What Makes These Work So Well ?
That each company I have worked for has wanted to build these .
Open to any thoughts , Science included :-)
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Curious what happened, why would they stop making them?
As much as they liked them and still talk about these they could never make them correctly .
I have been able to do so since the beginning 
Email me at griffinsurfboard@aol.com
I will help you make one
Still on my wife’s I pad waiting for our internet to be restored
really nice looking boards , well suited for rail fin designs .
we will talk more when it’s back .
do you still have demos maybe something short and HP suitible for me 5’8 140lbs
Me neither. Ha.
Not anymore
i would help you make one if you like
Cool! fantastic offer thanks, but if I made one even under your guidance and it didn’t click for me I really wouldn’t know if it was my build fault or what the real thing might have been
bud
harry outgrew (as we all do except you) his 6’0 custom 5fin fish so he’s using my 6’2" now
It might be too big for you he’s 5’6"-5’7" but was closer to 150-155 when he bought it.
It’s not HP but’ll it’ll paint you a picture of what’s possible with Greg’s 5 fin design.
It’d be a perfect groveler for the summer crowds
PM him
Sorry, I must have hit the “snooz” button.
You should try the " Happy" button sometime .
It feels pretty good .
Possibly try to talk and discuss design too :-)
Ask a design question please , I will answer .
These designs are almost 30 years old and are working head to head with the latest designs , imagine how they compared way back in their beginning .
I have surfed these thru all these decades ,4 of them ,adjusting fin sizes and placements for all sizes and shapes .
More than pleasing almost all who have bought them .
Is that not interesting enough for Mr .McDing ? :-)
It did take some effort on my part to do this and that is why you offend myself with such comments .
Off to work to make more very happy :-)
I have a question: Why do you put your fins further back than most other shapers?
i think the magic ingredient is the center fin … its ultimately what keeps it under control when a board with 4 fins would lose control…
i watched a heat of Kelly’s in Fiji in 2014 , hes on a perfect wave , perfect section and suddenly , inexpicably he oversteers after snapping under the lip and went over the handle bars … i didnt know what he was riding , but said to the guy i was watching with " that was a classic quad glitch out" fair enough , 30 seconds later , Kelly is paddling back to the boat , you see him hand over a quad and have a thruster handed back…
so what was the problem???
the trailing vortex and turbulence from the front fins interferes with the tail fins ability to function properly… the problem is further exagerated , the more radical you go top to bottom , as the side tail fin is more likely to encounter the turbulence from the front fins…
fins function best in clean green water…
seriously , i would love to expound on another 3 or 4 points , and discuss the evolution of quad fins , and differences from the intial boards we saw in the early 80s and what other options are available to combat the issue , how others effectively solved this Quad glitch … but for now , and the answer to your original question Grif …
you have the advantages of a quad fin , and the center fin solves the dis advantages when it counts ,
regards
BERT
They are placed and sized where they work best with the board design which the fins are part of.
Move them and that “best” disapears , still works but not special .
Using non directional flat bottoms with lower rocker I can place the fins in a very active position where you can ride the sweet spot all the time never needing to move forward or back - just go where you want , do what you want .
Thats just part of it .
Okay, so it’s been a week now since Greg posed his question “What makes these boards work so well?”.
And so far he’s never actually confirmed that anyone’s hit the nail on the head in answering the question.
Okay, I’ll take a punt at it; first I think we need to define the question a little better; from looking at the pics he’s posted, there’s a variety of boards in there (longboards, shortboards, and lots of different setups on them fin-wise).
But they’re all 5-fins, so I can only presume he’s asking why his 5-fin boards work so well.
I think the whole truth is that everything about them is what makes them work - outline, shape, construction, fins, fin-placement, etc, etc, etc. So I agree with what Oneula said above. Mind you, this is the case with every board, 5-fin or not.
So if I had to pick one thing, one element that makes all the difference in why they work so well, well, I’d say the fin’s design, construction and placement.
To refine my answer even further I’d say that the principles that were used in designing the fins and where they were placed is the real answer, as you can see there’s a variety of fin sizes, outlines (and probably different foils) and placements, but I wouldn’t be surprised if they all had some common principles used in how those different designs and placements were arrived at. What you’re looking at are very efficient fins, designed to perform in a certain way (possibly even custom designed for the specific board that they’re mounted on and the person who’s to ride the board) with minimal drag, maximal performance and placed in just the right spot.
Why do I say this?
Well, the impression I get of Greg (from what I’ve picked up here on Swaylocks threads) is that he’s a real fanatic about getting the fins on his boards just right.
And if you take into consideration his comments on this and other threads, it all starts to add up.
For instance, his comment about how the companies he’s worked for can’t get the boards to work without him, while he could get them to work right from the beginning; I think he’s given you a real hint there.
The impression I get is that during the 80’s and 90’s, the average shaper didn’t pay all that much attention to their fins or understand too well, the principles behind how the fins worked (or rather didn’t work as well as they possibly could). As long as the board turned, well that was good enough.
When FCS and easily interchangeable fin-sets appeared, fins started gaining attention, but very few board manufacturers actually produce their own fins, let alone custom fins for an individual board. Instead they’d use what was available to them from the fin system companies like FCS, Futures, etc.
Greg on the other hand does produce his own fins, and I wouldn’t be surprised if he produces custom-fins designed specifically for individual boards.
So if his 5-fins require a certain design of fin which none of the big fin-manufacturers produce, well, no wonder the companies he’s worked for can’t get his boards to work with what’s available to them off-the-shelf. And until they understand how to design the fins his 5-fins require and start producing them themselves, any 5-fins they build just won’t perform as well as the ones built by Greg.
Further evidence of this is I also recall seeing an interview he did where the interviewer asked him if he’d had a “Eureka” moment; a moment where suddenly the light went on in his head. He said yeah, it was to do with fins. That’s why his 5-fins worked right from the beginning as he’d already come up with the key to their success before he’d even built the first of his 5-fins.
So what is it that goes into his fins to make them so successful? Well, for instance they’re designed to provide the performance (lift) required with minimal drag. This is accomplished by ensuring a smooth, gradual and calculated change in pressure over the surface of the fin rather than the sometimes radical and vortex/turbulence-inducing uneven distributions of changes in pressure that occur over the surface of popular commercial fins.
One way this is accomplished in Greg’s fins is by having the chord-length gradually shorten from base to tip with trailing edges and centres of lowest pressure also moving constantly diagonally “down-wind” as you go from base to tip. This ensures spanwise movement of water is always in the same direction until it is cleanly shed at the tip and helps reduce trailing edge vortices (and the drag they produce) by realigning the flow of upper surface water to more closely match the direction of lower surface water when they meet after passing the trailing edge.
This is in contrast to some commercial fins, for example ones where the trailing edge curves in towards the nose of the board as it leaves the fin-base, and then out towards the tail of the board as it approaches the fin-tip) this means the chord-length starts long at the base, then as you move towards the tip it shortens radically, then lengthens again, then shortens again.
This means that you’ll get some sections where span-wise movement of water suddenly tries to head “up-wind” as it moves in the direction of the fin-tip because it’s encountered a section where the centre of lowest pressure is further forward rather than further back (despite leading edge sweep). And you’ll also get trailing edge vortices in some sections heading towards the base rather than the tip where it will collide with trailing edge vortices heading towards the tip from the base. Draggy.
As a result to quote Greg in another thread (where he’s describing this reduction in fin area from base to tip much better than I am: http://www.swaylocks.com/forums/fin-area-distribution); “My fins feel like wings lifting, planing and releasing with their smooth designed in loss of area from base to tip”, while many commercial fins are essentially just a rudder.
I’m not describing this well. Okay, lets start with this.
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Water likes to flow from regions of high-pressure to regions of low-pressure.
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The lowest-pressure area over the surface of the curve (camber) of a fin (as the water flows from leading edge-to-trailing edge) starts on or close to the leading edge and increases, generally peaking with the lowest pressures being reached on or around the maximum thickness of the camber before fairly rapidly turning to higher pressures again as it approaches the trailing edge. So, for simplicities sake, let’s call the peak of the camber (i.e. maximum thickness) the centre of low pressure.
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As water passes over the upper (cambered) section of a wing/fin it moves slightly in towards the base of the wing/fin. And the water passing over the underside of the wing/fin moves slightly out towards the tip of the wing/fin. When these two streams of water meet as they pass over the trailing edge of the fin, they’re heading in different directions, cross over and generate eddies which are known as trailing vortices. As you progress towards the wing/fin-tip, these eddies/vortices roll up to form one big vortex (called naturally enough a wing-tip vortex). This causes drag.
So, let’s say there’s two identical sections of chord sitting next to each other, however they’re slightly diagonally offset so that the centre of lowest pressure of one is diagonally offset from that of it’s neighbouring section.
Now seeing as water likes to flow from high to low pressure, on the section which starts a little “up-wind” (in terms of water flowing from leading edge-to-trailing edge), as the water flowing over it reaches it’s centre of lowest pressure, it could continue heading towards the trailing edge but there’s higher pressure there, whereas there’s another centre of low pressure diagonally “down-wind” of it on the section next door. So it’ll alter it’s course and be attracted a little-bit sideways towards that centre of lowest pressure on the section next door. This is called spanwise movement.
Now if the sections are staggered so that the direction of spanwise movement is towards the wing/fin-tip it will counteract the base-wise movement mentioned in point 3 above, so that by the time the water-flows from the upper and lower surfaces meet after passing the trailing edge, their differences in direction will be much less. Therefore smaller trailing vortices and less drag, while the required lift from passing over the wing still gets generated.
Whew, that was just a massive brain-dump (so apologies it wasn’t more succinct) and who knows if I’m right - it’s just me trying to put two and two together from looking at his fins and adding it to (what little) I understand of fluid flow. Please correct me if I’m wrong.
Well, Greg after all these guesses and comments from people (including me), is anyone getting warm yet as to why your 5-fin boards (I presume that’s what you mean’t) go so well?
Cheers all.
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Please start a threat about this.
I would very much like to read your thougts about this topic…
stoneburner … need to churn out some work now … will come back next week and start that thread…
in the meantime , check out if you can find a pic of a Glenn Winton quad , he discovered one way to eliminate or soften the negative classic quad glitch… i know Grif has 5 fins , but ultimately he combining the best of quad and thruster …
appart from the center fin which i feel is the most important on Grifs boards …
next is relative front/ rear fin placement …
rear fin size relative to placement…
rear side fin toe in…
rear fins neutral foil…
in order of importance …
regards
BERT
WELCOME back , Bert !
I look forward to reading more of your posts !
cheers
ben
Thanks L.I.T (and Greg of course) for your detailed technical explanation of the benefits of the always reducing chord length of Greg’s fins from base to tip. I think it’s pertinent that just about every aircraft wing plan shape I can think of follows this same line of thought. In light of this I would be interested in your’s and Gregs thoughts on straight edged fins which follow this principle versus Greg’s curved edged fins. What effect do you think a linear low pressure map line down the fins length should have on the way a fin surfs as opposed to an evenly curved low pressure map line?