What would be the effects of such a combination? I picked up my new longboard this past weekend (10’x23"x19"x15" - rounded pin) and the rails were somewhat harder than I anticipated, as well the harder edge extends from just behind the center of the board to the tail. I went with a 2+1 setup knowing I could pop out the sidebites. I am used to ridng a 10’ single fin classic style board does anybody ride a harder railed longboard with a single fin? I ask because when I rode it it did not feel as loose as what I was used to riding. It probably is just going to take time to get used to.
I ride them all the time. 10’ to 12’. Works fine. With your two plus one you might have to move the fin closer to the sidebiters to loosen the board up. Also you could try a cutaway or smaller fin.
I also ride that kind of board, My 2 cents, If the rails are hard & sharp at the tail the tri fin set up is over kill. if you do stay with that set up you should reduce the size of the center fin, but with that kind of rail I would stick a 9 or 9.5 cut away in it, dump the side biters & you will be amazed at the differance. http://www.raymosslongboards.com
True Ames makes a fin called the Velzy Classic. 9 1/2" or 10". I like this fin on longboards with harder rail edges near the tail.
My favorite longboard is a 9’0" single fin round pin. I would say the rails are much like what I see on short boards, a very slight edge in the nose, softening up thru the mid section (still low though) and hard in the last foot and a half or so in the tail. I use a basic 9" swept back fin about 6" up from the tail. This board fits the style I like to ride longboards with, a mixture of old and new. Im not sure what youre looking for in your board, but from what youve mentioned, you might want to move your fin around a bit to get the feel youre looking for.
If there is V at the middle of the board, then the edge is probably a plus for the design. A cutaway fin also works well with this combo. aloha, TW