BP magic

[Kern]

Even a minimalist BC will have a bit more positive buoyancy than a bp/w, but the combined weight of the backplate, webbing and hardware, wing and inflator, and any add ons like a can light combine to nearly equal the weight that came off the belt.
And as the OP suggested, now they are carrying the weight on their shoulders instead of their hips.

If people are overweighted and then shed some lead because they focus on proper weighting due to a switch to a bp/w, then thats great. Its still going to take a specific amount of weight to sink someone who is wearing a 7mm wetsuit and is positively buoyant.

Assume a person is properly weighted with a belt and BCD and then weighs himself on a scale, then switches to a bp/w and removes 10 lbs from the weightbelt and then weighs himself on the same scale, he should weigh about the same, maybe slightly less to counter the tiny amount of positive buoyancy inherent in the bcd.
As mentioned by Akimbo, you can't fool Archimedes.

Yep, that about sums up what most are saying.

 

[Crush]

Thanks to all, and in particular to Divedoggie,

Despite the poor wording of my OP, you have seen through to the crux of the question - what will the scale say?!

I now share, and did previously hold the opinion espoused by many of you - the scale will say (almost) the same thing, regardless of whether you wear a BP or a BC. Certainly there is benefit to putting weight on your upper back (as with the BP or with a properly weighted BC). However, I though that perhaps I was missing something obvious, and the answer appears to be "no." The weight taken off your belt is effectively added to your back (albeit in the form of SS instead of lead), save for at most two to three pounds if you have a Cadillac BC.

Thanks, all.

 

[Kern]

Thanks to all, and in particular to Divedoggie,

Despite the poor wording of my OP, you have seen through to the crux of the question - what will the scale say?!

I now share, and did previously hold the opinion espoused by many of you - the scale will say (almost) the same thing, regardless of whether you wear a BP or a BC. Certainly there is benefit to putting weight on your upper back (as with the BP or with a properly weighted BC). However, I though that perhaps I was missing something obvious, and the answer appears to be "no." The weight taken off your belt is effectively added to your back (albeit in the form of SS instead of lead), save for at most two to three pounds if you have a Cadillac BC.

Thanks, all.

You really will be surprised just how buoyant a RR BCD can be.

 

[fnfalman]

Compare apples to apples. Put 6 lbs in your BC/vest and toss that in. Then toss your 6lb backplate in. Both will sink.

Now go weight the combo of the jacket BC + 6lbs of weight and compare to the BPW with the SS hard plate (averaged around 6lbs).

As I understand it, the lightest jacket BC is around 4lbs. Plus 6lbs of lead, that equals to 10lbs. A BPW with SS plate is probably around 8lbs (6lbs plate + 2lbs wing & hardware). That's a saving of total package weight of 2lbs already.

Let's go back and revisit the jacket BC again. That 6lbs of lead will sink the BC, but how much ballast left over to help with sinking the diver? How much ballast does the jacket BC need to sink, 1lbs, 2lbs, 3lbs? Then whatever left is for the diver.

Let's say that a diver needs 8lbs of lead to sink.

The BPW with steel plate will need 2lbs of lead extra.

The jacket BC will need 8lbs of lead PLUS whatever lead the BC needs to sink itself.

I personally don't care who uses what. I like the advantages offered by the BPW. YMMV.

 

[it_mike]

Keep in mind, what it weighs on your bathroom scale is irrelevant. Bouyancy relative to weight is the key.

 

[Sas]

Thanks to all, and in particular to Divedoggie,

Despite the poor wording of my OP, you have seen through to the crux of the question - what will the scale say?!

I now share, and did previously hold the opinion espoused by many of you - the scale will say (almost) the same thing, regardless of whether you wear a BP or a BC. Certainly there is benefit to putting weight on your upper back (as with the BP or with a properly weighted BC). However, I though that perhaps I was missing something obvious, and the answer appears to be "no." The weight taken off your belt is effectively added to your back (albeit in the form of SS instead of lead), save for at most two to three pounds if you have a Cadillac BC.

Thanks, all.

Jacket BCs can be much more buoyant than BP/Ws, that weight disappears entirely so the scale will not necessarily say the same thing. I was correctly weighted in my BC before I switched to a BP/W and dropped 10lb off my belt and 4lb overall.

 

[Crush]

Jacket BCs can be much more buoyant than BP/Ws, that weight disappears entirely so the scale will not necessarily say the same thing. I was correctly weighted in my BC before I switched to a BP/W and dropped 10lb off my belt and 4lb overall.

Thanks, sas,

The 4lbs overall is what is of interest to me. I feel that when someone writes "I dropped 10 lbs off my belt" and doesn't post "but the plate is 6 lbs heavier than the BC" they are really giving, at best, a partial picture.

This is not an appeal to authority, but I have a Ph.D. in Physical Chemistry, so I am familiar with Archimedes' Principle, PV=nRT, etc.. I understand very well the differences between mass and weight and buoyancy.

 

[Sas]

Thanks, sas,

The 4lbs overall is what is of interest to me. I feel that when someone writes "I dropped 10 lbs off my belt" and doesn't post "but the plate is 6 lbs heavier than the BC" they are really giving, at best, a partial picture.

This is not an appeal to authority, but I have a Ph.D. in Physical Chemistry, so I am familiar with Archimedes' Principle, PV=nRT, etc.. I understand very well the differences between mass and weight and buoyancy.

mpetryk, have you had a chance to give a BP/W a go yet?

 

[fnfalman]

Thanks, sas,

The 4lbs overall is what is of interest to me. I feel that when someone writes "I dropped 10 lbs off my belt" and doesn't post "but the plate is 6 lbs heavier than the BC" they are really giving, at best, a partial picture.

This is not an appeal to authority, but I have a Ph.D. in Physical Chemistry, so I am familiar with Archimedes' Principle, PV=nRT, etc.. I understand very well the differences between mass and weight and buoyancy.

But the plate isn't 6lbs heavier than the BC. The plate is 6lbs and the travel BC Zuma (for example) is 4lbs. So it's only 2lbs or 3lbs heavier than the BC, if that.

Total dive weight for my Dive Rite BPW with steel plate is 63lbs (with my heavy 100cuft Faber tank). 65lbs for the same rig ready to dive (w/ 8lbs of lead) but with my Dive Rite Transpac; a soft plate BC that is neutrally buoyant instead of positively buoyant. The hard plate rig is 2lbs lighter than a soft plate that is neutrally buoyant.

 

[DiverLaura]

One thing that has not been mentioned is that although weight on the hips is fine, for some people a weight belt is basically not an option. The pull of a weight belt on the spine pulling it into lordosis (sometimes even just a 5 or 10lb-er) can be enough to make standing up after a dive brutally painful for someone that already has some lower back issues. Keeping it on (the weight belt) is also for some an anatomic challenge which is why items like the DUI weight harness is enjoyed by a fair number of people.

For both those people, putting the 6lbs on the back as SS backplate can be the difference between a great dive and a painful one.