turning a tri fin longboard into a single fin one, should I have different bottom contours or concaves or it could work?

hey, well

there`s a very good price for a tri finned longboard, good condition over all. 

the board is not a plank, is more performance oriented. 9.1 x 21 5/8 x 2 3/4 and there`s another very similar shape and same price 9.0 x 23 x 3

do you need different concaves and bottom contours in each case? tri fin or single fin longboards

thanks in advance 

I would say no but others may dissagree , I have seen plenty of guys riding  tri fin longboards be it 2+1 or thruster set up as a single fin , as a twin fin , a twin with trailer , they all work , they may not work in all conditions , always remember its the surfer not the board .

Design considerations are always subjective but I tend to go with the  opinion of the guy who made it as the first choice, i.e. the shaper chose a thruster fin configuration thats what he envisioned as working best for that shape, or single fin, as the case may be. If one would argue either setup works equally well on any given shape, then you remove the rationale to change it. Ride the board as made and learn its characteristics. If you have removable fins you have an open door to infinite possibilities without changing the fin plugs at all. After you have spent time with the board in a variety of conditions then only alter the fin setup as an informed decision. My 2cents worth of advice :-). Pretty much what Trevor said.

Yes fina can dramaticaly change the way a board surfs , but that change may not be either bad or good just different , and sometimes different is just what we need .

You are not filling us in completely.   I am guessing, but think that these boards have fin boxes and NOT “glass-on”.    Easy to experiment that way.  Remove the side fins and figure out a way to add a larger center fin without hacking it up and adding a center box.  Most “Thruster” longboards will also function well as 2 plus one.  In other words a center box plus side bites.  So if I were determined to do what you are referencing I would start by adding a center box and removing my side fins.  If the board won’t surf well as a single fin you can go to 2 plus one.  The only box or plugs you would be removing would be at the center.     Personally if a single fin is really what you want, I would pass on these boards.

Okay so far

 

do you need different concaves and bottom contours in each case? tri fin or single fin longboards? thanks in advance

Awright, it’s about the overall board, the rails, how big the fins are, where they are, rocker, etc, etc. Bottom contour is a small part of it. As well, everybody that builds a board has a different idea of the best combination of all those… which may or may not fit you and how you use the thing. 

If all the fins are removable, as a general rule you can take out the side fins and the board will still work. Maybe worse, maybe better, depends on what you like. You might want to use a bigger, longer fin if you use it as a single. You might like the tail a little looser and instead go smaller. Up to you.

Or leave it as is. Though you might wonder why the boards are for sale at a very good price. Did it work badly? Ugly color job? Previous owner moved to the Sahara and never coming back?

Now, here’s the thing. If you just have to have a single fin board, for whatever reason, nobody is holding a gun to your head, making you buy one of these two. It’s not a very good price if it’s the wrong board for you.For instance, you might see a Ferrari selling for short money, but if you live at the end of a ten mile dirt road in Alaska, it’s not a very good price for you, what you need is a good price on a Land Cruiser.

Hold off, the right board will come along. 

hope that’s of use

doc…

Good summary.

There’s a more to the singlefin design than just the fin.  If you’re trying to surf it as a single then the templates, rockers and rails are quite different than what they use for thruster boards. 

Pick a specific board and then surf it as per it’s design. Don’t try to make the square peg fit into the round hole.  

Exactly!   “Shapers Intent”.