*** Official Griffin Surfboards Thread ***

[Mr J]

I love the hydrodynamica discussion, but I'm also skeptical, until one day somebody attaches streamers onto the bottom of a board and fins and follows it around underwater with something like this (12mph top speed, maybe too slow).


I remember I took the (unpopular) side of the Luddite (aka Roy Stewart) when he was calling BS on Daniel Thompson. I don't doubt the surfing and shaping skills of DT but his use of hydrodynamic theories to explain his work just didn't convince me.

In your drawings, I was curious about the idea of fin lift due to cant. I was thinking the water is flowing parallel to the bottom, at maybe a 30 degree angle on turns, not up the fin (maybe I misunderstood your drawing).

Out of curiosity I did the hose test and did verify that the water I shot (trying to stay parallel with deck and at a 30 degree angle) did deflect down (up in photos) a wee bit, barely perceptible. There was no perceptible difference between the 4 degree cant of main and 9 degree cant of canards. I might try a video because to stop motion of photos doesn't show the water motion I was seeing.

The lift your drawing describes would lift the tail up, right? My anecdotal evidence of that is on my bonzers. I found if I tried to do a mid face turn on a steep wave the tail would pop/spin out. I attributed that to the 19 degree runner cant. I know the bonzer folks will not agree with my assessment and blame it on rider error, which may be true, but it happened enough to convince me it was a design issue.

Also, I could not replicate the canard effect with the hose. I think that would need solid water, not hose spray, but seeing how the canard deflects water, I'm pretty sure it does what it is meant to do (prevent cavitation/stall of mains). Of course your drawing of wing tip vortex begs the question- why is the canard so short? The stall would seem to be more pronounced at the tip, would it not? I did make deeper canards but have not tested them.

Canard

Main

cants

deep canard


On second thought, looking at the photos, maybe the upward deflection is just from impact in the absence of water flowing across the tip ( I was aiming the water close to the base).

Camber surfboards have attached streamers with a little camera mounted on the underneath. I also attached a streamer a couple of inches or so in from the rail on the hull and watched it point diagonally outward when the board was in trim which verifies the diagonal flow exiting the rail idea.

I don't know how much cant adds to lift - I would hope not much. I was just trying to come up with some explanation for the lift Teeroi described with his quad - most comes from Greg's water travelling up the wave face explanation I think. Nevertheless your bonzer experience suggest cant is a source of some lift.

I don't know how the little canards work, but their job could not be to reduce induced drag which occurs at the fin tip only.

 

[griffinsurfboard]

however at low speeds some of the ones with undercamber (equivalent to our concave) show a higher lift to drag ratio than flat. Lift to drag ratio would be the definition of planing efficiency I think.

This is pushed thru the air by a motor

Stick your hand out the window flat - little resistance
Angle it upward and your hand wants it rise = Lift - But it also wants to move rearward , Up the face like

Cup your hand and even more so - Up and Back

Thats the lifting sensation you feel

In the beginning you shaped your board with it's optimum rocker then put slight concaves in straitening that rocker
The centerline now not optimum , so rocker was increased until the center was more functional
You were told that extra rocker was for better performance when it was really to enable the concaves rocker to be functional
Short story

 

[griffinsurfboard]

At the peak of High rocker Deep single concave there was some amazing surfing done by Very talented surfers .

With the added direction of this bottom + extra curve and freer fins to compensate for the deep concaves direction these surfers used their leg tension to keep the overturning in check.
You could see them control the drift in turns with those freer fins while the concave accelerated making for very exciting moves with tons of rider input - not available to the common rider
Ultra sensitive and quick - Very quick and mostly short with constant movement - lots of action - rippage !
Big roundhouse cutbacks etc. not available - resistance is required for longer lines

 

[One-Off]

Camber surfboards have attached streamers with a little camera mounted on the underneath. I also attached a streamer a couple of inches or so in from the rail on the hull and watched it point diagonally outward when the board was in trim which verifies the diagonal flow exiting the rail idea.

I don't know how much cant adds to lift - I would hope not much. I was just trying to come up with some explanation for the lift Teeroi described with his quad - most comes from Greg's water travelling up the wave face explanation I think. Nevertheless your bonzer experience suggest cant is a source of some lift.

I don't know how the little canards work, but their job could not be to reduce induced drag which occurs at the fin tip only.

Just checked out the Camber Surboards site. Wow. Finally some hard evidence of water flow. How old is that video?

I wish they had more footage, not just take off and trim. A bottom turn to top turn, or bottom to cutback sequence, basically the flow happening during a rail to rail transaction, would be very informative. Also, next project film streamers on the fins.

The big surprise for me is that the water flowing past the engaged fin is going pretty straight, nose to tail, or as they say "axially."

I remember Maurice Cole holding a rocker stick diagonally across the bottom of his deep concaves, showing how the surface was flat, thus faster...but according to the Camber video that's not how water is flowing across the bottom.


ps Camber boards are seeming to do the opposite of Griffin's explanation of flat bottoms- slowing flow and increasing pressure at the rails to increase lift...correct me if I'm wrong.

Built from Science | camber

www.cambersurfboards.com

 

[griffinsurfboard]

ps Camber boards are seeming to do the opposite of Griffin's explanation of flat bottoms- slowing flow and increasing pressure at the rails to increase lift...correct me if I'm wrong.

If so they are more Misinformation

My post was child like to see and understand

Chose your path

 

[Mr J]

This is pushed thru the air by a motor

Re: undercamber - not really. As I said slow speeds foils tend to feature this - gliders.

Stick your hand out the window flat - little resistance
Angle it upward and your hand wants it rise = Lift - But it also wants to move rearward , Up the face like

Cup your hand and even more so - Up and Back

Thats the lifting sensation you feel

100% agree with this, That's a nice description of AoA. You didn't explicitly say it, but I think you would agree that high AoA of the deep concave comes with a cost - increased drag.

In the beginning you shaped your board with it's optimum rocker then put slight concaves in straitening that rocker
The centerline now not optimum , so rocker was increased until the center was more functional
You were told that extra rocker was for better performance when it was really to enable the concaves rocker to be functional
Short story

Simon Anderson has blogged about this - when concaves came in rockers went up, but yeah that's how I've done my own build light concaves - trial and error because I don't have the skills to know the right amount of rocker proportions to concave. It would take me too long to get deep concaves right with trial and error.

 

[Mr J]

Just checked out the Camber Surboards site. Wow. Finally some hard evidence of water flow. How old is that video?

I wish they had more footage, not just take off and trim. A bottom turn to top turn, or bottom to cutback sequence, basically the flow happening during a rail to rail transaction, would be very informative. Also, next project film streamers on the fins.

The big surprise for me is that the water flowing past the engaged fin is going pretty straight, nose to tail, or as they say "axially."

I remember Maurice Cole holding a rocker stick diagonally across the bottom of his deep concaves, showing how the surface was flat, thus faster...but according to the Camber video that's not how water is flowing across the bottom.


ps Camber boards are seeming to do the opposite of Griffin's explanation of flat bottoms- slowing flow and increasing pressure at the rails to increase lift...correct me if I'm wrong.

Built from Science | camber

www.cambersurfboards.com

It's quite old. The water towards the rails is going diagonally, towards the centre of the board straighter. So it must curve. and I theorise that the fins must straighten things out in the tail. I think rocker stick placed diagonally forward of the fins is a useful tool for surfboard designers (despite the flow curving). Greg does it and so does the shaper of my awesome local custom pu/pe. Just like we find measuring stringer rocker a useful design tool, despite water never travelling from tip to tail down the entire length of the stringer

I think one of the reasons Slater designs and Tomo gets away with putting channels in their board designs is that they confine them to the tail where the fins are boxing the water in straight, so there is not too much weirdness and quirks compared to boards with channels which extend forward of the fins.

I think you are right about Camber's design philosophy - the opposite of Griffin. Its not the same as MC either who is aiming for straight - they are putting a downturn on the edge of their rail only. So a diagonal rocker stick would not sit flat like with a MC - more analogous to the pic Greg posted showing how the rocker stick across the double concave showed water would be undulating. Whose heard of Camber surfboards?

 

[griffinsurfboard]

Oh boy are you GuyZ Lost

 

[Senor Sopa]

If we substitute "water displacement" with flow turning then yes to both lift and hold.

No to wrap! Two reasons, firstly water thrown upwards creates a downforce i.e suction.
No to hold - alaia have hard thin rails which release rather than wrap. In order to generate hold it would have to wrap through close to 180 degrees. Although I never developed the skills to ride waves on my skimboard, I did get to the point where I could run out into deep water - the combination of me travelling out and water rushing in got my board on the plane and I could do a reasonably deep turn - I used to stare down and watch the water release - it wasn't wrapping inwards. Its rails were comparable to an alai in profile.

A very good surfer I know had a classic 50-50 egg shaped rail longboar built for fun - he told me that it had less grip than the normal downrail and was prone to sliding out - the egg shaped rail is conducive to wrapping, but even that couldn't provide hold matching what the bite of the modern tuck could produce - you are a HP longboar rider aren't you? can you verify this behaviour comparison?

"flow turning" is essentially the same as "wrap"
Old skool longboars have significant roll on the bottom. This provides stability at the expense of drive/acceleration
The 50/50 pinched rails have a tight radius, the water will release closer to the apex. i.e no hold

On the skimmer, you experienced the water displacement part of the hold. Sinking the rail pushes water away, this weight of water is "hold"

I did the spoon experiment for you. See how the water "wraps" around the spoon? You can feel this in your hand as it grabs the spoon, moving it to the right.
This "warp" can be thought of as the rail holding in to the face.
Remember, this wrap is a long spiral. If the radius is too tight, the water won't wrap and will release, ending the forces at work.


The concave in the bottom of the boar is much the same. Lot's more volume of flow, hence less radius.

Most of the work of the fin is the outside surface, redirecting the water along the curve, providing force perpendicular to the fin surface. i.e. into the wave face

 

[griffinsurfboard]

Most of the work of the fin is the outside surface

Template design and size are the most important - that flat surface is a plane , not just a rudder , foil adds to that

 

[One-Off]

If so they are more Misinformation

My post was child like to see and understand

Chose your path

If so they are more Misinformation

My post was child like to see and understand

Chose your path

Don't be so defensive.

I think their CFD analysis confirms what you say about lift and release. I had to substitute "high pressure" and '"low pressure" for "lift" and "release." Their written explanation confirms what you say about the release of water past the apex and towards the rail in your boards. What they are doing, putting that "crook" near the rail is to increase pressure/lift at the rail, but to me it seems like it might increase drag. Whereas what you do with the flat bottom decreases pressure/increases release, minimizes drag. Intuitively I think what you are doing sounds better= faster. It confirms teeroi's description of your board not pushing back but going really fast. I'm on your team GG.

Nevertheless, I've come to like a very slight single concave, <1/8" because I feel it accentuates the release of the "Griffin style" hard edges. Also that feeling of lift, getting pulled up the wave. The combination makes the board get going really fast after just a quick check turn on take off.

In the end it's all about feelz.

 

[griffinsurfboard]

As I said

There is a Yuuge problem in that - constantly challenging real design experience

 

[griffinsurfboard]

It confrims teeroi's description of our board not pushing back but going really fast.

Fins were placed same as Concaved bottom - incomplete test

 

[teeroi]

Fins were placed same as Concaved bottom - incomplete test

Most certainly.

 

[Mr J]

Fins were placed same as Concaved bottom - incomplete test

I think there are some crossed communication lines here! You quoted One-off as "our board", he has since amended his post(I see post is edited) to "your board" as in Griffin board. You told me that your boards don't have the same fin placement as a equivalent concaved boards.

One-off was also saying that he can see how your boards would go faster (although it would give a feeling of less push back) - are you disagreeing with that?

 

[griffinsurfboard]

Changing fin placement will create more "Push Back" than a sunken planing surface

10 3/4" , 3 1/8" > 11 " , 3 1/2"

 

[One-Off]

Fins were placed same as Concaved bottom - incomplete test

I actually misspoke. The flat bottom teeroi mentioned was a Tokoro. So obviously the fins were probably in the wrong position.

ps GG, wondering why your five fins seem so far forward?

 

[griffinsurfboard]

The flat bottom teeroi mentioned was a Tokoro. So obviously the fins were probably in the wrong position.

its wise to change 1 feature at a time

 

[griffinsurfboard]

ps GG, wondering why your five fins seem so far forward?

its where they work best
Placements change thru the board sizes

9' board rears are 1 7/8" further up than a 6' board
Front fins are 3 1/4" further up on a 9' board
Spread increases too

 

[Mr J]

There is a Yuuge problem in that - constantly challenging real design experience

Absolutely, I believe experience trumps theory. I am not a surfboard designer. I just enjoy reverse engineering possible explanations for the way certain design characteristics have provided me with a certain surfing experience. My experiences of surfing are limited so I will listen to the experience of others who I deem reliable too - some surfers, some shapers.

When I challenge you it is because my experience does not match what you are saying, or I have an alternative explanation for why our experiences match. Most of the time my experiences do actually match what you say and my alternative explanation is just that - another way of describing something rather than disagreeing with your explanation. However you seem to take that as a direct challenge. I suppose I can get a bit argumentative sometimes just because I am in a funny mood LOL.