After spending countless dollars on weed fins, that seldom lived up to their hype, I decided to take the matter to hand. Literally. If you want a job done properly, do it yourself...
I needed a fin for my 135l rocket, and fins that are set forward on the box just don't do it for me. The snot weed that we get in Mandurah is diabolical to say the least. Even with some adhesive foam for the gap between the fin and the board, the weed finds a way in.
I grabbed some 3 ply that was lying around, not contributing to my somewhat anal perspective on what is vital for military precision, shedwise.
I glued two slabs on each side of the chord, now 9 ply, and whacked it on the belt sander, taking the chord down to 8mm. So with everything going to plan the finished product should be 11mm at the chord, on a 43cm fin with a 45 degree rake.
Might even slap some carbon cloth along the chord for rigidity, seeing the ply flexes easily.
Be interesting to see if its strong enough.
Oh and i think you work shop floor is waaayy tooo clean
Oooo yep I'll be there,camping
look for the camp cot near the subi
Now have a layer of csm, smoothed down to take the first layer of carbon. Trailing edge will show the overlap of glass, now razor sharp, needed to ensure the trailing edge will not be more than 1mm after the application of the carbon fibre. The trailing edge timberwise can only stand about 1mm without it giving up the ghost and splitting big time. Anyhoo it's off to osbourne park tomorrow to buy some carbon. Can't seem to shake this notion, even when I'm working on the fin that this bugger is going to snap when I put some effort on it. Maybe two layers of carbon??? Who cares, this is better than work!!!
Great shaping , what you basically will have is a timber cored carbon sandwich fin . Should be well strong . use unidirectional carbon on the outside . finish off with an acrylic or two pack primer and polish or wet rub ( another topic ) the final finish .
admire the skills .
G'Day Pepe, how long are you going to be around??
We're back now, but I have a bit of sorting out to do, relicense car etc.
Be good to catch up, and see this creation of yours.
Unidirectional, is not woven at all, all the carbon runs in the same direction, (along the fin). In the past I've pulled woven cloth apart, so I could do this, but buying unidirectional is heaps easier.
The last stuff I got (for new speed board), was from fiberglass and resin sales in Kewdale, but I wasn't all that impressed with it. It was only held together on ones side, made working with it very hard. Not sure where else to try, Kirkside didn't have any when I made my last board.
Now got unidirectional carbon fibre laminated on the fin and what can I say, it's black! Got to sand it down yet but the fibre looks well seated 
Looks good mate, have you got a layer or 2 of glass over the top of the carbon???? You don't want to sand thru the carbon, especially near the base.
Hi - how much, if any difference would it make to the flex of the fin to run the carbon at 90 deg to the bottom of the board (or angle of attack) instead of down the length of the fin?
I think there's more force on the fin longitudinally because of it's shape. Been wrong before, though. Might be fairly expensive using the uni at 45 degrees, seeing you'll have to buy almost twice as much. It's just the way it comes off the roll.
Next update: put open weave over the top of the uni, hopefully increase the strength. rebox overnight.
I hope its stiff enough!!
I would have used 4 layers of UD at the base and then staggered them out down the foil. I also would have run the twill on the 45 to reduce the torsional flex.
Good effort. It looks bloody nice!!!!!!!!!
Cheers guys, after typing replies for a while my computer decided to shut down for no apparent reason. Bugger.
Bender: lets see if it passes the acid test, the limestone test. Sorry you couldn't get out today, but the boys seemed to be going ok.
Bertie: thanks for the heads up on the strength bit. If I can get hold of some Paulonia,
(having a thing for timber) I'll follow your suggestions on the base.
Hey Yoyo, I'm just around the corner so grab a beer and we can work on the design stats.
The next image shows the fin in the box mould, the white stuff is mould release wax
so any spillage can be removed without drama. I've lifted the fin slightly more than 45 degrees to about 43...more to follow.
i might be able to arrange some paulonina for you. Will be offcuts though. may need dressing and laminating. whats the min length req for round 2?????
Came out of the split mould looking ok. I'll leave it for a couple of days now before drilling and fitting the barrel nut.
Looks fantastic there Pepe, I'm sure you won't go into the shallows, it would be a crying shame to elmo something that nice 
Did you use a standard foil section or do it by eye?
Looking forward to a report on how it performs.
Just by eye Nebs. Plywood makes it easier as does g10, using the grain or fibre rovings as a guide.
I'll be staying right away from the shallow bits
That is a work of art Pepe I would be putting it on a wall and admiring it rather than taking it within a kilometre of the limestone.
I look forward to seeing the smile on your face when it works really well.
