So ive found an old Mistral Explosion CHS 130litre. 288long x 59wide i think. Came with old elliptical PB fin about 33cm. Wide n very thick cord compared to todays fins. Much larger area planshape also.
Any benefit to using a modern slalom fin?
Im 105kg.
Guess the board sail range 5.5m- 7.5m.
What size fin for this ol relic?
That's obviously a big old board, and long and relatively narrow compared to modern gear.
Sailing it is something you'll need to experiment with and a thinner modern fin might indeed be faster than one with a fat chord.
The size of fin used will still depend on what sail size you choose. I'd be inclined to borrow any powerbox-head fin just to see what you find.
A 30cms freeride fin might be a good starting point - or a bit longer if you go for the 7m+ sail.
I'd also be wondering where to set the mast foot. My guess would be a the back of the track.
I might also shift the front footstraps forward as far as hole options allow.
I had one of those when they first came out. Sailed it with an Arrows Grand Slam 7.1m That felt huge at the time, a real beast.
I'd say use the mast track at the very back, older boards have them a long way forward.
Does the board look low rockered? How long is the planing flat? I'm guessing low rockered and long planing flat, modern slalom boards have quite a short flat section. So I think you will need quite a powerful lifty fin, otherwise it might keep ploughing into chop. Try the one it comes with first. The foot straps look quite far forward, especially the rear ones. So leave them alone. If you move your weight forward it might keep ploughing into chop. There is probably a reason why they are at the back to start with.
Select to expand quoteolskool said..
So ive found an old Mistral Explosion CHS 130litre. 288long x 59wide i think. Came with old elliptical PB fin about 33cm. Wide n very thick cord compared to todays fins. Much larger area planshape also.
Any benefit to using a modern slalom fin?
Im 105kg.
Guess the board sail range 5.5m- 7.5m.
What size fin for this ol relic?
I ride my Xantos 310 with a FF24 or FF28 and have blast, ( 61 wide). So comfy in short chop it's ridiculous. However mention pointers and all of a sudden I am no help at all, other than enjoy it, I am sure it will be a buzz.
Depend exactly which fin you are thinking of using, but something around 40cm is a starting point.
Don't exceed OFO [width 1 foot up, from tail], but maybe just try it with stock fin.
I have an Axxis 278. I use Select S1 35 fin. I was using mistral slalom fin (33cm long 270cm^2) before, wide chord and thick profile. It certainly feels more slippery and go upwind better.
Oldie , I think you know the answer , go big , if planing on the fin instead of the board , go down half a cm 
We know the saying , " too much power is just enough ".
Could be drinking 
Songofwind, thanks for info. Im 105kg n 7.5m sail. The mistral fin you have is same as i have. Ive got 38cm FO Nitro, 40cm MFC H1 to try. As usual NO WIND.
I have an F2 Sputnik 285 115 litre similar to the Explosion. I use 30-36 cm select powerbox fins. I also use a 36 cm G10 Select trim box fin on my 1992 Bic Presto 280cm, 122 litre LW Slalom. My 1992 Bic Rock 295 cm LW Slalom of 130 litres (which I haven't sailed yet having recently acquired it for $50 including fin and uni and mast foot and extension ) has a World Cup Slalom fin of 11 inches and the biggest fin I have for that is 35 cm (US box). The 40 cm fin for the Explosion sounds rather larger than would have been used in the day on the Explosion. It might be overfinned but try it and see and let us know. The 1996 Mistral Explosion II (successor model to yours) carried 36-38 cm fins with 5.8-7.3 race sails. The Race sails on the Mistral One Design for example..(89-90s vintage) were more powerful in the lower end than sails of today having tighter leeches as I understand it but the top end is less controllable but the top Mistral sailors carried their 7.4 m2 sails in 30 knots on the IMCO for example, so much is possible. Your 7.5 might be a 6.5 in the old days. A good thing about old boards is they don't depreciate like new boards.
