Bouyancy: 7mm vs 3mm

[RiverRat]

I've got a question that I think is along the same lines as the discussion in this thread. So here goes. I'm still diving wet, fairly new diver. I started diving tropical after my certs and was pretty confident that I got my weighting and buoyancy control figured out. In G. Cayman, using my 9# BP/W, AL80 and 3mm shortie I was diving 3# on my belt and using lungs to control my buoyancy throughout the water column. My diving became SO much easier. A real pleasure. I then start diving local in RI in my 7mm, 9# BP/W and steel tank. I was amazed at how buoyant this 7mm is in saltwater, even in fresh. On one dive I was several pounds underweighted and even after I kicked down to around 10 feet the suit compression started to become evident. I really didn't notice the 7mm compression issues during OW and AOW dives as I was most likely overweighted at this time anyway and not that deep. Even being underweighted or properly weighted I'm amazed at the amount of air I need to add to my BC to offset the significant compression. Nothing like diving the 3mm shortie. I understand the benefits of drysuit diving to keep warm, but will the buoyancy swing be minimal compared to a 7mm? I assume the non-compressable suits like the DUI TLS series are the way to go. I'm guessing that the extra weight required couldn't be that much more than my 7mm?

 

[String]

The suit compression isnt as much of an issue (although still exists with non compressed neoprene). The air inside a drysuit compresses as you descend just like a BC.

Eventually you feel tight squeeze which is painful, to counter this as the air in the suit compresses you add air to the suit to balance things out. The only problem with this is as you ascend that air expands and you have to dump it.

Think of a drysuit as another BC in respect to air managment.

The extra weight is probably the same or slightly less than a 7mm vest +7mm full body suit. Buoyancy swing is still an issue in drysuits though - its just handled differently.