View Full Version : Cutting down 70 cm fin to 55 or 62 cm

Del Carpenter
10th July 2007, 10:59 AM
I need more fins for my X-186. I have a chance to buy a stock 70 cm fin in near-new condition for about half the price of a new fin. How awful or functional are the results likely to be if I cut down the 70 cm fin to a 55 cm size or to a 62 cm size?

My only other Deep Tuttle fins are a 70 cm pointer fin and a 40 cm cleaver fin.

I'm not identifying the fin manufacturer because I don't want the answers to be about the general merits of the manufacturer.

Thanks for your input.

10th July 2007, 08:56 PM
You can shape your own idea of a good foil to a fin. However, it is a tedius job of sanding once you cut it down. You should also wear a face mask.

11th July 2007, 10:40 AM
Hi Del,
You can cut off a 70 cm fin to what ever length you want,.......but why do you want such a short fin on such a wide board?
We've cut 80 cm back to 58 cm at test sessions, and a few minutes with a file and a piece of abrasive cloth and you should be back in business.
Often when you cut a fin down, and eliminate some of the taper or radius at the tip the fin seems to actually work better.
As WSGuy suggests, carbon fiber sanding and filing can be a bit hazardous to your health, so a dust mast is a very good idea.
But again, what do you expect to gain with a 55 or 62 cm fin span on an X-186?
Hope this helps,

Del Carpenter
12th July 2007, 10:52 AM
Thanks, WSGuy & Roger, I might have started cutting and sanding without thinking about a dust mask.

When I use the X-186 in higher winds I hope a 55 cm or 62 cm fin will give me more speed and more control, compared with using a 70 cm fin. I'm assuming larger fins have more drag and I'm assuming that at some wind speed between 15 and 25 miles per hour the X-186 would be faster with a 62 cm fin than with a 70 cm fin. Is that correct? Sometimes with a windspeed of about 20 mph I feel like I go faster with a 40 cm cleaver fin than with the 70 cm race fin. I might be wrong about that, I don't have a GPS. On the control issue i feel like I must fight to prevent the board from rounding up more often when I'm using the 70 cm fin than when I'm using the 40 cm fin.

Take 7-10-07 for instance. The windspeed was strong enough I was planing my Equipe with a 5.5 sail. I think that was a strong enough wind the X-186 would have been faster with 55 or 62 cm fin than it was with a 70 cm fin. Is that likely to be correct?

12th July 2007, 08:37 PM
Hi Del,
I think you may be overlooking something here.
The differences between a 70 cm Formula race fin and a 62 cm race fin (not formula) are more than just the fin span.
The foils on the shorter fins (not a cut off 70 cm) will be thinner and the chord will be shorter.
They test these things before they make a production run and get all the proportions balanced out.
Also, what sail sizes are you using on the X-186.
If you are on a 5.5 m2 on your Equipe and then moving that same sail to the 186....?
I hope not, because the X-186 is not going to work well with a 5.5 m2 rig... probably ever.
What you are missing in this equation is that formula boards are designed to be sailed with formula sized sails.
20 knots of wind on a formula board is usually a 9.8-11.0 m2 rig.
BUT, the big formula rigs are very flat foils, with tons of twist at the top and are designed to be sailed extremely overpowered in only 2 directions UPWIND as high as you can go and Downwind, as low as you can go. Same applies to Formula boards. Upwind and downwind is what they do. Reaching is not!
If you aren't using at least a 7.5 m2 formula type rig on the X-186, then things are going to be pretty slow and very unbalanced.
You would probably be alot more happy on a 100 liter Carve with a 5.5 m2 rig in 20 knots.
Hope this helps,

Del Carpenter
13th July 2007, 12:56 PM
So, if I use a smaller fin I would be significantly better off by using one made for the size rather than cut down from a longer size.

The X-186 is my smallest board and might be my smallest board for several more years. I use from 4.5 to 11.0 sails with it. My 10.0 and 11.0 sails are old enough to not have much twist built in. The 10.0 is from about 1992. I think the 11.0 is from about 1995-96. My 9.5 is a 2004 Ezzy Infinity.

I'm not asking about "best". I'm asking about "workable, good enough, better than some".

When the wind is strong enough that 5.5 to 8.5 sails will get my X-186 on a plane while reaching would I be faster at some point with a 55 or 62 cm fin than with the 70 cm fin? Wouldn't fins smaller than 70 cm give me a better balance with sails that are 7.5 or smaller?

Reaching is as much what formula boards do as jibing is what an Equipe does. No board is the "best" at both of those particular parts of windsurfing, but both of them can actually do both of those things pretty well. Mediocre performance in windsurfing is still windsurfing and thats pretty good.

Unfortunately I think I would not be happy with any 100 ltr board. The winds I deal with on tiny lakes in the middle of the US have too many holes. I decide which board to use by considering the windspeed of the holes. Sail size depends on how big a sail I think I can hold onto in the gusts.