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Cutting 62cm carbon fin
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akrausz



Joined: 19 Sep 2008
Posts: 124
Location: Sarasota, FL

PostPosted: Sun Mar 17, 2019 11:20 am    Post subject: Cutting 62cm carbon fin Reply with quote

Any suggestions on cutting a fin to use with a smaller sail. I have an old 62cm carbon fin that needs work anyways.

Last edited by akrausz on Sun Mar 17, 2019 12:58 pm; edited 1 time in total
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dllee



Joined: 03 Jul 2009
Posts: 4059
Location: East Bay

PostPosted: Sun Mar 17, 2019 11:33 am    Post subject: Reply with quote

Cut it, foil it, seal it with epoxy, sand it.
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akrausz



Joined: 19 Sep 2008
Posts: 124
Location: Sarasota, FL

PostPosted: Sun Mar 17, 2019 1:07 pm    Post subject: Reply with quote

dllee wrote:
Cut it, foil it, seal it with epoxy, sand it.

Thanks, I'm thinking I would follow the board lady's technique. Just can't decide how much to cut.
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dllee



Joined: 03 Jul 2009
Posts: 4059
Location: East Bay

PostPosted: Sun Mar 17, 2019 1:46 pm    Post subject: Reply with quote

You also don't mention if the fin is carbon over foam, over glass, or over wood. Those need to be sealed and the sanding/finishing process is different.
You also didn't mention your board/sail/wind size, or type of board, so what can you expect?
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akrausz



Joined: 19 Sep 2008
Posts: 124
Location: Sarasota, FL

PostPosted: Sun Mar 17, 2019 2:36 pm    Post subject: Reply with quote

dllee wrote:
You also don't mention if the fin is carbon over foam, over glass, or over wood. Those need to be sealed and the sanding/finishing process is different.
You also didn't mention your board/sail/wind size, or type of board, so what can you expect?

Not sure what the core of the fin is, was wondering about that. 2004 Starboard Free Formula 138 liters, 96cm wide, deep Tuttle. The new smaller fin would be used to see how fast I can go with a 2018 North E-Type 7.3. Also going faster than ever on a new 75cm-wide freerace, regular Tuttle, which I prefer to be on with that sail, so this is just another option. I'm 210 pounds and James' windsurf calculator says 17.5 knots for a 7.3, but I think I would use it in less wind with the 138. Just reaching, blasting back and forth; don't need to go upwind. I have a bigger fin for my 8.3 cammed sail.



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dllee



Joined: 03 Jul 2009
Posts: 4059
Location: East Bay

PostPosted: Sun Mar 17, 2019 9:05 pm    Post subject: Reply with quote

Fform might still need the 62 for your weight, if you want to use the rear outboard straps. A 50 cm fin of equal area might also work, but where to find it.
I have several Starboard fins, but all in good condition so I don't know it's core material.
Foam needs sealing with glass and epoxy.
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joethewindsufa



Joined: 10 Oct 2010
Posts: 1067
Location: Montréal

PostPosted: Mon Mar 18, 2019 5:19 am    Post subject: Reply with quote

you're cutting a Curtis fin Sad

at 100+ kilos I use 48 cm with 8 meter sails
and 40 cm fin with 7 meter sails

for slalom you need that much more fin ??
50 for a 7.3 ??
would 44 cm not do the job ??

sell the fin and buy another ??
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akrausz



Joined: 19 Sep 2008
Posts: 124
Location: Sarasota, FL

PostPosted: Mon Mar 18, 2019 7:32 am    Post subject: Reply with quote

joethewindsufa wrote:
you're cutting a Curtis fin Sad

at 100+ kilos I use 48 cm with 8 meter sails
and 40 cm fin with 7 meter sails

for slalom you need that much more fin ??
50 for a 7.3 ??
would 44 cm not do the job ??

sell the fin and buy another ??

Joe, I know what you're saying. Love your blog and posts I've read in the forums.

My new 75cm-wide freerace came with a 44 and that works well. If it drops off, I would try the 96cm-wide free formula, before rigging a bigger sail. I think you have to look at board width first, then sail size. It comes with a 56 Drake but it seems flexy, and the cord is wider than the Curtis 62. I hear you, and suppose I could size up some screws to give the 44 a try, but I think this board would work best with at least a 48cm for me with my size 15's near the rail. It's a new for me board. How small do you go with your free formula?


Last edited by akrausz on Tue Mar 19, 2019 9:35 am; edited 1 time in total
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bred2shred



Joined: 02 May 2000
Posts: 957
Location: Jersey Shore

PostPosted: Mon Mar 18, 2019 11:26 am    Post subject: Reply with quote

Personally, I would not recommend cutting the fin. Fins taper as they progress from the base to the tip. Cutting off the end of the foil is going to eliminate much of that taper resulting in a much stiffer foil and a lot of induced drag since the foil will now be generating a lot of lift right at the tip. I wouldn’t be surprised at all if the trimmed fin was slower and/or more prone to spin out than it was before trimming.

You could try to thin out the tip after you cut the fin, but it’s going to be extremely difficult to achieve a consistent profile if your plan is to just go at it by hand with a sanding block. Modern fins are either CNC machined or molded using CNC machined match molds. These processes produce very exact profiles that you’re simply not going to be able to replicate by hand.

sm
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grantmac017



Joined: 04 Aug 2016
Posts: 647

PostPosted: Mon Mar 18, 2019 11:37 am    Post subject: Reply with quote

If I was going to shorten that I'd cut the top and re-base it. It looks like it was vacuum bagged which won't take to being thinned or reprofiled well.
Ultimately even paying yourself minimum wage for your time you'll find it cheaper to just buy something else.
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