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An approximate way to know the stability of a sup board without testing it

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Created by Mucel 23 days ago, 26 Sep 2021
Mucel
128 posts
26 Sep 2021 5:22PM
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Hello
I want to share with you a method that has worked for me to know the stability of supsurfing boards which I can't test. It's based on calculating the surface of the board. For sure there are many more factors affecting this topic, but, when you can't see&test the board, It's a first good approach, and has matched the testing I've made with real boards.

What I do is calculating the surface based on the following widths: maximum width, width one foot off the nose and one foot off the tail. It's a formula summing two trapezes, one from the maximum width toward the nose and the second one from the maximum width towards the tail. I'm missing the area from the top of the trapeze to the nose and from the top of the other trapeze to the tail.

The formula is the following:

Tail trapeze surface: (max width+ one foot off tail)/2 x (total length-60 cm)/2
Nose trapeze surface: (max width + one foot off nose)/2 x (total length-60 cm)/2

Total surface=tail trapeze surface + Nose trapeze surface (everything in same magnitude, cm)

The maximum width pont is supposed in the middle of the board which is not true, because I don't have normally this data. In case having it could be taken into account, modifying the formula

The boards with more surface calculated in this way normally are more stable. I've checked it with 10 boards.

For example the initial JP slate 7'2" x 28" was much less stable than a Quatro Carve 8'0" x 28'5" (both tested), having JP 3 more litres than the quatro. The JP had square nose and tail so it should be very stable for its size, but not in reality. The reason was the amount of surface you lost in length with such a short board. For stability maximum width is not the only dimension which matters, the length, width at tail and nose matter too.

For taking off stability in surfing stance the width of the tail is very important, IMO.

This doesn't pretende to be the ultimate tool, but in my case, when you can't test any board, it has helped a lot.

moogengronko
59 posts
26 Sep 2021 6:02PM
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I believe that, unfortunately , it ain't that simple! Rocker, rail shape, volume/construction/flotation/corkiness etc(comment STC?) also come in to it

FRP
446 posts
27 Sep 2021 2:04AM
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Mucel said..
Hello
I want to share with you a method that has worked for me to know the stability of supsurfing boards which I can't test. It's based on calculating the surface of the board. For sure there are many more factors affecting this topic, but, when you can't see&test the board, It's a first good approach, and has matched the testing I've made with real boards.

What I do is calculating the surface based on the following widths: maximum width, width one foot off the nose and one foot off the tail. It's a formula summing two trapezes, one from the maximum width toward the nose and the second one from the maximum width towards the tail. I'm missing the area from the top of the trapeze to the nose and from the top of the other trapeze to the tail.

The formula is the following:

Tail trapeze surface: (max width+ one foot off tail)/2 x (total length-60 cm)/2
Nose trapeze surface: (max width + one foot off nose)/2 x (total length-60 cm)/2

Total surface=tail trapeze surface + Nose trapeze surface (everything in same magnitude, cm)

The maximum width pont is supposed in the middle of the board which is not true, because I don't have normally this data. In case having it could be taken into account, modifying the formula

The boards with more surface calculated in this way normally are more stable. I've checked it with 10 boards.

For example the initial JP slate 7'2" x 28" was much less stable than a Quatro Carve 8'0" x 28'5" (both tested), having JP 3 more litres than the quatro. The JP had square nose and tail so it should be very stable for its size, but not in reality. The reason was the amount of surface you lost in length with such a short board. For stability maximum width is not the only dimension which matters, the length, width at tail and nose matter too.

For taking off stability in surfing stance the width of the tail is very important, IMO.

This doesn't pretende to be the ultimate tool, but in my case, when you can't test any board, it has helped a lot.


"Stability" is as you know a subjective experience that is influenced by the dimensions/ability of the rider, and the dimensions of the board and the condition of the water. That said I think it is fantastic that you are making a reproducible calculation for board to board comparisons that takes in consideration something more than volume. Perhaps post some numbers for the boards you have tested and the measurements that you made for the calculations? You never know where this may lead. I remember sending Bert Berger some calculation of surface area of the rider (rather than weight) for estimating the size of fins required for a particular board. It never went anywhere but who knows, board surface area calculations may be the ticket.

Bob

Gboots
NSW, 1246 posts
27 Sep 2021 5:18PM
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When i bought my 77 Flow at 83 L i thought it would be fine for a 65kg intermediate . It has been a nightmare off wave . Once on it is a pleasure .
I believe the instability is due to the lack of volume in the tail and sharply thinner out rails . Plus only 26 wide. Has a very narrow sweet spot . Bloody nightmare and I should really sell it . But she is soooo beautiful to look at ..
The similar volume Shroom is a breeze . But she is not so beautiful but definitely wife material

colas
4382 posts
27 Sep 2021 3:34PM
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Note that some brands give you the surface. For instance on all Gong models you have it, here for the Fatal 7'4": 13,279 cm2



It could be a way to somewhat refine your formula to see how the nose and tail (in the last foot) shapes alter your calculation.

colas
4382 posts
27 Sep 2021 5:28PM
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Gboots said..
When i bought my 77 Flow at 83 L i thought it would be fine for a 65kg intermediate . It has been a nightmare off wave . Once on it is a pleasure .
I believe the instability is due to the lack of volume in the tail and sharply thinner out rails . Plus only 26 wide.


Personally, I found out that a narrow board should not have a lot of volume, otherwise it is corky as hell.
83 L for your 65kg is a guild factor of 1.28. For my 97kg it would mean a board of 124 L, I had a 125l x 27"3/16 and it was an absolute hell
But a similar width board, but with only 105 L is stabler. Very tiring (no real rest position), but stabler as it does not roll like a tree trunk.

When countering a board that is rolling on the side, a high volume board will "bob up" and eject you to the other side, which is a very frustrating and humiliating fall. A low volume board will sink in the water, dampening its reactions.

slsurf
75 posts
28 Sep 2021 2:55AM
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I wish surface area would be a standard dimension its probably most critical component of stability. I even used the gong site to help estimate the nose/tail width I would need not having the mucel formula at the time. The gong site describes performance of their boards relative to the weight and ability of the rider. Then if you can't order gong, steal the volume and dimensions as useful comparison for getting your next board and voila!

shiny
11 posts
28 Sep 2021 10:12AM
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X2 on rocker having a massive impact, particularly on narrower performance shapes.

Gboots
NSW, 1246 posts
28 Sep 2021 12:50PM
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colas said..

Gboots said..
When i bought my 77 Flow at 83 L i thought it would be fine for a 65kg intermediate . It has been a nightmare off wave . Once on it is a pleasure .
I believe the instability is due to the lack of volume in the tail and sharply thinner out rails . Plus only 26 wide.



Personally, I found out that a narrow board should not have a lot of volume, otherwise it is corky as hell.
83 L for your 65kg is a guild factor of 1.28. For my 97kg it would mean a board of 124 L, I had a 125l x 27"3/16 and it was an absolute hell
But a similar width board, but with only 105 L is stabler. Very tiring (no real rest position), but stabler as it does not roll like a tree trunk.

When countering a board that is rolling on the side, a high volume board will "bob up" and eject you to the other side, which is a very frustrating and humiliating fall. A low volume board will sink in the water, dampening its reactions.


Thanks Colas.
My biggest issue has been losing stability right at moment when trying to paddle onto wave. It's 50/50 whether i fall in at that critical moment . Seem to tip towards one side as the nose starts to sink when paddling hard

colas
4382 posts
28 Sep 2021 2:51PM
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Gboots said..
My biggest issue has been losing stability right at moment when trying to paddle onto wave. It's 50/50 whether i fall in at that critical moment . Seem to tip towards one side as the nose starts to sink when paddling hard


This is due to your front foot (especially the heel) being too close to the rail for the nose shape.
(The wider the nose, the more tolerant the board to the front foot position)

Try to consciously keep your front foot very close to the stringer. And parallel to it so weight displacements between the toes and heel will not induce an uncontrolled roll to the side.

Another trick for pointed noses is to keep the tip of the nose well above the water, to avoid that the front rails engage in the water when the board has some roll, and push the nose to the side. So you paddle around to position yourself for the takeoff with the board nose tilted up for safety (you are focused on the incoming wave, not really paying attention to the nose position, so it is easy to fall) and then engage your weight forward into the drop once you are monitoring more your front foot and board nose position. Of course this is not possible when paddling with feet parallels.

Gboots
NSW, 1246 posts
28 Sep 2021 7:36PM
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ok thanks Colas . Will try this next time i try this board



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"An approximate way to know the stability of a sup board without testing it" started by Mucel