Weighting Adjustments

[QKRTHNU]

Got a question about weighting.

I'm a new diver. I was just SSI certified in Feb down in FL. I'm going on vacation soon to Grand Cayman. I'd like some advice on weighting for when I get there.

During my cert dives I found the following:

In the pool with no wet suit I need no weight to sink like a rock. Took about 7 blasts into the BC to get me off the bottom.

In the Gulf with a 3mm FJ & 3mm long-sleeve shorty I needed 18lbs to keep my self from floating off the bottom.

In Cayman I'll most likely not be wearing any exposure protection, maybe a skin-suit. Seeing that I sank so easily in the pool and following the 2.5lb/100lb body weight fresh-salt conversion I'm thinking I should only need 4 or so pounds at most.

Does this sound correct?

Also, I didn't learn much about weighting during instruction. Everything I've read talks about determining weighting at the end of the dive with 500psi @ 10-15ftsw. Is there any way to determine proper weighting at the beginning of the dive?

I hate the idea of going through an entire dive with improper weighting just to test it out at the end. All my diving is going to be requiring travel, so I'll most likely be using different amounts of exposure protection all the time. (I guess it might be worth purchasing an assortment of wet suits of my own so that I know what to expect in various conditions.)

 

[AzAtty]

You can work out weighting at the start of the dive if you want to do so. The reason you see all the materials on weighting at the end of the dive is because at the end of a dive, your main concern is being able to stay down at the safety stop. Therefore, adjusting your weight for end-of-dive buoyancy is what you'll usually see.

I'd suggest working out weighting issues in the pool before you go on vacation. If you want to start at the beginning of a dive, put on all your gear and hop in the pool. Load or unload weight until you're neutrally buoyant, and then add another 5-6 lbs. The extra 5-6 lbs is to compensate for tank "swing" as you breath it down (air inside a single AL 80 weighs 5-6 lbs, if I recall correctly). Then do the fresh-to-salt weight conversion, and you'll have yourself set, more or less.

Of course, buoyancy will change with depth, depending upon your exposure suit.

The only way to check your buoyancy is to get wet. However, if you want a starting point, for a person of an average build, you could start with the following estimates for salt water diving:

Dive skin: 1-4 lbs
3mm 1 piece: 5% of body weight
5mm 2 piece: 10% of body weight
7mm suit/hood/gloves: 10% of body weight + 3-5lbs

Then add 5-6 lbs for the tank.

The above chart isn't perfect, but it gives you a decent idea of what weight you'll need. The only way to get completely dialed in is to get in the water.

With regard to chart accuracy, I was fooling around in the LDS saltwater pool yesterday with a BC I bought for my brother. I was wearing my drysuit + 200g fleece undergarment. It took about 36 lbs to get me roughly neutral with a full AL 80 (I was a tiny bit heavy). According to the rest of the chart (which I haven't reproduced), that setup would require about 35 lbs for me (assuming no weight for tank swing).

If you have a lean build, you can subtract weight. If you're fluffy, add weight. Hope this helps.

 

[QKRTHNU]

Thanks for the advice!

Unfortunately I don't own all of my equipment yet, so I can't test out a full rig in the pool.

I guess I'll just have to estimate as close as possible ahead of time. At least until I have all of my own stuff.

 

[wreckchick]

When you get back from your lovely warm water dives, which I am oh so jealous about, if you feel like doing some nice quarry diving, let me know, I'm always looking for other local divers!

Rachel