WO1998038078A1

WO1998038078A1 - Boat hull

Info

Publication number: WO1998038078A1
Application number: PCT/SE1998/000338
Authority: WO
Inventors: Ocke Mannerfelt
Original assignee: Ab Volvo Penta
Priority date: 1997-02-26
Filing date: 1998-02-25
Publication date: 1998-09-03
Also published as: SE9700691L; SE9700691D0

Abstract

Boat hull with hull sides (3) which, via sharp edges, join a V-shaped bottom which has on the one hand longitudinal web strips (15) and on the other hand two transverse webs (7, 12) which are each divided into two parts (7a, 7b and 12a, 12b respectively) which extend from the respective edge (2) towards a smooth central portion (10) of the bottom, which is uninterrupted in the longitudinal direction.

Description

Boat hull

The present invention relates to a boat hull with hull sides which, via sharp edges, join a V-shaped bottom which has on the one hand longitudinal web strips and on the other hand at least one transverse web which extends from the respective edge in the direction of the centre line of the bottom so as to guide air in under the bottom when the boat is travelling at planing speed.

By designing a hull with transverse webs in the boat bottom, a type of "air lubrication" of the part of the bottom that is in contact with the water when the boat is travelling at planing speed is brought about. As a result, the friction between the hull and the water is reduced, which leads to higher speed for a given power take-off or lower power and lower fuel consumption for a given speed compared with a corresponding hull with a bottom without transverse web strips .

In previously known boat hulls of the type indicated in the introduction, the transverse webs extend transversely across the entire boat bottom from one edge to the other, which causes air to be distributed over the entire bottom surface aft of the web so that maximum reduction of friction against the water is achieved.

Such a bottom shape is optimum from the point of view of economy and performance for certain types of fast boats and in particular those with power units which utilize propellers for propulsion. On the other hand, it cannot be used in boats with water-jet units. This is because air under the boat would be sucked into the water-jet tunnel and give rise to serious impeller cavitation with attendant large losses in driving power. The object of the present invention is in general to produce a boat bottom configuration of the type indicated in the introduction, which prevents air being introduced under specific bottom surfaces, so that these slide in at least virtually air-bubble-free water when the boat is travelling at planing speed. In particular, the object of the invention is to produce a boat hull designed with transverse webs, which can utilize a water- jet unit as a power unit.

According to the invention, this object is achieved in that the transverse web is divided into at least two parts which are separated by an at least in the main smooth bottom portion which is uninterrupted in the longitudinal direction and begins in front of the web and extends as far as the stern of the hull.

Trials have shown that, by dividing the transverse webs and arranging an intermediate smooth bottom portion, it is possible to guide the air under the boat bottom in such a manner that the aft region of the smooth uninterrupted bottom portion slides in virtually air-free water. In this region, a water intake can be positioned, through which water can be sucked into the water-jet unit without risk of causing cavitation.

The invention is described in greater detail with reference to exemplary embodiments shown in the attached drawings , in which Fig. 1 shows a side view of a first embodiment of a boat hull according to the invention,

Fig. 2 shows a perspective view at an angle from below of the hull in Fig. 1,

Fig. 3 shows a diagrammatic cross-section through the hull in Figs 1 and 2,

Fig. 4 shows a side view of a second embodiment of a hull according to the invention,

Fig. 5 shows a perspective view at an angle from below of the hull in Fig. 4, and Fig. 6 shows a diagrammatic cross-section through the hull in Figs 4 and 5.

In the figures, 1 designates generally a bottom part of a hull which, via sharp transitions/edges 2, joins the hull side 3. The hull has a straight stern 4 and a V-shaped forebody 5 - seen in horizontal projection. Roughly midway between the front end 6 of the forebody 5 and the stem 4, the bottom part 1 is designed with a first transverse web 7 which has an edge surface 9 directed in the main at right angles to the bottom surface. The web 7 consists of two parts 7a and 7b which extend inwards from the edges 2 to a plane and smooth bottom portion 10 which is V-shaped and extends from a point 11 in front of the web 7 to the stern 4. Between the transverse web 7 and the stern 4, the bottom part 1 is designed with a second transverse web 12 consisting of two parts 12a, 12b of the same design as the first transverse web. The bottom surfaces between the first and the second transverse webs and between the second transverse web and the stern form inclined bottom surface portions 13, 14. The transverse webs 7, 12 are directed forwards at an angle so that, when the boat is travelling at planing speed, they guide air in under the bottom part 1. The hull is designed with conventional longitudinal web strips 15 in order to increase the lift. As can be seen from the figures, the hull has a greater number of web strips 15 in front of the front transverse web 7 than between the webs 7 and 12 and a smaller number of web scrips 15 behind than between the webs. In this way, lift is achieved that gives an optimum travelling position of the hull with an angle of attack of 3° to 4°.

The bottom portion 10 joins the laterally located bottom surface portions 13, 14 via sharp edges 13a and 14a, which results in air that is guided in under the bottom via the webs 7, 12 being prevented from being guided in under the bottom portion 10. As a further means of preventing the possibility of air being guided in under the bottom portion, the. transition between the bottom portion 10 and the laterally located surface portions 13, 14 can be designed with recesses. Such a recess 16 is shown by a dot-and-dash line. Fins can be arranged as a complement or an alternative to recesses 16. A fin 17 is shown by a dot-and-dash line.

The hull shown in Figs 1-3 is designed for a water-jet unit (not shown) and has an opening 18, to which the suction line of the water-jet unit is intended to be connected. In Figs 4-6, another embodiment of a boat hull according to the invention is shown, which is intended for a twin water-jet unit. Features that correspond to features in Figs 1-3 have been given the same reference numbers as in Figs 1-3.

The basic difference between the hull in Figs 1-3 and the hull in Figs 4-6 is that the plane horizontal bottom surface portion 10 between the transverse web halves 7a, 7b of the former is replaced by a smooth portion 20 which is V-shaped in a transverse vertical plane and constitutes a direct extension of the bottom portion in front of the front transverse web 7. Roughly at the level of the aft transverse web 12, the bottom portion 20 is divided into two parts 20a, 20b by a V- shaped recess 21 which extends aft to the stern 4. In the aft portions of the bottom parts 20a, 20b are openings 22, to which the suction lines of two water-jet units (not shown) are intended to be connected. So as to reduce friction in the recess 21, air can be guided in via an opening 23 which opens into a duct 24 with an air intake 25 located at a level above the waterline of the hull.

The invention has been described above with reference to an entirely plane, smooth bottom portion 10 and a V-shaped, smooth bottom portion 20. Within the scope of the invention, it is also possible to envisage designing the bottom portions 10 and 20a and 20b respectively to be slightly concave. The expression "in the main smooth" in the patent claims below is therefore also to include a transversely slightly concave, longitudinally uninterrupted bottom surface between the transverse webs .

Claims

C l a i m s

1. Boat hull with hull sides which, via sharp edges, join a V-shaped bottom which has on the one hand longitudinal web strips and on the other hand at least one transverse web which extends from the respective edge in the direction of the longitudinal centre line of the bottom so as to guide air in under the bottom when the boat is travelling at planing speed, the transverse web

(7, 12) being divided into at least two parts (7a, 7b and 12a, 12b respectively) which are separated by an at least in the main smooth bottom portion (10; 20) which is uninterrupted in the longitudinal direction and begins in front of the web and extends as far as the stern (4) of the hull, characterized in that the smooth uninterrupted bottom portion (10; 20) has in its aft part at least one opening (18; 22) which forms a water intake for a water- jet unit.

2. Boat hull according to Claim 1, characterized in that the bottom has two transverse webs (7, 12) which are arranged at a distance from one another in the longitudinal direction, are both divided into two parts (7a, 7b and 12a, 12b respectively) and are separated by a smooth bottom portion (10; 20) which is uninterrupted in the longitudinal direction.

3. Boat hull according to Claim 1 or 2, characterized in that the uninterrupted portion is a plane horizontal portion (10) between angled bottom parts .

4. Boat hull according to Claim 3 , characterized in that the smooth uninterrupted portion (10) is V-shaped with the point (11) directed forwards.

5. Boat hull according to Claim 1 or 2, characterized in that the smooth uninterrupted portion (20) is V-shaped seen in a vertical transverse plane.

6. Boat hull according to Claim 5, characterized in that the V-shaped smooth uninterrupted portion (20) between the transverse web parts has an uninterrupted transition to the V-shaped bottom in front of the web.

7. Boat hull according to Claim 6, characterized in that the V-shaped smooth uninterrupted portion (20) has a recess (21) which is V-shaped in horizontal projection and begins in the main at the level of a transverse web (12) and extends aft to the stern (4) .

8. Boat hull according to Claim 7, characterized in that the recess (21) communicates with an air intake (25) which is located above the waterline of the hull .

9. Boat hull according to any one of Claims 1-8, characterized in that the smooth uninterrupted bottom portion (10; 20) joins surrounding bottom surfaces (13, 14) via longitudinal sharp edges (13a, 14a) .

10. Boat hull according to any one of Claims 1-9, characterized in that the V-shaped bottom has a greater number of longitudinal web strips (15) in the forebody than in the afterbody.