GB2371777A - Buoyant board with a pivotable keel member - Google Patents

Abstract

A buoyant board 1 comprises a keel member 6 mounted perpendicularly to the underside of the board by means of a pivot pin 2 such that said keel member is free to rotate in a plane substantially parallel with the underside of the board about said pivot pin. The keel member may have a length equal to the board length minus the length of a tailfin 4 provided at the rear of the boards underside and the spacing between the keel member and the tailfin. The pivot pin may be inserted in any one of a number of holes space longitudinally along the centre-line of the board with the keel member being sized such that there is a clearance between it an the tailfin. In a separate embodiment a split tailfin is provided comprising a rigid section (11A, Fig 7) attached to the board and a pivotal section (11B, Fig 7) mounted to the rigid section by means of a hinge.

Description

IMPROVED SURFBOARD

This application relates to an improved surfboard.

It is well known that fishes and reptiles are able to propel themselves through water merely by swinging their tails from side to side.

Pojected area of body mass forward of tail section of these creatures, in their being greater than or at least equal to prpjectedareaof their tail sections, serves to convert sideways sweep of tail into forward thrust without their becoming unduly rotated under influence of sideways sweeping tail.

However, there is little to prevent the surfboard from rotating about its centre, first one way then the other should surfer attempt to drive board forward by means of swinging its rear end from side to side.

This fact becomes emphasized should we suppose for a moment that, as an experiment tailfin is extended to full length of underside of surfboard, a full length keel fixed to board that is, then surfer would find it difficult to rotate surfboard about either its front end, or rear end, or middle : there would be no forward drive either; that stretch of water upon which board rests would simply be stirred at best, board going nowhere.

It is for this reason then that surfboard rider must essentially lie down on surfboard and paddle with hands in order for it to make headway over water.

According to the present invention there is provided a hinged keel member securely fixed perpendicular to underside of buoyant board by way of hinge pin, about which keel member may turn.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which : Figure 1 shows underside of surfboard, with keel member in line of travel.

Figure 2 shows side view of board together with its tailfin, with long keel fitted.

Figure 3 shows side view of board together with its tailfin, with short keel, centrally located.

Figure 4 shows underside of"short keel member"surfboard in process of front end being rotated about its tailfin.

Figure 5 shows underside of"short keel member"surfboard in process of being driven forward by sideways swing of surfboard rear end.

Figure 6 shows underside of"long keel member"surfboard in process of being driven forward by sideways swing of surfboard rear end.

Figure 7 shows tailfin vertically split into two sections by way of hinge.

Figure 8 shows rear section of tailfin rotated some degrees left while rear end of board is in process of being rotated right.

Figure 9 shows rear section of talifin rotated some degrees right while rear end of board is in process of being rotated left.

Referring to the drawing the surfboard comprises buoyant board 1 and pin 2 about which keel member 3 may freely turn.

Underside buoyant board 1 a rigid tailfin 4 is provided.

It is shown in Figs. 1,4, 5, and 6 that keel members 3 and 6, in their not being fixed along their length to underside of surfboard, and having clearance 7 between board 1 and keel members 3 and 6 are free to turn about pin 2, thus mass of water acting upon keel members 3 or 6 in resisting turning force during rotation of rear end of board 1 and tailfin together provides fulcrum which enables tailfin 4 to power board 1 over surface of water as result of sideways swing of rear end of board 1 and tailfin together.

In order for surfboard to make way over water, surfboard rider, surfer for brevity, stands on board 1 in a manner that will allow him/her to power rear end of board 1 from side to side skateboard. fashion.

Long keel member 6, in its projected area being substantially greater than that of tailfin 4 readily transforms sideways swing of rear end of board 1 into forward motion from standing start with hardly any rotation of board 1 about its central axis.

Otherwise, surfboard shown in Fig. 4 does not provide great stability at low speed for reason of its having short keel member 3. Accent in this case being to get the best of both worlds : an ability to make progress over water at whatever speed together with manoeuvrability sufficient perhaps to turn surfboard on a sixpence., In order to execute tight turns surfer would be required to push front end of board 1 either one way or the other with front foot, keeping rear foot steady, so as to rotatesurfboard about its tailfin 4.

Once short keel member 3 surfboard picks up speed then keel member 3 more readily takes line of least resistance ; forward motion serving to help resist tendency for keel member 3 to rotate, thereby reducing energy loss and more positively transforming sideways motion of tailfin 4 into forward motion of surfboard.

As shown in Figs. 1,4, 5. and 6 short keel member 3 may be fixed to board 1 using any one of the conveniently spaced holes 5, it being a matter of choice of on part of surfer.

Projected shape of keel members 3 and 6 may take any form.

Projected area of keel members 3 and 6 need be sufficiently large fpr them to effectively employ mass of water as fulcrum about which board 1 may be driven forward over water under effect of sideways swing of rear end of board 1.

By way of splitting tailfin 4 vertically into two sections, named lla and llb, and lla being rigid front section, and lib being hinged rear section joined to section lla by way of hinge B, and top end of tailfin rear section 11b being located in radial slot 9 in board 1 by way of protrusion 10 vertically jutting from tailfin rear section lib, then angle of rotation of lib about hinge 8 would be restricted by length of radial slot 9.

Sideways rotation to the right of board 1 would cause tailfin llb to become rotated to left extremity of radial slot 9, in its first taking line of least resistence, then, in its being inclined more backwards than lla, 11b would exert a greater pushing force"backwards"on mass of water than lla on account of its greater angle of attack.

Above situation would exist right the way through first half of sideways sweep of rear end of board 1, llb effectively pushing mass of water backwards, that is until rear end of board 1

becomes rotated well past its centre line of rotation, whereupon lla takes over as pushing force, in as much as its angle of attack is now directed towards pushing water backwards, whereas lib now tends to push water sideways rather than backwards.

Above situation would exist throughout full sideways swing of

board 1 from left to right, so that pushing water backwards in its turn driving board 1 forward≈ takes place throughout complete arc of rotation of rear end of board 1: there being no lost motion as is the case with the crank at top or bottom of its swing.

Similarly should rear end of board 1 be rotated from right to left, lib would become located at right extremity of radial slot 9,. thus setting up exact reverse of drive system to that described above.

In case of split tailfin 4 board 1 becomes moved over surface of water more efficiently during sideways rotation of rear end of board 1 than might be the case with one-piece tailfin 4.

For greater efficiency still perhaps, tailfin 4 may comprise more than one hinged section, but that would be bordering on seeking total perfection efficiency-wise.

In as much as proposed improved surfboard may be powered by its rider the surfboard may be used on waters other than seabreakers.

Improved surfboard may be used on any stretch of open water deep enough to provide clearance for keel members 3 and 6, and tailfin 4.

Claims (7)

1. A hinged keel member securely fixed perpendicular to underside of buoyant board by way of hinge pin, about which keel member may turn.

2. A hinged keel member as claimed in claim 1 wherein keel member has a projected area substantially greater than that of tailfin.

3. A hinged keel member as claimed in claim 1 or claim 2 wherein keel member has a length about equal to board length, minus length of tailfin plus clearance between the two.

4. A hinged keel member as claimed in claim 2 or claim 3 wherein short keel member may be located by hinge pin inserted in any one of the several regularly spaced holes in-board.

5. A hinged keel member as claimed in claim 4 wherein length of keel member may be so small as to allow its fixture at any one of regularly spaced holes in board without fouling tailfin.

6. A hinged keel member as claimed in claim 5 wherein projected area of keel member may approximately equal projected area of tailfin.

7. A buoyant board substantially as described herein with reference to figures I-6 of the accompanying drawing.

7. A hinged keel member as claimed in claim 6 wherein depth of keel member and depth of tailfin would permit board to freely float in shallow water.

8. A split tailfin, rear end of same being hinged so as to provide a greater angle of attack to mass of water than does front section.

9 A split tailfin as claimed in claim 8 in which top edge protrusion extending from hinged rear section is located in radial slot.

10. A split tailfin as claimed in claim 9 in which more than one hinged rear section might be employed.

11. A hinged keel member substantially as described herein with reference to Figures 1-9 of the accompanying drawing. Amendments to the claims have been filed as follows 1. A buoyant board comprising a keel member mounted perpendicularly to the underside of the board by means of a pivot pin such that said keel member is free to rotate in a plane parallel with the underside of the board about said pivot pin.

2. A buoyant board as claimed in claim I wherein projected area of keel member is substantially greater than that of tail fin.

3. A Buoyant board as claimed in claim I and in claim 2 wherein hinge pin may be located at any convenient position about length of buoyancy board.

4. A buoyant board as claimed in claim 2 and in claim 3 wherein short keel member may serve to provide a smaller turning circle.

5. A buoyant board as claimed in claim 4 wherein long keel member provides the greater directional stability.

6. A buoyant board as claimed in claim 5 wherein a resilient tail fin is provided on the underside of the board.