Has anyone a link or info on matching fin sizes to sail sizes - or even a general rule of thumb?
Trying to get some range out of the one board so running a 98L Naish freeride board with 5.3m North, 5.7m Serverne & looking at a 6.7m sail too.
looking mostly flat-water blasting
Cheers!!!
a rough guide is sail size x 5 + - 2 depending on conditions = approx fin size for that size of board
I can't see why fin size has anything to do with sail size. Fin size should only depend on the board width and the type of sailing you're going to do. Whether you want to go upwind well or maximise your speed off the wind. I can understand you might want a smaller fin in windier, choppier conditions to keep your windward rail wetter and the board slower. I can understand that If you expect to go faster with a small sail then a smaller fin makes sense. It can still generate the required lift at the faster speed, but mostly we go slower as sail size gets smaller because of the chop.
The fin can only see the water going past, it has no idea what's going on up top.
I think it's an old wive's tale that fin size should match sail size. Took out a 5.3 the other day with a 36 cm fin - it was fine, it matched the 64 cm board width.
What's anybody's logic that a small sail needs a small fin?
the bigger the sail the further back on the board the force will act in a lateral direction, this puts more sideways force on the fin even though the total power gained from the sail could be the same as the power generated by a smaller sail in more wind.
from that I can't see why a small sail needs a small fin but a big sail should require a big fin
www.makanifins.com/
They match their fins on wave, freestyle wave and freestyle to board volume and sail size, for freeride boards they go on width and sail size. I just go for what ever feels right but big fins scare me....the biggest I run these days is a 28, no need to go bigger and it works on my 7.2 and 5.0 equally but then again so did the 23 cm fin? I try to run the smallest fin I can, it just makes the board behave. I think you will adapt eventually to what ever fin you have, I can remember starting out on a 145 with a 50cm fin and using it in 10-30 knots with everything from my 7.2 to a 4.5......worked but was not ideal.
First of all think, "how is the board doing 20kts". It's not just the sail, the fin is involved as well.
Windsurfer power comes from the difference in velocity between 2 fluids.
2 foils are used to extract power from this difference, 1 in air the other in water.
the smaller this difference, the larger the foils need to be, the greater the difference the smaller they can be.
My feeling is that the 2 foils need to be in balance otherwise there is inefficiency.
Then there are all the other variables, board width, sailor weight and height etc. that modify that balance
Of course sailsize and finsize is related. There are many boards where you don't feel the difference as much, however most people will notice it, when you give them a proper fin-size.
My 80cm wide board works with a 44cm fin and 7m2 sail, and 48 and 8 sail?
But not the other way around. There is no way to sail comfortably with 7m2 sail and 48 cm fin, and likewise with 44cm an 8m2....
http://www.riggeek.com/gear-calculator/for-windsurfers
jimbodouglass.blogspot.com/2010/11/updated-windsurf-calculator-online.html
Something else that isn't immediately obvious: your board doesn't travel straight where it's pointing, but crabs sideways a bit. This gives your fin an angle of attack to the water, otherwise you won't get any usable force from it.
I'm not sure about the physics of how the full dynamics work, but I do know that on bigger size sails I need a bigger fin, otherwise I get too much spinout and find it too hard to go upwind. As the wind picks up and I go down a sail size, I can get away with smaller fins. I tend to notice this most on my wave board, for what it's worth (sweet spot on a 5.2 is a 23cm fin)
the other factor that i also important is the velocity of the fin thru the water.
Fins work better as you pick up speed. Smaller fins requite a greater velocity before they start to work. They also reach a point where more speed will actually start to cause more drag,
In 15 knots with a 9 , sail you need a big fin to get the lift working early. sure you can put a smaller fin and it will work fine once you get up to speed but when accelerating or thru the luls it will tend to slide sideways.
so what we really need is an ajustable fin that retracts up into the board as we pick up speed :P
for the larger sails - heavyweight + larger boards
it is better for me to use 5*sail+4
example 10.0 --> 54.0 - use 53
---------8.5 --> 46.5 - use 48
---------7.0 --> 39.0 - use 40
james douglass used 0.1*C13^2+6.46*C13
which is 0.1 times the sail squared + 6.46 * the sail
10.0 -- 55 for freeride
08.5 -- 48
07.0 -- 40
which is pretty much 5 * sail + 5 !!!
I confess to following those equations in the past but have found that the brands and the sailing style to be just as important.
One brand will work for someone and be a totally failure for someone else. I find select tricky, black project amazing and have a C3 venom that is my speed fin which on the 2 occasions I have used it never lost grip once.....but I am not as fast as most.
