Surfing Waves

I'm helping a couple of my new surfing friends to buy their first board. They asked me a question that I was not really able to answer.

They looked at a 8'6 longboard but one is 58L and the other is 75L. I know more volume will give you more float, that's about it. One of them liked the the one with less volume more because it felt lighter. They also asked me what a lighter board will do and I just shrugged it off.

I looked at the GSI guide and I quote.

As a general rule, a beginner should be riding the equivalent of 100% of their body weight in volume. I.e. A beginner weighing 80kg should be riding a surfboard around 80 litres in volume. Alternatively, an experienced surfer can ride a surfboard that’s 35% - 40% of their body weight in volume.

BaNZ wrote: One of them liked the the one with less volume more because it felt lighter.

"Felt lighter" while actually standing on the board and riding or "Felt lighter" holding it in their hand in the store ?

waikikikichan wrote:

BaNZ wrote: One of them liked the the one with less volume more because it felt lighter.

"Felt lighter" while actually standing on the board and riding or "Felt lighter" holding it in their hand in the store ?

It was for holding the board. In terms of riding the board, they said they can't feel much difference. Bear in mind that they have surf no more than 5 times. They like it because it was lighter to carry.

I advised them to get the heavier (more volume) because it floats better so it will help with their paddle. It is also epoxy so it will be stronger than the other board.

For me - all other things being equal - more volume helps me mostly in paddling/wave catching. I find Surf Simplys volume-to-weight ratio a pretty good fit https://surfsimply.com/surf-coaching/volume-weight-ratios/

BaNZ wrote:It was for holding the board. They like it because it was lighter to carry.

In motorcycle safety school there's a phrase, " dress for the CRASH not for the RIDE ". You see those people in tank tops and shorts riding their sport bikes popping wheelies. They'll say it's too hot to wear a jacket and pants.

The same backwards thinking works for those wanting to get a shorter lower volume board so they "can" duck dive, yet can't get on a wave once they finally get out to the line up.

Volume like anything has it limits, too much and you can't sink in / engage the rail. Even drinking too much water is not good for you.

"Tastes great! Less filling!" Sorry, unabashed commercialism for those old enough to know.
(image source and historical information: http://www.omca.biz/2014/07/02/tastes-g ... s-filling/)

I recently explored this. So greater volume means you will ride higher on the water. That means you will create less of a profile under water. It follows then that you will have less drag when you paddle. That means it's easier to paddle faster, and I'm sure you can derive what benefits that gives

The drawback to volume is decrease in maneuverability. If you have a thicker board, when you turn you are trying to push more volume of board under water. The more volume you try to push under water the more difficult it will be to do so, so it will be harder to turn.

Warning; only keep reading if you want to nerd out

To get into the science of it, Archimedes Principe explains buoyancy. It says that the upward force of buoyancy is equal to the weight of the water displaced minus the force of gravity acting on the submerged object. So the greater the volume (size) of the submerged object, the more water weight is displaced, so the more upward force there is.
Fb = ρ x g x V
Where Fb is force due to buoyancy (in Newtons)
ρ is the density of the fluid (water is 8.3 lb/gal iirc)
G is the force of gravity
V is the volume displaced


To keep nerding if anyone is still reading:
(Switching to metric, and 1L of water weighs 1kg)
Let's say you have a 70L board and you want to know if you are going to completely submerge it when you get on it. So we want to know how much buoyant force it's going to produce when fully submerged.
We can modify the formula to give us kg instead of Newton's, buoyancy = density of water x volume displaced
So 1 kg/L x 70L = 70kg, so if you weigh 70k or less, when you sit on this board without waves or other forces, it will sit on top of the water, and when you lay down to paddle on it you will be out of the water.

One way to,defeat buoyancy is to increase your personal Plimsol line, your own body mass , a lot of bigger volume boards also have fat rounded rails as the bulk of the board is extended to the rails, sharp edge versus blunt edge penetration. Often the shaping of a rail indifferently towards the tail is forgotten. Egg shaped all the way down!
About personal body mass, remember your health!
If the volume increase is concentrated ie a thick short board, a major failing is that increased buoyancy is concentrated, the same volume in a long board, you have the advantage of applying leverage by your forward and back ward positioning on the board..
Drop knee turns come to mind.
Next length enables deep engaging of the tail to allow nose riding.

Cross stepping is smooth enough that it doesn’t break the tail engagement.