Seems I saw instructions on the web somewhere, but can't find it now. Good weed fins really are in short supply, aren't they?
There's been a few made down this way, they just rebased them at the right angle, (45deg for here).
If your going to do it pick one with a high thickness to chord ratio, because when the fin is angled back 45deg, the water flow length increases by 20%, but the thickness doesn't, decreasing the fin's lift significantly
Myself, Frant and Red all got new Lessacher weedfins last week. Just send Wolfgang an email and he will make you one. Prices are pretty reasonable as well.
www.designlessacher.com/Website/Fins.html
I recently reboxed a slalom fin taking it to 40 degrees from the vertical (because in the Mandurah estuary it was pretty useless and I wanted a low cost weedy). The low tech method I used was to
1) cut the fin off at the box,
2) cut the top of the fin at about 40 degrees
3) drill out the box until I could fit the fin in
4) glass the fin into the hollowed out box using resin with some mat shredded into it ( used about 40ml of resin)
Then I tested it.... it did 27 knots first try and seems good but as Decrepit says with a low thickness to cord ratio it does not provide great lift for going upwind (unless really powered.)
When fully powered it is ok so I am waiting for some wind to try it further. I have photos of the process if you are interested! Have used it a couple of time, done about 20 kilometers on it and it has held up fine.
i have pretty much done the same as decrep and evets have said..
i have rebased (for myself)3 different standard drake slalom fins that have come with the isonic 105 board (one was the centre fin off the starboard kiddy-),at 45deg for the mandurah weed.
i have got an old finworks tuttle box which i have used as a mould for aprox a dozen rebasings and its still going strong.
the only other mod i have done- on 2 of the drake fins i have attacked the leading
edge with a file and sand paper and sharpened the edge up to a bit of a point.
the fins perform great with all of them being rock solid in handling.
i recomend giving some serious thought to recycling your old slalom fins...you could end up with a gem
the fins not for sale yet? the blob of resin hasnt fully cure'd and it was given to me 18 months ago, dont worry ill let everone know and maybe we can have group auction