Ships – Hull or hull adjunct employing fluid dynamic forces to... – Stepped hull
Patent
1993-10-28
1995-09-26
Avila, Stephen
Ships
Hull or hull adjunct employing fluid dynamic forces to...
Stepped hull
B63B 132
Patent
active
054526752
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a boat hull.
This invention has particular but not exclusive application to outboard motor powered planing boat hulls, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as inboard powered planing vessels and airboats.
In general, outboard motor powered boats have evolved from hull shapes generally designed for inboard power. Such hulls generally include a bottom part including a keel extending from stem to transom, the keel and its immediate surrounds providing a planing surface at speed. One disadvantage of this traditional type of planing hull is the disruption of the water behind the planing surface, which leads to propeller inefficiency. Of course, in single motor applications, it is generally unavoidable that the planing surface precede the propeller along the centreline of the hull.
It has been proposed to partially overcome the disadvantages of traditional hull design by use of an extended transom or pod. However, the extended transom or pod places the weight of the outboard significantly behind the normal position relative to both the centre of gravity of the assembled rig and the planing surface at speed, disturbing the balance of the boat.
As an improvement in the traditional planing hull and avoiding the disadvantage of pods or extended transoms, it has been proposed to step the transom to the keel of the hull to separate the keel from the propeller. In general such stepped designs include the underside of the step as part of the planing surface or at least part of the bearing surface under displacing conditions. Accordingly, such surfaces are generally provided with strakes and other interactive protuberances. Australian Patent Application No. 17654/88 discloses a hull having a transverse step of generally horizontal disposition and extending from the transom for approximately 5 to 15% of the waterline length of the hull ahead of the transom. It has been found that the disclosed apparatus when planing interacts with the surface 17 as much as the keel 11, generating spray and turbulence ahead of the propeller, and thus providing a source of inefficiency.
The present invention aims to alleviate the above disadvantage of conventional boat hulls and further aims to provide an improvement over current stepped transom designs, and to provide a boat hull which will be reliable and efficient in use. Other objects and advantages of this invention will hereinafter become apparent.
With the foregoing and other objects in view, this invention in one aspect resides broadly in a boat hull of the type including a keel, a transom, and a recess extending forward from said transom, said recess extending ahead to relieve said keel for substantial part of the waterline length of the hull.
The hull may be of any suitable type including monohulls and multihulls. Where a multihull or power cat type hull is required, a recess may be provided for each hull or keel or alternatively the recess may extend across both keels.
Preferably, the recess relieves the keel forward of the transom for at least 25% of the waterline length of the boat at planing speeds, with it being particularly preferred that the recess relieve the keel ahead of the transom for at least 40% of the planing waterline length. Typically, relief of the keel for 40% of the waterline length on the plane will amount to approximately 25% of the waterline length under displacing conditions. For typical deep-V type hulls, such criteria Will translate to a recess length of at least 20% of the overall length, depending on the gross weight, speed and deadrise angle of the hull.
Preferably, the recess is configured such that at planing speeds the upper surface of the recess is substantially clear of the water surface. This provides for relatively uninterrupted water for the propeller, as well as decreasing the wetted area of the hull on the plane. A performance improvement, thought to be caused by the decreased wetted surf
REFERENCES:
patent: 1396831 (1921-11-01), Gardner
patent: 1831339 (1931-11-01), Brush
patent: 2791195 (1957-05-01), Almqvist et al.
patent: 3382833 (1968-05-01), Wukowitz
patent: 3547064 (1970-12-01), Glass
patent: 4655157 (1987-04-01), Sapp
patent: 5140930 (1992-08-01), Lund
patent: 5191853 (1993-03-01), Adler
Avila Stephen
Nevid Nominees Pty Ltd.
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