Hi guys,

been veiwing seabreeze for awile now but this is my first post (be gentle)

A conversation i had with someone the other day got me thinking. So i thought i would throw it to the experts, do you think pressure dings (mainly deck) reduce boyance over time?

Reason i ask is that the board i have been riding for the last 4 years (6'6 -19- 2 1/2) seems to be getting harder to paddle. Now before everyone tells me im getting older and weaker and all that sort of stuff. I'll let you know im the same weight and a hell of a lot fitter then when i got it made.

Got me thinking, people get thicker boards for more boyance, but if you compressed the foam on a 2 1/2 thick board to 2 before glassing would it be as boyant?

Compressed foam, 2 1/2 to 2 or less would equal a sharper rail and less pressure dings and cracked glass in the future but with same boyance? Or am i dreaming?

sorry for long ramble on first post, but just curious, let me know what you think, if you can be bothered.

cheers.

As Kearnsy said, great question,oh and welcome

Hi Guys, I am also new to the posting game, but have watched Legians surf report since day1...all good and check at least once a day to see where its pumping or not.

Ok, my 2c worth...If the boards are sealed then then the volume will be fixed. Surely compression only pushes air from one area to another and doesn't affect a overall volume of the board. Obviously cracks etc that allow air to escape will then reduce the volume.

yep said...


Got me thinking, people get thicker boards for more boyance, but if you compressed the foam on a 2 1/2 thick board to 2 before glassing would it be as boyant?

Compressed foam, 2 1/2 to 2 or less would equal a sharper rail and less pressure dings and cracked glass in the future but with same boyance? Or am i dreaming?

To answer your question - no

The boyancy of an object(s) is in a nut shell equal to the weight of the water (or what ever) it displaces to.

So if you were to compress the foam something that displaces less water would be less boyant. And it would be less boyant per volume because if would sink faster to reach an equilibrium by displacing the same amount of water faster to support it's weight. One of the reason lighter eps boards feel more boyant because there lighter per volume.

In terms of pressure dings yes they would cause a board to be less boyant (as long as the area is submersed) but if there bad enough to cause that big a difference it's time to get a new board anyways

Hope that made sense half way through the bottle of red

Oh and welcome.

cRAZY Canuk said...

yep said...


Got me thinking, people get thicker boards for more boyance, but if you compressed the foam on a 2 1/2 thick board to 2 before glassing would it be as boyant?

Compressed foam, 2 1/2 to 2 or less would equal a sharper rail and less pressure dings and cracked glass in the future but with same boyance? Or am i dreaming?

To answer your question - no

The boyancy of an object(s) is in a nut shell equal to the weight of the water (or what ever) it displaces to.

So if you were to compress the foam something that displaces less water would be less boyant. And it would be less boyant per volume because if would sink faster to reach an equilibrium by displacing the same amount of water faster to support it's weight. One of the reason lighter eps boards feel more boyant because there lighter per volume.

In terms of pressure dings yes they would cause a board to be less boyant (as long as the area is submersed) but if there bad enough to cause that big a difference it's time to get a new board anyways

Hope that made sense half way through the bottle of red

Oh and welcome.

The displacement works on the weight of the water displaced not the volume, so a ligther board does actually displace more weight than a board of the same volume that weighs more, which is why lighter boards feel more buoyant - because they ARE more buoyant.
This is also why there is a difference between buoyancy in seawater and fresh water, seawater weighs more due to the salt.

au_rick said...

cRAZY Canuk said...

yep said...


Got me thinking, people get thicker boards for more boyance, but if you compressed the foam on a 2 1/2 thick board to 2 before glassing would it be as boyant?

Compressed foam, 2 1/2 to 2 or less would equal a sharper rail and less pressure dings and cracked glass in the future but with same boyance? Or am i dreaming?

To answer your question - no

The boyancy of an object(s) is in a nut shell equal to the weight of the water (or what ever) it displaces to.

So if you were to compress the foam something that displaces less water would be less boyant. And it would be less boyant per volume because if would sink faster to reach an equilibrium by displacing the same amount of water faster to support it's weight. One of the reason lighter eps boards feel more boyant because there lighter per volume.

In terms of pressure dings yes they would cause a board to be less boyant (as long as the area is submersed) but if there bad enough to cause that big a difference it's time to get a new board anyways

Hope that made sense half way through the bottle of red

Oh and welcome.

The displacement works on the weight of the water displaced not the volume, so a ligther board does actually displace more weight than a board of the same volume that weighs more, which is why lighter boards feel more buoyant - because they ARE more buoyant.
This is also why there is a difference between buoyancy in seawater and fresh water, seawater weighs more due to the salt.

Sorry word that was escaping me was Density.

The weight of the water displaced and the volume of the water displaced go hand in hand - worded it wrong but yeah.

If you take 2 things that are the same shape the one that weights less will displace less water...... Boyancy is finding the equilibrium between the weight of the water displaced and the weight of the object. A lighter board will displace less water because it needs to submerge less volume to displace the same amount of weight weight in water.

Sasha - if you change the shape on one side and not the other you change the volume, think of taking a cube and poking in one of the faces and there will be less volume in it. Same thing. In the case of compreasion dents the change in the surface is so small that it makes no real difference (unless it's real bad).

Fill the dents with water.
Tip the water into a plastic bottle, and weigh it.

That's how much buoyancy the board has lost. My guess is that it's less than 500 mls, so less than half a kilo of buoyancy. Your weight fluctuates more than that on a daily basis.

I'll let you know im the same weight and a hell of a lot fitter then when i got it made.

This probably has more to do with it -- muscle is three times as dense as fat, so while your body has stayed the same weight, it has lost buoyancy!

Well done