We’ve received this great myth from reader Marc:

“Mrs. Peter Hart and Guy Cribb seem to disagree if very choppy water requires a bigger fin or a smaller fin than usual. I seem to recall having read both. One theory says that a smaller fin keeps the board flatter on the water, the other says that a larger fin prevents spin outs more effectively in choppy water. Could you shed some light on that?”

We sure can, over to Marco Wedele and Simon Bornhoft…

Marco Wedele:

“I personally think there are a few other factors that come into play here, it’s not as simple as being able to say you need a smaller or a larger fin in choppy water. Depending on how powered up you are or what kind of board you use, one or the other can be relevant.

“If you are really powered up and sailing with a large fin, then this will create more lift and it will be hard to get any sort of control.

“If you are underpowered and you are sailing with a smaller fin you won’t be able to push too hard of the fin, so spin-out can happen.

“As you see this is a tough one to answer, as it depends a lot on wind strength, the board and even sail size!”

“With regards to fin choice in chop, ‘listen to what your board’ is telling you!’ If the board is spinning out a lot, be it flat or choppy water, then soften the loading on your back leg and try a slightly larger fin.

:Conversely if you are very powered up and the windward rail or nose is lifting uncontrollably, this could mean you’re on too larger a fin.”

Here’s the Windwise fin formula to help you work out the right size fin for the sail and board you’re using:

Windwise Fin Formula for 115L-170L Freeride boards

Take the sail size you’re using, multiply it by 5, then add 4.

E.g. 6m x 5 = 30 + 4 = 34cm (+ or – a couple of cm’s using Fin Tuning Guide)

Windwise Fin Formula for 75L-115L Freewave/Wave Boards

Take the sail size you’re using and multiply it by 5, then add 2.

E.g. 5m x 5 = 25 + 2 = 27cm (+ or – a couple of cm’s using Fin Tuning Guide)

NB. Freestylers use a fin the size of a key ring about 18cm, so just shows how small you can go, even in chop!

Fin Tuning Guide

Possibly increase the fin size 1-4cm: Heavier sailors (+85Kg) / Struggling to get planing / Spinning out a lot / On a comparatively wide board.

Possibly decrease the fin size 1-4cm: Very Experienced or lighter sailors (-75kg) / overpowered conditions / Very narrow boards / Looking for an extra lose feel.