I searched but did not find a definative thread on Thruster Fin Placement. Seems Swaylocks could use a “Sticky” thread dedicated to Thruster Fin Placement.
Can anyone explain how most top sufboard shapers might determine Thruster Fin Placement?
I don’t know what others do but I have a set of fins with the tabs cut off and I do it roughly by eye to find the general placement I want for the rear fin and one of the thruster fins and then I get out my square to get my rear dots perfect.
I do things differently for toe in. I do everything based off of where I want the fins to point in relation to the tip of the board and the rail line. To do this I use a piece of masking paper that goes from the rear dot on one side to the nose. The paper acts as a strait edge that follows the curves of the board when I smooth it out. This lets me visualize how I want the water to flow. Once I’m happy I put a stick pin through the paper and dead center into the stringer at the nose and I extend my line from the first fin dot. Now I pull the pin, flip the paper and put the pin back in the same holes. I’ve now got a perfect mirror image to extend the line on my second fin dot. Basic geometry in action.
That’s what I do. Every board is different. If I was in a full on production environment I would use tricks to repeat the same thing over and over and speed things up. My method provides highly accurate results for me.
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I don’t have it handy, but I think it was Michael Ward who some years ago posted a chart used by ASI. Maybe someone else has it.
Another resource is Bruce McKee’s quad layout chart. I’m pretty sure it also includes placement for a rear center fin.
Of course, people’s placements will vary, but this will get you within the range of what is commonly used.
Michael Ward offered a lot of input around here in the past. I hope he’s doing OK now. I would not post this except for the fact that he put it out there at some point in time. If he sees it and doesn’t want it on Swaylocks, I’ll gladly take it down. If the numbers appear too small, simply right click and open in a new tab.
Standard for a board from sub six ft. thru seven ft. using the trailing edge as your point of reference ; 3—3 1/2” to the rear of center fin. 11—11 1/2” to rear of side fins. These simple measurements will work on most boards in this size range. Of course the longer and/or more technical the shapes need some adjustment. It is really all about the distance off the tail and rail. Wings, concaves, V etc play into it. But what I have outlined here works 95% of the time. Surprised you haven’t put a tape on an existing board. Because if you do these are the numbers that come up most of the time.
So is this chart suggesting that the longer the board, which I assume is board lenght on the far left in each of the two columns, that fin placement moves forward. And that these measurements are to the back of the fins.
I have put a tape to various boards. I was more looking for thoughts on what each factor does to the ride of the surfboard. I was hoping to find a thread here that had a good amount of discussion and insight on the subject to read and learn as it seems such an important factor in how a thruster surfboard will ride.
I assume top surfboard shapers take the same machined shape and try slight variations of thruster fin placements before releasing a model to the public.
@ oceanrider: Yes, generally speaking, as the board length increases the cluster moves forward and often tends to become more spread out (increasing distance between front fins and trailer).
With regard to tow-in, some guys stick to 1/4" of tow (based on a 4.5" base) regardless of the board length, while others use a reference point off the nose, which will inherently decrease the tow on longer gunnier shapes.
Of course, these are just baseline generalizations. There are no hard and fast rules.
The reason I do things the way I outlined instead of measuring with one of those fin measuring templates is because I once had a board coume out where I wasn’t happy with the alignment of one of the fins. When measuring back at the fins you only have to be off by a fraction for your ultimate fin placement to look way off. Aligning from the nose really helps you get accurate results.
Regarding toe in, I prefer to use my masonite full rail templates with a factory straight edge to align along the center of the stringer hanging some distance off the nose of the board, and weight/tape it into place, and another straight edge to draw a line from each rear dot to that spot well in front of the nose that I chose. My Quad fins all point to a spot ~22.5 inches in front of the tip of the nose on my latest build. I thought doing this drawing two dots for each fin would leave too much room for error, and time consumed to mark the fins was not a concern.
Being a front footed surfer and a Round pin, my cluster is moved a bit further forward than most and with proboxes for that 1/2 inch of adjustability fore aft, and the cant adjustments, well I have no complaints with the toe in and am enjoying the adjustability factor.
I totally agree. I’ve only measured off the nose. Way more consistent. What I have done is used my template flat on the floor to determine how far off the nose I should be aiming to yield the desired tow-in, but final marks on the board are always done off the nose.
“Slight variations”. “Cant”? Maybe? Variation on a Thruster every time they come out with a new model. Not likely. What works; Works. A Thruster by any other name or in this case; fin placement is not a Thruster.
Maybe some guys stick to 1/4”, but if you do that on shorter boards you wind up with a “dog”. Let’s not forget that the primary influence on “Toe” is board length. If you don’t take length of board into account you will “cross up” the toe or come out so close to the nose that it will inhibit everything about the board. How it paddles, catches waves, climbs, drops, turns etc.