BM vs SM weighting discrepancies

[guruboy]

Diving wet, I need 8lbs additional (on top of SS BP and weighted STA) with 5mm. SM, no additional weight with 5mm.

BM BP/W: 20# total (SS+BP+STA+lead)
SM SMS75: 0#

HP80: 1.75# empty
500psi: 1#
Valve : 1.75#
1st: 2#
SPG: 1#
Bolt snap: 1#
——————-
Total: 8.5#

If diving only one tank worth of gas, that adds 6.25# of extra air weight.
HP80: 1.75# empty
500psi: 1#
Valve : 1.75#
1st: 2#
SPG: 1#
Bolt snap: 1#
Unused air: 6.25#
——————-
Total: 14.75#

 

[guruboy]

That being said, in BM with an AL80 and a steel BP, I use 4lbs of lead. In SM, with 2 empty AL 80 (additional 3lbs positive) and no BP (another 3lbs positive) I only need 2 lbs.

SM seems in my case to require 8lbs less ballast all round and I honestly have no idea why.

AL80 empty: -3.75#
500psi: 1#
Valve : 1.75#
1st: 2#
SPG: 1#
Bolt snap: 1#
——————
Net 3#

So 8# vs 5#. Not that drastic a change.

 

[rjack321]

This person is most likely considerably overweighted! And the SM example after it is likely underweighted. My experience has been similar to @tbone1004 - it's usually the other way around - SM usually adds weight ...

I would disregard the scenarios you presented ...

You have no idea what you are talking about. I know MANY people needing roughly that amount of lead with a hp80 or hp100 cylinder, bp/w and drysuit in Puget Sound. And they aren't overweighted, but they do have enough gas in their suit to stay warmish at the end of a 1 hr dive in 48-54F water.

 

[sigxbill]

You have no idea what you are talking about. I know MANY people needing roughly that amount of lead with a hp80 or hp100 cylinder, bp/w and drysuit in Puget Sound. And they aren't overweighted, but they do have enough gas in their suit to stay warmish at the end of a 1 hr dive in 48-54F water.

I have dove that exact configuration many times in similar water. Notice also my use of the word, "likely." I did make the assumption that the BP was steel, so please forgive my assumption. Also notice that the OP changed his OP by reducing the lead quoted by eight pounds. But whatever you say ... cheers

 

[guruboy]

Also notice that the OP changed his OP by reducing the lead quoted by eight pounds.

I changed the numbers because I found out the original weights I used were for different drysuit undergarments. The updated numbers are for the same exposure protection now.

 

[Cyborg Pirate]

I am going have to agree people are way overweighted. Diving dry with Al BP/wing single Al80 I require 16lbs lead, 7mm 6lbs, 3mm, 2lbs. Diving SM. I get in no tanks just the SM wing and the gear I am diving with. Exact same amount of lead in each exposure suit. Adding the tanks.... with 2 Al80’s each has a 2lb weight on the cam band (opinions aside where someone stands on the weighting the tails of Al80’s I don’t care. They trim out nice and no tail float at end of dive). With the steel 72’s no additional weight. After a dive I have done multiple weight checks and I am weighted within .5 to 1lb of being completely neutral.

So again I am sticking with people are way overweighted to begin with.

 

[JBFG]

My SM system and BPW wing use pretty much the same amount of weight.

I’ve only tried both wet in salt water and there’s a 2lbs difference only