General BP/W questions

[RayfromTX]

Tbone is correct as is usually the case.

 

[Brian G]

While I have read a lot of good advice from tbone in the past, I fail to see the point this time. Johndiver made a quite civil post about the disadvantages of having a very negative rig. He did not claim that having ditchable weight would make you positive. He outlined some scenarios where having a very negative rig could make things more difficult. If I was doing dives with minimal protection and steel cylinders, then I would not choose a steel plate. Can it be done safely? Sure.

Regards,
Brian

 

[tbone1004]

While I have read a lot of good advice from tbone in the past, I fail to see the point this time. Johndiver made a quite civil post about the disadvantages of having a very negative rig. He did not claim that having ditchable weight would make you positive. He outlined some scenarios where having a very negative rig could make things more difficult. If I was doing dives with minimal protection and steel cylinders, then I would not choose a steel plate. Can it be done safely? Sure.

Regards,
Brian

do you define 2-4lbs as "very negative", also. I do believe he did state it would make you positive then edited it out otherwise I wouldn't have put words in his mouth.

I disagree that having the ability to ditch ballast and rise to the surface has no value in recreational diving.

*snip*
Why not configure your gear so you can at least rest on the surface, even though your BC has managed to fail or it is difficult to inflate because you ran out of air and may be stressed by this situation - making it hard to orally inflate the BC?

Another very real danger is a diver jumping in the water with the tank off and having a too heavy rig and nothing to ditch.
*snip*

so in there, he said ability to ditch ballast to rise to the surface, that is incorrect.
Diver is diving a steel 100, even "properly weighted" you can't comfortably rest at the surface with just the mass of the tank

The important part of what I was trying to say is the important point about lifeguard and basic diver training with recovery of a diving brick. A diving brick is 10lbs, if you can recover a diving brick from the bottom of a diving well, and swim it to the side of a pool without any fins on, you can afford to be 2-3lbs heavier than you "need" to be for the benefits of not diving with a weight belt. Hell depending on diving conditions and location, it's often safer to dive a couple pounds heavy so you can always make an "easy" descent

It's 2-3lbs, which correlates to 10-11lbs of total negative buoyancy at the start of the dive with a HP100. If I can kick up a 10lb diving brick and keep it at the surface, I can keep a 12lb rig at the surface with fins on. The difference between 8lbs of "perfectly weighted" or weighted with ditchable weights, and 10-12lbs if pretty negligible in the grand scheme of things, and comparable to the diver going from a HP100 to a HP130 just from the added gas. Is it "perfect" no, and if the diver dove predominantly without a wetsuit and a steel 100, I'd recommend going kydex or fabric for a backplate, but if the primary gear config as outlined in the start of the thread is with a 3mm wetsuit, then buy the right rig for the primary use and accept it.

I obviously have strong opinions on ditchable weight, but it largely stems from a background in technical diving where we don't have anything we can ditch even if we wanted to. The rigs themselves are negative enough to keep us down and to me that makes ditchable weight an equipment solution to a skills problem. Even in an emergency

 

[johndiver999]

I think that for many technical diving situations, there is no choice but to be "excessively" heavy. just from the amount of air that can be carried in 2, 3 or 4 tanks, makes the swing considerable during a dive. Tech divers can use double bladder BC's or dry suits to help mitigate this danger.

However for a single tank, recreational diver, I don't see the necessity nor the desirability to dive a rig that is more negative than is necessary and has zero means to ditch ballast.

If we go back to the original question, unless your body is unusually buoyant (which does not seem to be the case here) wearing a steel tank with a heavy steel plate and no wetsuit is not optimal because of the excessive negative buoyancy, the inability to drop ballast, the excess drag from always having extra air in the BC and a few other concomitant challenges that this sort of situation brings.

I think a more versatile and safe configuration would be to have a rig that (for diving with no wetsuit) is not excessively heavy and may have no ditchable lead and then add ballast when wearing a wetsuit, with some or all of the ballast being capable of being dropped if necessary.

 

[tbone1004]

@johndiver999 so we'll keep this short, you believe that 3lbs is considered excessively negative, and that the drag associated with that is noticeable. Got it.

Normal size AL plates are 2lbs, and with specific gravity figured in are about 1.2lbs negative. Steel plates are almost all 5lbs, and with specific gravity factored in are about 4.3lbs.

If you believe that is enough to warrant having to wear a belt or buy pockets for 4lbs of lead *because no one makes 1.5lb weights*, then by all means, go for it, but it sounds like the 3mm suit is the norm, and I'd buy for that. Diving 3lbs heavy is irrelevant and ditching it is going to make absolutely 0 difference in an emergency.

You're blowing this perfectly weighted and ditching weight thing way out of proportion IMO. There is a difference in a 7mm farmer john at 100ft that loses 20+lbs of positive buoyancy on top of 10lbs of gas in a big steel tank and plummeting to the bottom and being 3lbs overweighted.

 

[Magnus Lundstedt]

Yeah, I’ll have to compare the BP/W setups I’m considering and see which BP will be best suited all around, looks like aluminum is in the lead but I’ll have to research further.

I would prefer to change to AL tanks and go for the SS BP.

Is there any reason you need to have the steel tank and cannot switch to AL tank when diving warm water?

 

[halocline]

I haven’t dove the skin suit since switching to steel tanks so I’m not sure, but going from AL to steel with current BC and 3mm I went from 14lbs to 6lbs of ballast, and in skin suit with AL tank used 10lbs. So would use 2lbs by that metric, but then adding a SS BP I may be overweight. I don’t wear lead with the intention of ditching it but would if the situation called for it. I’m just trying to assess potential risk(s) and possible solutions.

If you're diving with a steel tank and just a skin, you'll probably be happier with the AL plate. The steel plate is great with AL tanks because it basically offsets the inherent buoyancy of the tank.

The strange thing I notice about your weight numbers is 10 lbs with just a skin and AL tank. Assuming the skin has almost no positive buoyancy, the tank has 4lbs, what do you need the other 6 for? To sink your jacket BC I guess, just another reason why those things are junk.