How to estimate the amount of weight with new gear

[fatgeorge]

Hi there!

I'm a new diver (got certified last Oct, got about 50 dives so far). I don't have my own gear so I rent. Figured out that the amount of weight I need varies depending on things I have hard time noticing.

For example, in the same water I needed 1kg with a 15L steel tank, this was quite comfortable. But with AL80 I put 2kg and could barely stay down, had to borrow one from a divemaster and still had to move to keep myself on a safety stop. 4kg seem to be optimal.

So far the only conclusion I've got was that if the weight is comfortable at the beginning of the dive, it's too little and I need one more. But wondering whether there are guidelines besides what PADI provides in peak buoyancy?

Thanks in advance.

 

[therookie]

Hi @fatgeorge. Welcome to ScubaBoard!

Yeah this takes a bit of experience, trial and error, and if you are so inclined there is an excellent Excel spreadsheet buoyancy calculator here on ScubaBoard that can help you figure this out in advance.

Reading your post I think what you are mostly experiencing is the difference in the "swing" between those two tank types when they are getting close to empty. The 15L steel is still negatively buoyant (pushing you down) but the nearly empty AL80 is postively buoyant (pushing you up).

Here's the link to the calculator:

Optimal Buoyancy Calculator

 

[fatgeorge]

Thank you! Didn't even know there's a ready to use one.

Is there a way to quickly estimate whether you've got enough/too much weight at the beginning of the dive looking as how quickly you're sinking motionless?

 

[therookie]

I remember there was a big discussion (like 10 pages) on this topic on ScubaBoard a few months back...

Overweighted at the start, underweighted at the end

Tons of excellent suggestions from people WAY more experienced than me on that topic. Maybe you've already read through that though...

 

[divingdayz]

I remember there was a big discussion (like 10 pages) on this topic on ScubaBoard a few months back...

Overweighted at the start, underweighted at the end

Tons of excellent suggestions from people WAY more experienced than me on that topic. Maybe you've already read through that though...

Yes, I remember that thread on weighting. There is lots of good information in that.

 

[fatgeorge]

Reading those now. The calculator is too overwhelming now, gonna read its manual too.

 

[therookie]

This is the quote from it that triggered my memory from your question about a way to check at the start of your dive:

The most reliable to weight yourself is Dr Bob's weight titration. With arms and legs crossed (to prevent sculling and finning), a full tank, bladder completely empty, and breathing normally, keep adding weight at 1 pound per inch above water, until your head is just awash. Exhaling should start your descent. This allows for all the weight you need at your safety stop.

So if you are weighted right, when you hold a normal breath your head should be just awash, and as you exhale normally you should (slowly) sink. If you're sinking quickly, you're probably overweighted. Not sinking at all, likely underweighted

 

[therookie]

Reading those now. The calculator is too overwhelming now, gonna read its manual too.

yeah, with that much power comes a fair bit of a learning curve. I leave most of it blank except for changes in exposure (wetsuit) and it has been 100% spot on for me. Everyone is different in terms of their "natural" buoyancy though.

 

[fatgeorge]

It's also the different rental gear, even the wetsuit buoyancy was different between two centers. Too many variables change, need more practice I guess.

 

[therookie]

Yeah there can be a difference based on how old the wetsuit is - the older it is, the more compressed it is and the less buoyancy it provides. Also shorty vs full, etc etc.

The spreadsheet does have options to handle all that stuff; just a matter of the learning curve...

Which is why most around here will tell you "go buy your own gear so you don't have to fuss with this"...