Kelly's decline(?) on Slater Designs. And his usage of odd surfboards.

griffinsurfboard

Duke status
Oct 31, 2004
25,653
6,905
113
Palm Coast , Florida
Visit site
I can see what Greg is saying though - less toe in means go faster, going faster means more lift from the bottom of the board (not the fins).

I'm sure you have seen customers say they feel controlled lift in the Emails I have posted

Its a concept you are not aware of - if they change fins it will go away

Board picked up last saturday , ridden in mush :



Hi Greg
Rode the modfish in thigh to waist high choppy swell this evening. Works great!!
Disturbingly fast, super smooth and easy as hell to ride. Same feeling of lift that the other 2 have.
Takes off at an incredible speed. Great board!! Thanks again
Jeff
 
  • Like
Reactions: Mr J

griffinsurfboard

Duke status
Oct 31, 2004
25,653
6,905
113
Palm Coast , Florida
Visit site
Everyone here has felt their boards plane on the fins , its that great sensation of flying across the face ready to go anywhere

Its what I try to achieve all the time rather than just in perfect situations

If your style of surfing is to wack back and forth constantly you will never allow your board to do this and be unaware of its existance .
 

Mr J

Michael Peterson status
Aug 18, 2003
2,250
1,454
113
Regional Vic, Australia
PRCD my high school physics is really basic and does not extend to knowledge of that equation.

My explanation: the angle of attack is defined as the angle a line drawn from the leading edge of a wing (fin), to the trailing edge makes with a line drawn for the direction of travel - don't need flaps to change that - whole wing tilts leading edge up to increase angle of attack. Similarly the whole fin can be swivelled one way or another on those 4ws boxes. However we are dealing with a sideways situation not vertical one. The force we want as we trim across a wave is towards the wave to stop our board from sliding out towards the beach. So with direction of travel to increase angle of attack we would actually need to toe our fins out if water was flowing against direction of travel. So straightening or toeing out (which we never do) increases angle of attack.

The reason we don't toe our fins out is because water gets "squirted" sideways on the inside rail. So a positive angle to water flow is achieved with the fin pointed in towards nose. The stringer line is not the direction of flow at the inside fin. Dead straight fins would be a bigger angle of attack, thus more hold, but a bugger to turn - at least on a tri fin - I built a near parallel twin fin which turned fine though. However if one was to play with 4ws and keeping toeing the fins out eventually a point would be reached where the increasing angle of attack no longer generates extra hold because the fin is stalling (water not sticking to the inside surface of the foil).
a picture to go along with the words PRCD. If we were to take toe in angle to stringer and approximate direction of travel then it would be negative and the board would slip away from us. Relative to flow is the one that counts because it is the flow that generates the forces.

The water curves outwards from the wave side rail which gives a positive angle of attack relative to flow despite the toe in. Imagine bringing that toe in line to point closer to the nose to increase toe in, the angle of attack actually reduces. So it is actually less toe in that generates the larger angle of attack and the greater hold.
AngleOfAttack.png
 

PRCD

Tom Curren status
Feb 25, 2020
12,514
8,551
113
a picture to go along with the words PRCD. If we were to take toe in angle to stringer and approximate direction of travel then it would be negative and the board would slip away from us. Relative to flow is the one that counts because it is the flow that generates the forces.

The water curves outwards from the wave side rail which gives a positive angle of attack relative to flow despite the toe in. Imagine bringing that toe in line to point closer to the nose to increase toe in, the angle of attack actually reduces. So it is actually less toe in that generates the larger angle of attack and the greater hold.
View attachment 103039
Is there still hold towards the tail as the rails become sharp? I thought sharp rails cause release which is why they're round until the tail. You can definitely see the flow in that bottom turn though. did you create some modeling software for this?
 
  • Like
Reactions: Mr J

griffinsurfboard

Duke status
Oct 31, 2004
25,653
6,905
113
Palm Coast , Florida
Visit site
I dont think anyone designs their fin setups around the outside fin

around 1980 many twins from Oz used increased toe in with more tilt

After bottom turning and flattening the board going up the face it would catch way more water pulling the board into a slight cutback after each turn

That toe in was reduced to correct it - only time iv'e seen attention to the outside fin

Side note :

Wade Tokoro has ridden more 9'+ guns that any shaper in Hawaii for the last 30 years - that counts Alot in making guns
 
  • Like
Reactions: Mr J and Waiehu

Mr J

Michael Peterson status
Aug 18, 2003
2,250
1,454
113
Regional Vic, Australia
Greg, I always enjoy your historic snippets of design info. Yes in the photo I stuck in the corner of my drawing we can see the outside fin is out of the water.

btw the pic I drew is looking down on to the deck of a board going left to match the pic. The fin where I drew the AoA is the inside fin.

The red line is the spray root which in a surfboard trimming or bottom turning is diagonal across the board as can be seen from the photo. I drew the spray root to line up with the outside fin so the fin is just breaking the surface which is a common situation.
 
  • Like
Reactions: need 4 speed

Mr J

Michael Peterson status
Aug 18, 2003
2,250
1,454
113
Regional Vic, Australia
Is there still hold towards the tail as the rails become sharp? I thought sharp rails cause release which is why they're round until the tail. You can definitely see the flow in that bottom turn though. did you create some modeling software for this?
PRCD, yes sharp rails are for release and yes there is hold in the tail. I have written a long post about this somewhere, but briefly the hold comes from the flat surface of the board immersed at angle not the rail - the hull is tilted and "pushes" sideways against the water which provides us with some horizontal hold force. I am satisfied with this explanation for a number of reasons, but one really good personal demonstration is my skimboard - it is 5/8" thick in the tail, hard edges, no fins. I can sometimes build enough speed to skim into deep water and bank it over into a turn - provided I bank it over at sufficient angle it grips really well despite the hard edge. Actually the hard edge helps because it makes it easier to submerge the rail/hull. Unless the board is banked over it has no directional sense at all and takes some strange waving of arms and body english to stop myself from going sideways, spinning around backwards etc. The skimboard is good balance training, but I don't think it is going to do anything for my surfing style :roflmao:

Actually no, we can't see the water flow in the photo - thats the beach side whisker spray you are looking at. The flow we are interested in for AoA and hold is on the wave side (the heelside of that surfer doing a backhand turn) - we can't see it because the board is in the way. I've added some footprints and whisker spray to my pic - so visualise looking down on top of it in a heel side turn. Hopefully that makes it easier to understand what I am trying to get across.

I just drew that with paint3d, it is not CFD, so just an illustration. However, we can say with a fair bit of certainty that water does curve outwards and exit the rail diagonally for a number of reasons. One of which is that years ago I attached a little streamer to the underneath of my surfboard - a piece of thin curly gift wrap ribbon. shiny purple and easy to see. Exact location I have forgotten, but it was something like a few inches in from the wave side rail between my feet. At all times I could see the ribbon stretched tight in the flow coming diagonally out from the rail. If the flow was straight the ribbon would have remained out of sight underneath my board. The only time it disappeared from sight was when I went into a cutback and my weight transferred to the opposite rail.

More recently and scientifically an Italian engineer did some CFD for Firewire and it did show something like that.

AngleOfAttackAndSpray.png
 

Mr J

Michael Peterson status
Aug 18, 2003
2,250
1,454
113
Regional Vic, Australia
THe other trade-off in a shorter board is the amount of room the shaper has to add rocker. Not enough rocker, and the board will catch rail or look choppy because you have to step on the tail so much to turn.
That's an interesting suggestion and seems quite reasonable, but I know it is not true for a couple of reasons - empirical rocker measurement and experience.

jkb once had plans to build a performance snub nosed shortboard approaching HPSB dimensions based on the rocker of his tiny Tomo planing hull. He had measured rocker at 6" intervals and because shape3d provides numbers every 3" I was able to extrapolate it by doing something like adding 3" at each end or something like that. The result was quite normal rocker. I also did something similar with my short Chilli 5' 2" Mini Bird stubby. So the curve on a short stubby is of comparable "radius" and it is possible to generate speed with an even footed technique.

Curve aside and just considering nose scoop clearance which is clearly less, from riding boards of different lengths it seems that the shorter boards go up and over lumps in the water more easily than longer boards, so not so much nose scoop clearance is needed. To take an extreme example longboards in small choppy waves will tend tend to slam up and down and plow water. At speed things are a bit different, but if anything it is the longboards that are the step on the tail to turn technique. Even HPSBs and step ups plow more water in bumps at slow speeds and chatter more at high speeds than the short stubbies.
 
  • Like
Reactions: PRCD, jkb and Aruka

Mr J

Michael Peterson status
Aug 18, 2003
2,250
1,454
113
Regional Vic, Australia
You need to make boards for a living -

All this marketed knowledge is "MarketIng"

Real design was created long ago , then spun for increased sales
Greg, I am not trying to sell anything. I can't even make myself a board that I am completely happy with, so need to keep grinding away at my keyboard job. I am just trying to find explanations using high school level physics and theory as to why certain designs work the way they do - reverse engineering what was created "long ago".

However, you have given me an idea - I am going to "market" my 2021 design on the Rusty talk to the shaper series thread ;)
 
  • Like
Reactions: Waterlogged05

Clayster

Miki Dora status
Oct 26, 2005
5,646
1,241
113
who cares. kellys a kook. still fking up surfing 30 years after the glass $hitter boars of the 90z. funny how ppl look up to the single biggest influence on giant crowds in surfing. i'd rather be on a 70's style singlefin with 1/10 the crowds and no smelly smater
Come on. it was gonna happen regardless of Kelly.
 

PRCD

Tom Curren status
Feb 25, 2020
12,514
8,551
113
You need to make boards for a living -

All this marketed knowledge is "MarketIng"

Real design was created long ago , then spun for increased sales
Where can we read about real design? It'd be amazing if some shapers *cough* made a brochure that explained the basic design principles and what they do, because an educated customer probably makes for a happier customer and shaper. Clayton Neinaber did this in one of his talks. Seems like a lot of shapers can't explain what works or why even though they make boards that work.
 
  • Like
Reactions: waxfoot

Swallow Tail

Billy Hamilton status
Oct 6, 2017
1,679
2,938
113
Your Mom’s House
I dont think anyone designs their fin setups around the outside fin

around 1980 many twins from Oz used increased toe in with more tilt

After bottom turning and flattening the board going up the face it would catch way more water pulling the board into a slight cutback after each turn

That toe in was reduced to correct it - only time iv'e seen attention to the outside fin

Side note :

Wade Tokoro has ridden more 9'+ guns that any shaper in Hawaii for the last 30 years - that counts Alot in making guns
Where can we read about real design? It'd be amazing if some shapers *cough* made a brochure that explained the basic design principles and what they do, because an educated customer probably makes for a happier customer and shaper. Clayton Neinaber did this in one of his talks. Seems like a lot of shapers can't explain what works or why even though they make boards that work.
shapers (and their equals in other industries) don’t share for a myriad of reasons.Some understandably so, others not so much.

Here’s a solid starting place, Steve Coletta knows a thing or 2 about how surfboards work



From my 35 + yrs of surfing I can say - from a practical stand point: IMO The best way to get boards that work for you is to stick w one shaper and do refinements to dial in what works best for you. Ride a bunch a boards from different shapers, the one that clicks the best - stick w that guy and dial in more w every new board. Way Better than scatter shot/keep crossing fingers buying the latest/greatest “models” being marketed by various brands, randomly finding something that works and flipping the ones that don’t.
 

Havoc

Phil Edwards status
May 23, 2016
7,682
12,216
113
in da hood next to paradise
shapers (and their equals in other industries) don’t share for a myriad of reasons.Some understandably so, others not so much.

Here’s a solid starting place, Steve Coletta knows a thing or 2 about how surfboards work



From my 35 + yrs of surfing I can say - from a practical stand point: IMO The best way to get boards that work for you is to stick w one shaper and do refinements to dial in what works best for you. Ride a bunch a boards from different shapers, the one that clicks the best - stick w that guy and dial in more w every new board. Way Better than scatter shot/keep crossing fingers buying the latest/greatest “models” being marketed by various brands, randomly finding something that works and flipping the ones that don’t.

but but but what about firewire!
 

Havoc

Phil Edwards status
May 23, 2016
7,682
12,216
113
in da hood next to paradise
Does Mark Price know you have a crush on him?
haha. he's been trying to wine and dine me to the dark side for years now lol.

btw, if u search for board reviews there are tons of these weird ppl all doing strictly firewire boar reviews with soloshot cam footage. they have a quiver of fireturd popouts and state they are intermediate/advanced when they are like fresh off a wavestorm. the devolution continues...
 

oeste858

Phil Edwards status
Sep 11, 2017
6,931
17,276
113
San Diego, CA
Uh huh. Why you searching for FW board reviews?? LOL. Bro you're obsessed!
and there's definitely zero kooks riding Mayhems or CIs in SoCal...
 
Last edited:
  • Like
Reactions: MathDebater