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.

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

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.

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!

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

ok thanks Colas . Will try this next time i try this board