GB2096962A - Boat with propeller withdrawable into the hull envelope - Google Patents

Abstract

The boat has a hull (1) with a tunnel (9A, 9B) into which a propeller (3) and its shaft (4) and bracket (4A) can be withdrawn to avoid damage to the propeller in shallow water or on beaching the boat. When the propeller is in the operative position below the hull, the tunnel is closed off by a pivoted hull skin portion (1A) mounting the bracket this preserving the smooth hull surface. Hull skin and propeller shaft pivoting is by hydraulic means. The skin and propeller may extend beyond the hull rear. Strakes (10, 11) deflect water from the tunnel. The tunnel space when unoccupied may contain inflatable bag(s). The skin may have a controllable hinged flap portion at its rear end. <IMAGE>

Description

SPECIFICATION Improved propeller driven boat This invention relates to a propeller driven boat.

For convenience, the invention will be described in this specification in relation to rigid inflatable planing hull craft but the invention is not limited to such craft.

Rigid inflatable planing hull craft are widely used. They may be driven by an outboard or inboard motor or motors. The propeller or each propeller is below the level of the hull of the craft and it is a problem that when such a craft is used in shallow water, or is to be beached, the projecting propeller(s) can be damaged. It is also known for the rear end of a propeller shaft to be journalled in a rudder post, with the rudder projecting below the level of the hull, In that case also the rudder of rudder post can be damaged by use in shallow water or when the craft is beached.

It is known to mount a propeller so that it can be withdrawn up into a tunnel in the hull, and it is also known to operate a propeller permanently in a tunnel in the hull. In the former case, the tunnel, which is permanently open to the water, affects the performance of the boat: this would be particularly so with a planing hull craft. In the latter case, a propeller which operates permanently in a tunnel is less propulsively efficient than one which operates in the water below the level of the hull.

It is an object of this invention to provide a propeller driven boat, for example a rigid inflatable planing hull craft, which can be used in shallow water or which can be beached, without risk of damage to the propeller (s), yet without the disadvantages of the known propeller tunnel arrangements.

According to this invention a propeller driven boat has a hull with i) a recess or tunnel into which a propeller shaft of the boat can be withdrawn and ii) a hull skin portion which covers the recess or tunnel when the propeller is in operative postion below the hull. The recess or tunnel may be such that both the propeller and the propeller shaft can be withdrawn into it. Thus in a planing hull for example its dynamic lift is maintained when the propeller is in normal, below the hull operation. Yet when the boat is to operate in shallow water or to be beached, the propeller can be withdrawn into the recess or tunnel. The hull skin portion may for example be a flap which is hingedly connected at its forward end to the hull, and the propeller shaft may be pivoted at an adjacent location, with a propeller shaft bracket being mounted on the underside of the flap.Thus in normal use, with the flap in the down position, the normal dynamic lift is maintained by the flap which is flush with the adjacent skin of the hull, and the propeller is below the hull for efficient operation. For shallow water operation the flap is lifted, for example by an appropriate mechanism, and the flap, bracket, propeller and pivotal shaft portion can enter the recess or tunnel. The propeller may continue to be operated in the recess or tunnel, particularly if the latter is open to a flat transom. In another, similar embodiment of the invention, the flap may extend rearwardly beyond the transom, so that in the flap raised position the propeller shaft is in the tunnel or recess and the propeller is above the level of the lower surface of the hull, but behind the transom.

In a third embodiment the hull skin portion, instead of being in the form of a flap, may constitute the lower part of a watertight box-like structure which fits in, and is upwardly retractable further into, the recess or tunnel.

The invention will now be described by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1-isa diagram of the lower part of the stern of a first embodiment of rigid inflatable planing hull craft; Figure 2 is a partial longitudinal section based on the diagram of Figure 1; Figure 3 is a partial transverse section; Figures 4 and 5 are views like Figures 1 and 2, but of a second embodiment; and Figures 6 and 7 are views like Figures 2 and 3, but of a third embodiment.

Referring to Figures 1 to 3, Figure 1 shows in very diagrammatic form a hull having a lower or under skin 1, a transom 2, a propeller 3, and a propeller shaft 4 pivotally mounted at 5 to a forward shaft portion, which is not shown and which is connected to an inboard engine. The hatched portion indicates a tunnel which is triangular in longitudinal section and rectangular in transverse section. The normal, down position and the lifted up or retracted position of the propeller and shaft are shown. In accordance with the invention the hull has a skin portion in the form of a flap 1 A hinged at 1 B to the fixed hull skin 1.

Referring now to Figures 2 and 3, the same parts are indicated by the same reference numerals. In Figure 3, the lowest part of the inflatable hull tube 6 is seen, above the water line 7. The centre line of the hull is indicated at 8. The tunnel is bounded by an upper wall 9A and side walls 9B, 9B; it is open at the rear in the transom 2. Referring to Figure 2, the flap 1A is pivoted at 1 B to the main hull skin 1, and the shaft 4 is pivotally mounted at 5 in a water tight gland, by way of for example a universal joint (not shown).

Obviously points 1 B and 5 are close together. The flap 1 A mounts a shaft bracket 4A. The upper, retracted position of the parts is indicated in Figures 2 and 3, and it will be understood that in the down position, the flap 1 A forms a continuous planing surface with the adjacent parts of the skin 1 , thus maintaining in unimpaired fashion the dynamic lift of the planing hull.

Figure 3 additionally shows strakes 10 and 11; strake 10 is formed as part of the hull skin 1 just below the gap 1 OA between the skin 1 and the flap 1 A; strake 11 is formed as part of the flap 1 A just below the gap 1 A between the flap 1 A and the skin 1. Since, with a hull having a deadrise angle of the order seen in Figure 3, water flow over the hull skin has a laterally upward component, the positioning of the strakes 10 and 11 tends to direct the water clear of the gaps 1 OA and 1 1A.

In this embodiment the opening of the tunnel in the transom could be closed by a slidable flap which could be slid, in a plane parallel to that of the transom, by appropriate means up and down with the flap 1 A. In this way the rear end of the tunnel would be closed when the propeller was in the normal down position.

Figures 4 and 5 show a second embodiment: the construction is generally similar to that of the first embodiment, except that the flap 1 A extends further rearwardly, to a point 12 astern of the transom, and the shaft bracket 4A is mounted at least partly on the flap extension, as seen in Figure 5. As will be appreciated, in this embodiment the propeller, in both its up and down positions, is astern of the plane of the transom. This embodiment is preferred for shallow water operation, since in its up position the propeller is not in the tunnel but in the water astern of the transom. Also with this embodiment the shaft angle can be slightly reduced, as compared with the first embodiment.

Also in Figure 5 there is shown an optional modification. The flap 1 A may be of unitary, rigid construction from the hinge point 1 B to the point 12. Alternatively, in the modification, the rearmost portion may be in the form of an adjustable trim tab 12A hinged at 12B to the main portion of the flap 1 A. This tab may be automatically or controllably adjustably movable (by appropriate means, not shown) in conjunction with the movable flap, or with the movable hull part described below with reference to Figures 6 and 7.

The purpose of such a trim tab would be to control undesirable characteristics produced by the variation in planing surface shape.

In the first two embodiments the direction of retraction of propeller and flap is at an angle to the vertical plane in which lies the centreline 8, as will be understood from Figure 3. However, in the third embodiment, seen in Figures 6 and 7, the direction of retraction is vertically upward and parallel to that plane, as seen in Figure 7. Also the flap 1 A is replaced by a closed, watertight box 1 3 of wedge shape in longitudinal section (Figure 6) and of trapezoidal shape in transverse section (Figure 7). The tunnel is formed by the walls 9A, 9B, 9B, but extends upwardly to a greater height, compare Figures 3 and 7. The bracket 4A is in this embodiment mounted on the lower wail 1 3A of the box 1 3B, and the wall 1 3A corresponds to the flap 1 A of the first two embodiments.

No rudder or rudder post is shown in the drawings. Nevertheless, the liftable hull skin portion could also mount the rubber, particularly if the propeller shaft had a rear mounting in the rudder post, as is known.

Although no means of raising the flap 1 A or box 13 is shown, such means could take various forms: one form would be in the form of a vertical hydraulic ram or rams fixed to the after face of the transom, and having a connection to the flap or box, for raising and lowering it.

Retraction of the propeller and shaft need not always be complete retraction; the amount of upward movement could be varied according to the conditions of shallow water operation, as will be understood.

In the tunnel above the flap 1 A or box 13, the space which is unoccupied when the propeller is in the down position could be filled with a controllably inflatable bag or bags: this would prevent the space filling with water and would assist buoyancy.

Although in the description of the three embodiments only one propeller and tunnel has been mentioned, clearly a boat in accordance with the invention-an have more than one such propeller and tunnel.

Claims (16)

1. A propeller driven boat having a hull with i) a recess or tunnel into which a propeller shaft of the boat can be withdrawn and ii) a hull skin portion which substantially covers the recess or tunnel when the propeller is in an operative position below the hull.

2. A boat according to claim 1 wherein the hull has a recess or tunnel into which a propeller and the propeller shaft can be withdrawn.

3. A boat according to claim 1 or claim 2 wherein the direction of withdrawal is upward at an angle to a vertical longitudinal plane of the boat.

4. A boat according to claim 1 or claim 2 wherein the direction of withdrawal is vertically upward.

5. A boat according to any preceding claim wherein the said hull skin portion is a flap hingedly connected at its forward end to the hull.

6. A boat according to claim 5 wherein the flap extends rearwardly to a transom of the boat.

7. A boat according to any of claims 1 to 4 wherein the said hull skin portion is the lower part of a box-like structure which is received in, and is upwardly retractable further into, the recess or tunnel.

8. A boat according to any preceding claim wherein the propeller shaft is mounted in a bracket which is carried by the said hull skin portion.

9. A boat according to claim 7 wherein the boxlike structure is watertight.

10. A boat according to any preceding claim wherein the said hull skin portion includes a strake adjacent one fore and aft edge of the hull skin portion.

11. A boat according to any preceding claim wherein the hut has a strake adiacent one fore and aft edge of the hull skin portion.

1 2. A boat according to claim 5 wherein the recess or tunnel is open at its after end.

13. A boat according to claim 8 when dependent on claim 6 wherein the bracket is at least partly mounted on the portion of the flap which extends rearwardly of the transom.

14. A boat according to claim 6 or claim 13 wherein a rearmost portion of the flap comprises an adjustable trim tab.

1 5. A boat according to claim 14 wherein the tab is a flap portion hingedly connected to the flap.

16. A boat according to claim 14 or claim 1 5 wherein the trim tab is automatically or controllably adjustably movable in conjunction with the flap.

1 7. A propeller driven boat constructed and arranged substantially as herein described and shown in the drawings.