DPV and buoyancy change with depth

[Akimbo]

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.

Temperature and water density will also change buoyancy. Just ask any submarine sailor.

 

[ginti]

Temperature and water density will also change buoyancy. Just ask any submarine sailor.

But these factors are not likely to change with depth, are they?

 

[Akimbo]

But these factors are not likely to change with depth, are they?

Definitely. Have you ever swam through a thermocline or dove near the mouth of a river that flowed into the ocean? Changes in salinity is the most noticeable by divers but you also see biological "clouds" that can change density. Temperature will change density and displacement due to thermal expansion or contraction of the DPV or submarine.

You have to be observant to notice it on something small like a DPV but it is a very big deal on a submarine.

 

[ginti]

Definitely. Have you ever swam through a thermocline or dove near the mouth of a river that flowed into the ocean? Changes in salinity is the most noticeable by divers but you also see biological "clouds" that can change density. Temperature will change density and displacement due to thermal expansion of the DPV or submarine.

You have to be observant to notice it on something small like a DPV but it is a very big deal on a submarine.

I didn't think about these factors when I first answered you, and honestly they are great examples!

I experienced changes in salinity only in caves accessible from the sea, but in a way, they are underwater rivers. But the change was not related to depth, indeed it was linked to the penetration distance. I have also found the "biological clouds" here (I never remember the name of these things!).

The thermocline is quite common in lakes, especially in summer, and in this case, it absolutely depends on depth.

 

[Jack Hammer]

Water temps, salinity, hardness, etc all make a slight difference in bouyancy. While my XK1 is perfectly neutral in Florida springs (it's kinda freaky), in my local water (fresh) it is just a tad bit negative. We can see temps above 70f/21c on the surface and down to 39f/4c at the bottom. That changes the bouyancy very very slightly. You have to be very close to neutral to begin with to even notice it.

 

[Akimbo]

The thermocline is quite common in lakes, especially in summer, and in this case, it absolutely depends on depth.

Thermoclines are very common at diver depths along the entire California coast. I have even felt thermal stratification while swimming along at the same depth in places like Carmel Bay due to deep sea upwelling funneled along abyssal canyons.

Divers don't experience it very often but river water changes density quite a bit after heavy rains. You can clearly see the mudline in the ocean. I have read that the Gulf Stream along the US Atlantic coast can also has significant salinity stratas.

Too deep for recreational divers but interesting: Submarines commonly hide in and below the biomass in the deep scattering layer.