Please help me with a weight question

[Artimas]

First the question, then why I'm asking:

How much weight would be your starting point for this setup in seawater?

7mm john and jacket (new)
5mm gloves
5mm boots
full hood
Seaquest Zone BC
130 steel tank
19cf pony

I'm 180 lbs.

I decided to use 26# as a starting point for this setup.


I got in the pool and worked on the weight, and in fresh water I actually needed 32#
to get neutrally buoyant on the bottom (9 ft.). That would mean more (?36#) in seawater.

With an old 7mm, Al 80, and no pony, I used 22# with no problem.I know new suits are more buoyant than used, but this seems like an awful lot of weight to me.

Any thoughts? Is that a reasonable weight requirement in general terms?

Thanks!

 

[nereas]

I think you have the right idea, by starting in the pool.

Whatever the pool gives you, with a full tank, then add 12 lbs to this for the ocean.

Or you can use an almost-empty tank in the pool, then add 6 lbs to what you get this way, to adjust for the ocean.

Remember that air weights 0.08 lbs per cu ft. With 80 cu ft of air, you have 6.4 lbs in your tank. So you need to take that into account, because you want your ocean buoyancy to be neutral when your tank is down to 500 psi, almost empty.

As you breathe your tank down, it will get lighter (more buoyant).

New suits, hoods, gloves, and booties are definitely more buoyant when brand new.

 

[don Francisco]

Since sea water is 2.5% denser than fresh, it provides 2.5% more bouyancy for the same displacement.

If you know what you need in freshwater, add 2.5%, or 1# for every 40, of your TOTAL weight, including, you, your insulation, your BC, the weights, and the tanks.

Estimating your total weight as described at about 280#s, I'd add 7# to what worked in the pool. In your case the big variable is the new vs. old suit and that's really hard to estimate, though I doubt it's 12# more, so I'd repeat the test after soaking the suit through.

Also don't forget that air weighs .075#s/cuft so you'll need to provide another 8#s to compensate for the weight lost as you breath off 110cuft from your tank, if you were perfectly neutral with a full tank.

As a point of reference, I weigh 190# and when I dove the Hood Canal in very similar equipment to yours except with an AL80, the shop recommended 30#s, and I ended up using 24#s very comfortably.

Reading your post, I'd expect that you'd be REDUCING ballast form your 22# AL80 weight, since the steel tanks weigh more than AL tanks, so you have a dilemma as to whether to use your proven salt weight and compensating for the steel tank, or using your pool experiment and converting to a salt water weight. Wish I could be of better help, dF

 

[nereas]

Physics and oceanography might help with an initial guess, yes.

I have found that most people need to add either 4lbs, 5lbs, or 6 lbs for the ocean, compared with the pool, depending on how big they are (vis a vis, how much neoprene they are wearing).

Women 4 lbs, men 6 lbs, and teens 5 lbs or thereabouts. That's the fast answer, although not exact science.

 

[spectrum]

The information above is all heading in the right direction. The good news is that you got into the pool and got an objective baseline in controlled conditions. The one missing item is how much air you had when you settled on 32 pounds. I will assume that a 130CF cylinder in a pool remained essentially full.

The 1/40 dry diver weight is as accurate as anything and makes for easy mental math.
you=180, your full cylinder=53,your required weight guessed upward=40, wetsuit, BC, fins, mask, etc=25 for a total of 298 pounds for a salt water adder of 7.45 pounds, you can decide which way to round things.

Now if you did establish the 32 with a full or nearly full tank you need to reckon with the 10.4 pounds of air in that cylinder. Of that a good 9 pounds will sometimes be gone at the end of the dive when you are trying to make a controlled ascent. So... if you did establish 32 with an essentially full cylinder you need to add 9 pounds or even a little more (9.5?). If the cylinder was significantly less than full you get to back this number down.

The bottom line is that you may need 32 + 7.5 + 9.5 for a total of 49 in the ocean!

Added:
Oh about the pony... My 19CF represents 4 pounds of negative buoyancy.You need to decide if that can be counted as weight and I don't know if that was in the pool. If you have it mounted such that it can be handed off such as a sling and you are diving with others then you could end the dive without it and should not remove any weight. If you cannot hand it off or use it alone for solo dives then you can consider counting it as part of your weight. It will also slightly ratchet up the dry diver weight.

Pete

 

[Artimas]

Thanks to all who replied.

Added info:

The tank was essentially full during the entire trial.
I kept the pony on, and it was full.

How much buoyancy should I estimate will be lost as the new neoprene compresses at depth?

How many dives until the buoyancy of the wetsuit becomes "normal"?

The estimates here range as high as 49# of weight to carry. Of course I have to fine tune and find out for myself, but does as much as 40-50# seem like a reasonable number to you? It seems like a lot to me, and I'm sure I'd be awfully tired lugging that around on the surface!

Thanks again.

 

[spectrum]

Thanks to all who replied.

Added info:

The tank was essentially full during the entire trial.
I kept the pony on, and it was full.

How much buoyancy should I estimate will be lost as the new neoprene compresses at depth?

15+ pounds is not unlikely. It will depend on the ratio of buoyancy to crush resistance and condition of the suit. Don't subtract that from your weight though since the neoprene will rebound near the surface at the end of the dive when you need to be in control.

How many dives until the buoyancy of the wetsuit becomes "normal"?

Again it depends on the suit and the profiles you dive. Don't expect big changes overnight.

The estimates here range as high as 49# of weight to carry. Of course I have to fine tune and find out for myself, but does as much as 40-50# seem like a reasonable number to you? It seems like a lot to me, and I'm sure I'd be awfully tired lugging that around on the surface!

Thanks again.

It seems oddly high to me as well. With that cylinder full and the build and gear you describe I would have expected the pool test on a full cylinder to be closer to 10 pounds, not 32. Maybe you have bodacious lungs?

Personally and only as a point of reference. In a 7mm (XL, ~205 LB) with 2X on the core, a HP80, in the ocean 24-26 pounds does the trick.

My first thought was that the pool test was flawed. Are you positive that the BC was dead empty? My fins happen to be slightly negative. Did you have any unusually buoyant accessories with you?

Pete

 

[Artimas]

Pete-

Thanks for the quick reply.

I am sure I don't have bodacious lungs (in fact, not much on me is bodacious!). I am pretty sure the BC was empty, I went to the bottom and emptied it, and the guy I dive with thought it looked empty.

I am somewhat overweight, as I am 5'7", but I don't think I'm so overweight as to explain needing all that weight, since other times I have seemed to have fairly normal weight requirements.

I didn't wear my fins, which are a bit negative, and didn't carry any additional accessories for the test.

I'm thinking about carrying 40# on my belt and 6# in my BC when I actually dive. Seems like a lot though. I may need to redo the test, but it would be very inconvenient.

 

[The Kraken]

I'll hazard an estimate of 22#.

the K

 

[spectrum]

Pete-

Thanks for the quick reply.

I am sure I don't have bodacious lungs (in fact, not much on me is bodacious!). I am pretty sure the BC was empty, I went to the bottom and emptied it, and the guy I dive with thought it looked empty.

I am somewhat overweight, as I am 5'7", but I don't think I'm so overweight as to explain needing all that weight, since other times I have seemed to have fairly normal weight requirements.

I didn't wear my fins, which are a bit negative, and didn't carry any additional accessories for the test.

I'm thinking about carrying 40# on my belt and 6# in my BC when I actually dive. Seems like a lot though. I may need to redo the test, but it would be very inconvenient.

That sounds like a safe place to start.

Try to have a few weights as 2 pound clip ons. You can double zip tie bolt snaps to conventional hard weights as temporary clip ons. This will make it easy to hand weights off and mess with trim placement.

Depending how well you can control buoyancy with your lungs and how much surge you dive in will help determine your actual need. Don't count on lung technique too much though, someday you may not be in a good situation but need to stay down.

Another thought..... How long did you spend in the pool establishing the 32? My wife's Seaquest Diva LX is notorious for having stowaway buoyancy. When I put that thing in the rinse barrel if makes like an Alka Seltzer forever. The first time I figured the bladder split a seam! If you were in and out and didn't do a lot or rocking and rolling it may have held some air outside the bladder. Your BC is probably not a cushy but it's worth checking.

Remember that you are much safer starting a few pounds heavy and trimming than going in light and being out of control at the end.

Pete