Overweighted at beginning of dive but underweighted at end in shallows

[NauticalNick]

Hi all,

Recently went to Curacao and I'm not sure if it's just a matter of figuring out my new gear or what but I figured someone here might have some insight. Many of the dives there seem to have to the later 1/3 of the dive in the shallows where we ran the tanks relatively low at the end of our hour given we were only a few meters from the surface. Using AL80's and I was using a 5mm wetsuit but I found at the beginning of the dive I would be overweighted and have to put a fair amount of air in my BCD to level out at ~20-25m. That was relatively fine as I prefer to be a bit overweighted for initial decent. This issue is that for the end of the dive, with a bit of waves, it was a real struggle to maintain that 4-6m of depth and not just float to the surface. I drained all the air in my BC from every valve and even tried rotating my body around to get any last bits of air but no matter what I did I would just start floating up to the surface on my inhale.

Not sure if this is just one of those thing where there's nothing you can do but wondered if anyone had come across this and if they had any solutions.

For reference I am ~185 lbs and was using 14lbs of lead

Thanks in advance.

NN

 

[tursiops]

You are ALWAYS overweighted at the beginning of the dive; you are 5-6 lbs heavy to allow for the use and loss of 5-6 pounds of air during the dive. Perhaps you were only 3 pounds heavy; but then you'd be 2-3 pounds buoyant at the end of the dive. 14 pounds with a 5mm wetsuit is not unusual.
Solution #1: add a couple MORE pounds at the beginning, and see if the end is better.
Solution #2: run your tank down to 3-500 psi at the end of the dive, while in shallow water, and see if you are light, neutral, or heavy. Adjust your weight on the next dive to be neutral AT THE END.

 

[Rob9876]

Simply put: if you struggle to hold a safety stop at the end of a dive, then you generally need more weight.

As you may recall, because of gas use you'll always be more buoyant at the end of the dive than at the beginning. Everyone is different, but especially with a 5mm wetsuit and AL80 tank, needing more weight doesn't sound crazy to me. While some people (especially on this forum) obsess about how much weight they use, there's really no prize for using less -- so just add a couple of pounds and see how that works.

 

[Sparksi]

Hi there,

I'm going to make some heavy assumptions and jump right to conclusions, but this is quite common and could easily be explained by a lack of experience. I don't know how many dives you've got, nor how you have done your weight checks during and after your courses.

For a novice diver your (and my) size in a 5mm suit 14lbs doesn't sound too much at all. Of course this depends A LOT on the gear you are carrying and pther factors, too.

The fact that you might have felt "a little light" at the end of the dive and got concerned if you'd be able to maintain neutral bouyancy is really all it takes for your breathing to go up just a tad bit - hence making it even more difficult. Then you try to force-exhale to get negative and get down a bit - only to make your breathing go up. Happens to all of us, especially in the beginning.

Unless there is an obvious reason not to, I would just add a pound or two. Just to get you more comfortable at the end portion of a dive and gain experience.

Again, heavy assumptions there, just my two cents.

 

[arew+4]

Hi all,

Recently went to Curacao and I'm not sure if it's just a matter of figuring out my new gear or what but I figured someone here might have some insight. Many of the dives there seem to have to the later 1/3 of the dive in the shallows where we ran the tanks relatively low at the end of our hour given we were only a few meters from the surface. Using AL80's and I was using a 5mm wetsuit but I found at the beginning of the dive I would be overweighted and have to put a fair amount of air in my BCD to level out at ~20-25m. That was relatively fine as I prefer to be a bit overweighted for initial decent. This issue is that for the end of the dive, with a bit of waves, it was a real struggle to maintain that 4-6m of depth and not just float to the surface. I drained all the air in my BC from every valve and even tried rotating my body around to get any last bits of air but no matter what I did I would just start floating up to the surface on my inhale.

Not sure if this is just one of those thing where there's nothing you can do but wondered if anyone had come across this and if they had any solutions.

For reference I am ~185 lbs and was using 14lbs of lead

Thanks in advance.

NN

Well the tanks going to get 5 lbs boyant as it nears empty, at 5-10 meters the 5 mil suit is probably 3lbs boyant or so. Which means you are effectively 6-8 lbs lighter at the end of the dive. 14 may be high but not OMG high If you are getting worked up about it you might be shallow breathing on full lungs.

I find i have to get vertical and dump my shoulder valve to get my BC empty.

 

[KenE]

You are correctly weighted when you can safely hold a safety stop with an empty tank (500psi). Everything else is proper use of a BC. The wetsuit compresses when you descend, so naturally you will need to add gas to BC to compensate. The wetsuit decompresses when you ascend to your safety stop. So, it is critical that you make all your weighting decisions based on buoyancy at the safety stop. As mentioned above, the air you breath out of the tank also adds to your buoyancy. This is why we recommend to have an empty (500psi) tank when evaluating weight during safety stop.

 

[xan]

This is relatively common: your wetsuit compresses at depth and loses buoyancy, and with a full cylinder, you're heaviest at the start. Your weights are meant to offset the buoyancy change for the end of the dive (with the Al 80 CF I'm guessing you used) and so you might be actually underweight if you can't hold the stop then. With time and somewhat more practice, you may be able to have less dramatic swings in buoyancy due to breathing, too. Try to stay in trim (rather than get vertical), as that provides more resistance in the water column.

Unfortunately there's not a great solution if you want to dive in a wetsuit; you could look into neutrally buoyant exposure—either Sharkskin / Lavacore etc., or a trilam drysuit—where you might be able to take off a significant chunk of lead as there aren't any such dramatic buoyancy swings. When available, steel cylinders will help you reduce additional weight by 2 - 4 lbs as well.

Anecdotally (since everyone's bioprene is different), I dove my Sharkskin in Curaçao a few months ago, with a carbon fiber BP/W and 4 lbs of additional lead. Was able to cruise at 2m depth with 50 bar without trouble. It used to be 14 lbs in Bonaire a few years ago (though, as a starting diver, had a host of other issues). I'm a big fan/proponent of neutrally-buoyant exposure for that reason

You mention some of the gear is new: a wetsuit will lose some of its buoyancy with use, so between that and you getting additional experience, you may be able to shave off some pounds in the future.

 

[NauticalNick]

Thanks very much for all of the comments as they are very helpful. I think you're probably right in that I need a few more lbs to be neutral for the safety stop and I was probably trying to micromanage my breathing/buoyancy out of frustration.

 

[GJC]

Info - Optimal Buoyancy Computer

The Optimal Buoyancy Computer A tool to help nail buoyancy and improve safety, before you splash 1) How much lead should I carry with my new wetsuit? 2) How big a wing should I buy? 3) Will my BCD support my lead, both at the surface and when my wetsuit is compressed at depth? 4) Will my BCD...

scubaboard.com

Using just a couple of the buoyancy calculators available online, I get results that show 16-20 lbs for a 185 lb male in a full 5 mil suit.

 

[johndiver999]

Thanks very much for all of the comments as they are very helpful. I think you're probably right in that I need a few more lbs to be neutral for the safety stop and I was probably trying to micromanage my breathing/buoyancy out of frustration.

When you screw up and fail to take enough lead on a dive, and you are playing around in the shallows... just pick up a decent sized rock and carry it. Far easier than struggling to stay down and failing to breathe properly.

Always bring the rock back to shore for the next dive... or add some lead to the belt - your choice.