Help me with my weights

[Doc Harry]

Okay, I need some advice on weighting in my 3mm wetsuit for recreational OW diving in saltwater.

My weighting is PERFECT when I'm in my 7mm wet suit. If I completely relax and close my eyes, I come to rest in the horizontal position. Plus I'm not overweighted (i.e., I can hover at the 15-foot safety stop with a nearly empty BC and 300 PSI in my tank).

But when I switch to my 3mm wetsuit I can't get myself weighted correctly. I float vertically even if I mount my tank high. I've only got 6 pounds on my weight belt but I'm still slightly overweighted (i.e., I have to keep a lot of air in my BC at the 15-foot safety stop). I even put 3 pounds in Keel weights on the upper tank bands to try to get me horizontal, but that just makes me even more overweighted.

DETAILS

Me: 6'00", 195 lbs.
My gear: Aluminum BP (2lbs), STA (2 lbs), weight belt, Jet fins

With 7mm Wetsuit/Gloves/Booties/Hood:
-6 pounds in Keel weights on the upper tank bands
-8 pounds on the weight belt
-tank mounted slightly high
-I float horizontally when relaxed
-Easily hover at 15 feet with 300 PSI and little-to-no air in the BC

With 3mm Wetsuit/Booties:
-3 pounds in Keel weights on upper tank band
-6 pounds on weight belt (too little?)
-tank mounted REALLY HIGH
-I float vertically when relaxed but easily swim in horizontal position
-Have to keep BC inflated at 15-foot safety stop with 300 PSI or I sink like a rock

SOLUTIONS?

For the 3mm wetsuit, I think I need to get rid of the STA and move 2 more pounds to the Keel weights on the upper tank bands?

Am I carrying too little weight (6 pounds) on my weight belt? I'm afraid of shifting weight from the weightbelt to the Keel weights and then having only, say, 2 or 4 pounds of ditchable weight.

 

[Charlie99]

With 3mm Wetsuit/Booties:
-3 pounds in Keel weights on upper tank band
-6 pounds on weight belt (too little?)
-tank mounted REALLY HIGH
-I float vertically when relaxed but easily swim in horizontal position
-Have to keep BC inflated at 15-foot safety stop with 300 PSI or I sink like a rock

SOLUTIONS?

For the 3mm wetsuit, I think I need to get rid of the STA and move 2 more pounds to the Keel weights on the upper tank bands? Am I carrying too little weight (6 pounds) on my weight belt?

Sounds like too MUCH weight on the weightbelt if you need to have air in BC, and you float vertically. You need less lead down low, so take the excess weight off the belt.

You might also try fins that aren't so negative.

 

[H2Andy]

you are going to need less weight in your 3mm (of couse), and the problem is going
to be with trim: i.e. where to put whatever weight is left over

i would solve the problem in two steps:

1. figure out HOW MUCH weight you need in your 3mm with an empty-or near empty
tank to be neutral to slightly negative on the surface. that way you know you'll
be able to control your ascent at the end of the dive

2. once you know how much weight you need, try to distribute it in a way that
won't kill your trim. mount your tank high, put some weight up top, put the rest
on your belt. sounds like 6 lbs is too much on your belt, btw

 

[Doc Harry]

1. figure out HOW MUCH weight you need in your 3mm with an empty-or near empty
tank to be neutral to slightly negative on the surface. that way you know you'll
be able to control your ascent at the end of the dive

2. once you know how much weight you need, try to distribute it in a way that
won't kill your trim. mount your tank high, put some weight up top, put the rest
on your belt. sounds like 6 lbs is too much on your belt, btw

Thanks.

I know that I need 10 pounds total in my 3mm wetsuit. If I keep my BP/STA (4 pounds), then I need only an additional 6 pounds. If I put that 4 to 6 pounds in the Keel weights to correct my trim, then I have only 0 to 2 pounds of ditchable weight. Isn't that too little in the way of ditchable weight?

I like the idea of less negative fins. And yes, I plan to start diving dry ASAP.

What to do?

 

[CJ-62]

New to the board so sorry for any breach of protocol.

Don't understand the admonition to place tank high, unless it is steel, i.e. a Luxfer 80 aluminum tank would be about +4 bouyancy at 300 psi.

I dive dry in PNW with BP/W so may not comprehend the 3mm thing. In a practice session from 30fsw, dropping 4 lbs got me moving from neutral rather nicely.

By the way getting less negative fins would help this issue but I use 2lbs at the ankles in a USIA dry suit to keep my size 11's under strict control.

My $.02, experiment at the nearest beach and good luck.

 

[H2Andy]

then I have only 0 to 2 pounds of ditchable weight. Isn't that too little in the way of ditchable weight?

well, not counting the plate, i would feel uncomfortable with more than about
6 lbs of non-ditchable (that's for my warm water, wet, set up). 4 non-ditchable
would be even better.

how much ditchable you have is not really the issue. the thing is not to have
too much unditchable weight.

 

[H2Andy]

Don't understand the admonition to place tank high, unless it is steel, i.e. a Luxfer 80 aluminum tank would be about +4 bouyancy at 300 psi.

yup, the bouyancy will be unaffected by tank placement, but the trim will.

so if you have a "heads up" trim (i.e. "feet down") moving your tank towards your
head will help get you horizontal.

and vice-versa

 

[CJ-62]

yup, the bouyancy will be unaffected by tank placement, but the trim will.

so if you have a "heads up" trim (i.e. "feet down") moving your tank towards your
head will help get you horizontal.

and vice-versa

I didn't make my point clearly, sorry.
If the tank in question is a Luxfer AL80, at 300 psi it is generating +4lbs of "lift" at its center of bouyancy, maybe 10" higher than the weight belt.
If the tank were a steel Faber 100, with the same 300psi, it would represent a -7lbs of weight at the same point. The Luxfer is 26" long and the Faber is 24", both are 7.25" dia.
Obviously, this swing of 11 lbs from two identically placed, similarly sized tanks would have a big change in your trim in addition to your required weighting.
Moving the tank towards your head will not help get you horizontal if the scenario is an aluminum tank, tested near empty, with the majority of your weight at your waist.
That was what I should have said the first time.

 

[Juls64]

One thing to consider, At 6 foot, you are somewhat tall. With a 7mm, there is more neoprene on the legs, thus making them more bouyant than in a 3mm.

You may need to consider this as you make your adjustments. Moving the tank, or any of the weight you have, higher, may help you.

Juls

 

[sharpenu]

An empty AL80 is not weight, it is buoyancy. Since it is +3 lbs, moving it towards your head makes you more vertical. Moving a steel tank (mine is -1 empty) towards the head will lower the head, making you more horizontal. Picture your body as being a see-saw with the fulcrum being your center of mass.

...tank.....................weight
head --------------^----------------feet
...................center mass

If the tank is buoyant, it will pull up on the head; if negative, it will push down. Moving the tank or weights away from the center of mass pronounces the effect, towards the center of mass lessens the effect. That is why the fat kid has to sit closer to the center of the see saw than the skinny kid for them to balance.