Multi-hull boat

Abstract

A multi-hull boat 50 comprising a pair of side by side hulls 21, and a wingdeck 22 extending between the hulls 21, wherein the hulls 21 include inner topsides 23 which are adapted to inhibit the hulls 21 from pitching.

Description

FIELD OF THE INVENTION [0001] The present invention relates generally to boats and in particular, to multi-hull boats. [0002] Although the invention will be described with particular reference to power catamarans, it will be appreciated that the invention may be incorporated into other types of multi-hull boats. BRIEF DISCUSSION OF THE PRIOR ART [0003] A catamaran is a type of boat which has two side by side hulls which are joined together by a wingdeck. The portion of the side of each hull which faces the other hull and which is located above the waterline is referred to as the inner topside of the hull. The inner topsides of the hulls together with the underside of the wingdeck define a hollow region or tunnel. [0004] There are two main types of catamarans: sailing catamarans and power catamarans. Sailing catamarans are primarily wind-powered and include one or more sails for catching the wind. In contrast to sailing catamarans, power catamarans are usually primarily powered by an...

AI Technical Summary

Benefits of technology

[0027] The inventor has found that adapting the inner topsides to inhibit the hulls from pitching improves the rough water ride of multi-hull boats and inhibits waves from slamming into the wingdeck. Inhibiting waves from slamming against the wingdeck reduces the potential for structural damage to the wingdeck. It also assists in minimising the wetted surfaces and therefore the drag of multi-hull boats in various conditions.

[0031] Preferably, each inner topside includes at least one chine, and at least one inclined surface which is inclined towards the other inner topside. The chines and the inclined surfaces are able to inhibit pitching of the hulls in rough water which inturn inhibits waves from slamming into the wingdeck. In particular, the chines and the inclined surfaces are able to cushion the descent of the boat into a wave and to deflect the wave so that the wave is inhibited from slamming against the wingdeck. The chines and the inclined surfaces also increase the reserve buoyancy of the boat.

Problems solved by technology

This is undesirable because it can make it uncomfortable for those who are onboard the catamaran and can damage the wingdeck of the catamaran.

This problem sometimes occurs because there is inadequate tunnel volume or clearance between the wingdeck and the water to accommodate the waves which pass between the hulls.

If the strength of the wingdeck is increased so that the wingdeck is able to withstand greater slamming loads, and the overall weight of the catamaran is increased as a consequence of the strengthening, the problem can become even worse.

In some cases it is a lack of reserve buoyancy or overloading in the bows that will cause a catamaran to pitch more than it should and therefore drive the wingdeck down into the waves and cause slamming against the wingdeck.

Planing power catamarans do create aerodynamic lift at higher speeds, which softens the ride, however when conditions cause them to come off the plane they are vulnerable to heavy slamming, particularly as many of them have very little or no wingdeck clearance when at rest.

Whilst the noise and dramatically increased structural loads are the obvious effects of low wingdeck clearance and tunnel volume, there are some other less obvious effects which slow the vessel and decrease fuel efficiency.

This causes drag by increasing the wetted surface of the vessel, and sometimes causes a kick in the stern if there is a small slam.

The resultant drag slows the vessel or places a greater load on the engines of the vessel which results in increased fuel consumption.

This effect can be caused by either the shape of the hulls or by the hulls having too narrow a beam which causes the pressure waves created by the bow sections to meet too early under the wingdeck rather than aft of the boat.

Unfortunately, it has the disadvantage of increasing the wetted surface of the vessel dramatically and therefore slowing the vessel, making the vessel more vulnerable to a second wave pooping it (i.e., breaking over its stern).

It also increases the fuel consumption of the vessel as more power is needed to overcome the wetted surface.

Whilst these do not add to the wetted surface dramatically, they are very noisy and, if they strike a relatively weak area of the wingdeck, they can damage the wingdeck due to the localised nature of the force which they exert on the wingdeck.

Unfortunately, like all design features, there is a different “balanced” wingdeck clearance which is practical for different size vessels.

If the wingdeck clearance of a particular vessel is higher than the balanced clearance for that vessel, the vessel will look silly, the accommodation which is available on the vessel will be greatly reduced, or the vessel will have too much windage and will consequently be difficult to manage in a cross wind.

Whilst the mathematical distinction between displacement and planing hulls is much harder to define in power catamarans, the requirements for seakeeping are not.

Higher bows with their increased windage have a detrimental effect on the windward ability of a sailing cat as the windage pushes the bows to leeward.

In particular, the leeward bow of sailing catamarans tends to be depressed.

This will lead to a more severe slam when it does occur and a far more dramatic slowing of the vessel as not only is the wetted surface of the vessel increased, but the vessel will also be required to climb over the wave rather than slide over it.

Other disadvantages to starting the wingdeck further aft on a power catamaran are reduced torsional rigidity and increased wetness as the spray off the bows is compressed between the hulls and blown up between them on to the deck.

Although the stringer types break up the water reasonably well and stiffen the panels of the wingdeck, they do not provide much reserve buoyancy.

The wide shallow type were not much good for anything as they just filled the tunnel volume up and provided more flat panels for water to slam against.

Whilst these go some way to breaking the water up and increasing the buoyancy of the vessel, they often negate the benefits by funnelling the water into the now two smaller tunnels located on either side of the third hull and increasing the velocity of the water when it finally hits the wingdeck panels.

This slows the vessel and increases the power required to maintain the speed of the vessel.

Unfortunately, because of the lack of reserve buoyancy in their small outer bows, wave piercers have a strange corkscrew motion in a quarter following sea and therefore an inclination to suffer wave slap on the outer sections of the nacelle, which can be both noisy and damaging.

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