Drysuit weight

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scottg541

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Here's a question that has been asked a million times, but i'd like some opinion for a specific situation.

I currently dive a 7mm wet suit with about 28 pounds

Everything else remaining the same, i am switching to a drysuit.

It is a shell (trilam) suit and i will be wearing T100 polarwear underneath.

Any idea on expected lead change?

Thanks in advance,
Scott

ps. I will try it in the water, but want to pour some lead first, so i'd appreciate some opinion to get a rough idea.

Thanks,
Scott
 
scottg541:
Here's a question that has been asked a million times, but i'd like some opinion for a specific situation.

I currently dive a 7mm wet suit with about 28 pounds

Everything else remaining the same, i am switching to a drysuit.

It is a shell (trilam) suit and i will be wearing T100 polarwear underneath.

Any idea on expected lead change?

Thanks in advance,
Scott

ps. I will try it in the water, but want to pour some lead first, so i'd appreciate some opinion to get a rough idea.

Thanks,
Scott

Beware- Junk Science coming! Please, I'm begging those with extensive knowledge of physics to restrain themselves.... :wink:

Scott, I often mix and match drysuit undergarments to water temps, so I came up with a way to make a rough estimate of their buoyancy to get an initial lead requirement.

Of course, now I have a list of the combinations and weight required, so it's not necessary to estimate unless I make radical changes.

I simply estimate the volume of water the undergarments will displace.

Before anyone jumps to conclusions, it should be noted that it is more than prudent to perform a final adjustment of weight, in the water. :11:

This method may simply save you a couple trips back to the shore when making that final weight adjustment.

Method.

I place the undergarments in a 5-gallon pail, compress them moderately and estimate how many gallons of water they will displace when worn.

Using 8 lbs per gallon usually gets me within about 10% of the lead actually needed when determined at final adjustment.

Example.

My winter undergarments for winter, when compressed moderately, overfill that 5-gallon pail a bit.

Throw in some buoyancy for hoods and gloves.

Make a rough estimate. Test it in controlled conditions and adjust.

With my single tank and pony bottle setup, I use about 50 pounds of lead in saltwater.

Like I said, it's a rough estimate, but it can save some time when you're determining your final weighting for your new gear.

This is also handy if you eventually add a little more insulation later.

Ball up the additional insulation in your hands, estimate it's volume and add weight accordingly.

Otherwise, the short answer to your specific question is I'd have to see the specific undergarment to guess.

Having only seen a description of that undergarment, and assuming a medium or large size, leads me to believe it might not require much more weight than your 7mm.

Does it look like it will compress down to about 3 gallons of displacement? :)

Dave C
 
Dave C
- that is simple and it appears sensible.

I just tested my first drysuit out yesterday. I estimated weight by listening to a couple people's own "rules of thumb" - then confused at the difference, I just averaged together the result from each of these "rules"

Not surprising that I ended up about 2 lb light - for initial diving.

What surprised me was that by my third dive, I had dropped down the two and another two. So maybe the "average of all rules-of-thumb" worked well.

I just finished cleaning my gear when I read this thread. Got me a bucket and I estimated the volume of my undersuit garment. Looks like this rule of thumb probably would underestimate in my case by about 5 lbs.

But hey, this does take into account the thickness of the garment and the diver's size. I've been an engineer for over 20 years - what is wrong with "fudge factors" and empirical curve fitting, anyway? Seems like a good approach that just needs some refining.

How many drysuit divers can measure their undersuit garments and compare to the weight they dive? If this thread collected a hundred (or two hundred) examples, we could really get after this problem...

How about drysuit divers post the following:
-Mildly compressed volume of their undersuits
-corresponding weight used in salt water and fresh (steel or Al tank?)
-generalized diver skill level and number of dives logged
-number of dry dives logged
-approximate difference in weight used when first diving dry and used at last dive (salt and fresh)​

I'm just a newbie drysuit diver - my stats won't help much...

Dr Dirt

Undergarment Vol: 3.5 gallons
Dive weight with steel 95 cuft - 28 lbs saltwater
Used very thin gloves and a 7mm/5mm hood, no collar
Diver skill beginning/intermediate.
Logged dives = 74
Never used the drysuit in fresh.
 
drdirt:
I just finished cleaning my gear when I read this thread. Got me a bucket and I estimated the volume of my undersuit garment. Looks like this rule of thumb probably would underestimate in my case by about 5 lbs.

I usually estimate or measure the buoyancy of the hood and gloves and add that amount that to the estimate of the undergarments' buoyancy.

Did your gloves and hood account for part of the 5 lbs underestimated?

But hey, this does take into account the thickness of the garment and the diver's size. I've been an engineer for over 20 years - what is wrong with "fudge factors" and empirical curve fitting, anyway? Seems like a good approach that just needs some refining.

I agree on all counts, but refining the process doesn't seem worthwhile mostly because there are too many subjective factors when simulating the compression the undergarment will undergo at depth.

How many drysuit divers can measure their undersuit garments and compare to the weight they dive? If this thread collected a hundred (or two hundred) examples, we could really get after this problem...

Good question. Still, it's a very minor and infrequently encountered issue, that is the issue of figuring weighting for new undergarments, so this method has limited use anyway.

After all, the point is to save a diver a little trouble, perhaps allowing that first dive with the new undergarments to continue without having to make much of an adjustment to weighting.





How about drysuit divers post the following:
-Mildly compressed volume of their undersuits
-corresponding weight used in salt water and fresh (steel or Al tank?)
-generalized diver skill level and number of dives logged
-number of dry dives logged
-approximate difference in weight used when first diving dry and used at last dive (salt and fresh)






I'd find that interesting, but that's because I have way too time to kill this winter! :wink:

I'm just a newbie drysuit diver - my stats won't help much...

Why not? You're able to determine your minimum weighting needed with an empty tank. That's useful info.

Dr Dirt

Undergarment Vol: 3.5 gallons
Dive weight with steel 95 cuft - 28 lbs saltwater
Used very thin gloves and a 7mm/5mm hood, no collar
Diver skill beginning/intermediate.
Logged dives = 74
Never used the drysuit in fresh.


Is the 28 lbs the calculated rough estimate, which turned out to be about 5 lbs too light for you? Or is it what your minimum weighting turned out to be?

I think it would be interesting to compare the calculated rough estimate to the actual minimum weighting needed to be neutral with the empty tank.

That might tell us the real value of this rough estimate method.

By the way, my "ideal" weighting is about 5 pounds above the minimum needed for neutral buoyancy with an empty tank.

Unlike some, I like to have a bit more air in the suit because I've found it to be warmer.

Dave C
 
For the standard under garments provided by Bare (not sure of the weight) with AL80 doubles and a 6 pound SS backplate diving the 50# Oxycheq wing and a Bare NexGen Bilam, reef gloves, 5mm hood and 5mm boots I use 8 pounds but may have to increase that when I get down to 500-1000 pounds of pressure. I am 5' 10" and 220 pounds. This is for fresh water.
 
dave4868:
I usually estimate or measure the buoyancy of the hood and gloves and add that amount that to the estimate of the undergarments' buoyancy.

Did your gloves and hood account for part of the 5 lbs underestimated?

Probably get less than a pound. (When I washed the hood, it stayed submerged in fresh water with a 1 lb weight on it).

I think the five lbs came more from the subjective things - and maybe because the volume premise might be flawed.

Could a new trilaminate suit require more weight because it is stiffer - and folds don't lay as flat as an old one?



dave4868:
[/INDENT]Is the 28 lbs the calculated rough estimate, which turned out to be about 5 lbs too light for you? Or is it what your minimum weighting turned out to be?

28 lbs worked well for me on my third dive. I did two safety stops for conservatism and for neutral buoyancy practice - I managed to hover at 35 and 20 feet well. I didn't manage to stay at 15 well (pretty much empty BCD and drysuit) - oh, and my steel 95 was at about 1000psi at the end.


dave4868:
I think it would be interesting to compare the calculated rough estimate to the actual minimum weighting needed to be neutral with the empty tank.

That might tell us the real value of this rough estimate method.

The prediction was 8-1/3 lb/gal x 3 gal = 25 lb. (neglecting the weight of the undergarment).

I found 28 worked well - but I struggled on the first dive where 30 lb seemed too light.


dave4868:
Unlike some, I like to have a bit more air in the suit because I've found it to be warmer.

Dave C

Good point, I'll keep that in mind for colder dives.

I like as little air as possible for stable hovering during safety stops.
 
drdirt, I may be misunderstanding what you're saying your ideal weighting should be.

Were you saying it's 28 lbs?

Or was that the weight that seemed about 5 lbs light?

Were you saying your ideal weight should be about 33 lbs?

drdirt:
Could a new trilaminate suit require more weight because it is stiffer - and folds don't lay as flat as an old one?

You're probably right, because the folds trap a little more air, perhaps. Not much, I'd guess.

drdirt:
28 lbs worked well for me on my third dive. I did two safety stops for conservatism and for neutral buoyancy practice - I managed to hover at 35 and 20 feet well. I didn't manage to stay at 15 well (pretty much empty BCD and drysuit) - oh, and my steel 95 was at about 1000psi at the end.

Sounds like you were saying that the 28 lbs "worked well" only for the early part of the dive before your tank became lighter and your depth shallower.

Not being able to correct positive buoyancy during the dive, especially when trying to do a safety stop, is not desirable, as you appear to state ("didn't work well").

From what you said, 28 lbs seemed a few pounds light, as your recent post indicated, since your tank wasn't close to empty and, at 15', you apparently still couldn't vent enough air to keep from being positive.

Just so I can understand how close the bucket weight estimate came to your ideal weight, let me lay out a couple things.

You originally mentioned in post #3:

drdirt:
I just finished cleaning my gear when I read this thread. Got me a bucket and I estimated the volume of my undersuit garment. Looks like this rule of thumb probably would underestimate in my case by about 5 lbs.

and

drdirt:
Undergarment Vol: 3.5 gallons
Dive weight with steel 95 cuft - 28 lbs saltwater

The way I read it,

3.5 x 8 = 28 lbs estimated weight needed to counteract the buoyancy of the undergarments.

And that weight left you a bit light with 1000 psi left in your 95 cf tank.

By the way, what's the empty buoyancy of that tank?

If you were saying 28 lbs seemed about 5 lbs light, that would make sense to me.

I apologize if I seem to be a little slow in understanding what you said.

Tweaking my weighting real close to the minimum just isn't worth the occasional problems that can result, especially at the end of the dive, such as being colder with less air in the suit, struggling to stay neutral in surge or very shallow depths, not being able to maintain a safety stop depth, etc.

I'm happy to have the slight disadvantage of the more rapid buoyancy changes that result from having a little extra air in the suit. Not to mention the hassle of carrying extra weight. (The walk to the water is getting harder every year!)

drdirt:
The prediction was 8-1/3 lb/gal x 3 gal = 25 lb. (neglecting the weight of the undergarment).

I found 28 worked well - but I struggled on the first dive where 30 lb seemed too light.

Probably just had some unvented air. Happens to me often at the beginning of the first dive. Seems the undergarments get settled or less lofty after that.

drdirt:
I like as little air as possible for stable hovering during safety stops.

That's a benefit, for sure, to reduce the degree of buoyancy change.

Personally, even at 10' or less, I rarely have difficulty maintaining neutral buoyancy with my extra 5 pounds and the extra air (5/8 gallon).

Then again, I always have a flag with me and that makes it easier to keep a stable position in the water column.

But that's probably considered cheating! :D

Dave C
 
scottg541:
Any idea on expected lead change?

For me and my Viking Sport I use less lead. 3 lbs less in fact. With my Viking Extreme which is a lighter suit I use more lead, 5 lbs more. That's contrasted to my 7mm wetsuit.

The total weights are no weight belt with the Viking Sport and 8 lbs on a belt with the Viking Extreme.

My BP/W and it's weight plate are a total of 13 lbs which means I use 13 lbs to get down with the Viking Sport and 21 lbs to get down with the Extreme.

So the answer is...

It varies depend on suit, even the same brand. PS, the weights are similar to what I use on a DUI Shell.
 
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