DPV and buoyancy change with depth

[Texasguy]

Would I be correct to assume that DPVs don't change buoyancy with depth because they don't change in size (don't compress)?

So, if trimmed at some shallow depth, it would remain trimmed at any depth?

 

[rduquesnoy]

I was taught that it depends on the DPV.
From my theory notes: Some DPV's may have slight changes in buoyancy at different depths due to O-ring compression.

The DPV's I have used so far (Divertug, Suex) never had this issue.

 

[Wibble]

Correct. It doesn’t change shape thus doesn’t change buoyancy characteristics with depth. Unless it floods!

 

[ginti]

I was taught that it depends on the DPV.
From my theory notes: Some DPV's may have slight changes in buoyancy at different depths due to O-ring compression.

The DPV's I have used so far (Divertug, Suex) never had this issue.

Note: I have never used a DPV

Why would O-ring compression affect buoyancy? The volume change due to compression should be minimal...

 

[rduquesnoy]

Note: I have never used a DPV

Why would O-ring compression affect buoyancy? The volume change due to compression should be minimal...

I agree that the compression will be minimal. It was just mentioned in the GUE DPV 1 course notes as something to take into account .

 

[ginti]

I agree that the compression will be minimal. It was just mentioned in the GUE DPV 1 course notes as something to take into account .

I checked it too, the course mentions it, but I still cannot understand it. How big can DPVs' o-rings be?

 

[grantctobin]

The older Gavin hulls compressed and as such, would be more positive than is ideal when near the surface. Most newer scooters do not have this problem, but the double magnus does have some hull compression at bigger depths.

 

[ToneNQ]

The thing to be wary of is punching along behind the DPV for 10mins, slowly getting deeper. If you're having a good time you're not adding air to the wing. When you reach the wreck and slow down, suddenly you're hard on the inflation button to stay off the sand.

The two brands I have used don't change buoyancy, they're non-compressible sealed compartments, they displace the same water within their rated pressure range.

 

[Jack Hammer]

The course is talking of general things that can happen. Not everyone buys, rents, or borrows the latest high end scooter. There are quite a few older units in use and on the market.

With older scooters a shift toward negative bouyancy was more common as the air inside the plastic bodies compressed allowing the hull to flex inwards as well as the o-rings compressing allowing the nose to push closer to the tail. It added up. Some scooters were very negative to begin with and neoprene sleeves or other methods were used to offset that.

Bouyancy change also happens on some scooters with metal bodies. My XK1 has been below 200'/60m with no change in bouyancy. My Sierra gets slightly more negative as it gets deeper. The change still happens even with some modern scooters. Design and materials make a big difference.

 

[ginti]

The course is talking of general things that can happen. Not everyone buys, rents, or borrows the latest high end scooter. There are quite a few older units in use and on the market.

With older scooters a shift toward negative bouyancy was more common as the air inside the plastic bodies compressed allowing the hull to flex inwards as well as the o-rings compressing allowing the nose to push closer to the tail. It added up. Some scooters were very negative to begin with and neoprene sleeves or other methods were used to offset that.

Bouyancy change also happens on some scooters with metal bodies. My XK1 has been below 200'/60m with no change in bouyancy. My Sierra gets slightly more negative as it gets deeper. The change still happens even with some modern scooters. Design and materials make a big difference.

Thanks, very helpful!