I want to have a go at making my own fins as they are very expensive for what you get i think .And with all the clever people on this forum I figuered somebody would be making there own .I have a 103 lt f2 xtc and the fin that came with it is a mfc move 35cm .I was thinking about 45cm for light wind days & 25 cm for heavier days .Im 70kg and have 4,5,6,7.4 90% time its 7.4 as its mainly light i want to get 8.5ish & am hoping to build a fin collection to suit As a bit of mucking around i have made timber blanks to get the shape i want .It has been suggested to me to try & buy a blank & use stock removal to get shape but this seems to be a uneccessary i have though of casting but who knows .Im sure the wise sages of seabreeze do?...............

No point trying to mould them you need a complex 2 part mould (making the mould is an art in itself) and ideally a lot of pressure to make a very little bit of resin go a long way (it is predominantly fibres in there)

Best to lay up your own blanks with glass and / or carbon and epoxy, in between 2 bits of 1" steel plate and use a hydraulic press (like a mechanic's bearing press) to let it set under a tonne or so.

Or buy blanks and shape.

Be aware (as H20 says) it is doubtful you'll make a fin as good as your MFC. There is a LOT of R&D in them and you will not shape it as precisely by hand until you have made a LOT of fins.
I'll add to that and say is is a pain in the sphincter also as shaping them makes a heap of glass dust that is not good for your health, makes you itchy and generally annoys others in your household and the neighbours.

I'm making mine out of timber and carbon/glass, means most of the shaping is done with timber, although there is still quite a bit of glass sanding to do.
The trouble is, I haven't made any bigger than 30cm, I'm not sure if this method is strong enough to withstand the leverage of longer fins.
for my smaller fins I've used cedar/carbon, light, stable and strong.
I've had a 19cm weedy in my speed board for about 3 years, had a big collision with something that did big damage to the leading edge and delaminated one side, but it still got me back to base, took a bit of work to fix it but it's still going now.
With a standard tuttle box, there's a lot of compressive load at the top and bottom of the base. With longer fins softwood just may squash here.
I've just finished a 34cm weedy, I've tried jarrah at the base and cedar at the tip.
It's in the board now, but so far it hasn't been in the water.
The box in this board is a standard chinook tuttle, but it is several mm deeper than standard, so I've used the full depth of the box, to reduce the levarge and compressive loads as much as possible.

And just to be on the safe side, I make them on the thickish side, about 9%/10% chord to thickness ratio.
If you want to do 50kt and are worried about cavitation, I think 7% is possibly asking too much.

I've thought of moulding, but I think it's really only worth the effort if your going to make several fins the same.
Granted you could make a blade mould for your biggest fin, then blank the bottom section to make smaller fins.
Then a separate mould for the base.

I'll second what hoop says. I invested years and $$$ in R&D developing my fins to make them better for me.

G10 production fins are a bargain. Especially if you then take to them with a sanding block and clean them up. There are plenty of cheap 2nd hand rejects lurking in the dusty corners of shops and sheds just waiting for some TLC to transform them into weapons you can be proud of restoring... If you want cheap performance and have time, a good eye for shape and can drive a sanding block, this is your best option IMHO.

Start trawling

slowboat said...

I'll second what hoop says. I invested years and $$$ in R&D developing my fins to make them better for me.

G10 production fins are a bargain. Especially if you then take to them with a sanding block and clean them up. There are plenty of cheap 2nd hand rejects lurking in the dusty corners of shops and sheds just waiting for some TLC to transform them into weapons you can be proud of restoring... If you want cheap performance and have time, a good eye for shape and can drive a sanding block, this is your best option IMHO.

Start trawling

Here is an example of some Torquay 23cm wave fins that have been revitalised for a 92 twinnie - and so far they work a treat compared to the stock 17 cm fins.