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G’day
<div>I have just purchased a 6.5m Tushingham T4 freeride sail and using it on my Angulo Sumo with a stock 31cm fin. I want to try this sail on my RRD FSW 96L which comes with a 28cm freewave fin.

<div>My question is what would be a suitable size fin for the 6.5m and 96L FSW

<div>Tomorrow i’m going to try the sail on the FSW and perhaps try the 31cm fin with it. Does anyone have any thoughts or experiences with similar size board and sail?

I have used a KA Kult 6.4 and Koyote 6.6 on that board with the stock MFC 28 fin and it worked OK. Try the 31 but it may be a bit big for the tail width. I guess you will find out.

I've used a Gaastra Matrix 6.5m with a Fanatic 95 Freewave and down to a fairly thick/powerful 25cm wave fin, but it was marginal for light wind. My 28cm freewave fin seems a good match for the 6.5m.

I guess it depends on the conditions. Flat water or ocean sailing?
I use JP weed-wave 26 on either 6 or 7m with my 96L FSW.

Maybe this helps:

jimbodouglass.blogspot.com/2010/11/updated-windsurf-calculator-online.html

There is a tab for fin size.

35, 32, 29 are what I use with that size sail on medium boards 104, 95 Litre.

For FSW and freeride boards I find that a really simple fomula I learnt on a clinic a few years back really works well:

5 x sail size + 2

So a 6m sail would be 5x6+2 = 32cm

Doesn't need to be spot on. As an example I have a 6m sail and use a 33cm fin on my 96L FSW which is close enough.

I understand that fin size can vary depending on conditions but for normal powered up conditions it works for me every time.