Calculated weight for new drysuit seems odd, second opinion needed

[BlueTrin]

Thank you very much guys. Unfortunately I have never done any weight checks so far. My instructor never asked me to and never taught me. I never thought about it. Recently I got in touch with some technical things and wanted to go into that direction. That´s how I found this balanced rig calculator and read about how important it is to be properly equipped with suitable weights.

So normally you’d use your previous dives or a calculator to get a good estimate.

Then you’d ask your buddy to carry a few weights he can give you and you’d carry a few weights you can give.

At some point, when it is safe to do so, you’d either try to hold a stop or start a descent and make sure you can hold a stop while breathing normally.

You want to find the minimal amount of lead so you can descend and hold a stop

If you do a weight check with more gas than 50bar then you need to remove the weight of the gas itself as you’d be heavier. If you dive a drysuit, don’t do a weight check with a totally empty drysuit, because you’d not want to do stops with no air in the suit as it’d very cold: use what you’d use for a normal stop.

Then you probably want to add a tiny bit more lead more than your ‘perfect’ weight so you don’t end up at the surface accidentally.

If you do your weight check in fresh water, you need to know your delta between fresh and sea water.

I think this website explains better than I do:

The most accurate weight check - International Training - SDI | TDI | ERDI | PFI

Want to get your weight right? You need to read this one. Learn all of the ways you can conduct a weight check and how different factors affect the amount of weight you’ll need. Proper weighting can make or break your buoyancy so this isn’t an area where you should just wing it.

www.tdisdi.com

 

[SlugLife]

(Coming from a Math/Physics background)

TLDR: Doing a weight check is many times easier and more reliable than any calculator.

An online calculator can at-best give you a very rough estimate. The problem is you need to either have (a) measured positive/negative bouyancy in water, or (b) a precise volume ... which is most easily measured by putting the thing in water, and measuring the amount of water displaced. In short, you're going to just have to get in the water, one way or another.

Nerd time: (You could technically do (b) by having a full container of water, an empty one, and a way for water to pass between them, submerging the item, having the excess water run off into the other container, and measure the amount of water in the formerly-empty container ... but that's not worth the effort especially for large items like a drysuit)

You can submerge individual items, on a scale, and measure the positive or negative buoyancy (a pain for a dry-suit). That easiest to do with negatively-bouyant items, since you can lower them on a line, off of a dock in a few feet of water, with the line attached to the scale. For positively bouyant, you can add lead-weights and subtract the difference, for example an empty aluminum tank, plus 5lbs of lead, scale reads 3.5lbs, which means 1.5lbs positively buoyant.

If you didn't have access to water (ex: going on a vacation dive in salt water, but no ocean locally), I'd probably suggest starting out with more weight than you think you need, but have them in pockets. Hop in the water, check buoyancy, ditch excess weights onto the boat/shore 2lbs at a time, and when you're good go dive.

 

[Gandalf-the-Diver]

I have found that the following calculator is pretty darn accurate, for drysuit calculations.

Estimated Diving Weight Calculator | DiveBuddy.com

This scuba diving calculator determines the estimated diving weight needed for proper buoyancy.

www.divebuddy.com

 

[grf88]

The biggest factor in your first calculations was that you used the actual weight of your tanks and not their weight in water. Look up the buoyancy numbers for your actual tanks and use that. It will get you closer but there is no substitute for actually getting in the water and doing a check.