Proper Weighting for drysuit and backplate and wing

[stuartv]

It's just a different feeling than my aqua lung axiom i3 BCD. Which I use 14lbs of droppable weight with 4lbs of trim weight with my HP100 steel tank and drysuit. Just seems to be counter intuitive. Maybe the axiom BCD is a little more buoyant?

Your steel BP is probably about 6# negative. With 4# droppable, plus 4# of trim weight, that's 14# of ballast.

You said with your i3, you used 14+4, or 18#. If your i3 is 4# buoyant, then that would all add up and make sense. And I guess it's totally possible that your i3 is 4# positive.

That weighting is using the F1 fins for both? Those are pretty negative. If you have been using different (close to neutral) fins with your i3, that would account for some of the difference in weighting (i.e. it would mean your i3 isn't necessarily 4# positive buoyancy).

That is one of the beautiful things about a stainless steel back plate and wing setup - how much lead you can take off your rig.

 

[Alan De Lucio]

Your steel BP is probably about 6# negative. With 4# droppable, plus 4# of trim weight, that's 14# of ballast.

You said with your i3, you used 14+4, or 18#. If your i3 is 4# buoyant, then that would all add up and make sense. And I guess it's totally possible that your i3 is 4# positive.

That weighting is using the F1 fins for both? Those are pretty negative. If you have been using different (close to neutral) fins with your i3, that would account for some of the difference in weighting (i.e. it would mean your i3 isn't necessarily 4# positive buoyancy).

That is one of the beautiful things about a stainless steel back plate and wing setup - how much lead you can take off your rig.

I have been using Atomic split fins which are positively buoyant.

 

[cool_hardware52]

My goal WRT to weighting is to end up with the least amount of ballast required to hold a shallow stop with near empty tanks.

Exposure suits compress, obviously wetsuits are compressible neoprene, but nearly all drysuit undies compress too.

If we assume ones last stop or safety stop will be conducted at 15 ft then it's about 1.5 ATA. vs 1 ATA at the surface.

Every diver knows that if they start neutral at the surface and descend to 15 ft without adding gas to their BC they will become negative. The more buoyant the exposure suit the more negative they will be by the time they reach 15 ft. A wetsuit that's 20+ lbs positive at the surface can easily lose 6-8+ lbs at 15 ft. So can a drysuit due to the compression of the undies.

Typical single cylinders holds 5-8 lbs of useable gas. That means that a diver who is wearing a buoyant exposure suit and is using normal sized single cylinders can weight themselves so they are eye level at the surface with *no* gas in their BC. The compression of their exposure suit will offset the weight of the gas they may consume during the dive. For a diver using buoyant exposure suits and typical single tanks starting the dive negative by the weight of their gas only insures they will be overweighted for the entire dive and need 6-8 lbs of gas in their BC at their shallow stop.

Can a diver weighted as I recommend control their ascent from 15 ft to the surface? Sure. Wetsuits rebound slooooowly, and the diver won't be but a few lbs positive until they are very near the surface anyway. Add to that one should not be planning on pulling a vacuum on their cylinders on a routine basis either, meaning their tank is most likely 1-3 lbs heavier than it would be fully evacuated.

A diver that is a few lbs buoyant can exhale and swim down should the (unlikely) need arise to descend at the end of a dive with an empty tank......

What are the benefits of not being overweighted?

1) Easier buoyancy control, a smaller bubble to manage during all phases of the dive

2) The implications of BC failure are greatly reduced. BC's are reliable devices but failure is not unknown. If a diver is weighted per my recommendations, eye level at the surface with no gas in their wing and a full cylinder, then if they can kick back to the surface it will require very little to no effort to stay at the surface. Contrast that with a diver who is 8-10 lbs over weighted........

Keep in mind that these weighting recommendations only work for divers wearing substantial exposure suits and using 72-80-95-100-120 tanks.

A diver in board shorts or a 3mm cannot expect their exposure suit to lose 5-8 lbs of buoyancy at 15 ft. That means tropical divers will need to start the dive negative by at least a portion of the weight of their back gas. The good news is the diver using no exposure suit need never be more negative than the weight of their gas.

Tobin

 

[stuartv]

I have been using Atomic split fins which are positively buoyant.

Ah ha! Definitely a good call on the F1s with the drysuit. I use those, too. They are so negative, it really helps me with keeping my feet from floating up and hanging me upside down. And they're that much less lead I have to carry, too. Win, win.

 

[Alan De Lucio]

Thanks for all the advice guys. Yeah I like my Atomics when wearing my wetsuit and Axiom i3. But the F1's are great with the drysuit.