Proper Weight in Dry Suit vs Wet Suit

[JoeTPhilly]

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?

You could get a weighted single tank adapter. That would add about 5 pounds to your aluminum backplate. You could also go with a SS backplate and a weighted STA which would put you at about 12 pounds.

 

[lattehiatus]

My personal experience - I like my O'Three MSF500 (recently replaced by the MF5, essentially the same suit), but had to add 12 pounds of weight compared to a 7mm wetsuit with 7mm hooded vest.

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]

You could get a weighted single tank adapter. That would add about 5 pounds to your aluminum backplate. You could also go with a SS backplate and a weighted STA which would put you at about 12 pounds.

So the STA would only require that I re-thread the cam bands, right? Hmmm…

 

[inquis]

Should you mention the SS plate to Santa, bear in mind there are two commonly available thicknesses: around 5 lb (3mm) or 10 lb (6 mm). Most people seem to go with the 5 lb (keeping options open for thinner layers, trim weight placement, air travel, or perhaps even doubles down the road).

 

[JoeTPhilly]

So the STA would only require that I re-thread the cam bands, right? Hmmm…

Yes. Below is a photo of a Halcyon weight and STA I recently sold. The weight weighs in just over 5 pounds and the STA weighs just under a pound. The lead is thinner at the ends so you can weave in the cam bands. With the cam bands/buckles and your aluminum plate you would be at about 7 to 8 pounds. With a SS plate around 12 to 13 pounds.

 

[JoeTPhilly]

A couple observations from this thread. First, relating to the linked thread Question - Wing Size Regret: 30 or 40 pound? and the weight amounts posted in this thread, maybe one should not be so absolute in stating only a 30 pound wing is ever needed. With the weight amounts posted in this thread near or above 30 pounds, maybe a 40 pound wing would be appropriate?

Two, maybe look into diving double HP100s for cold water diving.

 

[Litefoot]

A couple observations from this thread. First, relating to the linked thread Question - Wing Size Regret: 30 or 40 pound? and the weight amounts posted in this thread, maybe one should not be so absolute in stating only a 30 pound wing is ever needed. With the weight amounts posted in this thread near or above 30 pounds, maybe a 40 pound wing would be appropriate?

Two, maybe look into diving double HP100s for cold water diving.

I did read that thread and that question has crossed my mind. I guess I’ll experiment with the weighting and see where it leads.

 

[Boarderguy]

A couple observations from this thread. First, relating to the linked thread Question - Wing Size Regret: 30 or 40 pound? and the weight amounts posted in this thread, maybe one should not be so absolute in stating only a 30 pound wing is ever needed. With the weight amounts posted in this thread near or above 30 pounds, maybe a 40 pound wing would be appropriate?

Two, maybe look into diving double HP100s for cold water diving.

I did read that thread and that question has crossed my mind. I guess I’ll experiment with the weighting and see where it leads.

When diving with substantial weight, especially when dry, you should have your weight broken up between your rig and a weight belt or a harness. Nobody here is suggesting putting 30lbs of weight on the rig. I like to keep at least half on me and rest on my rig on the off chance I need to doff under water. If everything was on my rig I'd cork faster than a champagne bottle.

 

[Celt]

My personal experience - I like my O'Three MSF500 (recently replaced by the MF5, essentially the same suit), but had to add 12 pounds of weight compared to a 7mm wetsuit with 7mm hooded vest.

I’d say it depends on what you wear underneath and how much air you like in the suit.

 

[stretchthepenn]

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?

As @rx7diver posted, the question is somewhat moot because many divers will puff up their drysuits for the purpose of extra warmth while they're hovering for a deco stop or a basic safety stop. However, this practical answer doesn't fully address your question.

Before you start your dive, you'll purge your drysuit and eliminate bubbles that might cause your suit to burp on entry. Then, when you enter the water, the surface water pressure will force any residual air out via the arm/shoulder dump. You'll be pretty darn well vacuum-packed.

Thing is, you're going to be pumping air into the drysuit during the dive to loft your undergarments, so when you come back to shallow water, your undergarments will retain residual air. You might get squeezed a tad, but you're unlikely to achieve the same level of vacuum-sealed tightness that you felt on entry, and you'll have to deal with that tiny bit of buoyancy.

Thus, the strict answer to your question is yes, you will need to account for slightly positive buoyancy during a safety stop.