Flanged fin for watercraft

The invention relates to fins for watercraft such as surfboards, surf-skis, sailboards, kayaks, canoes, skiffs, water-skis, and also "soft" plastic watercraft such as polyethylene boards. These fins have an apertured, basal flange; each fin being affixable, in a variety of positions, to the underside of the watercraft via fixing means extending through the apertures in the flange and into the fabric of the watercraft.

TECHNICAL FIELD 
This invention relates to finned watercraft, such as surfboards and the 
like, of the kind having a stabilizing fin or fins, and especially to fins 
suitable therefor. 
BACKGROUND ART 
The sport of riding a board on the crest of a wave as it approaches the 
shore is old. European seafarers of the 18th century reported having seen 
this feat performed in the "Sandwich Islands". 
In course of time, knowledge of this new, exciting sport spread from Hawaii 
to California, from whence it was introduced into such other countries as 
Australia, South Africa and so forth. 
The traditional surfboards were heavy, curvilinear wooden artifacts, from 
12 to 20 feet in length, and only the strongest surfers could readily 
handle them. 
Subsequently, more modern surfboards began to be made from plastic, 
polyurethane foam, and fiberglass, with the fin set into what is termed a 
"fin-box" let into the underside or fixed insitu with fiberglass. While a 
fin-box admittedly provides a fin, set therein, with good resistance to 
laterally-applied force, the original object of the insert fin-box was 
apparently to allow for ease of transport, inasmuch as boards with the 
fins removed could be safely stacked one on top of the other. Damage of 
fins in transit was a major problem. 
With a single fin, even moderately difficult conditions are enough to cause 
the "spin-out" which is so frustrating and even dangerous to the rider; 
this phenomenon to be caused by insufficient lateral adhesion between fin 
and water, and so attempts were made to counteract it by increasing the 
depth and lateral area of the base of the fin. The result was excessive 
drag and loss of maneuverability owing to the "keel effect" of the 
enlarged fin, which led to even poorer performance. 
Variations of the finned board have been tried out (boardriders being 
notoriously prone to experiment) for example, laterally-spaced paired fins 
(the so-called "twin-fin board"). This produced a surfboard which was 
slightly more maneuverable and capable of "tighter" turns under ideal 
conditions but which tended to "spin-out" in big waves. It should here be 
noted that what in a conventional marine hull is called the chine is, in 
surfing parlance, termed the "rail". When a turn is made on a surfboard it 
is canted sideways and this action, with the keel effect of the fin keying 
in to the moving water, allows the turns to be made. A board having 
laterally paired fins will, when canted hard enough onto one of its rails, 
permit a quite tight turn, but is physically more difficult to cant over 
because the water funnels between the two fins and tends to keep the board 
wholly in the water, making turns difficult to accomplish. 
Laterally-spaced, equally-sized triple fins have some advantages over and 
above paired fins inasmuch that such a board requires somewhat less "rail" 
to make a turn, but suffers from the fact that the two outer fins tend to 
over-react to such an extent that fine control may be compromised. 
As a modification of the triple fin format, an arrangement involving a 
large centre-line fin flanked by two smaller, offset fins has been tried 
out but with limited success. Tandem fins have also been investigated and 
even five fin arrangements are not unknown. More significantly, recent 
experimentation has led to multi-fin arrangements in which the outer fins 
are angled with respect to the longitudinal centre-line of the board so 
that the leading edges of a laterally-spaced pair of fins are closer 
together than their trailing edges. 
Coupled with the increasing proliferation of multi-fin boards is the trend 
for boards to be made shorter --as short as 5 feet--and also to be 
lighter. Such a combination results in tail-heavy boards, unbalanced by 
the sheer weight to their fin-boxes, if the box system is utilized. 
DISCLOSURE OF INVENTION 
It has now been found feasible to dispense completely with both fin-boxes 
and labor-intensive fixed fins, by the provision of a fin affixing system 
which permits single or multiple fins to be rapidly and inexpensively 
mounted upon the underside of watercraft, such as a surfboard or the like, 
in a variety of positions. 
Therefore, in accordance with the present invention, there is provided at 
least one fin for watercraft (e.g., surfboard) or the like; 
characterized in that the or each fin has an apertured, basal flange; the 
or each fin being affixable, in a variety of positions, to the underside 
of a said surfboard or the like, via fixing means extending through the 
apertures in said flange, and thence into the fabric of the watercraft, 
which watercraft requires no fin-box to be installed therein. 
The invention also relates to watercraft comprising one or more such fins, 
generally including, but not limited to, surfboards, surf-skis, 
sailboards, kayaks, canoes, skiffs and water-skis, and also to "soft" 
plastic watercraft, such as polyethylene boards e.g., the popular "Boogie" 
boards.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS, and BEST 
MODES OF CARRYING OUT THE INVENTION 
FIG. 1 is a side elevation of a fin in accordance with the present 
invention and shows that portion 1 of a surfboard or the like craft to 
which an inventive fin 2 is to be affixed. Fin 2 may be of a suitable 
plastic material; for example, a polycarbonate reinforced with fiber 
plastic (e.g., as sold under the trade name "LEXAN"). 
It will be seen that fin 2 does not have the conventional root which slots 
into the fin-box of a standard board, the base 3 of fin 2 being adapted 
merely to "sit" on the board; base 3 is flared out as shown in FIG. 2. 
The base, or, more aptly, the basal flange 3 has forward and rearward 
extensions 4 and 5 respectively, each of which is provided with 
appropriate slotted apertures--see FIGS. 14, 24 and 25--so that the 
inventive fin 2 is enabled to be adjusted in relation to the undersurface 
of the board. 
Extensions 4 and 5 are affixable to board 1 by such as bolts 6 and 7, each 
perhaps 1/2" to 1" long, which are adapted to screw into co-acting, 
threaded inserts 8 and 9 sunk into the fabric of the board. 
Extensions 4 and 5 have tapered ends 10 and 11, so that they are somewhat 
faired into the board's shape, fore and aft. The bolts and inserts are 
advantageously made from some rust-resistant material such as monel metal, 
fiberglass resin itself or a plastic such as Delrin. As will be 
appreciated, it is quite a simple task to drill two suitable holes into 
the surfboard and to push home the threaded inserts 8 and 9, preferably 
after applying a compatible adhesive. Hollow hulls required a suitable 
sealed thread, with the screws fitted from within, and extending through, 
the hull, whereby the fin may be attached thereto by hexagonal nuts or 
other equivalent fastening means. There may be a layer of some 
compressible material, referenced 12, between board 1 and fin 2, to 
discourage any chipping of the surface of the board, and to encourage 
flush fitting. Surf wax may also be another choice. 
FIG. 2 is a self-explanatory front view corresponding to the depiction of 
fin 2 in FIG. 1. The base of the flange 3 is preferably slightly curved or 
concave (not shown). 
FIG. 3 illustrates a preferred embodiment in the form of a 
multiple-threaded insert block 13 having, say, 5 threaded holes therein, 
each adapted to take a screw such as those referenced 6 and 7 in FIG. 1. 
Such a block 13 may be cemented into a suitable cavity in the underside of 
the surfboard, using a compatible adhesive, and to ensure its retention in 
the cavity, block 13 may be provided with a pair of grooves 14 and 15. 
FIG. 4 shows how a board may be fitted with a plurality of threaded inserts 
8 and 9 so that the angular disposition of a fin may be selected, while 
FIGS. 5 and 6 illustrate the range of selectable longitudinal, lateral and 
angular positions of the fins possible with various arrangements of 
inserts and/or multiple insert blocks. The slots in extensions 4 and 5 
enable, for example, a fin to be affixed to the board via threaded holes 
16, 17, and 18, 19, etc. 
FIGS. 7 and 8 show another fin shape having a main fin portion 20, an 
apertured basal flange 21. The trailing edge of the fin has a "compound 
curve" such as 22, 23 but, more significantly, has a pair of 
laterally-extending secondary fins 24 and 25, preferably curved, fore and 
aft (not shown). Under certain wave conditions, these extensions 24, 25 
enable easier wave entry and better turns to be performed, and the board 
feels more stable and responsive if the `wing` is the correct size, and 
curve, for the craft. 
By now the reader will have realized that the very spirit of the present 
invention resides in dispensing with a surfboard fin-box and labor 
intensive fixed fin, and providing in lieu thereof a simple and 
inexpensive fin-securing system, in which a fin is affixed directly to a 
surfboard, preferably employing bolts or screws accommodated in 
internally-threaded sunken inserts. FIGS. 9 and 10 illustrate such fins. 
FIG. 11 clearly indicates how fin cross-sections may differ. As will be 
seen, while the center fin 26 has the conventional aerofoil section, the 
lateral fins 27 and 28 are generally planar on one side. 
With regard to FIG. 12, it is a known fact that, in triple-finned 
surfboards, the angle between the lateral fins and the lower surface of 
the board will affect performance--very extreme angles having, indeed, 
been tested. Thus, in the present invention, the base lines of the fins 
may be deliberately angled, as exemplified by the angle subtended between 
the center-line of a lateral fin 29 and an undersurface 30 of a surfboard. 
A further advantage of surfboard fins affixed in position with inserts or 
blocks over the conventional fin-boxes is that, should for some reason one 
or more fins be removed, the resulting empty holes can very easily be 
temporarily filled but, even if they are left empty, cause no drag, 
whereas an empty fin-box results in quite considerable drag and 
turbulence. It is contemplated that surfboards molded without fin-box 
recesses will be supplied with various sets of fittings to the purchaser's 
choice and that the purchaser will be able to drill the holes in the board 
to give the fin arrangement required. 
Many other advantages accrue from surfboards constructed according to the 
present invention, such as the question of "tail-lift". 
Early surfboards were made with a generally linear bottom contour but with 
the fore end slightly upswept--the so-called "nose-lift" of the board. 
This design proved to be not wholly satisfactory and subsequently boards 
have been made with a full sheer, giving so-called "tail-lift" to the 
board and providing superior turning qualities and less keel effect. 
As will have been appreciated, the spirit of the invention lies in the 
abolition, or at least in the non-use, of fin-boxes into which the tang of 
a conventional fin is adapted to fit. 
The method of the present invention is superior to both fixed and fin-boxed 
fins as shown in the following table: 
______________________________________ 
ITEM FIXED FIN FIN BOX INVENTION 
______________________________________ 
Performance 
good medium good 
Strength good high-overkill 
good 
Surfboard 
medium-bad very bad minimal 
damage if 
broken 
Ease of experience experience easy 
fitting only only 
Flexability 
none fore-aft unlimited 
of position only 
Materials 
G.R.P., wood 
G.R.P. poly- 
polycarb 
foam, others 
carb, others 
others 
Base fitting 
not possible 
possible possible 
correction fore - aft (unlimited) 
Before-use 
6 to 12 6 to 12 30 mins. 
fitting time 
hours hours minimum 
Appearance 
good ugly good 
Material resin; brush; 
resin; rovings; 
drill or router; 
requirements 
rovings; jig; router; 
epoxy glue 
to fit glass mat; sander machine 
(G.R.P. choice) 
sander machine sandpaper; 
sandpaper; blade 
blade; tape 
Advantages 
invisible removable - removable; ease 
join interchange of positioning 
fins (change of 
angles) 
inbuilt angle; 
do-it-yourself; 
quick-fitting 
lightweight; 
interchangeable 
fins; inexpensive 
tooling; also 
fits fin boxes 
`BOOGIE` not possible 
only in fits "soft" 
fin fitting production boards (e.g., 
process polyethylene). 
______________________________________ 
Attention must now be drawn to some further preferred variations and to 
this end reference should be made to the following drawings, FIGS. 13 to 
27. 
Now while the aim of the invention is to do away with fin boxes and fixed 
fins, it is realized that some board-riders may wish to fit new fins to 
their existing fin-boxed boards and this can, or course, be easily 
accomplished by screwing the fin into the fabric of the fin box instead of 
into the board itself. Because of different brand boxes and their 
complimentary fin tangs being of different widths in the box, this system 
is unique in being universal. In a further variation, not shown, expanding 
or "umbrella" screws may be employed, sealed in with rubber or neoprene 
O-rings. In yet a further variation, rustless self-tapping screws may 
replace the screw/insert arrangement, to allow screw fixing directly into 
the craft itself. 
FIGS. 13 and 14 depict an inventive fin, FIG. 14 having a T-shaped slot 31 
forward of the leading edge of the fin. As seen in FIG. 13, the base 32 of 
the fin should be well-flared at the sides 33. 
These flares should provide sufficient width at the base of the fin to 
oppose lateral deflection of the fin tip relative to the base without 
causing damage to the skin of the board. The varying thickness gives a 
more uniform spread of load at the fin/board interface--the need to 
reinforce the board in the area of the fin by providing an extra layer of 
glass being much reduced. The width of the fin at T is advantageously half 
that of the base 2T, and base 32 may be cambered 3.degree. each side, 
although this will vary according to fin area and flex. 
Although the method of fin-fitting relies on screws there is no reason why, 
if desired or when optimum positioning has been achieved, they should not 
be bonded to the board by such as the epoxy adhesive sold as "Araldite", 
although it is contemplated that most users would prefer the removable 
aspect of the system of the present invention. 
A fin may be "raked" by such as a washer or shim placed between fin and 
board, while a fin may even be made to "stand proud" of its board--an 
arrangement thought to have some advantages under certain conditions. 
While the foregoing specification has been couched in terms of surfboards, 
it is envisaged that the present invention also has application to the 
fins, keels and centreboards of other watercraft such as soft `BOOGIE` 
boards sailboats (such as eighteen-footers), sailboards, catamarans, 
surfskis, kayaks, canoes and the like. FIG. 15 shows the underside of a 
suitable flanged centreboard or keel having slots 34 for the reception of 
fixing bolts. 
FIGS. 16 to 21, and 22, 23 show outlines of eight different fin shapes as 
under: 35 "sailfin"; 36 "trapezoidal"; 37 "football"; 38 "toucam"; 39 
"foot"; 40 "flash"; 41 "sailboard"; 42 "surfski"; all of which relate to 
the present invention. 
FIGS. 24 and 25 show typical dimensions of the basal flange slots of one 
embodiment of the invention, dimension A being 5.5 mm; B being 15 mm; and 
C 9.5 mm. In FIG. 26, dimension D, the thickness of the basal flange, is 4 
mm. 
Finally, FIG. 27 depicts an inventive left-hand fin, showing that side 43 
is curved, while side 44 is planar. The width of a typical basal flange 
may be 35 mm, and the planar sides 44 of laterally-disposed fins face 
towards the centreline of the board. As has been stated, the base of the 
flanges may be slightly concave to follow the contour of a board's lower 
surface. 
From the abovegoing, it will be readily appreciated by those skilled in the 
art that may other variations and modifications may be made to the 
invention without departing from the spirit and scope thereof as set out 
in the following claims.