Side Mount MultiStage LIFT Question

[v101]

Hello -
I wanted to ask some others if they have enough lift with their BC's when doing a multi-stage side mount dive?

My setup is as follows:
Modified SMS 100 (Cave Adventurers in FL)
2 LP 85's
2 AL 80's
Drysuit - very thin undergarments

When I do single stage dives (2 LP-85's & 1 AL 80) the BCD is fine, no issues, have adequate lift all is good.

When I do a multi stage dive, the BCD is FULL, the OPV sometimes pop's and I feel I dont have enough lift to stay off the bottom for the first 800 PSI or so until the AL stage gets a bit lighter. So what I have been doing is to close my dump valve on my Drysuit, and inflate a bit more gas that I usually do into my drysuit, and that has been working, then once the stage gets lighter I can dump the gas in my drysuit, and I am then ok, usually at that point, we drop the right stage, and then with just 1 stage left, we continue the dive, and all is good with lift and the BCD.

Wanted to get some thoughts on what others do, or if anyone has any other ideas for getting a few extra lbs of lift when the right bottle is full.

 

[decompression]

I have to say that is strange. Are you wearing much weight other than your rig and tanks? The 4-5 lbs of air in one Al 80 shouldn't make much of a difference considering the lift capacity of the SMS 100.

Most LP 85's are -6 full and neutral empty. So -12, -16 (air+lead) for the ALs, and guessing -20 in lead for the drysuit. So your are -48 ish compensated by by the drysuit and the wing with 52 lbs of lift. Even when you add in light cans and gear it's manageable. The only thing I can see is your not adding much air to the drysuit which isn't necessarily a bad thing but if not, you are reaching the lift capacity of the wing (at the beginning of the dive).


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[TracyN]

I have this issue as well. When they do the modifications they take a bunch of the lift out. With 2 85's, 2 AL 80's and an oxygen bottle my wing is at absolute capacity and my opv valve is popping. If I don't compensate with my drysuit I may not get off the floor of the cave. It's a flaw with the modifications. I am thinking about taking out one of the wing tucks that they do and that should solve the problem

 

[decompression]

Good point Tracy, does Ed mod the lift that much? Being out west I've yet to see the Ed mods (100 or 75) up close.


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[tbone1004]

It's not that he takes that much out, it's more that the nature of that style rig removes a lot of lift. You start with a quoted 52lbs, the mods probably drop it to 40 or so. The real killer is that the tanks hanging on the rails and the crotch strap pulling the backpad down remove that much more lift. If you loosened the crotch strap and mounted the tanks somewhere else the wing could fully inflate by separating the backpad from your body, but it can't do this, so I think real world lift is probably around 30lbs or so. The reason the OPV's go early is because you are fighting the weight of the tanks and the extra pressure of your crotch strap. You have almost 14lbs of air in the 85's plus their inherent negative buoyancy, so depending on what pressure spring is in the OPV, it has to fight the full weight of those tanks and the pressure induced by the crotch strap as soon as the outer wings are filled to lift the pad up. Bad design imho and all but impossible to get the full quoted lift.

Nature of the beast. Remember that the guys at CA dive neoprene drysuits so there is some inherent buoyancy in the suit that helps to compensate.

My Nomad has similar but different issues due to the mods that I have made to the top of it. Its design does not have the backplate going over the wing anywhere except the shoulder straps, so it loses comparably little lift, 50lbs quoted down to probably 45 or so, but I need every bit of that if I'm diving with a 5mm

 

[bamafan]

The SMS100 with the mods has about 35 pounds of lift. I had to untuck the top of the wing. With the mods it wasn't really a question of lift as I could compensate at the beginning of the dive with the drysuit the problem I had was the problem of all the lift being in the butt. It works great till you are using tanks such as Faber 108's / 120's that get butt light. With 3 or 4 stages and Faber lp 120's all around 1/3rds left I was literally hanging onto rocks on deco with my feet almost straight up. It is a problem with having all the lift that low in my opinion.

 

[decompression]

So, it would seem the Ed mods don't mix well with certain steels and multi stages.........


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[v101]

The SMS100 with the mods has about 35 pounds of lift. I had to untuck the top of the wing. With the mods it wasn't really a question of lift as I could compensate at the beginning of the dive with the drysuit the problem I had was the problem of all the lift being in the butt. It works great till you are using tanks such as Faber 108's / 120's that get butt light. With 3 or 4 stages and Faber lp 120's all around 1/3rds left I was literally hanging onto rocks on deco with my feet almost straight up. It is a problem with having all the lift that low in my opinion.

Did you notice any difference in your TRIM when you untucked the top of the wing? my trim is spot on with 2 LP 85's/100's/120's etc. The Faber's as you said do get butt light after they get sucked down a bit, My LP 85's are all worthington, and I dont notice them doing this like the Faber's do.. my steel HP 100's are good throughout the entire dive...

I was thinking of un-tucking the wing a bit to compensate a bit, but I dont want to have my trim all messed up... :-(

I will check out the SMS 75 and see if it has any additional lift vs the modded SMS 100.

Someone was suggesting to me to stretch out the spring a bit in the OPV, and it will allow a few extra lbs of lift. But I am not sure about this... I would hate for the OPV to NOT work, and then risk blowing out the wing when I am far back in a cave...

the other option I was toying with was a SMB and just inflating that and carrying it under me, for the first part of the dive, I can deflate it and stow it once the bottles get sucked down a bit...

---------- Post added August 23rd, 2015 at 10:26 AM ----------

So, it would seem the Ed mods don't mix well with certain steels and multi stages.........


I think it depends on the person, the drysuit, etc. When you watch Edd dive with multi-stages, he is fine, no lift issues, even with 3-4 stages on... Another fellow was diving with us, in a SMS 75 and he had no issues either with 2 stages.. other divers I talk to with 2 stages in a modded SMS 100, they are fine, and others have the lift problem where they are having to inflate their drysuit a bit more than normal to give them the extra lift they need to stay off the bottom...

My wing was full, and I was blowing the OPV, but there are differences in body composition, drysuits, etc. so that might be the difference.. ??

I am using a crushed neoprene drysuit;

 

[decompression]

Following.....


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[v101]

I will have to give my modded sms 100 a weight test to see how much lift I have.. The boys at CA say it has about the same as the SMS 75, which hollis web site says
40 lbs. / 18 kgs. lift

Maybe getting a SMS 75 wing, which has a few more lbs of lift will make the difference...