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Old 28th January 2008, 02:55 PM   #1
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Default Fins - length and such

How does it work with fins and there compability towards sail size ?

What happens if you use a fin that is to big ?
How do you know how big fin you should use ? I mean if the original is to small, how do you know what to buy ? (length)

Or is it just to try ? Fins are pretty expensive so you can't buy that many of them :/
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Old 29th January 2008, 12:06 AM   #2
Join Date: Sep 2006
Posts: 459

Too big and board will want to twist up to windward.Hence wide boards holding down bigger fin.May also cause tail to lift and control problems.
Too small creates later planing (more side lip initially) and poorer upwind performance (esp at lower speeds)
On occasions there are positives to using "wrong" fin. Setting absolute Vmax (IMO) you will put up with negatives to get better offwind speed and enhanced control a smaller fin (can give)
On the hand if you want to be real quick off block you could use "too" large a fin. (Helps initial planing) and work around problems you then encounter.
If you encounter control problems and or overpowered change fin first.(to a smaller one)Its sometimes enough without changing sail.

Its trial and error.
Good place to start though is
Multiply sail size(in metres) by 5 and then add 2 (or 3 ) (Eg for a 6 metre .5x6 =30 then add 2 giving 32cm)
Obviously there are large /thick/thin 32cm fins but on average its a good guide and works over a surprising range.I like to use same range of fins to overide design/thickness differences) (Eg My Fanatic 36 in performance is almost exactly same as my Northshore 32)
Try and build up a quiver of second hand fins.(Ebay is great for it) Then when you know exactly which you want buy them new.(Resell old ones back on Ebay)
It really is worth messing about with fins and changing them.(Its as important as sail size)
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Old 29th January 2008, 12:21 AM   #3
Join Date: Aug 2006
Location: Dallas, Texas USA
Posts: 799


Floyd is correct, but in very simple terms, fin size is determined by many, many variables.

Board width
Sail size
Wind speed
Board speed
Body weight
Water state (chop)
Skill level
Function (free sailing, waves, slalom, formula, freestyle, speed, etc.)

Best to talk to experienced windsurfers in your area or a shop. You can probably find used fins pretty cheap if you look around. For beginners, fin quality (expense) isn't a big deal. Getting the right size and design is important, but spending a lot of money is not needed at this time.

As your skills and experience improve, upgrading your fins will become more important.
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Old 1st February 2008, 02:10 AM   #4
Join Date: Nov 2006
Location: Niobrara
Posts: 110


Some of the fin companys have detailed sail ranges for their fins, others none. The companies taht offer great support are True Ames, GSport, Maui Fin , Select, Tarifa, FinWorks, I like the look of Nik Bakers line and Kevin Prichard has his MFC for sale on his blog at a good price delivered, most of the shops have knowledgeable staff reference size, Gorge Surf Shop, Windance, Big Winds and DELTA Windsurf , all US shops great staff.
good winds
carvesalot is offline   Reply With Quote
Old 1st February 2008, 03:34 AM   #5
Join Date: Aug 2006
Posts: 237

Good comments above. I have a similar fin-size calculator at this link under the "Fin Size" tab. It's based on the recommendations from True Ames:

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Old 1st February 2008, 04:52 AM   #6
Join Date: Aug 2006
Posts: 1,483

Mathematical modeling of gear selection is for sure a very complex issue...I'm a bit skeptical to predict gear selection with a magic mathematical formula. Both calculators shown above were way off the mark for the real world conditions. Fins size for a slalom board is not the same as for a wave board with same sail and wind for the first model (the 110 L volume cutoff has a very distinct outcome between a 65 kg or a 100 kg rider IMHO). Sail range were way too small and fins way too large for the second model in 20-40 knots winds.

a) Example of real world gear selection in 20-25 knots wind with a 5.4 sail, 183 cm x 65 kg rider:
1) HS105, Carve111 or S-Type 93: identical 26 cm slalom fin is fine (30-32 slalom fins cm is way too large).
2) Kombat 86 : 24 cm wave fin is fine (30 cm freeride fin is way too large).
3) Acid 62 : 21.5 cm wave fin underpowered; 21 cm wave fin well powered; 20 cm wave fin overpowered (23-24 cm wave fins is too large).

b) Another example with Kombat 86 and identical 6.9 sail in 12-18 knots wind:
4) outboard and back straps : 30 cm fin is fine for freeriding.
5) inboard and front straps : 23 cm wave onshore fin is fine for wavesailing.

c) 3.6 sail on Acid 62 : I have no power and am sinking in 24 knots wind as predicted by the second model. I need at least 10 knots more to get going on a planing mode (real world wind range 35-40 knots with this combo)...

Cheers !


Last edited by Jean-Marc; 1st February 2008 at 05:18 AM.
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Old 1st February 2008, 05:04 PM   #7
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What I understand here, there's no actual right when it comes to choosing a fin. I mean, you just have to try and learn.
Of course you have to choose a length that's in between the boards recomendations and the right type of fin. Then it's just up to the sailor to say if it's good or not.

I'm I totally wrong here ?
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Old 1st February 2008, 06:29 PM   #8
Join Date: Feb 2007
Posts: 37

Forget about calculators, nowadays they don't work. Too many variables affect on this. The best way is to ask in forums providing enough information (board/sails/style/your weight/conditions).
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Old 1st February 2008, 09:11 PM   #9
Join Date: Sep 2006
Posts: 459
Angry They do work.But read post. (And try them)

Thats nonesense kimax.

You always need a place to start .
x5 adding 3 ; might not be perfect but it certainly gives a (good) starting point especially for people who need to ask.(ie beginners or folk not at extreme of sport)
Poster is not aking what fin to use on his speedboard chasing Antoine;or for his waveboard looping with Mat.He`s asking for general advice !

Using this is never going to put you out with absolutely wrong fin; certainly could listeing to certain folk on here.

Have you even tried it with a few sail sizes ???

Fair enough give your advice but dont deride other people`s.

Calculators DO work .(within reaon and for a GUIDE !!!)
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Old 1st February 2008, 09:49 PM   #10
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Sail x 5 Plus Fin Sail x 5 Plus Fin
4.0 20 3 23 6.6 33 3 36
4.2 21 3 24 6.8 34 3 37
4.4 22 3 25 7.0 35 3 38
4.6 23 3 26 7.4 37 3 40
5.0 25 3 28 7.6 38 3 41
5.2 26 3 29 7.8 39 3 42
5.4 27 3 30 8.0 40 3 43
5.6 28 3 31 8.2 41 3 44
5.8 29 3 32 8.4 42 3 45
6.0 30 3 33 8.6 43 3 46
6.2 31 3 34 8.8 44 3 47
6.4 32 3 35 9.0 45 3 48

Not far out ????
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