Silly question perhaps....

[on_two_wheels]

I've got about 20 dives in my Whites Fusion drysuit and just recently did a proper weight check. I've just gone by feel more than anything. The weight check resulted in confirmation my weight was pretty close (water just at top of mask). My question is...is that really accurate for a drysuit? It's done that way with a wetsuit but a wetsuit loses buoyancy with depth. A drysuit gains buoyancy at depth since we add air. Something doesn't make sense to me.

 

[PfcAJ]

Drysuit buoyancy is more or less constant since you add gas to it to offset the squeeze and vent during the ascent.

IMO, the only real weight check is at 10ft with near empty tanks and an empty BC with enough gas in the DS to be comfortable.

 

[Bubbletrubble]

PfcAJ is correct. For a shell drysuit (which the Fusion is), drysuit buoyancy is more or less constant throughout the dive.

We all have our own ways of doing weight checks. I prefer to do the weight check at the surface with a comfortable amount of gas in the drysuit and an empty BCD bladder. On a medium breath, the water is at eye level. I do it this way so that if I ever lose/use all of my gas, I'm 100% certain I can be neutrally buoyant at shallow depths (shallower than even safety stop depth). I take note of the amount of remaining breathing gas...and compensate for it in my weight requirement calculations. I know the buoyancy swing of each of my tanks so it isn't necessary to breathe down the tank to near empty for the weight check.

For the most part, I get my weighting close and don't sweat it. Typically, I'm probably 1 or 2 lbs. heavy.

Hope this info helps...

 

[on_two_wheels]

Doesn't temps have some variable on this? There's temps at which just taking off the squeeze is enough but if it's really cold, I may add a little more to get the full loft of undergarment. As I said, this is more curiosity than anything else. I'm comfy with my current weighting and performance diving dry. Just like to know as much as I can about what the hell I'm doing.

 

[Bubbletrubble]

Doesn't temps have some variable on this? There's temps at which just taking off the squeeze is enough but if it's really cold, I may add a little more to get the full loft of undergarment. As I said, this is more curiosity than anything else. I'm comfy with my current weighting and performance diving dry. Just like to know as much as I can about what the hell I'm doing.

It sounds like you want us to advise you to weight yourself heavier when the water temperature is colder. I really don't think you want to approach things in that way. Wear the appropriate undergarment(s) for a given water temp and conduct your weight check with just enough gas inside the suit to keep your undergarment maximally lofted. More air than that inside your suit may complicate bubble management.

If your undergarment is maximally lofted and you're still cold for a given water temp., then you should probably wear a thicker or more thermally-efficient undergarment. Using argon (instead of air or any helium-containing mixes) for drysuit inflation may help, too.

 

[on_two_wheels]

I'm not looking for advise at all, actually. I'm just curious about the weight check at the surface and holding safety stops vs being comfortable at depth. As I just wrote in my previous response, I'm pretty happy with my weighting. Again...I simply want to have more understanding of WHY it works rather than "it just does." As for temps, all reports on my last dive suggested mid 60's. Pass a thermocline and it got down right COLD. Too late for a different undergarment. I am aware of the benefits of argon but haven't spent the money on it yet....someday.

 

[Bubbletrubble]

I'm just curious about the weight check at the surface and holding safety stops vs being comfortable at depth. As I just wrote in my previous response, I'm pretty happy with my weighting. Again...I simply want to have more understanding of WHY it works rather than "it just does."

Your drysuit is a buoyancy compensator device. If your shell drysuit + undergarment system has 25 lbs. of positive buoyancy at the surface with just enough gas inside to keep the synthetic fibers in your undergarment maximally lofted, it will have the same amount of positive buoyancy at 100 fsw with just enough gas inside to keep the synthetic fibers in your undergarment maximally lofted. Sure the inside of your drysuit will have more air molecules at greater depth (due to greater ambient pressure) but it will displace the same amount of seawater and thus exert the same amount of buoyant force.

Here's a simpler example. A wing from a BP/W setup is spec'd for a certain amount of buoyant lift. For example, my wing has 30 lbs. of lift. If I fill it up completely with air at the surface of the water, it will be 30 lbs. positively buoyant. If I deflate it completely, bring the same wing down to 100 fsw, and inflate it maximally with air, it will still be 30 lbs. positively buoyant. A drysuit is essentially just a watertight bag to which you can add/subtract gas.

As for temps, all reports on my last dive suggested mid 60's. Pass a thermocline and it got down right COLD. Too late for a different undergarment.

Most of my dive buddies here in San Diego have two different undergarments -- one for summer bottom temps (high 50s, low 60s), and one for winter bottom temps (high 40s, low 50s). We choose which undergarment to wear based on the time of year and dive location. If we go up to Monterey in the winter to dive, we'll take the heavy undergarment. If we're going to Catalina in the summertime, we'll usually take the light undergarment. When I ask divers about dive conditions and the water temp, I'm only really concerned about the water temp at depth (or whatever depth I'll be spending most of my dive). The reason I bought a drysuit was to stay below the thermocline. FWIW, on a trip to Catalina two weeks ago, I actually wore my heavy undergarment because of dive reports I'd been hearing.

On a side note, consider getting a pair of drygloves. Drygloves really make a difference in maintaining fine motor dexterity. I also have prominent wrist tendons, so I would get a fair amount of leaking in through my wrist seals when manipulating objects with my hands during a dive (checking SPG, operating camera, holding my pistol-grip light). The $100 I spent on the Viking Bayonet dryglove system was one of the best scuba purchases I've made.

 

[seahorsey]

sorry posted twice..

 

[seahorsey]

"Your drysuit is a buoyancy compensator device."
Bubbletrouble, this raises an interesting beginners' question:I'm still wet (till next weeks' course) but my buddy dives dry - is it safe to dive with a BC with 23 to 28 lb lift when you're wearing 30+ lb weights with your drysuit?! My buddy has a bag suit. Me, I'm looking at the Mares Ice, 'exclusive patented neoprene called High-Density." I don't think it's quite crushed, (CAN'T be, at the price) but neoprene anyway. Is there a difference in just how unsafe it is to dive with the warm water BC's with these suits? Or can I rely on the suit to take over where the BC gives out in its' lift capacity?

 

[TSandM]

I differ slightly with BubbleTrubble -- I DO weight myself slightly heavier in very cold water, to make sure I can carry enough gas in the suit to stay warm during the ascent. Weight checks are typically done while floating at the surface, where you are vertical, and the suit is largely empty; that's why I don't do them there, but rather in 4 or 5 feet of water, in a horizontal position, and with the amount of gas in the suit that I want to have there until the end of the dive.

seahorsey, it's good you are thinking about this. You want your wing to be able to compensate for the loss of lift if your dry suit floods. That means you either need a bladder big enough to do it, or you need some ditchable weight to where it can. Which means you really do need to know how positive your dry suit with undergarments is.