AU5975098A - Boats and boat hulls - Google Patents

Description

BOATS AND BOAT HULLS

TECHNICAL FIELD OF THE INVENTION

THIS INVENTION relates to boats and boat hulls.

The invention has particular but not exclusive application to motorised catamarans and hulls for motorised catamarans and for illustrative purposes reference will be made to such application. However it is to be understood that the invention could be used in other multi-hulled vessels.

BACKGROUND ART

Catamarans generally have significant advantages over mono- hulled boats, notably their ability to put out in rougher weather, the two hulls providing greater lateral stability than one hull . The performance of a catamaran depends on many factors including the shape and size of the individual hulls and the tunnel between the hulls. These factors in particular affect the ride of the boat as well as its aerodynamic and hydrodynamic performance. At speed, some water is displaced outwardly and downwardly from each hull while some is induced upwardly between the hulls causing drag on the inside walls of the hulls and in some cases increases in payload or speed can cause the water between the hulls to make almost continuous contact with the tunnel top and also inner hull sides, thereby further increasing drag and preventing efficient planing. It will be appreciated that in such circumstances large increases in engine power are required to gain small increases in speed.

Typically, the propellers are positioned adjacent the respective aft ends of the two hulls of a catamaran. In some cases each propeller is direct coupled to an outboard motor and in other cases the propeller is shaft driven by an inboard motor directly or via a stern drive arrangement which typically includes two right angle gear drives. In use, catamarans have a tendency to rock from side to side whereby each hull and its associated propeller move upwardly and downwardly in the water whereupon the propellers are subjected to varying loads and therefore apply varying amounts of propulsion to the boat. Such action causes cyclic torsional loading of the drive train and also vibration which passes from the drive train whether part of an outboard unit or a stern drive arrangement to the motor causing undesirable wear. In many cases motors and drive train parts require reconditioning or replacement after an undesirably short period of use. In cases where two inboard motors are utilised, the motor compartments are often too small and too low in the respective hulls to meet the manufacturers specifications so that optimum engine performance cannot be achieved. Furthermore, in some cases the motors are so low that they are in danger of damage due to water encroachment via the exhaust system.

The use of two inboard motors and associated drive trains is also undesirable as they require much more space and are of much greater weight per unit of horse power than one motor and additionally greater boat space must be dedicated to fuel storage. Whilst two outboard motors do not impinge on hull space to any great detriment, it is well recognised that outboard motors generally consume fuel at a greater rate than inboard motors and therefore are more expensive to run. Furthermore, outboard motors also sit much lower and closer to the waterline than is desirable and can be swamped in poor conditions. Additionally, the motors breath sea spray which can be damaging. Attempts have been made to overcome some of the aforementioned problems by constructing a catamaran hull having a centre pod near its aft end between the main sub-hulls. Catamarans constructed with such hulls can be propelled by a single propeller extending from the aft end of the pod and driven by a single motor mounted in the pod. However, catamarans constructed with such known hulls have not been entirely satisfactory as they generally have a tendency to lift at the stern particularly at high speeds creating steering and handling difficulties, especially in poor sea conditions wherein they tend to dive or plow rather than plane and are subject to broaching. It is an object of the present invention to provide a boat or boat hull which has improved aerodynamic and hydrodynamic performance characteristics . It is another object to provide a boat or a hull for a boat which alleviates one or more of the aforementioned disadvantages relating to engine performance.

It is yet another object to provide a boat or a hull for a boat which alleviates one or more of the aforementioned problems relating to boat handling performance.

DISCLOSURE OF THE INVENTION

With the foregoing in view this invention in one aspect resides broadly in a boat having two spaced apart side hulls joined by a cross deck and defining therebetween a flow passage above the water line and below the cross deck, each side hull having an inner wall and an outer wall, said inner wall and said outer wall converging at their forward ends to form a bow, each said inner wall including a forward portion and a rearward portion, said rearward portion being joined to said forward portion by a side transition portion in the form of a rearwardly facing step such that the width of the flow passage between said rearward portions is greater than the width of the passage between said forward portions, said side transition portions causing an abrupt expansion of the flow passage. It is believed that at speed the abrupt expansion of the flow passage causes a void to be formed behind the side transition portion which advantageously decreases drag on the rearward portions of the inner walls. Furthermore, the expanded flow passage allows the water level in the flow passage adjacent the rearward portions to fall such that drag on the tunnel top of the boat is reduced or eliminated when in the dynamic planing condition. In another aspect the invention resides broadly in a boat having two spaced apart side hulls and an intermediate hull between the side hulls, each side hull having an inner wall and an outer wall which converge at their forward ends to form a bow and the intermediate hull having spaced apart side walls which converge at their forward ends to form a bow, the forward end of the intermediate hull being disposed rearwardly of the forward end of the side hulls and the side hulls and the intermediate hull being joined by a cross deck, said side hulls defining therebetween and forward of the intermediate hull, a forward flow passage above the water line and below the cross deck and each side hull and the intermediate hull defining therebetween a rearward flow passage above the water line and below the cross deck, the aggregate of the cross sectional areas of the rearward flow passages generally being approximately equal to or greater than the cross sectional area of the forward flow passage when the boat is in the static displacement disposition. In order to achieve this end, the inner wall of each side hull preferably includes a forward portion and a rearward portion and said rearward portion is joined to said forward portion by a side transition portion in the form of a rearwardly facing step extending outwardly from said forward portion such that the width of each rearward flow passage is generally greater than half the width of the forward flow passage between said forward portions, said side transition portions being adapted to cause an abrupt expansion from said forward flow passage to said rearward flow passages. Preferably, the intermediate hull is disposed nearer the after end than the fore end of said side hulls and preferably, the cross sectional shape of the side hulls is such that the aggregate of the cross sectional areas of the rearward passages is also generally approximately equal to or greater than the cross sectional area of the forward passage when the boat is in the planing dynamic condition. It will be appreciated that the flow passages referred to above are often referred to as "tunnels", the underface of the cross deck and the walls of the side hulls together with the waterline effectively forming a forward tunnel and a rearward tunnel . These terms are used herein interchangeably with the terms "forward flow passage" and "rearward flow passage" respectively. Preferably, the cross-deck is constructed such that the forward tunnel top is contiguous with the rearward tunnel top or in the case where an intermediate hull is included, with each rearward tunnel top. However, some variation in performance characteristics may be achieved by including a tunnel top transition portion by way of a rearward facing step or ramp such that the rearward tunnel top or tops are spaced from the waterline by a greater distance thus further increasing the cross sectional area of the rearward passage or passages.

Preferably, the lower face of the intermediate hull includes a forward lower face portion and an aft lower face portion joined by a rearward facing step and is constructed such that in the static displacement condition and also at low speeds both the forward and aft lower face portions are below the water line but at relatively high planing speeds the aft planing surface is above the water line. Advantageously, the tendency for the boat to lift at the aft end is decreased at high speeds in such form of construction. Furthermore, the rearward facing step and the aft lower face portion together define an effective void which suitably may accommodate the propeller whereby "surface drive" may be achieved as boat speed increases if surface drive is desired.

Preferably, the outer walls of the side hulls also include a forward portion and a rearward portion, said rearward portion being joined to said forward portion by an outside transition portion in the form of a rearwardly facing step such that the width of each side hull is reduced rearward of the outside transition portion. It is believed that at speed the abrupt narrowing of the side hulls causes a void to be formed behind the side transition portion which advantageously decreases drag on the rearward portions of the outer walls . It is also preferred that the side hulls include chines towards their fore ends whereby the buoyancy forces applied to the side hulls may increase sharply with rising water line such that the tendency for the boat to dive with increasing speed is inhibited. Preferably, such chines extend substantially horizontally when viewed in profile.

Preferably, the outer side wall of each side hull near the aft end converges inwardly to join with a stern wall extending to the inner side wall thereby providing a stern wall of decreased area when viewed from behind. Advantageously, such smaller stern wall area of truncated arrow shape allows easier reversing of the boat.

In another aspect the invention resides broadly in a boat having one or more hulls, the or each hull having spaced apart side walls, said side walls converging at their forward ends to form a bow and the or each hull including a forward portion and a rearward portion, said rearward portion being joined to said forward portion by side transition portions in the form of rearwardly facing steps, said steps being such that the width of the or each hull is reduced rearward of said side transition portions and said side transition portions being so made and arranged as to cause a void rearward thereof at speed thereby reducing drag on the sides of the or each hull. In another aspect the invention resides broadly in a hull for a boat, the hull including spaced apart side hulls as previously described joined by a cross deck.

In yet another aspect the invention resides broadly in a hull for a boat, the hull including two spaced apart side hulls and an intermediate hull as previously described, said side hulls and said intermediate hull being joined by a cross deck.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that this invention may be more readily understood and put into practical effect reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein:-

Fig. 1 is a side elevation of a boat according to the invention and showing datum frames marked 0 to 8 for use in illustrating the cross sections at those frames;

Fig. 2 is a sectional side elevation of the boat of Fig. 1 along line 3-3 shown in Fig. 3;

Fig. 3 is a cross section through the hull of the boat of Fig. 1 near frame 5 looking from the aft end;

Fig. 4 is a cross section through the hull of the boat of Fig. 1 near frame 6 looking from the aft end;

Fig. 5 is a cross section through the hull of the boat of Fig. 1 near frames 7 and 8 looking from the aft end; Fig. 6 is a cross sectional plan view of the hull of the boat of Fig. 1 at the waterline when in a static displacement condition; Fig. 7 is a cross sectional plan view of the hull of the boat of Fig. 1 at the waterline in the planing dynamic condition;

Fig. 8 is a front view of the hull of the boat of Fig. 1 illustrating the cross sectional shape of the hull at frames 0 to 8 and at various intermediate frames between frames 0 and 8.

Fig. 9 is a plan view of the boat of Fig. 1.

Fig. 10 is a side elevation of another boat according to the invention and showing datum frames marked 0 to 8 for use in illustrating the cross sections at those frames;

Fig. 11 is a sectional side elevation of the boat of Fig. 10 along line 12-12 shown in Fig. 12;

Fig. 12 is a cross section through the hull of the boat of Fig. 10 near frame 5 looking from the aft end;

Fig. 13 is a cross section through the hull of the boat of Fig. 10 near frame 6 looking from the aft end;

Fig. 14 is a cross section through the hull of the boat of Fig. 10 near frames 7 and 8 looking from the aft end; Fig. 15 is a cross sectional plan view of the hull of the boat of Fig. 10 at the waterline when in a static displacement condition;

Fig. 16 is a cross sectional plan view of the hull of the boat of Fig. 10 at the waterline in the planing dynamic condition.

DETAILED DESCRIPTION OF THE DRAWINGS

The boat 10 illustrated in Figs. 1 to 9 includes a hull 11 constructed of glass reinforced plastic (GRP) although other embodiments may be constructed of other commonly used boat building materials such as steel, aluminium, fibreglass or kevlar. A super structure 12 is secured to the hull at the coaming line 14 in known manner to provide a cabin 13 and various other features of known type. The hull is a one piece moulding comprising two spaced apart side hulls 16 and 17 and an intermediate hull 18 positioned therebetween and nearer the aft end than the fore end. The side hulls each include spaced apart outer and inner walls 21 and 22 extending substantially fore and aft, the outer and inner walls converging at their forward ends to form a bow 25. Each inner wall comprises a forward inner wall portion 23 and a rearward inner wall portion 24 which both also extend substantially fore and aft and being generally parallel being joined by a transition portion 26 in the form of a rearwardly facing substantially vertical wall which is located in the vicinity of the centre of buoyancy of the boat. The transition portion defines a forward hull portion 27 and a rearward hull portion 28 forward and rearward thereof respectively and it will be appreciated that the forward hull portion is of substantially greater width than the rearward hull portion at the water line. In the forward hull portion both the outer wall and the forward inner wall portion converge downwardly and inwardly whilst in the rearward hull portion the rearward inner wall portion 24 is substantially vertical whilst the outer wall 21 converges downwardly and inwardly towards the rearward inner wall portion.

At the aft end, the outer wall and inner wall of each hull are joined by a substantially vertical stern wall portion 30 which extends across the full width of the boat at the stern as will become clearer later. Each stern wall portion 30 includes an inner part 32 extending directly across the boat and an outer part 31 which meets the outer wall portion at about 45 degrees. In other words, the rear outer corners of each side hull are truncated whereby a smaller stern area is presented making for easier reversing of the boat.

The intermediate hull 18 is formed by two spaced apart side walls 36 and 37 extending substantially fore and aft and converging at their forward ends to form a bow 38. The side walls converge downwardly sharply towards their lower edges to form a bottom wall 40. At their aft ends, the side walls 36 and 37 are joined by a substantially vertical intermediate stern portion wall 39 extending therebetween. The intermediate stern wall portion extends upwardly to join with the stern wall portion 30.

The outer walls 21 of the two side hulls extend upwardly to the coaming line where they are connected to the super structure

12 and the forward wall portions 23 of the inner walls 22 of both side hulls extend upwardly to join with a forward cross deck portion 41 extending therebetween whilst the rearward wall portion 24 of each side hull extends upwardly and is joined to the upper edges of the walls 36 and 37 of the intermediate hull respectively by two rearward cross deck portions 42 which are contiguous with the forward cross deck portion 41.

The bow 38 of the intermediate hull is positioned generally between the transition portions 26 of the side hulls. It will be seen that the forward wall portions 23 of the side hulls and the forward cross deck portion 41 together with the surface of the water at the waterline generally define a forward tunnel 43 through which air may pass during forward movement of the boat the air exiting the forward tunnel then flowing through, the two rearward tunnels 44 defined by the walls 36 and 37 of the intermediate hull, the rear wall portions 24 of the respective side hulls, the rear cross deck portions 42 and the surface of the water at the waterline.

It will be appreciated that the aggregate of the widths of the rearward tunnels at the water line is generally substantially the same as the width of the forward tunnel. However, the transition wall portions 26 cause a sudden enlargement at entry to the rearward tunnels which reduces drag. It will also be appreciated that immediately trailing the bow 38 the aggregate width may be slightly less when in the static displacement condition. When in the planing dynamic position as illustrated in Fig. 7 the aggregate of the widths of the rearward tunnels 42 adjacent the bow 38 at the waterline is slightly greater than the width of the tunnel 43 at the waterline. Generally, the aggregate of the cross sectional areas of the rearward tunnels 42 is substantially the same as the cross sectional area of the tunnel 41 immediately forward of the transition portions 26. It is believed that the abrupt increase in width of the rearward tunnels created by the transition portions 26 creates a void marked "A" in Fig. 6 which decreases drag on the rear wall portions 24. Notably, as boat speed increases the length of the void towards the stern increases so that drag is reduced as speed increases . The bottom wall 40 of the intermediate hull is ramped upwardly near its aft end to provide an elevated rear bottom face 48 which in the static displacement condition is disposed below the waterline as illustrated in Fig. 6 and in the planing dynamic condition is disposed above the waterline. Advantageously, the ramp portion 49 provides a suitably inclined rearwardly facing wall through which the propeller shaft 61 can extend whereby the propeller 62 can be located in a partially protected position aft of the ramp portion. At higher speeds it will be appreciated that the intermediate hull creates a void immediately behind the ramp portion 49 with the waterline below the elevated rear bottom face 48 so that the propeller operates in "surface drive" conditions. It will be seen that the engine 63 is mounted in the forward portion of the intermediate hull and torque is transmitted to the propeller via the shaft 61. Advantageously, only one engine and propeller are utilised allowing both side hulls to be used for storage, positive buoyancy or cabin purposes if desired.

The side hulls 16 and 17 include opposed lower chines 51 and 52 formed in the outer wall 21 and the forward portion 23 of the inner wall 22. The chines extend fore and aft and converge at the bow. When in the static displacement condition as illustrated in Fig. 6 all of the chines except for the foremost portions are disposed beneath the waterline but when in the planing dynamic condition as illustrated in Fig. 7 most of the chines are disposed above the waterline and advantageously present a significantly larger surface area of the hull to the water thus significantly decreasing the tendency of the boat to plow or dive upon forward pitching as the hull enters the water. A further chine 53 is provided in the side wall 21 above the chine 51 and presents a downwardly directed face for enhancing lift at higher speeds .

The forward portions 23 of the inner walls 22 are joined to the cross deck 41 by a transition portion 55 which extends upwardly and inwardly and when looking rearwardly is substantially constant in incline whereby an increasing surface area is presented to the water which also assists in decreasing the tendency of the boat to plow or dive particularly in very rough seas . The boat illustrated in Figs. 10 to 16 is the same as the boat illustrated in Figs. 1 to 9 in many respects and for ease of understanding corresponding reference numerals have been utilised where appropriate but prefaced by the numeral 1. The outer walls 121 are each stepped inwardly by a transition portion 165 rearwardly of the centre of buoyancy of the boat in much the same manner as the inner walls 122 are stepped outwardly by transition portion 126 (as described in relation to the earlier boat). Advantageously, the void created behind the transition portion reduces drag on the outer wall. The bottom walls of the side hulls 116 and 117 are also stepped upwardly rearward of the transition portion 165 to create a rearward bottom portion 164 which is believed to reduce drag on the bottom of the side hulls in similar manner. In this boat also, the intermediate hull has a sharper bow having a "wavebreaker" profile and thus extends further forward than in the other embodiment. Additionally, the cross sectional shape of the intermediate hull has been changed to increase the aggregate cross sectional area of the rearward tunnels. In another embodiment of the invention (not shown), the intermediate hull 118 is removed and the engine is supported by the forward cross deck portion 141 with the propeller shaft 161 being supported in the rearward tunnel by bearings hung from the rearward cross deck and drive being provided by a "V" drive arrangement. Advantageously, such a boat offers some of the advantages of the boats described in relation to the drawings .

It will of course be understood that the embodiments given herein are illustrative only and that many further modifications of constructional detail and design may be made, as will be readily apparent to persons knowledgable in the field concerned, without departing from the broad scope and ambit of the invention as defined in the appended claims.

Claims (14)

1. A boat having two spaced apart side hulls joined by a cross deck and defining therebetween a flow passage above the water line and below the cross deck, the underface of said cross deck forming a tunnel top and each side hull having an inner wall and an outer wall, said inner wall and said outer wall converging at their forward ends to form a bow, each said inner wall including a forward portion and a rearward portion, said rearward portion being joined to said forward portion by a side transition portion in the form of a rearwardly facing step such that the width of the flow passage between said rearward portions is greater than the width of the passage between said forward portions, said side transition portions causing an abrupt expansion of the flow passage.

2. A boat having two spaced apart side hulls and an intermediate hull between the side hulls, each side hull having an inner wall and an outer wall which converge at their forward ends to form a bow and the intermediate hull having spaced apart side walls which converge at their forward ends to form a bow, the forward end of the intermediate hull being disposed rearwardly of the forward end of the side hulls and the side hulls and the intermediate hull being joined by a cross deck, said side hulls defining therebetween and forward of the intermediate hull, a forward flow passage above the water line and below the cross deck and each side hull and the intermediate hull defining therebetween a rearward flow passage above the water line and below the cross deck, the aggregate of the cross sectional areas of the rearward flow passages generally being approximately equal to or greater than the cross sectional area of the forward flow passage when the boat is in the static displacement disposition.

3. A boat according to Claim 2, wherein the inner wall of each side hull includes a forward portion and a rearward portion and said rearward portion is joined to said forward portion by a side transition portion in the form of a rearwardly facing step extending outwardly from said forward portion such that the width of each rearward flow passage is generally greater than half the width of the forward flow passage between said forward portions, and said side transition portions are adapted to cause an abrupt expansion from said forward flow passage to said rearward flow passages .

4. A boat according to Claim 2 or Claim 3, wherein the intermediate hull is disposed nearer the aft end than the fore end of said side hulls.

5. A boat according to Claim 2, 3 or 4 wherein said cross sectional shape of the side hulls and the intermediate hull is such that the aggregate of the cross sectional areas of the rearward passages is generally approximately equal to or greater than the cross sectional area of the forward passage when the boat is in the planing dynamic condition.

6. A boat according to Claim 1, wherein said cross-deck includes a tunnel top transition portion formed by a rearward facing step or ramp such that the underface of the cross deck forming the tunnel top of the rearward flow passage is spaced from the waterline by a greater distance than the underface of the cross deck forming the forward flow passage.

7. A boat according to any one of Claims 2 to 5 , wherein said cross-deck includes a tunnel top transition portion formed by a rearward facing step or ramp such that the underface of the cross deck forming the tunnel tops of the rearward flow passages is spaced from the waterline by a greater distance than the underface of the cross deck forming the forward flow passage.

8. A boat according to any one of Claims 2 to 6 , wherein the lower face of the intermediate hull includes a forward lower face portion and an aft lower face portion joined by a rearward facing step and is constructed such that in the static displacement condition and also at low speeds both the forward and aft lower face portions are below the water line but at relatively high planing speeds the aft planing surface is above the water line.

9. A boat according to any one of the preceding claims, wherein the outer walls of the side hulls also include a forward portion and a rearward portion, said rearward portion being joined to said forward portion by an outside transition portion in the form of a rearwardly facing step such that the width of each side hull is reduced rearward of the outside transition portion.

10. A boat according to Claim 9, wherein the side hulls include chines towards their fore ends whereby the buoyancy forces applied to the side hulls may increase sharply with rising water line such that the tendency for the boat to dive with increasing speed is inhibited.

11. A boat according to Claim 10, wherein the outer side wall of each side hull near the aft end converges inwardly to join with a stern wall extending to the inner side wall thereby providing a stern wall of decreased area when viewed from behind. Advantageously, such smaller stern wall area of truncated arrow shape allows easier reversing of the boat.

12. A hull for a boat, the hull including two spaced apart side hulls joined by a cross deck and defining therebetween a flow passage above the water line and below the cross deck, the underface of said cross deck forming a tunnel top and each side hull having an inner wall and an outer wall, said inner wall and said outer wall converging at their forward ends to form a bow, each said inner wall including a forward portion and a rearward portion, said rearward portion being joined to said forward portion by a side transition portion in the form of a rearwardly facing step such that the width of the flow passage between said rearward portions is greater than the width of the passage between said forward portions, said side transition portions causing an abrupt expansion of the flow passage.

13. A hull for a boat, the hull including two spaced apart side hulls and an intermediate hull between the side hulls, the forward end of the intermediate hull being disposed rearwardly of the forward end of the side hulls and the side hulls and the intermediate hull being joined by a cross deck, the underface of said cross deck forming a tunnel top and said side hulls defining therebetween a forward flow passage above the water line and below the cross deck, and each side hull and the intermediate hull defining therebetween a rearward flow passage above the water line and below the cross deck, the aggregate of the cross sectional areas of the rearward flow passages generally being approximately equal to or greater than the cross sectional area of the forward flow passage when the boat is in the static displacement disposition.

14. A boat having one or more hulls, the or each hull having spaced apart side walls, said side walls converging at their forward ends to form a bow and the or each hull including a forward portion and a rearward portion, said rearward portion being joined to said forward portion by side transition portions in the form of rearwardly facing steps, said steps being such that the width of the or each hull is reduced rearward of said side transition portions and said side transition portions being so made and arranged as to cause a void rearward thereof at speed thereby reducing drag on the sides of the or each hull.