*** Official Griffin Surfboards Thread ***

Senor Sopa

Billy Hamilton status
Mar 11, 2015
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Perhaps not error, but deliberately not handing out an example of his rail intellectual property?

Greg sent me this email in 2017

Gregory Griffin wrote:
Late 60’s Mike Hynson validated the downrail , it had no tuck like the tail of modern boards
Dick brewer modified it by putting a small round contact point for control - suction -
This tucked edge design is the most efficient rail shape and can be adjusted in many ways
Flat surface before edge then tuck for suction - vary the size of tuck for how much is desired .
Then at the top of this tuck pull the rail inward to release that suction off of it
If the transition of the edge is smooth into the tuck it does not sheet water off , it climbs the tuck then releases where the rail pulls in toward the deck , if you build an edge at the bottom it does drift more .
That angle of the rail and size of it controls penetration
3 parts creating this engineered rail shape
I will draw up one




I think I understand what he is saying, although I'm still at the painting by numbers/trial and error stage when it comes to putting it into practise and making myself a rail with the desired proportion of properties.

He didn't make the diagram in case anyone is wondering.
Great quote, I told you about the rail wrap!
 

caramel_Sea

Michael Peterson status
May 29, 2008
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someones sellin this on fb
View attachment 139487 350


5’7 Greg Griffin Mod Fish 5 Surfboard
$350



Public meetup


Door pickup

Message







Details
  • Condition
    Used - like new
5’7 x 19 3/4 x 2 3/8 Modfish 5 - Excellent Condition
Believe that one was a custom I ordered: Cheater 5 fin/quad shortboard with a touch more tail rocker
 

ghostshaper

Phil Edwards status
Jan 22, 2005
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Perhaps not error, but deliberately not handing out an example of his rail intellectual property?

Greg sent me this email in 2017

Gregory Griffin wrote:
Late 60’s Mike Hynson validated the downrail , it had no tuck like the tail of modern boards
Dick brewer modified it by putting a small round contact point for control - suction -
This tucked edge design is the most efficient rail shape and can be adjusted in many ways
Flat surface before edge then tuck for suction - vary the size of tuck for how much is desired .
Then at the top of this tuck pull the rail inward to release that suction off of it
If the transition of the edge is smooth into the tuck it does not sheet water off , it climbs the tuck then releases where the rail pulls in toward the deck , if you build an edge at the bottom it does drift more .
That angle of the rail and size of it controls penetration
3 parts creating this engineered rail shape
I will draw up one




I think I understand what he is saying, although I'm still at the painting by numbers/trial and error stage when it comes to putting it into practise and making myself a rail with the desired proportion of properties.

He didn't make the diagram in case anyone is wondering.
The error is in the outline.

In our conversations, I know Greg shared the same philosophy as Maurice regarding his rails: small round w the sharp bottom tuck. I'll dig up a pic of what I made.
 
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Mr J

Michael Peterson status
Aug 18, 2003
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Great quote, I told you about the rail wrap!
@Senor Sopa I was thinking about your explanation when I dug up that old email from Greg and I am glad you called me out and picked up on that.

Greg's design understanding and ideas is something I have a lot of respect for. However I am sticking to my guns and at the same time understanding (I think) and agreeing with what Greg wrote.

I always agreed with you that there is some rail wrap. I also agree that the rounded rail encourages wrap - let's just pick up on one piece of that email
"Then at the top of this tuck pull the rail inward to release that suction off of it"


I think he is talking about the top of the rail above the apex if it bends round sharply into the deck then there is more release less suction - the corollary is that make the top of the rail more rounded and there will be more suction. I think this is your understanding (it is mine also).

Where we disagree is that you think the rounded rail holds more because there is more wrap and suction, whereas I say the rounded rail holds less.

My belief is from experience so I have attempted to reverse engineer why.

I've had complaints about my 2 dimensional diagrams not showing true direction, but I think they are useful because forces can be split into vectors Vectors (mathsisfun.com) so looking at a 2 dimensional cross section can show the forces in that plane. We do need to consider forces in other planes too. My 2 d drawing hasn't improved so here is a view from another plane

water isn't really travelling in a perfect vertical line up the rail like some of my diagrams have been drawn - its more like this.

the vertical component is wrap and suction and the horizontal component is water traversing along the outline of the board - outline has a very shallow curve compared to rail section and water will plane on this with pressure rather than suction. So we can see that the main body of the rail is producing pressure pushing the rail out of the water. Only a small section at the top of the rail has suction. Rounded rails increase the area of horizontal traversal (pressure) - rail gets pushed out of wave and reduces the amount of angled flat bottom pushing a sideways vector - I think that it is the flat bottom that provides the hold. Therefore the rounded rail holds less and I haven't disagreed with Greg's statement above.

RailPressureSuctionVector.JPG.png
 

caramel_Sea

Michael Peterson status
May 29, 2008
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I just realized that I still have Greg's file for my 5'6 twin/twinzer. Hit me up if you want it, and I can dig it up and send it to you.

Caveat: there's an error in it somewhere and you'll still need to hand shape the rails. My friend who cut it, said, "you should've just hand shaped this."

edit: but you might have to do something nice for need4speed to make you some fins for it
The CNC guys always want to put rails on my files, gotta shape that crisp tuck by hand!
 
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Mr J

Michael Peterson status
Aug 18, 2003
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The CNC guys always want to put rails on my files, gotta shape that crisp tuck by hand!
Yes, best to produce a file with reduced tuck then add it by hand. One thing I have been taught is not to produce a super fine hard edge in the tail rails - it just makes it harder to wrap the glass and get the air bubbles out, instead shape it hard then take a little of the corner off. The resin dam and sanding is what produces a pro standard hard edge.

In the main body of the rail putting in a crisp tuck is fine due to the more gentle angles allowing the glass to wrap. That's mainly aesthetics under a clear glass though, so no need to get it super fine - the glassing is going to round off any crispness. It should be neat though to act as a guide to the sander.
 
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