Questions about bouyancy with wetsuit

[Cheerpig1]

I am getting ready to do my first open water dive ever.....(yay me!!!)
In the pool we worked on bouyancy and weights. I understand that you should carry weights at approxamatly 10% of your actual weight. ( I weigh about 112) My first try I could not sink (descend) at all. Subsequent dives I was too heavy, but eventually with about 5 lbs in each side of my BCD I was fine. (10 lbs total)

Well, I am going to do my first OW dive in freshwater, but this time I will be wearing a 7mm wetsuit (I get cold really easily yes even here in AZ). I know I need to adjust my weights to compensate for this. I am thinking I should only add about 1 lb on each side? (am I at least close?) How much do I need to adjust my weight by, or is that something we will work on at the beginning of the dive? (How much of an adjustment is typical when going to salt water from freshwater as a side note)

I know the test is to be able to float at eye level when you are properly weighted, but in the pool when we discovered I did not have enough weight on me, the instructor had to remove his equipment, get out, and get more weights for me. (I just want to be better prepared). Any help is appreciated as I have learned so much and feel more comfortable after reading these posts knowing that other people have the same issues and concerns as I do!!!

 

[Web Monkey]

I am getting ready to do my first open water dive ever.....(yay me!!!)
In the pool we worked on bouyancy and weights. I understand that you should carry weights at approxamatly 10% of your actual weight.

That's just a guess and has no particular meaninig, except that that number works for some people.

I know the test is to be able to float at eye level when you are properly weighted, but in the pool when we discovered I did not have enough weight on me, the instructor had to remove his equipment, get out, and get more weights for me.

The above is the only way to get an accurate measurement, however it should be done with an almost empty tank.

Your instructor having to get out of the pool is not your problem. Students needing more weight shouldn't be a surprise to him, since it happens all the time. You need what you need, and that includes doing an actual buoyancy check to find out. He should have had extra weights where he could reach them.

Don't let anybody rush you or blow you off. Being properly weighted will make everything else much easier.

Terry

 

[nivla80]

You would probably do a weight check before descending, and honestly, i don't think one more pound on each side is sufficient, assuming you don't wear a weight suit in the pool. I'm 130, and when i don a 7 mill farmer john, i take down at least 16 lbs, with an aluminium tank. (probably becos i'm still pretty much a newbie)...

After getting my BP/W setup, i take down 10 lbs, with an SS backplate..

Hope this helps!

 

[fppf]

I'm a large guy, 6'1" and 220 lbs.
In the pool I wear 8 lbs for classes, in a 7mm 2 piece farmer john and an AL80 I wear 24-26 lbs depending on the dive.

 

[Racket]

I wear 8 lbs for a pool dive, and 24 lbs with a al80, 7mm Fj w/ 5mm hood , and gloves.

I am 5'10 175 10% BMI

 

[ronbeau]

I am getting ready to do my first open water dive ever.....(yay me!!!)
In the pool we worked on bouyancy and weights. I understand that you should carry weights at approxamatly 10% of your actual weight. ( I weigh about 112) My first try I could not sink (descend) at all. Subsequent dives I was too heavy, but eventually with about 5 lbs in each side of my BCD I was fine. (10 lbs total)

Well, I am going to do my first OW dive in freshwater, but this time I will be wearing a 7mm wetsuit (I get cold really easily yes even here in AZ). I know I need to adjust my weights to compensate for this. I am thinking I should only add about 1 lb on each side? (am I at least close?) How much do I need to adjust my weight by, or is that something we will work on at the beginning of the dive? (How much of an adjustment is typical when going to salt water from freshwater as a side note)

I know the test is to be able to float at eye level when you are properly weighted, but in the pool when we discovered I did not have enough weight on me, the instructor had to remove his equipment, get out, and get more weights for me. (I just want to be better prepared). Any help is appreciated as I have learned so much and feel more comfortable after reading these posts knowing that other people have the same issues and concerns as I do!!!

I know the test is to be able to float at eye level when you are properly weighted, but in the pool when we discovered I did not have enough weight on me, the instructor had to remove his equipment, get out, and get more weights for me. (I just want to be better prepared).

Another option if you don't have the availability of a tank with about 500 PSI in it is do the same test WebMonkey mentioned but with a full tank. Air weighs about 1 pound per 500 PSI. As a result if you do the test with a full tank you would add 1 pound every 500 PSI except for the last 500 PSI.

In other words, if you have a tank with 3000 PSI you would subtract 500 PSI (keep this as a safety margin) which leaves you with 2500 PSI. Divide the 2500 by 500 PSI per pound and you get 5 pounds.

As a result, you would add 5 pounds of weight to the amount you determined in your "flost at eye level" test. This 5 pounds of weight accounts for the weight of the 2500 PSI of air that you will use during your dive which weighs 5 pounds.

 

[Steve50]

To answer your side note - from fresh to salt water multiply your total weight (you + equipment, including weights) times 2.5%. This assumes the same suit is being used. Most people would be in the 4-8 lb more, range.

 

[spectrum]

Cheerpig1

It sounds like your instructor either isn't competent in determining weight or is lazy. Forget that 10% rule there are a dozen variables that go into the right answer. You should already be doing this in the pool and yes if the open water dive is the first time for that 7mm suit it must be done then though getting in for a pool session with that suit may be a lot easier depending on the OW site.

You are on the right track with the eye level thing but more completely it goes:
Remember to set your weight so that you bob at eye level at the end of your dive with an empty BC, an average breath, your feet still (crossed) and about 500 PSI in your cylinder. A deep breath should get your mask out of the water and a deep exhale should sink your mask. Do all of this while breathing from your regulator. The end of the dive is the defining moment for your weight requirement and you want just enough to let you stay down in the shallows with a light cylinder.

To do this at the onset of your first dive with a full cylinder you will then add 5 pounds to the weight determined to account for the air you will use. Repeat the check at the end of the dive with the cylinder near 500 PSI since once everything has soaked for an hour you will all of the stowaway air out of everything and you may be able to remove a few more pounds.

Why 5 pounds? Air weighs .08 pounds per cubic foot so the air in a common 80 cubic foot cylinder weighs .08 X 80 = 6.4 pounds. Since you will not be emptying the cylinder 5 pounds is a decent allowance. Most of this stuff is physics.

To allow for this procedure put what you estimate to be the essential weight on your belt or in ditchable pockets. then put the potentially extra weight in accessible pockets or hang clip-on weight to D rings. Get in the water for a few minutes to get everything reasonably wet and for your breathing to normalize. Now start handing off extra weights until you get the eye level thing happening. Then add the 5 pounds back so you won't cork when your cylinder gets less buoyant. Someone now needs to get the extra weight put away or leave it near an underwater landmark (or on a platform if that's the case) so you can retrieve it on the way out.

You mention being too heavy at some point in your pool work. Understand that having air in your BC is not a sin. In the pool with a full cylinder you should be heavy and will probably need some air in your BC even in a swimsuit. A seasoned diver carefully weighted can control this with lung volume but you're probably not not there yet. Once you add a 7mm suit to the equation it will compress as you descend and become less buoyant requiring you to compensate by adding air to your buoyancy compensator ( clever name huh?)

Don't fret this weighing stuff just work through it understanding the principles behind it all. Once you know the answer it's yours to keep. Even better news is that as that as you evolve as a diver you will need less weight as you relax and learn to better control your lung volume.

When you make it to the ocean it's a simple transition if none of the gear changes. Just add 1 pound for each 40 pounds of your total dry diver weight. So as a lass of 112 pounds with a 35 pound cylinder 12 pounds of gear and 18 pounds ( a guess) of weight which totals: 177 (hope I didn't scare you with that :11: ) pounds you need to add 4.4 pounds. Add 4 or 5 depending on how close to being over or under weighted you were in freshwater.

Why 1 pound for 40? Because the specific gravity of seawater is about 1.026. The denser water will require you to be denser (heavier per volume unit) to be neutral, that's what the lead is all about. Round it to 1.025 for real easy math and you see the .025 (2.5%) mentioned by steve50. Divide 1 by .025 and you get the 40 pound value I mentioned. It's the same calculation but to me it's easier to do multiples of 40 on the fly.

Congratulations on completing your pool work and good luck on your check-out dives, we expect a full report.

Pete

 

[fisherdvm]

I think one of the advantages of checking for buoyancy at the end of a dive rather than at the beginning is that you get all the air bubbles out of your suit that might still be trapped at the beginning of the dive.

If you were buck naked and your BC doesn't have a pocket that trapped air, then it doesn't matter if you did it at the beginning (assuming you know your tank capacity to calculate the weight of the air of a full vs empty tank) or the end.

 

[DandyDon]

Well, I am going to do my first OW dive in freshwater, but this time I will be wearing a 7mm wetsuit (I get cold really easily yes even here in AZ). I know I need to adjust my weights to compensate for this. I am thinking I should only add about 1 lb on each side? (am I at least close?) How much do I need to adjust my weight by, or is that something we will work on at the beginning of the dive?

Yeah, if you want to imitate a cork.

One way is to take the suit to the pool and see how much weight it takes to sink it alone, then add to what you need. Or just put on the suit, gear up, take a used tank with 500# left and do the real weight check. Probly close to 20# or so.

You are on the right track with the eye level thing but more completely it goes:
Remember to set your weight so that you bob at eye level at the end of your dive with an empty BC, an average breath, your feet still (crossed) and about 500 PSI in your cylinder. A deep breath should get your mask out of the water and a deep exhale should sink your mask. Do all of this while breathing from your regulator. The end of the dive is the defining moment for your weight requirement and you want just enough to let you stay down in the shallows with a light cylinder.

Good advise. I'd add 2# to that as I like to be able to get back down easily even at that point, but that's me.

For saltwater, I add 4#, but I'm twice as big as you. 2 or 3# maybe be enough. Even tho weights are often supplied by the Inst and the charters (not always) it is good for a diver to own and travel with 2 - 1# soft weights for final trimming.