Buoyancy of drysuit vs wetsuit

[bluebanded goby]

For most of my diving in Southern California I use a 7mm wetsuit, and with my single E7-100 steel cylinder and 6-lb backplate need 8 pounds on my belt.

However, I also have a DUI TLS350 drysuit, and have been thinking of getting it out. When I've used it, I've usually dived it with a 300g fleece jumpsuit and polypro shirt and pants. It's been quite a long time since I've used it, but my logs indicate that I typically needed ~19 pounds (13 on belt 6 on tank straps). These were all around the same time period, so a weight gain or loss by me is not a factor.

I'm just wondering why the drysuit setup is so much more buoyant than the wetsuit. Is trilam fundamentally more buoyant? Or is this caused by the bit of air I'd typically add to make the drysuit comfortable?

And most of all: Do most divers find a difference like this when changing between wetsuits and drysuits of the types I'm using? If so, how do most people deal with it?

 

[oldschoolto]

You have all that air you need to sink... Unlike the 7mm wetsuit that fills with water and will lose buoyancy as you go deeper.

Jim...

 

[rhwestfall]

is it easier to pull a sponge underwater (that would be your wet suit), or a sealed zip-lock bag of air (your dry suit)?

 

[bluebanded goby]

Okay, thanks. So, is my variation in weighting requirements typical of what other divers find using gear like this (i.e. about a 10- or 11-pound swing between wetsuit and drysuit)? Do most people just grin and bear it?

 

[elgoog]

For most of my diving in Southern California I use a 7mm wetsuit, and with my single E7-100 steel cylinder and 6-lb backplate need 8 pounds on my belt.
However, I also have a DUI TLS350 drysuit, and have been thinking of getting it out. When I've used it, I've usually dived it with a 300g fleece jumpsuit and polypro shirt and pants. It's been quite a long time since I've used it, but my logs indicate that I typically needed ~19 pounds (13 on belt 6 on tank straps). These were all around the same time period, so a weight gain or loss by me is not a factor.

Without knowing how buoyant your wetsuit was (age, quality, condition) a 5lb difference sounds about right to me.

Is trilam fundamentally more buoyant? Or is this caused by the bit of air I'd typically add to make the drysuit comfortable?

The trilam itself doesn't add a ton of buoyancy, it's the insulation that will do it. If you're only adding enough gas to offset squeeze, the amount of lead needed for this is not appreciable compared to what's needed for the insulation.

And most of all: Do most divers find a difference like this when changing between wetsuits and drysuits of the types I'm using?

I certainly did. I went from a super buoyant 8/7mm semi-dry to TLS350 with 400g Thinsulate and needed to add weight.
There's too many variables, just with the various combinations of insulation, that could impact your weighting and I'm sure you'll get answers all across the board here but, IMO, this is common.

If so, how do most people deal with it?

I keep a very detailed log with the equipment used, how much weight, how it felt, etc. You can approximate the amount of weight you need based on the various positive and negative buoyancies of your gear to start with and make adjustments as needed.

 

[rhwestfall]

for single tank & dry, I have bolt on weight plates that add 10# to my rig. I used to use a weight harness, but in reality, I hate cranking up the weight on my belt or at my hips....

 

[tbone1004]

the trilam suit itself offers essentially 0 inherent buoyancy vs. your wetsuit. The difference is going to be how much air you put in the suit. That will be determined by how thick your undergarments are as they will trap air, and how much of a suit squeeze you use when you dive. You can take that tls350 and dive it with the same amount of lead as your 7mm, potentially less if you have really light undergarments on, or you can require over 50lbs of extra lead if you dive like the Michelin man.

All up to how much are you either have to or choose to put in the suit

 

[boulderjohn]

I was used to diving with a dry suit in water that was in the 60° range, and then I went to Puget Sound and assumed I would need a lot warmer undergarments. I brought my really warm stuff that I had bought but never used--unnecessarily, as it turned out. I did not think there was enough lead in Seattle to sink me.

 

[Marie13]

I was used to diving with a dry suit in water that was in the 60° range, and then I went to Puget Sound and assumed I would need a lot warmer undergarments. I brought my really warm stuff that I had bought but never used--unnecessarily, as it turned out. I did not think there was enough lead in Seattle to sink me.

I experienced that this weekend on my first cold(er) water dives - 48F (Mermet Springs quarry in southern Illinois). I had my new Fourth Element Arctic on top of Fourth Element Xerotherm base. I ended up needing 22 lbs of lead on top of BP and 5 lb STA insert. I was shocked I needed that much. Learning experience...