I have just got my hands on a 60cm wide JP Slalom V 92 and currently my smallest fin is 34cm. I weigh 90kg. I am looking to buy a smaller fin for GPS speed sailing to be used with my 5.8m race sail. The board is quite a bit wider than full-on speed boards so I wasn't sure how small I should go. I like the look of the KA speed fins (swept back too for weedy places) but they seem too small for my board. I'm thinking that I probably should just get a slalom fin in the 28-30cm range. Does anyone have any words of advice or experience trying to make smallish slalom boards go fast? Thanks

I personally I wouldnt go smaller than a 30cm maybe a 28.
Lots of good fins Brands out there C3, Techtonics, Debs, KA, TM, Vector.
Iv been using the C3 fins and are very happy with them good top end and plenty of control. http://www.c3-fins.com/C3_web/home.html

ta Vando

I wouldn't rush to go too small. This board and a lot of newer slalom boards still need decent fins to get out of the water to go fast. Martin Van Meurs has run this board almost to 38ish knots with I think a C3 Venom 38.

Would look at C3 Venom 32 or JP Slalom 32 for going quick off the wind. Venom felt nice and the bigger JP's I've used in it feel great for slalom.

You'll love the board though. Easy to go fast on in lots of different wind and water.

Sam.

You've got some pretty fast repliers there but they don't seem to agree. For the same proportions a 32 cm fin has 50% more area than a 26.

You can go too small particularly if you don't go fast enough or deep enough off wind. To generate a given amount of lift at a certain speed a smaller fin has to be run at a higher angle of attack. This directs a bit of the lift in the backward direction - induced drag. Too big and the friction of the water moving over the surface of the foil dominates.

It just so happens that because induced drag decreases with the square of velocity and friction drag increases with the square of velocity, the minimum is when they are both equal. If you are somewhere close to the minimum you're said to be in the drag bucket.

Thus small fins are good provided you're going fast enough and at a deep angle where lateral forces aren't as great.

If you told the speedsters how fast you were planning on going they'd probably get closer to the same length.

But hull drag is significantly greater than fin drag - so if your fin length/footstrap leverage combination allows you to better comfortably trim that big draggy board you'll probably go faster.

That's just the old rule of thumb - " Use a fin as long as the distance between the centres of your front footstraps"

Check that measurement on your JP... and go with a 32cm fin.

I have the same board and have been using JP fins.
I asked the same question on the NP Maui forum and recieved replies from Kevin Ozee and Martin Van Meurs. Kevin basically said anything other than 34 is not worth it. He reckons smaller equals not enough lift and bigger was too much drag.
MVM advised that with C3 or JP you can go bigger than normal.
Heavier sailors can get away with bigger fins. Have used 6.7 RSR and 36 Jp to help with planing. Then 6.2 RSR with Gen III JP 34 and as Sam said it felt slippery/nice.
Admittedly this is from your average punter so like everyone else says a 32 for speed would be cool.
Hope this helps.

Where are your footstraps?

I use to always go straight to the back but at Sandy Pt last year I moved the rear strap one hole forward and grabbed another 2knots almost straight away. The lifty feeling I was getting disappeared and was able to get the drive out the board and fin that I was looking for.

Sam.