Fresh Water / Drysuit => Salt Water / Wetsuit

[mwilding]

I am used to diving in the NE with my drysuit in 50 degree F fresh water. I wear a trilam drysuit with fleece and polypro undergarments. My weighting is: 2lb Aluminum BP, a 2 LB, 14 LBs ditchable weight - total 18LBs with a steel HP 120 tank.

Next week I am going to Key West where the water temp is 72-75 degrees F. I figure a full length 3mm will suffice for thermal protection, but don't have any dives logged with my BP/Wing in this config or in salt water yet...

I pulled out my AOW text and the Peak Performance Bouyancy chapter has a handy chart for estimating weighting. It says for a trilam drysuit with undergarments, I should have 10% of my body weight plus 3-5 LBs or 21-25LBs. I am perfectly weighted at 18LBs with a steel HP 120. For a 3mm wetsuit, 5% of my body weight (+6LBs for going to salt water) should suffice for a total of 15LBs. I will probably be diving with an AL80, so anyone want to guess what the proper weighting will be?

I have a SS plate and an AL plate. I was thinking about taking the SS plate which with the STA would give me 8 LBs non-ditchable on my back. A 3LB shot bag in each weight pocket would give me a total of 14 LBS a little under the "recommended" weight, but I have a BP and not a jacket BC...

 

[simbrooks]

I dive around 16# with a 3mm full suit down here with AL80, i am going to the SS BP in the next few weeks, i would imagine only needing around 8-10#ditchable then. Using the PPB i should be using 18# for salt, go figure, its only a rough number, if you have the time do a pool test with an AL80, BP/wings and 3mm and add 6#, work from there once you get down here.

 

[ArcticDiver]

You have several variables to consider. No matter what you do now it is a guess. So, if initial weighting is going to be a guess why not let an experienced guesser to it? Just tell the DM if boat diving, or your LDS guy if shore diving what you have been using. Then follow their recommendation for the first dive or two.

They see lots of folks like you and are used to making guesses. Most of the time they come within a couple pounds. Usually that couple pounds will be on the heavy side, which is good. You don't want any uncontolled ascent because you are under weighted.

After the first couple dives you can change to your heart's content.

 

[Genesis]

6lbs with an AL80 and a SS BP, assuming a 3 mil full wetsuit is what I need and if you're height-weight proportional) you'll probably be close.

If you use the AL plate, you'll need 8. If you can find an HP steel, you'll only need 2lbs or so.

That, by the way, is a very nice warm salt-water configuration for a single. If you carry a cannister light you can get rid of the belt entirely!

 

[Charlie99]

You can always go back to square one, and start with the buoyancy of your body and then work from there.

If you have a pool you can figure it out by noting how much air, if any, you have to exhale before you sink. Figure about 6# of buoyancy change for full lungs to empty lungs. (Of course, if you have weights available, you can use them to estimate your personal buoyancy better.)

Then just total that up with all your equipment your buoyancies to get everything to balance out.

You will need about 3 or 4# to compensate for the positive buoyancy of an empty AL80.
Your 3mm wetsuit will probably have 4 to 6# of positive buoyancy, depending upon your size.
Add about 6# more to compensate for the fresh to saltwater change.

Balanced against this is the negative buoyancy of your chosen backplate, plus lead to make up the difference.

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As others have noted, it's a lot better to start off a few pounds heavy, then you can drop a pound or two with each dive until you are dialed in.

 

[Diver0001]

I am used to diving in the NE with my drysuit in 50 degree F fresh water. I wear a trilam drysuit with fleece and polypro undergarments. My weighting is: 2lb Aluminum BP, a 2 LB, 14 LBs ditchable weight - total 18LBs with a steel HP 120 tank.

Next week I am going to Key West where the water temp is 72-75 degrees F. I figure a full length 3mm will suffice for thermal protection, but don't have any dives logged with my BP/Wing in this config or in salt water yet...

I pulled out my AOW text and the Peak Performance Bouyancy chapter has a handy chart for estimating weighting. It says for a trilam drysuit with undergarments, I should have 10% of my body weight plus 3-5 LBs or 21-25LBs. I am perfectly weighted at 18LBs with a steel HP 120. For a 3mm wetsuit, 5% of my body weight (+6LBs for going to salt water) should suffice for a total of 15LBs. I will probably be diving with an AL80, so anyone want to guess what the proper weighting will be?

I have a SS plate and an AL plate. I was thinking about taking the SS plate which with the STA would give me 8 LBs non-ditchable on my back. A 3LB shot bag in each weight pocket would give me a total of 14 LBS a little under the "recommended" weight, but I have a BP and not a jacket BC...

I think with a steel 120 and a 3mm wetsuit that I would sink easily without any weight at all in fresh water. In salt I'd need max 2-3 kg (what is that about 6 lbs). I figure the steel plate is all you'll need. Take an extra 2 kg with you for the buoyancy check just in case.

R..

 

[Don Burke]

There are too many loose numbers bouncing around here.

I would just take the rig I intend to dive to a pool, come up with a weighting for fresh water, and then add a pound for each forty pounds of overall weight. That will put you pretty close for salt water.

 

[ArcticDiver]

There are too many loose numbers bouncing around here.

It has been great entertainment, well not great, maybe just humourous, watching folks try to calculate their weighting when making a major change in their rigs. When you come right down to it all the calculations are just a mathematical way of making a guess.

Bet you adjust your weight a few pounds one way or the other no matter whether you make your guess with the math, make it with your gut, or just accept the DM's guess. Which one you use depends on how much fun you get from playing with loose numbers.

 

[Genesis]

I think with a steel 120 and a 3mm wetsuit that I would sink easily without any weight at all in fresh water. In salt I'd need max 2-3 kg (what is that about 6 lbs). I figure the steel plate is all you'll need. Take an extra 2 kg with you for the buoyancy check just in case.

R..

I doubt it w/o the plate. An empty HP120 is only about -1.5. That 3mil wetsuit is plenty buoyant at the surface.

With a SS plate you might be just about right in freshwater w/o a belt though.

 

[reubencahn]

I doubt it w/o the plate. An empty HP120 is only about -1.5. That 3mil wetsuit is plenty buoyant at the surface.

With a SS plate you might be just about right in freshwater w/o a belt though.

I don't know. I use an AL plate with an HP100. With a 3mil, I use no weight. With a 5mm, I use 2lb.