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waxfoot

Michael Peterson status
Apr 21, 2018
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PS: For his audience @griffinsurfboard , surely this is sufficient level of information? When you speak to a newbie or a beginner on any topic, do you dive directly into the deepest nuances possible, or do you start with basics?
 

Mr J

Michael Peterson status
Aug 18, 2003
2,250
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Regional Vic, Australia
This is the key to the graphics on the underneath of the board. There is a diagonal line of high pressure where the front dry part of the board enters the water called the "spray root", because of the ridge of water that forms there and the lift it produces. Lift fades off towards the tail, with some suction (blue colour) on the inside rail. There is also some suction on the waves side side of the fins and a little downstream of the stringer which is at the top of a double concave. Ignore the green on the dry part of the front rails, that is there just for decoration.

FlowPattern.png
 

Mr J

Michael Peterson status
Aug 18, 2003
2,250
1,454
113
Regional Vic, Australia
PS: For his audience @griffinsurfboard , surely this is sufficient level of information? When you speak to a newbie or a beginner on any topic, do you dive directly into the deepest nuances possible, or do you start with basics?
I think Kale Brock does provide some informative videos. Kales feed back of the different setups is nice and might encourage more people to try this sort of experiment and is sufficient and appropriate for a newbie to different fin setups.

I have some problems with the guest shapers explanations though.

The guest shaper says the fins are a hydrofoil that produce lift. Fins (unlike the single sided hull) are a hydrofoil but they do not produce lift. They produce a sideways force which as a surfer I call hold. However the shaper did say they stop the tail from sliding out, so that is correct which just means lift is a terminology problem.

The explanation that quads have more surface area and therefore more drive, is simplistic. A massive single fin of comparable area would not achieve anything comparable. However the shaper does go on to say that a centre thruster fin creates more drag and side fins less drag - this is true, as a rule quad is faster than thruster and thruster is faster than single fin - in shortboards anyway. I think it is what the fins do to the way a boards rails sit in the water. The single causes the board to have more rail drag I think, then there is the extra "drive" of the multi fin overcoming the drag - I get confused on that.

The description of a thruster was that the centre fins allows the board to pivot and the front fins adds the stability sounds almost the opposite way round to me, if say adding a trailer to a twin. I expect there is some pivoting across the whole cluster. One of the things I like I about pointed tip AM fins and in particular Griffin fins with its narrow base centre fin is that the rear fin can break out of its hold in a tight turn when hacking the lip. I think what is happening is the low pressure side of the centre fin is having its laminar flow broken which means the centre fin loses about half its hold allowing the board to pivot around the front fins.
 
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griffinsurfboard

Duke status
Oct 31, 2004
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Palm Coast , Florida
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