Question about weighting in a thick suit

[Bubbletrubble]

Simple answer. Do a proper weight check.

As Blue Sparkle explained, if you have a full tank during your weight check, simply add enough weight to compensate for that gas (approx. 5-6 lbs. for an AL80). This should get you weighted appropriately for end-of-dive conditions, i.e., empty tank, medium breath, no air in BCD, at a shallow depth.

If you are weighted properly, your initial descent should be comfortable, and you shouldn't have to fight to remain at depth during your safety stop.

diveprof pointed out that any instructor who knows you aren't used to a thick wetsuit will recognize that you need to do a weight check. This should be the case. If the instructor forgets, please remind him/her. It's important to be properly weighted for your class dives -- it's a safety issue.

 

[TexasKaren68]

It sounded like a lot to me too (though I'm only a beginner, so certainly no expert). I personally only use 15 lbs of weight, but my bodyweight is a little less than hers. However, she did say that she did a weight check in a 5mm wetsuit and needed 22 lbs -- if that's accurate, she's clearly going to need more than 22 lbs in a 7mm wetsuit with hood.

The 22 pounds was in salt water and the lake will be fresh water. I will be wearing an awful lot of wetsuit though.

 

[dumpsterDiver]

Is this true? I may be wrong (not an expert!), but wouldn't one just figure out their buoyancy/weighting for themselves with full tanks, and then add weight to compensate for the weight of the gas breathed by the end of the dive (which would be the same in any tank for a given volume)? I don't see why one would add more for a tank that went positive at the end of a dive vs. one that stayed negative, given that you first get your weight "right" and then add for weight of used gas (for the end of the dive).

Am I off base?

I'm thinking of my own (limited) experience in a 5mm suit and either an AL63 or an LP95. In both cases I figured out the right weight for me to dive in, and then added weight to compensate for lost gas (about 4# for the AL63 and 6# for the LP95). But my calculations didn't change due to the AL63 being positive when empty (+2.6#) vs. the LP95 staying negative (-1.6#)

You are correct, the other individual is not.

 

[dumpsterDiver]

The 22 pounds was in salt water and the lake will be fresh water. I will be wearing an awful lot of wetsuit though.

I would take about 2 lbs more for 7mm in freshwater versus 5mm in saltwater.. And I suspect youu will be overweighted a little.

 

[scubadiver888]

TexasKaren68, bring 30 pounds of weight. If you are using 22 pounds, 5mm, salt water then fresh water means less weight but 7mm means more weight. Start with 22 pounds and see if you sink. If not, add some more weight until you can just sink. Then add the weight of the air you will use during the dive. Air weights approximately 0.0807 pounds per cubic foot.

AL80 = 77.4 cu.ft. = 6.25 pounds
HP100 = 99.5 cu.ft. = 8.03 pounds
HP119 = 123.0 cu.ft. = 9.93 pounds

Important thing to note, an AL80 does not have 80 cu.ft., an HP119 doesn't have 119 cu.ft.

Some people will say you never breath a cylinder down to 0 PSI so if you leave 500 PSI in the tank, you will use 64.5 cu.ft in an AL80 or 5.21 pounds. So you could be safe adding 6 pounds. For an HP100, 8 pounds. For an HP119, 9 pounds. Personally, I assume there is a chance I'll breath the cylinder down to 0. In which case it is an emergency situation and I don't want to be positively buoyant at that moment.

 

[Quero]

The 22 pounds was in salt water and the lake will be fresh water. I will be wearing an awful lot of wetsuit though.

Any rule of thumb is just a starting point, and you will need to do a weight check anyway. But by using a rule of thumb you shouldn't be wildly off target with way too much or way too little, which makes the adjustments at the time of the weight check easier. The rule of thumb that I use, with the assumption that the tank you will be using is the same type and size as the one you have used in the past--

For each 1mm of neoprene beyond what you used when you knew what your correct weighting was with a different suit, add two pounds. So since you used 22 lbs with a 3mm full suit and you will be moving up 4mm, you add 8 pounds. For the switch from salt water to fresh water, you subtract weight. The amount will depend on how much water you displace (your body mass), but for most average-sized people that will be about 5 pounds less for fresh water than for salt water.

So if I were your instructor, I'd probably start you on 25 pounds for the weight check and adjust from there.

 

[Adam2010]

i dive with a 7mm and i need about 32lbs with a hood and gloves. i weight i little more then you that the best guess

 

[spectrum]

hi Karen,

We all know that it's a shot in the dark but I do have experience with a similar suit. When I was diving my Avid jacket BC I used 18 pounds in fresh water with a 80 CF HP cylinder. My suit & vest are XL.

If I were to dive an AL80 I'd need to add 2.5 + 4.4 , or about 7 pounds for a total of 25.

You will have a decent amount of upper body buoyancy with that suit so I'd start with 4-6 of those pounds up in any trim pockets you may have.

I'll let you interpolate from the men's XL size to see if your neoprene factor is significantly different. You are better off making the first dive 4 pounds heavy than 2 pounds light.

Pete

 

[TexasKaren68]

Thanks everyone. I'll discuss it with my instructor but will most definitely need to bring more weight than what I own. I'm trying to not have to rent any gear but the tank for local dives, and have purchased 20 pounds of lead so far (that stuff ain't cheap). I'll pick up another couple of 4 or 5 pound weights this week. I do have trim pockets on the back of my BD, and could reasonably fit my two 2 pound weights back there.

I wonder if I should try to cram all the weight into my BC, or put some of it on a weight belt. Pros? Cons?

 

[Blue Sparkle]

Depending on how much lift your BC has, you might want some of the weight on a belt so that your rig will float on the surface without you in it. That may not be an issue but it's something you can calculate ahead of time.