View Full Version : Calculating fin size
14th September 2009, 05:03 AM
I'm trying to work out which fin(s) I should be using with my 2008 Futura 144. I'm around 92kg in weight, and on a good day, and early intermediate standard.
The board came with a 50cm fin, but when really powered up on a 6.5 Tushingham I find the nose waves around a lot - I've not had the same problem with a 7.5 or 8.5 sail, so I'm guessing I have too much lift
I looked up the fin size calculator on Boards and that suggests a 38 cm fin ... but that seems to be out of the expected fin range for the board.
I checked your tuning page - which says fin size is important but doesn't say how to calculate it ..
Could you suggest how I go about calculating the right size?
14th September 2009, 12:41 PM
show size fin to sail size on a MFC fin would be suitable on your board. I would thing 40 42cm would be 'bout right. 50cm is for a rather large sail.
14th September 2009, 11:32 PM
At 92 kg on a 6.5, fully powered, I am guessing that the board is too big for the conditions. A smaller fin would help with control in high wind conditions, but 50 cm isn't large for a board that's 80.5 cm wide in winds from 12 - 20 knots. Over 20, you should be on a smaller board.
When you are on the 6.5, what speed is the wind? Do you have a smaller board?
15th September 2009, 04:11 AM
Here are two popular fin size calculators that you can try:
(I've seen you've tried that already)
When you've tried them, now it's best to forget them ;-)
No, I'm serious. They give you just the guidelines and using the right fin will come from experience. Similar to recommended sail ranges for different boards, they will rarely work as quoted.
Now on to your gear. As an early intermediate it's OK for you to try a 6.5 on your F144, but that sail is way too small for that board - 80cm wide (while an 8.5 is close to ideal). Look at experienced sailors in your area, they will be probably on 95-115 l boards when it's blowing enough for 6.5. To extend your board's range into higher wind a bit, try a fin around 42 (with a 7.5). After a while you'll probably realize you don't wan't to use your Futura with a smaller than 7.5. So take quoted ranges (both sails and fins) with a pinch of salt and try a lot of gear.
16th September 2009, 04:23 PM
Thanks to all who replied, I'm now considerably less confused though a bit concerned about impact on my bank balance !
I've a limited range of kit, and I was trying maximise its use - on the day in question, windspeed was around 20-25mph, which from the sail calculator (thanks Screamer) seems about right to be using a 6.5. Just that it seems it was on the wrong board (but it was still fun ...)!
I do generally use a 7.5 or 8.5, and I've no doubt that others were using lower volume boards; I just don't have one yet.
So armed with your feedback I think I have some choices:
1) get a smaller board; (that will have to wait unfortunately)
2) experiment with, say, a 42 cm fin (less expensive therefore more likely)
3) don't sail when the wind is too strong for a 7.5 (no chance!)
Given the comments about recommended sail sizes (6.5 to 10.0 for the 2009 Futura 144, I can't find the figures for the 2008 model), what would be the likely largest sail size I could sensibly use with my board? Apart from the obvious physical challenge to handling a big sail, wouldn't it risk damage to the board going above the recommended range?
16th September 2009, 05:13 PM
I'm pretty sure 10.0 should work ok, I'd get as light rig as possible (so not a full race on machine, but rather a 2-cam freerace/freeride or no-cam, like Retro). They will get you on plane earlier, are way easier to rig, tune and handle and when overpowered you'll switch down to your smaller sail.
16th September 2009, 09:39 PM
We all want to maximise the range of our equipment, that's understandable. However there is a point when going bigger or smaller simply won't give you anything, just worse handling. I've tried that a lot. A 10m won't damage your board, but try one if you can before buying. For a heavy sailor I'm not sure it's advisable to go to the absolute recommended max. My guess is that 7.5 and about 9.0/9.5 (7.5 and 8.5 a bit too close) would cover all the useful range you could get from your 144 (but again, try and see). Marek is right wrt sail type, 2/3 cam freerace better than full-on race.
18th September 2009, 01:47 AM
Thanks for the really helpful feedback. I would agree the 8.5 is a bit close to the 7.5 though - I was perhaps too influenced by an attractive secondhand price. Not too much lost though and going straight to the biggest sail might have been too much for my standard at the time.
So thanks again,
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