Spin-out
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"As soon as I land from a little chop hop, my fin just
lets loose; feels like I don't even have a fin on!"
"I am blazing along, and just start to jibe, and wooooah!!,
I have lost my steering!"
What is spinout? Spin-out,
cavitation, ventilation, slip-sliding,...whatever you want to call
it, it is not fun. In order to prevent it, it may be helpful to
know what causes it. Spin-out is caused by air reaching the
low pressure side of the your fin. It sneaks in from the
back of your board when you least expect it. The harder the
sailor pushes against the fin, the more vacuum (or low pressure)
is created on the windward (upwind) side of the fin. Water
rushes faster and faster past the fin struggling to remain
attached to the surface of the fin, looking for an opportunity to
separate from the fin. This can easily occur if air enters
the equation, for example if the board becomes even slightly
airborne. Once a channel of air is made from the fin to the
back of the board, it is quite difficult to get rid of it.
At this point, the fin becomes totally useless, and no longer
functions like is should.
How do I get rid of it, once it starts? Once
you are spinning out, usually you are totally out of control, and
either fall, or slow down to sub-planing speeds so that the water
can re-attach to the board. Here are a couple advanced
techniques to try next time you spin-out:
- Bear off the wind and sheet out while pulling the board back
beneath you with your feet, so the fin is "slicing" through
the water rather than pushing it.
- Chop hop your board (while spinning out). Sounds
tricky, but with some practice it will allow you to correct
the spinout without falling off a plane. Chop hop like any
other (without pushing against the fin) and while in the air
bear off a little and pull the tail underneath you. It is important
to land in a way that your board is not putting any lateral
pressure on the fin, or you will be spun out all over
again.
Here are some suggestions to reduce the
frequency of spin-out.
Slice the water when landing
When jumping (or even getting your board out of
the water 1 inch) you provide a path for the air
to travel to your fin. In order to close this
path, you need to bear off (turn downwind) in the
air, so that when you land, your fin slices
through the water, and eliminates the opportunity
of the air to reach your fin. After your board is
back covering the water, you can redirect your
board.
Absorb the bumps
Another helpful hint is to bend your back leg a
bit to help absorb the chop, and keep your board
covering the surface of the water. Bending your
back left also puts a bit more downward pressure
on the back of the board, and also helps keep the
air channel closed.
Move your fin forward
Moving your fin a bit forward, and away from the
tail (where the air comes in), helps. Also having
a cutout on the back of your fin increases the
distance from the tail to the back of the fin,
yet doesn't effect the center of resistance
(effective location) of the fin. The concept of
the flapper you may have read about for the tails
of race boards is based on the principle of
keeping the area behind the fin covered so air can't easily reach the fin.
Move your mast base back
Moving your mast base further back in the track
will position your sail more upright (not tipped
way back behind your board), and may reduce the
pressure you put on your back foot.
Use a slotted fin
If all of these things fail, you can always use a
slotted fin. A slotted fin forces water through
out the slot and constantly clears the air off
the low pressure side of the fin, and as a
result, keeps you from spinning out. The
disadvantage of slotted fins is drag.
If you are using a blade fin they can be fairly "high strung".
This type of fin has a short chord length (length
from front of back of the fin as the water
travels), which has low drag, and provides a lot
of lift (gets you upwind), but is a difficult fin
to use in low speeds, and is hard to control at
most speeds.
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