Proper Weighting

fisherkid · Apr 8, 2009

I had an experience this last dive trip that brings up my question.

I did a buoyancy check recently at a local park. At fourteen pounds I was able to slowly sink when I emptied my lungs with an empty bc. When I went out on the dive boat I was using the same setup but I couldn't get down. The guide added two pounds to me but that still wasn't enough. he added another two pounds and I was able to get down.

I was slightly negative throught the dive and I forgot to do a buoyancy check at the end of that dive.

The variables are that when I was doing the original weight check at the park the salinity may have been slightly lower due to the fact that it is near a freshwater canal. The other variable was a thin hooded vest. The DM on the boat said it shouldnt really matter though. I took his word on that.

My question to you is "what's up with my weighting?"

PS I'm 6' 170lbs I wear a three mil wetsuit and sometimes a 1.5-2mm hooded vest.

muddiver · Apr 8, 2009

The answer is exactly what your question is. There is no scientific formula to find your diving weight. It is a trial and error process that will have to be done with each exposure suit setup you dive and will varry, like you said, with the salinity and temperature of the water you are diving.

A rule of thumb is multiply your body weight by 0.10 and add four pounds. Usually that will give you a good starting point that will be a little heavy for a 5 mil to 7 mil full weight suit.

I have a log of all my different exposure suits (3/2 wet, 5 mil wet, dry, etc.) and the weight that I found to be the optimum for each.

You will also have to add or subtract for different gear you might take/or not take on a dive. A dive light can add 1 lb to 2 lb. Some camera housings are 2 lb or more buoyant.

Teamcasa · Apr 8, 2009

Sadly there is no perfect formula as each person's native bouyancy differs.
Do the the end of dive bouyancy check with <500PSI in the tank. It is the only way to be sure of your proper ballast requirements.

RonFrank · Apr 8, 2009

Weighting will change any time you change exposure protection. It may also change when you change BC's.

One problem I see is that it sounds like you did your weighting with full tanks. You can do so, but you have to then compensate for the weight change in the tank throughout the dive.

There is nothing wrong with diving a bit heavy, and in fact that is much better than diving light. It sounds like your weighting is close. You need to do a weight check at the end of the dive, or in a pool with a tank with 500psi in it. You should do your weighting both with, and without your hooded vest, it will make a difference. I'd pick either fresh, or salt, not brackish.

After you dive for a while you get comfortable with what you need to add/subtract for different add on items like a hood. generally not much for a hood, but I add a couple lbs for my 5mm full face cold water hood. Actually, I often forget to do that!

don Francisco · Apr 8, 2009

The "scientific" answer to your question is the weight that works right is the right weight. Generally you'll want something close to the minimum to keep you neutral at 15' with 500psi in the tank and an empty BC. With experience using different equipment in different waters you'll be able to fine tune and predict your exact ballast needs.

Based on your post I'd guess that the "park" weight was probably close to ideal, but off the boat you needed to offset salinity with added ballast equal to 2.5% of your total dry weight, or .025 x 240 = 6#s, if going from totally fresh to seawater, (less if from brackish to seawater) plus possibly a bit extra because subconcious tension made you retain some air in your lungs, requiring additional ballast. With time, you'll be able to fully relax at the start of the dive, and shed those few extra pounds.

fisherkid · Apr 8, 2009

Thanks for the replies so far. The weighting check was done with 500 PSI.

Is there a specific number to increase by from fresh to salt. I have a pool and it's alot easier to do it there than a boat. Actually how does one go about doing a weight check from a boat?

Adam

I see that the post above has a formula for fresh to salt.

Nemrod · Apr 8, 2009

fisherkid:
I had an experience this last dive trip that brings up my question.

I did a buoyancy check recently at a local park. At fourteen pounds I was able to slowly sink when I emptied my lungs with an empty bc. When I went out on the dive boat I was using the same setup but I couldn't get down. The guide added two pounds to me but that still wasn't enough. he added another two pounds and I was able to get down.

I was slightly negative throught the dive and I forgot to do a buoyancy check at the end of that dive.

The variables are that when I was doing the original weight check at the park the salinity may have been slightly lower due to the fact that it is near a freshwater canal. The other variable was a thin hooded vest. The DM on the boat said it shouldnt really matter though. I took his word on that.

My question to you is "what's up with my weighting?"

PS I'm 6' 170lbs I wear a three mil wetsuit and sometimes a 1.5-2mm hooded vest.

I am not using a BC in this pic, no octo, no nothing, just a military harness. I have 16 pounds shot on. The suit is a 5mm Rubatex G231 which compresses very little. Yes, I swim down, then I swim around, then I swim back up. By the end of the dive I am a bit positive but not enough to prevent a safety stop. I use my lungs as a BC. If I carry my camera I take off two pounds.

Here a friend glides by, also in military harness, no BC, no octo, depths were 100 to 60 feet.

Sharks don't have a BC, no swim bladder either, they are the perfect minimalist:

Once you learn to dive without a BC then your weighting problems tend to disappear.

Pics by N.

N

Steve50 · Apr 8, 2009

Nemrod:
Once you learn to dive without a BC then your weighting problems tend to disappear.

Pics by N.

N

Just where do you put your cell phone, keys, chapstik.....

LeadTurn_SD · Apr 8, 2009

Great pictures Nemrod, as always.

Best wishes

LeadTurn_SD · Apr 8, 2009

fisherkid:
Thanks for the replies so far. The weighting check was done with 500 PSI.

Is there a specific number to increase by from fresh to salt. I have a pool and it's alot easier to do it there than a boat. Actually how does one go about doing a weight check from a boat?

Adam

I see that the post above has a formula for fresh to salt.

Using your pool and then doing the fresh - to - salt water conversion will get you pretty close. The advantage your pool has is that you can test with a near empty tank at 10 feet or so. Shoot for the minimum weight you need to achieve neutral bouyancy with a near empty tank.

From a boat you can have a buddy or crew member pass you weights as you float on the surface until you find correct weighting. If the weather is calm and there is no huge rush to get the dive going this works, but often boat crews are in a hurry and the weather may not be cooperative.

Best wishes.

Proper Weighting

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