how to know what to use

[galeforce79]

when windsurfing, how can one tell if the fin size is right for the sail/and board size? i have 2 sails, 60, 7.5 and a 295 130L board, and one fin size. what is a good way to tell if the fin is too big or too small?

[spyder]

theres been some good posts in the past on this topic, you might search for them to get more info.

fin size depends on a lot of factors, fin shape & design, sail power, and board shape & size. so its fairly complicated what fin will work great, vs one that works so-so.

fins are either blade, curved (bumpnjump/chop), slanted (weed), or swept-back (waves). they have different foils, and aspect ratios. a wider fin will have more low end power, whereas a narow fin will have better speed.

you can get into a bunch of technical blah-blah about fins, but it comes down to getting a fin from a known good fin company (finworks/rainbow for example) that is approximately big enough for your setup and then trying it.

a simple way to tell if the fin is working...if the fin spins out, it probably is too small, if the board rides out of the water, and fin walks, its too big.

another problem is upwindability, blades track better than curved fins, but the curve helps when turning and control in the chop. so there is a compromise.

note, fin spin-out, can be due to a lot of reasons, such as gouges in the fins foil. but simply, it can be because its too small to hold the sails power.

in your case, i would put in a something like a 17-20 blade for the 7.5 and maybe a 14-16 slightly raked fin for the 6.0.

if you just want one fin, id go for maybe a slightly raked (Rainbow Teardrop for example) 17. but it might be a bit much for the 6.0 in higher winds.

hope this helps.

[gemoore]

Spyder is right on, but Id go one point further.

Having a few fins in your quiver can do wonders for increasing the maximal range in which you can use your board. Dollar for dollar, having extra fins is probably the best buy in windsurfing (outside of lessons!).