DIY weed fin?

After reading some excellent posts on the subject, I think I might embark on a little project.

I have a few questions:

1) How do you estimate ideal fin length for a weedy? Is it the same as for a regular fin? If, for example, you are currently happy with a 40cm freeride fin, would you want to use a weed fin the same length?

2) How does one "un-box" a fin? Prior to re-boxing it, I mean?

3) Should I hack up a perfectly good G10 fin or is it better to stick to an old carbon fin -- keep in mind that I will be chopping a bit off and using fibreglass cloth & resin - unless there's another way.

4) Is there a good website which explains how to do it? I should've made that the first question, I know.....


Actually, I think that's all for now.

Thanks in advance!


PS I found this thread already, good stuff!

www.seabreeze.com.au/forums/Windsurfing/Gps/Weed-Fins/

1st, a weed fin which is 40cm is measured from the box, or level with the bottom of the board. So a weedie at 40cm will be 56.4 cm long from the front of the box to the tip. The calculation for a weedie @ 45 degrees is 1.41 x the length. Getting complicated yet ? So if you want to mess around with the angle, you'll be trading off weed shedding ability but picking up lift, by moving the angle up to around 40 degrees. The calculation then becomes 1.39 x the length, so a 40cm weedie at 40 degrees becomes 55.6cm from base to tip.
On the box removal: I use a 9"x6" table top belt and disc sander, using the disc to remove the box. Remembering that I want to keep the shape of the fin without taking any more off than necessary. It helps not having a weak point around the base of the box.
Next thing you want is a split mould for the base.
Hopefully someone will take over from me as I have to go do some work (so I can earn enough to buy some more fins )

It's the depth measurement that's important to retain the balance of the board ( if you want to keep the footstraps on the rail). I've found a 32 weedie does pretty well as a replacement for a 36 upright on a 64 wide board. The centre of lift must be a bit higher on the weedie but it's OK. Anything smaller and the windward rail wants to drop. It's a lot of fin with a fair bit more drag, 42cm in the longest direction, but I think it best to tolerate the drag in favour of having the board feel balanced.

I've tried 38 degrees, it's Ok if the weed is light and you can get up to speed before you strike the first strand. In thick weed it's hard to get going.

45 degrees will plough through anything.

Thanks for the wrap Leo, does my heart good to here your enthusiasm.

I think the problems with weedies increases with their size, that makes them more likely to flex.
A thin long weedy won't be much good at all.

I don't bother "unboxing" I just cut the base off at the required angle, and include the old base in the new, helps the fin sit square in the mold.

Unless the fin is thick, (9% thickness to flow ratio or more) and low aspect ratio, G10 by itself is usually not stiff enough for a weedy much over 25cm.
As before mentioned, this is where carbon comes in, but make sure it goes all the way thru the base. (In this case I do remove the old base moulding), this will thicken and stiffen the fin.

The thing to remember with changing fin angles is the accompanying change to thickness to flow ratio.
This is the main reason why a standard foil raked back 45deg doesn't work very well, as far as the water is concerned it's become about 20% thinner.

the new one from the mould she looks good keef

Looks good Leo, I've been tossing up whether to try a mould or not, but I keep changing my ideas on shape.

Currently I'm trying fins with a curved leading edge, less rake at the base (30-35deg) and more at the tip (40-50de4g).
Mainly because our worst weed problem grows up from the bottom in shallow water.
The weed on the surface gathers together and forms dense "weed island" even a 45deg fin comes to a dead stop when hitting them. So the idea is to avoid the weed islands, and use a fin more upright on average.

I need a weed fin for Safety Bay, Tuttle box, for my 85 Sonic with a 5m Koncept.
Any recommendations?

Regarding fin length, the Lessacher website: www.cameraid.com/lessacher/weed.html recommends the 40cm weed fin for sails around 10.5m, and 32cm for 8m...

Made this mould for a freestyle fin, it's basic and a little messy but pops them out with little trouble.. It's a little big, and so far I have just cut the copies in half and reboxed the tips, or I plan to use it as a base to grind down new shapes to then make more moulds from..

I'm sure there is a better way but I've got more important projects than fins, which don't do anything..

here's an old tiga re boxed, i think it was called wind action , its a G10 laminated in some sort of rubber, had to rout 5mm or deeper and laid up carbon and re foiled amazingly the carbon has a perfect bond the tip is full rubber stuff and flexes its weird, just have to give it a go
the box is designed for the forward set fins so you don't drive holes into the bottom of your board getting them out as well as hitting rocks where the fin useually smashes the box and exposes the core
decrepit have you tried a couple of layers of 9oz satin its extremely hard to sand

do you guys sail in swamps or something ????