*** Official Griffin Surfboards Thread ***

One-Off

Tom Curren status
Jul 28, 2005
10,863
5,637
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33.8N - 118.4W
@One-Off I did a very brief experiment when I had finished washing my wetty today. Brief because I was getting cold. I dragged a plastic spoon across the surface of the water in my washing bucket. I was holding it by the end of the handle and dragging lengthwise applying a little downward pressure. It did not dive to the bottom - it planed across the surface. There is a difference between a thin stream of water from a tap and the mass of water behind a 12 second period wave. That's why I don't believe hosepipe experiments have much value either.

Its just experience that tells me wide light single in powerful waves gives a feeling of sitting out of control on the surface - I reverse engineered the theory that the it is the lift of the concave from water exiting the rails diagonally. Wide for me starts at 19", because of this experience I only ride narrow and this stops the out of control feeling in powerful waves. You have made light single concaves - how wide and how long were they and did you get to take them out in reasonably powerful waves? What was your impression?
When the waves get serious I have a 7-4 for points and a 8-3 for my local reef. Both are flat bottoms..... :unsure:
 
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Mr J

Michael Peterson status
Aug 18, 2003
1,864
1,069
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Regional Vic, Australia
...
V bottom with concave set within the V panels on a DVS full carbon 7'4" quad fish with full rails and running GTF-1 carbon twins only.
If you want to go wide with a concave making it a double or V double is one solution. On the downstream side of the V there will be line of low pressure which helps reduce uncontrollable lift. Although @One-Off observantly noticed that the Camber surfboards underwater camera did not show flow crossing the stringer the camera was mounted on the tail of the board where the fins tend to box in the flow. I would imagine it would cross the stringer further up in certain circumstances - and a reason Greg did not like the double, V double or any V for that matter.

To quote Greg: "The flow does not have to go up and over this ridge along the rail"

pic from his photobucket. Thread link here https://forum.surfer.com/index.php?threads/rocker-and-concave.236132/#post-3545101

Ridge.png
 
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One-Off

Tom Curren status
Jul 28, 2005
10,863
5,637
113
33.8N - 118.4W
If you want to go wide with a concave making it a double or V double is one solution. On the downstream side of the V there will be line of low pressure which helps reduce uncontrollable lift. Although @One-Off observantly noticed that the Camber surfboards underwater camera did not show flow crossing the stringer the camera was mounted on the tail of the board where the fins tend to box in the flow. I would imagine it would cross the stringer further up in certain circumstances - and a reason Greg did not like the double, V double or any V for that matter.

To quote Greg: "The flow does not have to go up and over this ridge along the rail"

pic from his photobucket. Thread link here https://forum.surfer.com/index.php?threads/rocker-and-concave.236132/#post-3545101

View attachment 137813
You think the fins are boxing in flow in front of the fins? I don't think so. I am now of the opinion that a straightedge placed diagonally across the bottom is misleading....unless you're side slipping.

I came back to this thread because it occurred to me that another great Griffin died in a motorcycle accident.Screen Shot 2022-09-14 at 4.54.53 PM.png
 

One-Off

Tom Curren status
Jul 28, 2005
10,863
5,637
113
33.8N - 118.4W
I'm dusting this one off and giving it a go. First time in years. Original Griffin five fin set. At that time he was very generous in advising me on fin placement, even board dims, for my second (and only balsa) compsand build.

ps new build in early stages in background.

IMG_6851.JPG
 
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JDJ

Miki Dora status
Mar 1, 2014
4,011
3,084
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The OC
Damn. Wish that I never sold the thruster Greg made me. That board paddled into everything with little effort. I always planned on getting another ….