 3A and 3B. The sides of the central hull 5A,5B and 7A,7B converge to a point lying on the centre line at each end of the hull to form a pointed bow and stern, while the point of maximum beam lies at or aft of the longitudinal midpoint of the hull. The central hull also has a generally horizontal plate 4A and 4B extending out from both sides of the stern in the plane of the bottom of the hull (6A, Fig 2), said plate extends from the stern, forward to the point of maximum beam and has outer edges that are parallel with the centre line of the vessel.

Description

The invention relates to trimarans. The central hull of existing vessels experience a full water flow about their aft facing under water surfaces. This causes drag. Usually this drag is minimised by light weight construction. Such weight restrictions limits the use of these vessels.

It is the object of this invention to introduce air to the under water aft facing hull surfaces, thereby reducing the drag prior to being lifted out of the water by heeling of the vessel. In this instance'a sailing trimaran.

According to the present invention a trimaran comprising a central hull and two outer hulls identical and symmetrically arranged one on either side of the central hull that is symmetrical about its center line and cross means joining all three hulls, the central hull supporting the vessels weight when upright and stationary, having a maximum beam at or aft of its midpoint, comprising bow, outer and lower sides, such that the bow sides diverge to the said midpoint the lower sides continue from the midpoint to the stern with the addition of a plate attatched to the said lower sides as an aftward extension to the stern such that the projected under water area is not less at the stern than at midships and that the said plate is as wide at the stern as at the hulls midpoint together with its longitudinal edges parallel to the center line, and the said outer sides aft of the midpoint substantially converge to the center line above the afore said plate of the lower sides.

A specific embodiment of the invention with reference to the Figures/to Figure/ Figures/and Figure/are perspective viewes of the vessel from astern.

Figure being of a sailing trimaran and Figure pizza power trimaran.

Figure is a view of Figure/in elevation and Figure 3 a plan view of Figure/.

\ Figure 4 Figure Figure 9 Figure 0 Figure 2-are all elevation views of the central hull in Figure and Figure/4.

Figure S- Figure 7 Figure 1 Figure I ! and Figure/3 are cross sectional views of the central hull in Figure/and Figure/ at locations identified in each elevation FigureFigure Figurec' < /0 and Figure With reference to Figure l and Figure Z. and Figure the central hull/is connected to the two outer hulls 2A 2 R that are symmetrically arranged about the vessels center line and connected to each other by cross members 3 3s The central hull is also symmetric, Beneath the waterline a bow side 7 leads to a midship midpoint. A lower side continues from the midpoint to the stern. A plate 4 ils an aftward continuation and extension of the lower side. Sidesof the hull are an aftward continuation of the sides at the midpoint and substantially converge to the center line terminating at the stern above the upper surface of the lower side or plate .

Figure 2 shows a mast/0 rudder 1 and a keel that is fixed or moveable 8. Figure/ shows a proposed layout for a power vessel with the two outer float hulls-c2with an integrated bridging structure 3C joining all three hulls. The two outer hulls may be of a shape that allows the vessels propulsion units within.

In Figure 4 Figure 6 Figure g Figure/ Figure/2. the line Z. represents the chine line in each respective Figure in cross section.

I The liner-vis an extension of the liney-Z, and indicates the outer edge of the extension plate Lf,. The two said lines should form a continuous fair curve.

Figure represents the the sections of a hull in which the angle of deadrise at the stern is generally horizontal with little change throughout the stern part.

In Figure 7 the angle of deadrise at the stern is generally horizontal but has decreased throughout the stern part.

In Figure Cj at the stern the angle of deadrise is generally horizontal and has decreased throughout the stern part but in a different way than shown in Figure 7.

In Figure If is shown a hull in cross section having an angle ouf/. degrees deadrise throughout the stern part.

In Figure I 3 shows a solution that combines the desirable features of Figure//and Figure 7. In Figure/7 and FigureZ3 a buttock line (the line of intersection of a vertical longitudinal plane with the lower sides) taken through the discontinuity in the plate ; to produce the line-in Figure/Z. The said discontinuity viewed in plan is parallel to the center line. Figure t 3 shows the outer part of the plate 4 C cranked upwardly outward at aL decreasing angle throughout the stern part. At the stern" part 4- c to be generally horizontal.

The Figures/'-/4 are only simple representational diagrams.

The said plate ; Xc may be when viewed in cross section planar, actuate, or multi curved changing gradualy from one cross section to the next.

Similarly the lower sides of the central hull may be planar, arctuate, or multi curved changing gradualy from one cross section to the next.

In all embodiments of the invention it is preferred to extend the outboard edge of the said plate 4 outwardly to at least the vertical that II Co cuts the waterline at that widest midpoint.--. - . The vessel is only viable taken as a whole, the center hull will not operate, it is laterally unstable, without the two outer float hulls.

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In operation at low speeds below y '"/' < ? the flow of water over the upper surface of the plate 4 and the sides 5 will be at a level similar to that of the vessel's- ; wate. rlihe'. when uDright' : and. at & tiohary. With increasing speed 7-/-2 range a progressive an. R t.. ionary. 1 mcreaslng spee WL.. - - range a progresslve reduction in the quantity of water flow'over the upper surface of the plate S occurs, ant eventually the upper surface looses

all water flow. Bow down trim has become evident. The vessel is not planing as there is not sufficient upthrust from the dynamic pressure upon th underside of the hull. The bow down trim comes as the result

of the hydrostatic upthrust upon the plate as the water is replaced by air. This in conjunction with the vessels at rest longitudinal position of its center of gravity causes the hull to pivot. Increasing the speed ./''increases the dynamic upthrust in the bow ple/Lvi part to restore the hull to a level position. It will be noticed that the vessels center of gravity has lifted above its location when

the vessel was stationary. Further increases in speed are available without the threat of porpoiseing, as the hulls center of gravity is unlikely to wander aftward of the dynamic center of the hulls underside.

For low drag at low speed it is necessary to minimise the pressure differential across the wake. To achieve this an unristricted supply

of water from laterally outward of the hulls sides 5" and its streamline flow above the plate A and into full intimate contact with the sides is essential.

It is therefore preferable that access to the sides-3 should be laterally totally open. This is available using Figure In practice this Figure S- hull form may be less acceptable than a hull with deadrise Figure 7 but with a restriction on the water accessability to the sides This will increase the projected cross sectional area of the vessel and thefore increase its drag.

Figure aims to minimise the increase in the projected cross sectional area.

A prefered embodiment is shown in Figure 12 and Figure 1.. 3 in which the outer part of the plate 4 is cranked to a smaller angle of deadrise than the more inward part . The cranked plates twisting longitudinally so that at the stern it is generally horizontal.

Claims (6)

1. CLAIMS Claim I.

   A multi hulled vessel of trimaran configuration that comprises two outer hulls that are symmetrically arranged about a longitudinal center line with connecting beams to which is attached along that center line the main bouyancy provider a double ended central hull of symmetrical form having on each side of its center line a bow, a maximum beam at or aft of the midpoint here-in-after called the maxpoint, outer sides, lower sides at least in the stern part, and lower side plate, the said bow leads divergently of the center line to the hulls said maxpoint thereof and aftwardly to the said outer side that converges substantially to the center line at the stern, the said lower side continues from the said maxpoint to the stern, the said lower side plate is attached to the hull providing an aftward continuation of the said lower side, this plate has upper and lower surfaces and-is generally horizontal athwart ships at the stern extending forwardly

   throughout the hulls stern part to the said maxpoint, the . outer edges of the plate being parallel to the hulls center line.
2. Claim 2.

   A hull as claimed in Claim I in which the outer longitudinal edge of the said lower side plate extends outwardly beyond the vertical that cuts the waterline at the said maxpoint.
3. Claim 3.

   A hull as claimed in Claim I and Claim 2 in which the said lower side and said lower side plate are generally horizontal in the stern part of the hull.
4. Claim 4.

   A hull as claimed in Claim I and Claim. 2 in which the said lower side-and said lower side plate twist longitudinally from athwartships horizontal at the stern to an angle of deadrise at the said maxpoint.
5. Claim 5.

   A hull as claimed in Claim I and Claim 2 in which the said lower side and the said lower side plate twist longitudinally about an axis parallel with the hulls center line but outward from it, twisting from athwartships horizontal at the stern to an angle of deadrise at the said maxpoint.
6. Claim 6.

   A hull as claimed in Claim I to Claim 5-inclusively with

   0 reference to Figures 5 Figures 7 and Figure 9 are structured using straight lines but may be equally valid using curved lines appropiate to maintaining the essence of the description.