How to make tri-core composite carbon fins

General Discussion
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Its been a while since there’s been a how-to here on sways so I thought that I would put one together. Last week Christian (cj3) and myself decided to try and make a fatty composite fin. Our original plan was to make it with only corecell but we decided that it needed to be stronger. These fins are what we came up with. They ended up at about 72 grams a piece and seem to be plenty strong (they’ve only been out for 3 surfs) and between 3/8th and 1/2 inch thick. In order to make these fins you need to create a fin panel to cut the tabs out of. I bagged it all together with perf peal ply so it has a low resin ratio. I made enough for a lot of fin sets. Next I cut out the balsa and corecell fin templates. The first time we made fins we cut out the tab slots after we glued the balsa and corecell together - this way is much easier. I glued the tabs/balsa/corecell together with 5 minute epoxy in one shot. I used an old cutting board to squish the whole thing together

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The first picture is of the completed panels with a shaping line drawn on them. The line is at 13% of the base. The next picture is the roughly shaped fins. I like taking a break after the main work is done so I have a fresh eye.


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These pictures show the laying out of the fins. I like working of a sheet of poly bag - it makes cleaning up a whole lot easier. I used 2 layers of 6 oz and 1 layer of carbon per side. Ken (Airframe) showed me the cutter on bottom of the picture. It cuts carbon like butter. To seal the bottom of the fins I made little booties of 6 oz. This time I also put some fin roving outside the booties (I think it will seal better). I started the bagging by laying out two layers of paper towels, perf peal ply, glass, carbon, then fin. I like to wiggle the whole thing together. Next I put in about 10 strands of fin roving.



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Everything is now in the bag. Its taken me 2-3 hours to get to this point. I’m not showing how to bag the center fin because I haven’t figured out how to do it yet (actually, I have a good idea but I haven’t tried it out yet so I don’t want to give any bad advice) The fin in the picture is my first attempt (which was a large twin fin) and the fins in this how-to are for a thruster setup.


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awsome

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thanks DanB. good to see some good ol’ sways…

to ad a bit to fin making here is a photo of some wood fcs i have been tinkering with…

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yep , and a tweak or 2 and a seriously good production process can occur that delivers fins like these …

you have all the right elements there …

these ones are single core , but the same concept …

regards

BERT

ps , have to say , impressed with the progression happening in backyard composites …

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…thanks heaps for posting , guys !

i eagerly await seeing more …

? and , riding reports , pleeease ?

cheers !

ben
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Nice work Dan.

Did you give consideration to cloth directionality with regard to fin flex, or are they designed to be stiff? I know Cj3 stiffens up his ‘normal’ fcs fins with a layer of CF sometimes…

If you were to make one for a longboard center, could you make it in 2 single-foiled halves for the table- bagging, and then freebag the 2 halves together?

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Bert

We went thicker (3/8")and brought max camber forward on the these fins and kept the template the same as the ones they were going to replace.

Are there some placement or design changes that need to done to make these go?

I have used them twice as the front fins of a five fin set-up and have had a very noticeable decrease in squirt and speed. I did notice a more possitive feel through turns but in the small weak waves I could not get it going and had to go back to the fcs AM1 fiberglass fins.

Last night I refoiled them and brought the camber back a bit and thinned them out a touch. They will still have more thickness and forward camber than the fcs but not as drastic.

Will report back on changes

Christian

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JJP - I was thinking of a similar idea to your wood fins. Now I think that I’ll have to give it a try :slight_smile: I decided to post this in response to a conversation that Christian and I were having about sways).

Bert - Nice looking fins, but now I need so see them straight on so I can copy the foil :wink: !!! Christian and I were debating if a single core was possible (but now we know better ). I was planning on giving the single core a try on my next set, and now I know I will). Its really fun playing around with making fins. I just took the ones in this tread out of the bag and they are a big improvement over my first go. Any tips you want to pass on.

Ben - I bet it would work as two half fins glued together, but I think I would go with a solid plywood core with corecell glued on either side and free bag it. I’m going to give the free bag (compared to bagging it to my table) approach this evening on my center fin. I’m a little worried about warpage, but I’ll never know unless I give it a try. The smaller fins are sure a lot easier to foil that the single fins.

Paul - I knew I was going to do this post when I saw your comment about the cost of lighter fins. These only cost a little over $10 per set and would a good way to use up some of your scrap foam.

Christian - The new foil looks a lot better (although you can’t tell from the pictures). They don’t have so much of a massive appearance and somehow look speedier :wink: I’m also confused about any performance gains. On one wave they will fly then the next wave hey will slow me down.

Chip - I knew this would make you smile! I’ve had them out in some really bad conditions so I don’t really have a good idea of how they go. They feel great paddling and I think this light weight/positive buoyancy in noticeable.

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Quote:
Ben - I bet it would work as two half fins glued together, but I think I would go with a solid plywood core with corecell glued on either side and free bag it. I'm going to give the free bag (compared to bagging it to my table) approach this evening on my center fin. I'm a little worried about warpage, but I'll never know unless I give it a try. The smaller fins are sure a lot easier to foil that the single fins.

Where are you going to put the intake?

:stuck_out_tongue:

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Gee I dunno Bert…backyard composites is not that difficult.

What’s really difficult is making a living off recreational composites.

Seems like the guys making the big bucks are in defense or yatchs.

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there is a reason i am posting again on sways…

going to try to strick to how to topics on glassing, boxes, fins. etc…

i have been working on the wood fcs on an off for years. basically when i go to build something i say “how would i build 100 of them” and go from there… came up with a pretty cool tab cutting system that i’ll unvail on sways someday.

the tough part of the wood fcs is the tabs… have a bunch of wet delamed sets lying around… but i think i am past that now… the nice thing is they look cool, are so light, and are just plain cheap to make…

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if you mark the tabs accurately with a diamond tip scribe

then cut them on a scroll saw with high quality hss blade or diamond blade

then hold them in a vice upside down and clean them up with a flat bastard file

very quick

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Paul,

OT, but Google Earth have updated bits of NZ with high aerial images and c-bay is one of the bits - so you might be seeing a bit of tourism soon.

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Hey Bert, would you be willing on giving any hints on setting the base angles on those CF futures fins in your post? I’ve made fins before with g10 but that futures angle on the base of the side fins is an odd one to reproduce.

Do you work it all out on the easier to shape high density foam first then bag or are you adding the base on afterwards? Just trying to imagine how you would go about dealing with the angle.

I’m making some quad guns and last winter I found that the plastic material of the futures quad sets cavitates in the larger surf. Futures wants $50 a fin for their G10 quad sets. At that price I’d rather make my own. If not no worries I can understand just seeing a picture of them starts the juices flowing.

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for custom core , its make the fin as usual with glass/carbon all the way to the base then some extra on the bottom 1" , the base contours is done in a secondry molding process …

Dan first impressions are thickest part too far forward , leading edge still too edgy ,and standard foil toe in angles …

you also have to consider that these fins excel in a different speed range …

the slower the wave the faster they go in comparison , as they are generating maximum lift and ability to pull into turns at low speeds …

they are also more effective when being worked …

at higher speeds , then the cross section of the foil is directly related to drag , plus there is a slight increase in viscous or surface drag as the surface area is increased relative to the template because of the fuller foil …

your fins are your control surface , or one of them , control is directly related to drag , drag is control …

good small wave boards require the least drag possible , but how do you get control …

this is where the fins play the biggest role …

the full foil is a small wave adaptation , therefore to get the best from them , they should be matched to the appropriate small wave board design …

you also have issues with vector forces …

so the 2 ways to alleviate this is to soften your inside leading edge dramatically , this reduces the pull or lift on the fin , but still allows for high attack angles before stalling plus still gives good pull or lift once the turn has been initiated …

the other is to increase toe in by a degree , this reduces the perpendicular lift(vector x 2 fins acting on the board ) forces acting on both fins and ultimately the board when going straight …

both these options reduce straightline drag , and also make the fins even more effective at high attack angles …

changing variables , means changing other variables to compensate …

they are the subtle tweaks to tune for this set up …

regards

BERT

www.sunovasurfboards.com

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Mahalo Bert! I found a picture of these http://www.swaylocks.com/forum/gforum.cgi?do=post_attachment;postatt_id=708;guest=8009131 that gives me a pretty good idea of where to start. Thanks again

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JIP, nice to see you posting again. I have many of your old posts printed in a notebook.