fin length

[wseetoh]

To all the expert out there, what is the effect of an undersize or oversize fin in both light wind and overpower wind condition?

In light wind, would an oversize fin make the board plane earlier?

In overpower wind, would an oversize fin make the board plane earlier and ride faster if the rider can apply the right foot pressure?

What about undersize fin in both light wind and overpower wind condition?

If one only want to have one fin but 2 sail, would be it better to have a bigger fin for the bigger sail and sail oversize fin with the smaller sail or vice versa?

Talk to different people and u have different answer but my own sailing experience seems to be smaller fin plane later but ride faster in stronger wind but perform badly when use with bigger sail.

[<Wahrau>]

Read this

http://www.bluefinz.com/technique/finselection/index.html

[sukhdev]

To all the expert out there, what is the effect of an undersize or oversize fin in both light wind and overpower wind condition?

In light wind, would an oversize fin make the board plane earlier?

 anything that gives more lift will help you plane earlier, ie bigger sail, bigger fin, wider hull. too big  a fin (ie fin length is much greater than the 1 foot off measure) will make the board difficult to handle once planing. just as too big a sail creates overpowered feeling, same for fin.

In overpower wind, would an oversize fin make the board plane earlier and ride faster if the rider can apply the right foot pressure?

 within reasonable limits, yes, especially for upwind sailing, though its much less true for downwind/reaching

What about undersize fin in both light wind and overpower wind condition?

 undersized - board will be slow to plane, sticky when planing, spinout more and will not power out of gybes.

If one only want to have one fin but 2 sail, would be it better to have a bigger fin for the bigger sail and sail oversize fin with the smaller sail or vice versa?

 neither. if a fin is matched correctly to a board it should allow you to handle a broad sail range. the best way to do this matching is based on the board's 1 foot off measure, rider weight/strength and the sail size/type used. For example I have an old ML75 that I still use, it has a one foot off measure of 54cm. I use a 52cm Mirage on it and I don't change fins for any sails between 7.5 to 9.8. I can use a 48 for the 7.5 and get more reaching speed but that one fin covers a big sail range for me.

Talk to different people and u have different answer but my own sailing experience seems to be smaller fin plane later but ride faster in stronger wind but perform badly when use with bigger sail.

 you are correct.

[rograd]

Some fin size calculator:
http://www.boards.co.uk/kit/

Bobas32

[wseetoh]

Thanks for all the replies.  Very helpful.
Interesting, though, using the fin calculation on the uk website produce much smaller fin than I would have thought eg.using the parameter, it recommended 47cm fin with a 9m sail on a big board - I would have expect something between 54-60cm for someone in the 70kg class.

[sukhdev]

i'd still go with one foot off with some small caveats. your example of 9.0: using it on a formula board in high winds i'd stick with a 66cm say but using it on a board like the ml75 i have or the thommen rs75  i'd be using something in the 48 cm range. on the sonic 110 a 42cm would do fine.

same sail, different hulls, different usage. a 9.0 on the hyper doesnt need more than 42 for reaching purposes. i hope the above sort of makes some sense.

[<Andrew>]

All good advice above. I would also suggest that you not limit yourself to just one fin. Your board and sail are designed to handle a wide range of sailing conditions and some additional fins will help you to maximize their performance.  Also, a fin is relatively cheaper than other rig components and easy to change out when conditions warrant. A simple fin change can make a big difference on your sailing. Ask your surf shop to recommend other fins.

[RickyBRA]

Hi Sukhdev,

Your explanation makes a lot of sense.
However I wonder if the HS105/125/133 aren't an exception. Looking at the boards pictures it seems that at 1' they are way larger than the fin size you got the best performance from your review. The hull shape enhances fin performance?

When I tried for a couple of hours a HS105 with 44 stock fin + Gaastra  Echo 6.6(sure not the best combo) in 12-15 knots, I noticed how hard I had to load the fin to get the proper trim.
Even my stance was way backward.But I liked the board anyway.

So,is the "amount of load" you have to put on the fin also a good clue to get the right fin size?
 
Cheers,

[sukhdev]

Ricky, agree with you, hyper is an exception. With a 6.x (not the echo    ) I find a 32 is all I need, even though the 1 foot off is quite large. Alot of the problems we've seen with the hyper are people using fins that are way too big. I don't know why the hull works well with very small fins, maybe that weird deep concaves and spine create their own lift of some sort.

with a 44/6.6 combo, that load that you felt may just be drag. the first time i sailed a combo similar to that i was suprised at how much strain there was on my legs. i changed down from a 42 to a 32 and the overall trim and effort was miles better.

[RickyBRA]

Hi Sukhdev,

Drag???I think I'll have to digest it  
Do you think that same strain would be there in a more conventional hull? I mean,a conventional hull with a way larger fin?What about tail walking?
By the way,I think the HS design just so cool  

Cheers

[sukhdev]

Ricky,

my reasons for thinking it may be drag...

the first time i took the hyper 105 in swells was with a 7.5 and the stock 44cm fin. coming in down the swells my thighs were strained, the way your legs feel when you are dragging seaweed or plastic on your fin on a conventional board. I swopped to a 44cm tectonics spitfire which i know well. it was better but the strain was still there. Went down to a 36cm and it was miles better. finally used the 7.5 with a 34 for reaching and it felt really fast and smooth.

my pure guess and speculation is that the strain i felt was a combination of the fin dragging from both its size and its shape (last year's stock fin was ugh, the new fins are better).

on a conventional hull too big a fin seems to porpoise the board because the lifting point is outside the rails of the board. this doesnt happen on the hyper because the 1' off is broad enough to offer leverage against even a 50cm fin say. if the mast foot is too far back that will then excarbate tail walking but tail walking is usually curable with proper mast foot/boom height positioning.

there is something happening with the hyper that makes for a hull that seems to accelarate very quickly; its noticeable in the way the hull glides through lulls that would stop other boards planing. I dont know how it affects fin sizing but from testing and experience its clear the hull needs fins way smaller than traditional rules of thumb would suggest.

[RickyBRA]

Hi Sukhdev,

Thanks for making things clearer for me.You really got a point here.
Maybe the double concave makes the water flow better with less disturbances around the fin which in turn creates lift more easily.
Anyway, it's a great idea and I really want to get one.

Cheers,