Overweighted at beginning of dive but underweighted at end in shallows

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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...

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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.

I use 14 lbs with a 5 mm full suit and a 5/3 mm hooded vest with an AL80 and a back inflate BC. 185 lb is about my weight. There is a lot of individual variation, find your best weight and use it. I dive about a pound heavy, better than the alternative of being too light. Make sure you empty your BC at the start of the dive and again at the end. I have a little air in my BC at the end of the dive and do a very slow ascent from the safety/last deco stop, a minute or more for the last 15 feet.

 

[lowwall]

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.

This was common advice in the days before the BCD was invented. This was also before most people were diving over tropical reefs. And before most people were aware of the cumulative damage that scuba divers could do by grabbing bits of the bottom and moving them somewhere else.

But every dive is different and it could be useful in a pinch.

 

[TMHeimer]

I assume you were shown how to do a proper weight check during the cert. course. Have you done one with your new equipment?

 

[crofrog]

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

Echoing what others have said. Just carry a bit more weight to be neutral at the end of the dive. Just to share some of the “extremes” it’s not uncommon for FL cave divers to be 30-50lb lighter at the end of the dive than the beginning because of how much gas they’re bringing

 

[johndiver999]

Echoing what others have said. Just carry a bit more weight to be neutral at the end of the dive. Just to share some of the “extremes” it’s not uncommon for FL cave divers to be 30-50lb heavier at the end of the dive than the beginning because of how much gas they’re bringing

Man they must fart a lot when getting out. Hard to believe they can make that much gas, but they are often "big Guys" huh?

 

[happy-diver]

This issue is that for the end of the dive, with a bit of waves

Yeah try a block of extra weight at a time and your dreams will come true even at a few feet in choppy seas

Which again leads me to the ocean

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.

This was common advice in the days before the BCD was invented. This was also before most people were diving over tropical reefs. And before most people were aware of the cumulative damage that scuba divers could do by grabbing bits of the bottom and moving them somewhere else.

But every dive is different and it could be useful in a pinch.

and when the ocean decides to throw enough tonnes of rocks and other ocean goodies out onto the grass itself

Check out the huge seas out there over on the reef and the fisherman dude

There was actually twice as much stuff, thrown on the grass but had no film

Enough tonnes for the bulldozer people, to spend two days pushing it back

for the people who don't go near the ocean unless there is nothing to see

Yeah I was sitting in the lounge wet weather gear with an oar in my hands

happy-divering

 

[Belzelbub]

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

Probably a touch light on the weight. Add a couple pounds and see where it gets you. If you have a buddy that can help you, make it 18lbs on your next dive, with 2 lbs easily removable. During your safety stop release all the air from your BC, and see what happens. If you are sinking, try handing 2lbs off to your buddy and see if that does the trick.

Just another thing to add, your instructor should have clearly explained the buoyancy shift as the cylinder empties. If they didn't do this, they did you a bit of a disservice.

Also, another point. You'll need to repeat the weight check at the end of the dive in the future. Your wetsuit will become a bit less buoyant as it ages. Also, if you switch to a different tank, you'll need to adjust weight. Freshwater vs. saltwater will also call for different ballast. Not to mention the fact that newer divers tend to need a bit more weight than experienced divers. Mostly comes from newer divers holding a bit more gas in their lungs.

 

[divezonescuba]

Once you figure out how much weight you actually need, don't let anyone talk you into using less. Certified divers are responsible for themselves. I have seen a number of underweighted divers drift to the surface unable to maintain their safety stops. Myself included when I was open water certified and listened to the insistent dive guide.

A common conversation in destination locations is our salt density is different than other places, you don't need that much weight or you're the same size that that other person over there and that person uses less weight. Or the reason why you can't sink is because your wetsuit is dry.

Another common one is your wetsuit compresses under water. Wetsuits do not compress as much as many people think. There is a vast difference between dense neoprene and air in a drysuit. A good condition reputable scuba wetsuit compresses minimally. Conventional neoprene compresses less than stretchy neoprene. An old wetsuit may not compress at all because it is already flat. My 5mm wetsuit does not compress to 0.5 mm with 10 atmospheres of pressure at 300 feet.

A lot of new or inexperienced instructors do not understand proper weighting. They learned that if you can float at eye level with no air in your BCD and a normal breath of air that you are neutrally buouyant. If you do that with a near empty tank, you are actually around 5 pounds positive. Do it with a full tank and you are around 10 pounds positive at the end of the dive with a near empty tank. That is because your head weighs 10-11 pounds. Maybe 12 pounds in the case of some people on Scubaboard. If you float at eye level with a near empty tank, half of your head is above the water so you are about 5 pounds buoyant. So, if you use only enough weight to float at eye level with a near empty tank, with a full tank, you may be able to descend. But, you are likely to become positive some time during the dive and may have difficulty making your safety stop.

As previously discussed, the only sure way to tell is at the end of a dive with a near depleted tank, can you still maintain your safety stop.

A better way is at the end of the dive, is to keep taking off weight with a near depleted tank on the surface until you cannot descend. Then add weight 2 pounds at a time until you can descend slowly. That will give you a small margin of error on the heavy side. It is better to be slightly overweighted than slightly underweighted. If you are slightly underweighted as you have experienced, you may not be able to do your safety stop.

 

[tursiops]

A better way is to keep taking off weight with a near depleted tank on the surface until you cannot descend. Then add weight 2 pounds at a time until you can descend slowly.

Alternatively, be neutral at the surface with a full AL80 tank, i.e. at the beginning of a dive,and then add 5-6 pounds to compensate for gas that might be used.

 

[NauticalNick]

Probably a touch light on the weight. Add a couple pounds and see where it gets you. If you have a buddy that can help you, make it 18lbs on your next dive, with 2 lbs easily removable. During your safety stop release all the air from your BC, and see what happens. If you are sinking, try handing 2lbs off to your buddy and see if that does the trick.

Just another thing to add, your instructor should have clearly explained the buoyancy shift as the cylinder empties. If they didn't do this, they did you a bit of a disservice.

Also, another point. You'll need to repeat the weight check at the end of the dive in the future. Your wetsuit will become a bit less buoyant as it ages. Also, if you switch to a different tank, you'll need to adjust weight. Freshwater vs. saltwater will also call for different ballast. Not to mention the fact that newer divers tend to need a bit more weight than experienced divers. Mostly comes from newer divers holding a bit more gas in their lungs.

Yes, I certainly learned that a while ago and remember that. This is just the first time diving where I have spent so much time in the shallows at the end of the dive (20+ minutes) where it became a bit of an annoyance.

All great points though to factor in.