View Full Version : Rule for choosing the right fin size ...

20th May 2008, 07:59 AM
Hi Roger,

What it's the rule for choosing the right fin. Right know I have 145 liters board, with the standard 48cm fin and a 7.5 sail. At some points I start to "spinning", and have to get out from the straps in order to get control again on the board.

Other thing I notice, it's that I have a friend with 133 liters board and a 6.5 sail (with cams) and 48 cm fin, that when the wind goes down a litter bit, he still get planning easy, and It takes me more effort, and some point didn't get planning at all. Im using a no cam sail, I don't know if the cam it's a issue here to early planning or if it's the fin size.

Im looing to buy a good fin (like Tectonics Maui), but have a couple of questions?

1- It's a 48 cm fin appropiate for a 7.5 sail and 145 board (Im 198 pounds weight).
2- Did you gain performance and speed with a top quality fin (like tectonics), even if it's the same size as the standard fin ?
3- It's there a rule to select a fin size for a specific sail size?
4- Did a cams sail makes a difference in early planning?

Thanks a lot Roger, as always for your good advise.

20th May 2008, 11:49 AM
Hi Jamespr43,
I'm going to paste in your questions here and deal with them one at a time....OK?

1- "It's a 48 cm fin appropiate for a 7.5 sail and 145 board (Im 198 pounds weight)."
48 cm would seem about right for a 7.5 m2 rig, at your weight, but the tail width of your board, the type of sail you are using, and a couple of other things can combine to make the 48 cm fin less appropriate.
Also, if you want to plane earlier, and use a larger sail, then a deeper span fin, and a wider tail width are probably the best keys to success.
You can go with a big fin, but if you do not have the tail width to use it effciently and control it when you get up to speed, the big fin doesn't get you much.

2- "Did you gain performance and speed with a top quality fin (like tectonics), even if it's the same size as the standard fin ?"
Normally, the answer to this is yes, if you buy a CNC machined G-10 fin it's probably alot closer to it's "design profile" than a molded fin.
Virtually all fins are "hand finished", but the "set over" Dennis Parton uses at Tectonics is the smallest in the industry so Tectonics fin are always very high quality due to very little "hand finishing".
But, the other "fin artists" (Deboichet, Chuck Ames, Wolfgang Lessacher, Curtis Hesselgrave, and some others) can hand finish a fin from scratch, using templates and come up with the same quality or better because they can look at and feel tiny imperfections that make all the difference in a fin's performance.
So, buying a top quality fin normally gives you better performance, but not always as there are numerous things that come into play that can make one design or concept in a fin work really well, or not so well.

3- It's there a rule to select a fin size for a specific sail size?
There are some rules or formulas for calculating what size fin works with what size sail, but none of the formulas I've seen take into account the tail width of the board.
Some "fin size calculators" introduce sailor weight into the formula and I've found this to be very important.
So, the answer is that there is nothing that's specific and measureable enough to work in all cases.
Good guidelines are available, but again, the guidelines may or may not apply to your situation.
Experience counts for alot here. If others where you sail are using a particular brand; model; and size fin with sail sizes similar to what you have, these would be very good fins to "check out" because it's easy to see that they are working in your conditions.

4- "Did a cams sail makes a difference in early planning"?
This depends entirely on the "type" of sail your no-cam sail is.
If you have a Free Race sail (Sailworks Retro; and a number of other "no-Cam" free
race designs from other sail lofts) then the cambers may not make a great deal of difference in early planing.
If you have a regular "recreational" sail without cams, then yes, I would say that a cambered "free Race sail would be better for early planing.
And, this all depends on if both your sail, and the cambered sail are rigged on truly appropriate masts. If you don't have a mast with bend characteristics that match the
design of the sail, then you aren't getting the full performance or full range.
And, how you tune your sail can make a huge difference in it ability to provide you with
early planing performance.
This is one reason I don't find the annual "sail tests" in the magazines to be particularly "helpful".
They are fairly non-objective, and someone from the magazine (who we hope knows something about rigging sail) rigs them up.
It varies from magazine to magazine and even sometimes to individual testers whether or not the sails ever get "tuned" for different condtions.
So you can have a sail that's really good in light winds (from a good design and lots of testing by the R&D folks that made it), but it gets tuned initially on a higher wind day, and never gets "retuned" to bring out it's early planing performance. So, it gets poor marks for "early planing". A bit of tuning, to enhance the light wind performance, and the results might be very different.
The problem is that the folks at the magazine never tell you how the sail was tuned, or if it was ever "tuned for the current conditions".
Hope this helps, and I'm sorry that I cannot be more specific, but if you tell me what board and what fin, your sail brand/type/size, and the conditions (wind speed and chop height and type of water (sea water vs freshwater) only then can I give you a more specific answer

20th May 2008, 06:20 PM
Thanks Roger,

Here are the specs:

Board Type its a F2 Stoke 145 liters with a factory 48cm Fin (Power Box)
Board Lenght its 260, width 75, Didn't know the tail size
Sail Type it's Severne Gator 7.5

The conditions are normaly 15-20 knots, sea water, with little to moderate chops.

What about the "spinning", it normaly happens when I'm going upwind, and take a chop, It's that a signal of a fin lenght problem? Would I be better with a 50cm fin, and will get me planning early ?

Thanks again Roger

20th May 2008, 10:29 PM
Hi Jamespr43,
OK, I couldn't find the 1 foot off measurement for the F2 Stoke 145 liter either, but from the look of the board it's certainly in the 55-65 cm range I would think.
So, you have a fairly narrow tailed board so the 1 foot off length to fin length ratio probably is not ciritical in your situation.
You have also "introduced" something that may be more liked to technique or the type of fin you are using than to an actual fin quality issue.
If you are "spinning out" (i.e. "spinning" in your terms, pushing the fin loose by overloading it, in my terms) it could be a fin quality issue, but since it seems to happen when you get slightly up off the water after hitting a bit of chop, it very well may be that your "technique" has you pushing a little too hard on the fin when going upwind.
The fin works well when all of it is engaged fully in the water, but it "spins" when you continue to push on it with only part of the the fin in the water because your board has "gotten some air" due to hitting chop.
You could get a larger fin, but that might solve one problem (the spin outs) but create another (control issues because your fin is simply too big for the conditions.
You could change your stance a little (stand up a little straighter and don't push quite so hard on the fin, by changing your boom height and harness line length.
You could change to a more forgiving fin design ( I couldn't find a photo of the stock F2 Stoke 145 liter fin either).
If your stock fin is a swept pointer design (large curve radius on both the leading and trailing edges) you might want to try a more vertical slalom type fin to eliminate the spinning, but this may alter your turning and jibing performance a little.
Getting a 50 cm fin to replace a 48 cm fin is probably not going to change much (unless your stock fin has some quality issues).
If you want earlier planing, I'd suggest either a 52 cm or 54 cm for the fin size to be really noticeable.
BUT, what you gain on the bottom end, you may lose is control issues on the top end, so if you are going to be fully powered up, you probably want to use the 48 cm fin.
I think a Tectonics Tomcat 48 might solve your spinning problems, and it's an excellent fin, for sure.
Hope this helps,

21st May 2008, 09:43 AM
Hi Roger,

Thanks for your valuable help here. I would be looking to contact Dennis for the Tomcat Fin 48cm.


21st May 2008, 11:27 AM
Hi James,
The Tectonics fins are also available from Sailworks.
Check them out:
Hope this helps,

21st May 2008, 07:18 PM
Roger, Thanks, Im placing the order at sailworks. Just another question, what did you think about KA Koncept sails ?? Im seeing a lot of people at GPS Speed using it ??


21st May 2008, 10:33 PM
Hi James,
I've seen some KA Koncepts.... and I may have sailed one once, but I really have no experience with them.
I don't comment, good or bad, on things I have no experience with.
The sails I've seen seem to have pretty good build quality, and the guys sailing them seem to like them.
They are probably very good sails, but I don't see any results that indicate they are remarkably faster than other speed slalom sails.
Hope this helps,