buoyancy test..... HUH ?

[Tassie_Rohan]

This has been a very helpful thread topic.

I logged my 9th and 10th dives this weekend.

I had still been diving with the amount of weight given to me for my cert class... 16 pounds. I knew I was severely overweighted, so I started cutting down this weekend.

On the first dive, I dropped 2 pounds. At 14, I was still very overweighted.
On the second dive, I dropped another 2 pounds. At 12 pounds the "plummeting" feeling was gone. It was more like 'drifting' to the bottom.

So, I'm a 5'10" guy, average build, about 170 lbs. I dive a 3/2 suit, and a jacket style BC. Can anyone similar post a good guess at what will be my 'ideal' weight?

Thanks!

I have a similar build. I'd take a stab at 6 lbs, possibly a bit more if your BC is very buoyant.

I went for my first warm water dive in nearly a year a few weeks back, and had to hire a 3 mm wetsuit. The dive operator suggested I use a whopping 16 lb with the suit. I started with 9 lb, re did the end of the dive weight check, and ended with 4-5 lb (which is what I normally use). This includes the 1 lb Al backplate I wear. I could drop to 3 lb but if I'm mucking around in the shallows (or am doing a deco dive) I may go to 6 lb to make sure I stay down while shallow.

As an aside an interesting exercise is to hover while a friend hands you lead weights - and use your breathing to maintain neutral buoyancy (from shallow breaths after exhaling to deep bottom of lung breaths with a slow inhale: no breath-holding please). Your can usually take on and off a few extra weights just by breathing control. However don't try this until you are already in full control of your bouyancy.

Cheers,
Rohan.

 

[BKP]

I have a similar build. I'd take a stab at 6 lbs, possibly a bit more if your BC is very buoyant.

I went for my first warm water dive in nearly a year a few weeks back, and had to hire a 3 mm wetsuit. The dive operator suggested I use a whopping 16 lb with the suit. I started with 9 lb, re did the end of the dive weight check, and ended with 4-5 lb (which is what I normally use). This includes the 1 lb Al backplate I wear. I could drop to 3 lb but if I'm mucking around in the shallows (or am doing a deco dive) I may go to 6 lb to make sure I stay down while shallow...

Cheers,
Rohan.

I am *very* impressed with your weighting, above, in what I'm assuming to be salt water (warm water), and trying to figure out how you do that...

The 4-5 lbs. you normally use, would account for a standard AL80's positive buoyancy at 500psi (approx 2.6 to 4 lbs., depending on how far you breathe it down).

Then there's the 3mm wetsuit's buoyancy...

And there is also salt (warm) water's additional buoyancy (specific gravity of 1.03 compared to fresh water's 1.0)...

Sounds like the dive operator's suggestion of 16 lbs. would be relatively close on a guess (although maybe a couple lbs. to the heavy side), unless, of course, you're a sinker...

You must be a sinker... I bow to your buoyancy efficiency...

Poses an interesting question... I think I'll start a thread...

 

[Tassie_Rohan]

Cheers for that BKP - however there’s no competition for who has the least weight: the important thing is to have the correct weight. For a 3 mm this may be up to 12 lb for more rotund individuals who wear larger suits and have some inherent buoyancy, or 5 lb for whippets like me. I noticed most of the DM’s I was diving with on my last two tropical trips also had two weights on (around 5-6 lb) so its not that uncommon.

My partner who is learning to dive in a 3 mm started out with 4 weights (10-12 lb), dropped to 3 (9lb) and, once she is completely comfortable in the water, will probably end up with 2 (6 lb). With each weight drop her trim/posture in the water got better and her use of breathing to control buoyancy improved.

Having a backplate helps - BCs have a lot of padding and tend to be floaty. Ditto an old abused wetsuit. At 5 lb and 5 metres things are fine unless I suck the tank dry – which is something I try to avoid.

One experiment to try is put your wetsuit in a mesh bag and add weights until it sinks (remove any trapped air first): I thing you'll find most 3 mm suits will sink with far less than 16 lb - thats the weight I used to use for a 7 mm two-piece wetsuit.

Cheers,
Rohan.

 

[BKP]

Having a backplate helps - BCs have a lot of padding and tend to be floaty. Ditto an old abused wetsuit. At 5 lb and 5 metres things are fine unless I suck the tank dry – which is something I try to avoid.

One experiment to try is put your wetsuit in a mesh bag and add weights until it sinks (remove any trapped air first): I thing you'll find most 3 mm suits will sink with far less than 16 lb - thats the weight I used to use for a 7 mm two-piece wetsuit.

Cheers,
Rohan.

Ohhhh... you're cheating with what I'm assuming is a SS backplate .
You're right -- I believe a standard BCD is more positive then a BP/W rig. (what *do* you figure the backplate adds in negative weight?).

I also agree about the 3mm suit... I'd hazard it adds about 4 to 6 pounds positive, depending on the size (S, M, L, XL, etc.).

And, you're certainly dead on, that it's not the quantity of weight, rather getting the weight correct for the diver. There is nothing better then that feeling of perfect weightlessness with an empty wing at 15 to 20 feet.

When I dive fresh water, I'm at 6 lbs. in a 3mm, however, that's with a compact AL80, which still has a negative buoyancy empty (and again, that's in colder, fresh water).

Around here, in salt, I just haven't seen such low weighting with a standard AL80, and 3mm suit -- and I'm always looking for clever ways to drop a couple of lbs...

-Barry