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A range of fin types and shapes: (from left to right):
slalom/race, freeride, freewave single, freewave
thruster setup (tri fins) and freestyle
Ultimately the exact angle of attack for planing or spinout will
depend on a combination of speed, course sailed, wind
speed, sailor skill and weight, water state and the size, type
and condition of the fin.
Setup variations are:
1) Single – one centre fin.
2) Thruster (or tri-fin) – three fins: one centre fin plus a pair of
smaller fins either side further forward. These cannot be
driven against by the back foot as much as single fins yet
offer a good balance between manoeuvrability and drive.
Switching from a single fin to tri-fins on a freewave board will
result in a significant shift in how smoothly and easily the
board carves, especially if, at the same time, the footstraps
are moved from the outboard position with double back
strap to the inboard position with a single back strap.
3) Quad – four fins: one pair of small rear fins near the middle
plus another pair of even smaller fins on the outside a little
further forward. These allow the hardest carving, precise
grip on the bottom turn, radical sliding-out/pulling back of
the board on the top turn, the softest landings and, being
shallow, the smallest chance of catching the fin on
anything solid under the water. At the most radical end of
wavesailing they are often preferred as, during the hardest
bottom turn carving, there will always be two fins biting into
the turn when it matters most.
4) Twin – two fins: one pair of small rear fins.
To balance our ride, the side force of the sail must be matched
by the side force of the fin and board. This is Newton’s Third
Law: ‘for every action there is an equal and opposite reaction’.
So why don’t we need a fin with a surface area of 7.0m to
balance against a 7.0m sail? Well, water is significantly denser
than air and has a greater viscosity (liquid thickness/resistance
to flow) so a fin can be much smaller than the sail to produce
the same amount of balancing force. The forward motion of
the windsurfer also creates a proportionate amount of drag
(which limits speed and performance) which we have to
accept. A thinner fin with a higher specification and in good
condition will create less drag and go faster than a lower
quality, thicker fin in poor condition.
Fin characteristics, setup and types
Fin profiles, like boards, come in many shapes and sizes. The
profile determines how it behaves and this in turn contributes
greatly towards the feel and function of the board.
Fin characteristics (that have to keenly balanced by fin
designers) are:
• Length: a longer, straighter fin is better for lighter wind
straight line blasting and a shorter, more swept-back fin
is more suited to a higher wind manoeuvre-oriented style
such as that of wave/freewave sailing.
• Aspect ratio: high = longer and thinner for lift and
speed, low = shorter and thicker for manoeuvrability.
• Surface area: greater = more lift, lesser = less lift.
• Thickness: a balance between thinner for less drag and
thicker for less flex.
• Rake: how steep the fin is angled back. More rake =
less drive.
• Stiffness: this is determined by the elastic behaviour of
the material. Loading up a fin causes it to flex as all
material is subject to bending. Too much flex can reduce
performance yet help to provide a more forgiving ride and
produce springback in wave fins for increased grip and
projection off the lip.
Two options for a 103 freewave board: either a single
28cm centre fin or a thruster setup with a 20cm
centre fin and two 11cm side fins
uk
WIND
SURFING