Proper Weighting while using Drysuit

[CAPTAIN SINBAD]

This is a question for seasoned drysuit users.

After my drysuit class I just purchased my first drysuit. Before I head out to try it on boats, I want to know what is the best procedure for determining the ideal weight when using a drysuit? For Wetsuits I knew that if I am diving a 3mm suit in salt water with AL 80s, I have to use X pounds on the belt. That number would never change.

For a Drysuit it could vary because your undergarments change season to season. I got my drysuit certification during peak winters and had to dive in the snow using a lot of thermal protection. These dives will be different and so would be the lead.

So what exactly is the best procedure for weighting yourself before a dive? I am thinking I could load up the lead on my belt using a wild guess. Then jump in the water from a dive boat, hang on to the ladder and have the DM pass weight to me until I feel I can sink with just releasing my breath.

Second way of doing it could be ... weight myself in a sweet water pond with exactly the same undergarment that I plan on using in the boat. Then add 15% more weight during my real dive to compensate for salt water.

Makes sense? or no.

 

[Jim Lapenta]

The second method could work. The first is just plain foolish. Why not do a proper weight check? I did my drysuit weighting the same as a wetsuit. Put on just the suit and burp it. Then got in the water with fins, mask, and snorkel (see it can be useful sometimes) then added weight until I could begin to sink slowly. Then added the BC and redid the check. Next when I went to a BPW I had a baseline. Took 6lbs off the belt to account for the plate and came out pretty good. I write all this stuff down so that I know how much weight with what undies, tank, and BC. For saltwater I'd add about 6lbs and start there.

 

[w ripley]

I've got a question: Does the weight belt work counter to air movement in the drysuit? I've been diving dry a long time, but always with a backplate and no weight belt, so thought I'd ask.

 

[elan]

No the weight belt does not prevent the air movement

 

[Bubbletrubble]

So what exactly is the best procedure for weighting yourself before a dive? I am thinking I could load up the lead on my belt using a wild guess. Then jump in the water from a dive boat, hang on to the ladder and have the DM pass weight to me until I feel I can sink with just releasing my breath.

Since you'll have a full tank while conducting the weight check, this method will guarantee that you'll be too light once you use up some of the gas in your tank. Don't forget to add an additional amount of weight to compensate for the remaining gas in your tank.

Second way of doing it could be ... weight myself in a sweet water pond with exactly the same undergarment that I plan on using in the boat. Then add 15% more weight during my real dive to compensate for salt water.

FWIW, I wouldn't recommend diving from a boat on one's first unsupervised drysuit dives. Too much can go wrong. A benign shore dive site is the way to go.

I'm not sure where you are getting the "15%" weighting figure. Add 2.5% of your total weight (diver + diver's gear) to compensate for the greater density of salt water vs. fresh water. For most people, that's approx. 6-7 lbs.

 

[rostyvyg]

Since you'll have a full tank while conducting the weight check, this method will guarantee that you'll be too light once you use up some of the gas in your tank. Don't forget to add an additional amount of weight to compensate for the remaining gas in your tank..

Why don't you do a shore dive? Get the initial weight check in shallow water, add 6 lb to compensate for air you would use during the dive, then at the end with 500 - 600 psi air left in your tank do weight re-check - you might discover that you need 1 - 2 lb more, or 1-2 lb less then you had in the beginning of the dive.

 

[bygolly]

If you have access to a pool set up a weight belt with a good assortment of weights starting with 5's and 6's finishing with 3's and 2's. Put about 40lbs on the belt. Lay the belt on the bottom of the pool and attach a floating line to the end with the heaviest weights. Get in the pool beside your floating scuba rig with your suit and undies on. Burp it well and while breathing on your rig start pulling up on the line until you sink below the surface. The amount you pull up off the bottom will be the weight you require to sink you and your suit. It is interesting to watch while doing this test how much the weight changes between empty and full lungs. Now weigh your submerged rig (with empty tank) using a fish scale. Hopefully it does sink with an empty tank (it might not with an Alu). The weight of the rig submerged is the weight you can deduct from the weight you observed on the belt. If your rig floats add weight to it until it sinks. In this case add this weight to what you found in the first step. For salt do as Bubbltrubble said...use your total weight (diver and rig) and multiply by 2.5%. This will be what you need to add for the sea.

 

[Bubbletrubble]

@CAPTAIN SINBAD: I wrote this up and posted it in another thread. You might find it helpful.
Apologies if your drysuit class covered all of this...

How to get weighting right for a new drysuit diver:

1. Conduct a proper weight check in the drysuit in the same kind of water you'll be diving in.

Elements of a drysuit weight check include:

• Wearing all of your scuba gear (including the same tank you will be diving with)
• With enough gas inside the drysuit to offset squeeze
• In horizontal trim (to prevent unintentional escape of gas inside the drysuit)
• At a shallow depth (safety stop depth or shallower; I prefer just below the surface)
• With a "medium" breath
• With no gas in the wing
• Compensating for any remaining gas in the tank
• Determine the minimum amount of lead weight needed to be neutrally buoyant.

2. Figure out weight distribution that promotes static horizontal trim for you.
This will be a work-in-progress as you figure out how much body/arm/leg positioning affects trim.

• Start off with all of the lead weight (ballast) attached to the diver in the form of a weight belt or weight harness. This will probably result in head-up/feet-down trim.
• Start shifting the weight in small increments towards your head (to trim weight pockets or weight pockets positioned on tank cambands) until it's easy to stay horizontal.

If you change your undergarments (or happen to own another set), it's best to simply do another weight/trim check. Repeat all of the above.

Understand that, due to the buoyancy swing that can be managed with one's lungs (10 lbs.?) and the ability to distribute a fair amount of gas inside the suit, there's a significant "slop factor" built into this weight determination. Get it close and that should be good enough.

 

[TSandM]

To address one of your questions, yes, your weighting will change with any change of undergarments. Any time you change what's in your suit, you have to do another weight check.

My favorite way to do a weight check is to bleed the tank down at the end of a dive, while I am swimming upslope. I keep a comfortable amount of gas in the suit, and figure out how much weight I have to have to hold a 10 foot stop like that. The problem with doing weight checks at the surface is that your legs and torso are hanging down below you and are really squeezed. If you figure the minimum weight you need when the suit is like that, you commit yourself to getting the suit THAT empty at the end of the dive, and that can be hard to do.

If you don't have access to a salt water shore dive prior to your trip, I'd definitely get in a pool or lake and figure out your weighting there, and use the 2.5% correction. (Remember, that's 2.5% of the total weight of you and your gear!) I would also like to echo, though, the warning about doing any kind of ambitious dive when you don't have much experience with the suit. It's VERY easy to get into an uncontrolled ascent in a dry suit. The last class we taught did 7 dives in their dry suits before doing the last day off a boat, and I had to experience being dragged to the surface by a student out of control on that 8th dive. It's not fun.

 

[CAPTAIN SINBAD]

Thanks so much for all the info everyone. This is indeed very informative.

Is it really uncommon for people to do weight checks from/during a boat dive? Not everyone has access to a shore dive and (as BubbleTrouble points out) you should do a weight check in the same water in which you are diving, wearing the same gear you are diving. The only way to ensure that for a lot of people would be to do weight checks from the dive boat prior to the main dive. I believe they do that in Galapagos liveaboards by taking the boat to a calm secluded spot before heading for their main dive but, I could be mistaken.