Ships – Hull or hull adjunct employing fluid dynamic forces to... – Having fluid channeling or entrapping configuration
Reexamination Certificate
2001-04-27
2002-07-30
Basinger, Sherman (Department: 3617)
Ships
Hull or hull adjunct employing fluid dynamic forces to...
Having fluid channeling or entrapping configuration
C114S290000, C114S291000, C114S343000
Reexamination Certificate
active
06425341
ABSTRACT:
This invention relates to a boat hull.
TECHNICAL FIELD
This invention has particular but not exclusive application to outboard motor powered monohull 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 multihull vessels, seaplane floats or the like, inboard powered planing vessels, inboard outboard powered planing vessels, jet powered boats including personal jet skis (personal water craft) and airboats.
BACKGROUND OF INVENTION
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 with monohulls, 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. This problem is exacerbated with the new heavier
4
stroke outboards becoming popular around the world.
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 (Haines 1988) 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.
U.S. Pat. No. 1,396,831 (Gardner 1921) discloses a hull having a hull relieved by a cavity, the side walls of the cavity being configured to rake directly aft from the keel step to the transom and the recess defined thereby opens out essentially across the full width of the transom. The rake angle of the side walls, diverging sharply from the step, introduces cavitation in the turns. That this appears to have been an inherent problem with the apparatus disclosed in the cited reference becomes apparent when it is observed that the propeller is shown very low in the water. The decreased buoyancy of the aft portion of the vessel brought about by the substantially full-width transom opening results in the transom opening of the recess being fully submerged, and is thus not vented through the transom to assist initial release. The disclosure will also, by virtue of the limited lift aft and small planing surface area at the transom, be prone to porpoising until planing at high speed. Given the long length of the recess, this would have further increased the cavitation tendency mentioned earlier.
FIG. 1
of the reference illustrates an apparatus wherein the top surface of the recess is minimally above the water line at rest. At low speed the cavity would be fully submerged as the application of power tended to drive the stern downward.
Similarly, reference DE 410034 (Bonnemaison 1925) discloses apparatus having a recess which is triangular and thus has all of the disadvantages inherent in the Gardner apparatus. The recess is almost full length and again it is full width at the transom. With the very small planing surface area near the transom, the present applicant doubts that the design would work and if it were to be operable at all, very large levels of power would be required to get it planing and it would be very prone to porpoising at low planing speeds.
With reference to U.S. Pat. No. 1,831,339 (Brush 1931), this discloses apparatus including a recess which is parallel sided and transverse to the boat at the front, like that referred to Australian patent application No 17654/88 (Haines 1988). The step extends for the full width of the hull and thus does not have stability in turns, since the downwardly depending side portions are substantially absent for a considerable distance aft of the step. The aft planing surfaces at each side of the hull are substantially flat and high lifting, preventing vessel trimming at speed. The disclosed apparatus uses a complex bottom in an attempt to have all 3 water contact points separated, and in this respect the disclosed apparatus is directed to effectively a planing multihull or foil borne apparatus rather than a planing monohull. The separation of the planing surfaces appears to be driven by a belief that all parts of the boat should operate in undisturbed water. This would greatly add to the manufacturing costs and because each of the rear planing surfaces is essentially horizontal, it will give excess spray in front of the propeller and so cause cavitation like the apparatus disclosed in 17654/88.
With reference to U.S. Pat. No. 3,547,064 (Glass 1968), the disclosed apparatus has a recess that is triangular and full width with the attendant disadvantages described above. The cited disclosure describes a hull adapted to touch the water at the transom immediately in front of the propeller when on the plane. The disclosed apparatus thus lacks the advantage of AU668684 of minimising the water disturbance in front of the propeller.
As the transom is not open, venting internally is necessary until the boat runs at very high speed. The disclosed apparatus has two delta shaped contact points with the water. As a result of the transom contact and the full width step, the venting is complex and therefore expensive. Because of the relatively small contact area at the transom, the applicant would expect that the disclosed boat, like the Gardner and the Bonnemaison designs, would be very prone to porpoising until running at very high planing speeds. The disclosure of the reference is express, at page 2, line 60, that the rear recessed section should be parallel with the front planing section. Page 4, line 3 of the disclosure also states an aim of trying to develop an air cushion requiring complicated venting and an attempt to introduce ram air.
WO 89/02846 (Monocat Powerboats) discloses apparatus having a catamaran form aft for planing With a deep-V form forward for sea keeping qualities. The disclosed apparatus is borne on three points. The tunnel shape is not a shape consistent with efficiently getting the boat on the plane or allowing the propeller (or propellers in the case of twin motor applications) to be mounted high and therefore to decrease the boat draft. The drawings of the reference show high speed ocean type race boats where these attributes would have not been important. The apparatus does not disclose placing the propellers behind the tunnel because the water there will be very disturbed because of the divergent shape of the tunnel. This design therefore will not achieve the objective of having relatively undisturbed water in front of the propeller and so increase the propeller efficiency. The drawings of the cited reference show the propellers behind the deep vee and this is only acceptable in race style boats using very expensive surface chopper propellers.
Australian Patent 668684 discloses a boat hull of the stepped type including a keel having a single planing surface adapted to substa
Basinger Sherman
Berkowitz Marvin C.
Nath Gary M.
Nath & Associates PLLC
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