Hey, so a big thanks in advance for the help. I am looking to make my first shortboard and have head my head stuck into this thruster research for a few days now.
If you guys could help with fin placement, toe in (measured off the nose?), and cant that would be amazing…
A bit about me… 6’ 180 pounds. usually ride a single fin shortboard or longboard so am a big fan of good drive. looking to use this board in fast beach break conditions from waist high to overhead.
Do what you think is best for you. Here’s what I did yrs back when I shaped a thruster for a local guy:
I decided on 11" up for twins, and 3" up for rear. And we put them off rail 1 1/4", or 1 1/2", I believe we settled on 1 1 /4"? Toe in 1/4", and we canted them out slightly. That Said,
I built and sold it so I didn’t get to try it. But I did happen to see him riding my board, and he looked to be surfing really good. Was it him or the board? I dunno? But my board didn’t hamper his performance whatsoever. On rear fin I see guy’s been setting them at 3 1/2" also. So 3"-3 1/2" is fine. The toe in can also be slightly less, or same. This is just how we did it. I’m sure others w more exp could steer you better. But this is what we did ( myself & surf buddy glasser friend)… I think we’re simply copy n measurements of boards during the time (83’).
If you want drive then straighten everything up. That being said, it looks like you already have a lot of planing surface on your design which will help keep you on top of the water so I wouldn’t go too straight with my fins if I were you. On a 6’0" thruster you can do something around the 11 1/4" for the front fins, 1" off the rail, toe 1/4" and cant arond 5-7 degrees. Rear fin around 3 1/8 - 3 1/2. You really just have to figure out what you are used to riding already and what you want to change. Also, you can always mock up your fins on the board to see how they look too, that always really helps. Hope this helps a bit.
My first several boards I tended to try and straighten the toe to 1/8-3/16 in cases where normal would have benn 1/4 – I thought I wanted the boards to go faster than what I was used to buying, “pound for pound.” I think I experienced more loss of pivot and turning comfort than gain of speed. My rockers and bottoms are getting better now, and I just go with 1/4 for thrusters on shortboards, without feeling like I’m losing speed, although I’ll confess that I run most of my boards as quads for the additional speed and overall feel.
For placement, I’ve found that my favorite shapers are usually within 1/16-1/8" of Mckee’s placements for their modern shortboards like the one in your link. I copied a CI Whip (changing it to suit my own weight/body type), and found that I would have started my ProBox center box a bit further back than the original CI placement (proportionately) if I had it to do over again.
Thanks guys, that’s great help. especially with the measurements how does shifting the whole setup back or forwards or just the sides or back fin change drive as well? With my single fins it seems to just be a sweet spot on each board, not a particular thing going back or forward…
More importantly though, how do I measure the cant? use a protractor?
been a while fiberglasshi! how’s hawaii treating you?
As far as the measuring off the nose, seems like a concept, but not a reality. If you tried with a straight edge to actually measure to the nose of your board, and then change the point from 1 inch to 2 inches, you would find you are changing the fin maybe 1/32 of an inch. less than the thickness of a layer of 4 oz cloth. just pick a measurement off parallel and go with it. More than 1/4" will drag. “less is more’ in this area. 1/8” will work almost the same as 1/4" toe. But 3/8" will really be noticable. The straighter fin will go faster, so that overcomes the stiffness of too little angle. Too much toe in will slow you down, to the point that you won’t be turning all that well anyway.
There are some basics that go into it. Several have been stated above. I always start with placement of the center fin. 3–3 1/2 inches off the tail. What determines that distance is personal preferance and the length of the board. Once you’ve established this measurement everything else is based on that. The average fin base is 4 inches. Using that # measure four inches from the front of of the center fin. That will be your established point for the trailing edge of the side fins. Put those numbers to gether and you will have 11—11 1/2 inches to the trailing edge of the outside fins. I never set fins based on the distance from the fin slot or center of fin to the outside rail… Too much room for error.The only reason a shaper would use the outside raim to measure from would be if the shaped blank is unsymetrical and the shaper doesn’t want to correct the outline. Measure from the center of the blank using a shapers square. Measure out to each rail from the center. You are measuring to the unfoiled inside of the fin. This is based on the 11-- 11 1/2" that was established for the Side fins. If you have a symetric shaped blank the distance fom the outside of the fin to the rail will be the same on both rails. Make a pencil mark on each rail at this point. Measure fourinches forward from that rear mark. Line up you square at center of blank again. Make a mark 1/8 inch less on each rail. That gives you a 1/8 inche tow. Usually if a board is longer and wider you would tow more. Like 1/4 inch. If you were to set a straight edge on the side fin marks you would want that straight lne to come out somewhere outside of the stringer or center line. Don’t cross them up or come out on or in the middle of the stringer. It’ll be a dog. Cant is usually two, four or six degree. All of this is pretty established when it comes to Thrusters. The debate begins with Quads. Ask a glasser like Acqua. They know more about fin placement than most shapers. Lowel
how does shifting the whole setup back or forwards or just the sides or back fin change drive as well? With my single fins it seems to just be a sweet spot on each board, not a particular thing going back or forward…