Proper Weight in Dry Suit vs Wet Suit

[Litefoot]

So I'm diving (ha ha!) into the dry suit world and have a first question; probably the first of many. So as I ponder weighting requirements, I'll be deleting the equivalent flotation of a 7mm wetsuit and adding a trilam dry suit and undergarments (base layer and Thinsulate 150 uni-suit). My concern is being able to maintain depth at the end of a dive at the safety stop. If I start with a single full HP100, do I go through the same process as a wet suit or do I need to account for buoyancy of a partially-filled dry suit at 5m (1.5 atm). Or is there negligible squeeze at the safety stop and the dry suit will have most of the air purged?

Will I be roughly the same buoyancy between the two or will I expect to be more buoyant with the dry option?

Maybe I should ask another way. SHOULD I ASK FOR A WEIGHT BELT edit: (OR A SS BP) FOR CHRISTMAS?

 

[rhwestfall]

Weight harness, and/or a heavy backplate....

And steel tanks!

You will have squeeze at any depth. Air takes away squeeze and allows insulation to have air space to maintain warmth.

 

[inquis]

I run my suit vent in the same place throughout the dive. This allows me to achieve the same degree of loft & suit buoyancy regardless of depth or orientation. Basically, when stable at a given depth, I roll slightly to vent. If anything comes out, I had too much and this fixes it. If I just descended, I'll lightly press the inflator while rolled until a few bubbles trickle out and then I stop adding. I use the wing for any remaining buoyancy needs.

I carry enough lead so that I'm neutral with empty wing at reserve pressure -- whether I'm holding at 20 ft or 5 ft doesn't matter. I would guess with those layers and the vent all the way open that you'd use the same amount of lead that you use with your 7mm. Start there, at least.

Close the vent a few clicks if you like a little more loft (less squeeze), but don't overdo it. The problem with running too much air in the suit is that a slight change in orientation may dump and reduce buoyancy, messing up your prior actions to be neutral. Additionally, the vent on a suit is MUCH slower than a wing, so ascents can more easily get out of control. Lastly, there's more places for that gas to migrate and often expand in the process. There's a reason people end up headed feet-first toward the surface in their drysuit class. Keeping the majority of the buoyancy gas corralled in the wing tends to keep your trim more stable (since it can't really go very far).

A drysuit class SHOULD teach that there are 2 approaches: 1) enough suit air for a comfortable squeeze & wing for the remaining buoyancy and 2) suit for all the buoyancy needs and wing when on the surface. (See previous as to why I think #2 sucks.) At first glance, #2 sounds easier (one inflator, one vent), but in practice I find #1 easier, especially on ascent -- the suit venting is transparently controlled with your body angle, leaving only the single wing vent to manually press.

 

[inquis]

SHOULD I ASK FOR A WEIGHT BELT edit: (OR A SS BP) FOR CHRISTMAS?

Yes, and yes. You'll use different undergarments, and will need to add lead somewhere. Putting it all on the rig (integrated weight pockets) may not work well trim-wise. It's also nice to hand up the weight belt to the boat crew before climbing the ladder without all that weight when you're using the really thick layers.

 

[VikingDives]

Good question, but the answer is, it depends. The amount and quality of material you'll use under your drysuit will determine the weight you'll need.

I keep track of every bit of exposure protection I wear under a drysuit, and I have a pretty good idea of what weight that will require.

Given where you're diving, I'd suggest that you'll likely need about 2 more pounds in a drysuit (assuming you're properly weighted) than you'll need in a 7mm, but you aren't going to know until you know how much stuff you need to wear under your suit to stay warm.

Dive length also plays a factor. I wear the same exposure protection under my suit for a 30 minute dive at home that I'll wear for a 2 hour+ dive in Mexico.

If I'm doing 2 hours at home, I'm bulking up quite a bit to stay warm.

 

[rx7diver]

A lot of drysuit divers (myself included) will add a bit more gas to the suit during safety or mandatory deco stops (for a bit more warmth during these periods of relative inactivity). You might keep this in mind when you're dialing in your weight requirements.

rx7diver

 

[crofrog]

Make sure your drysuit valve is all the way open get in trim inflate the suit while dumping the wing to maintain neutral bouyancy until some gas comes out of your dry suit exhaust valve.

That is a good point to understand how much you can loft the suit and how much buoyancy it can contribute. Once you have that point ascend to 20ft venting the suit on the way up with out trying to get crazy and pump the air out of it.

That’s going to give you what the suit will feel like when ascending from a deeper dive. Adjust your weighting so that with the suit having been comfortably vented your wing is close to empty.

 

[Celt]

So I'm diving (ha ha!) into the dry suit world and have a first question; probably the first of many. So as I ponder weighting requirements, I'll be deleting the equivalent flotation of a 7mm wetsuit and adding a trilam dry suit and undergarments (base layer and Thinsulate 150 uni-suit). My concern is being able to maintain depth at the end of a dive at the safety stop. If I start with a single full HP100, do I go through the same process as a wet suit or do I need to account for buoyancy of a partially-filled dry suit at 5m (1.5 atm). Or is there negligible squeeze at the safety stop and the dry suit will have most of the air purged?

Will I be roughly the same buoyancy between the two or will I expect to be more buoyant with the dry option?

Maybe I should ask another way. SHOULD I ASK FOR A WEIGHT BELT edit: (OR A SS BP) FOR CHRISTMAS?

If you like your 7mm wetsuit and wish to dive dry, check out O Three, MF5. 5mm neoprene drysuit. Warm with an ordinary track suit or similar. Very little change in weighting and buoyancy. Just ask for the suit for Christmas (£1325)

 

[Litefoot]

If you like your 7mm wetsuit and wish to dive dry, check out O Three, MF5. 5mm neoprene drysuit. Warm with an ordinary track suit or similar. Very little change in weighting and buoyancy. Just ask for the suit for Christmas (£1325)

That looks like a very nice suit at a good price. I ordered a Seaskin trilam suit already, but if the neoprene version has been available in front zip, I might have opted for that; for the very reasons you pointed out so well.

 

[Celt]

That looks like a very nice suit at a good price. I ordered a Seaskin trilam suit already, but if the neoprene version has been available in front zip, I might have opted for that; for the very reasons you pointed out so well.

All the best, another marvellous adventure on the way.