Weighting question

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pro99line

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Location
Theodore, AL. USA
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I have not made a dive with my new steel tank. With my equipment and an AL80 I used 10lbs in fresh and 22lbs in salt which is a difference of 12lbs. Now my question is, if I test my weight in fresh with the new steel tank and just say I now use 4lbs in fresh (I am not sure of the actual number since I haven't been in fresh with the tank yet), is it safe to say I should start with 4lbs plus the 12lb difference and try that in salt as a starting point and adjust from there? or is there a better way to calculate going from aluminum to steel. BTW it is a XS Scuba HP100 steel if you are wondering. I am just trying to find a starting point so I can adjust and then do my dive and hopefully fine tune some more. I have posted the specifications of the old cylinder and the new one.

AL80
Buoyancy*FULL - 1.4 lbs.
Buoyancy*HALF + 1.5 lbs.
Buoyancy*500 psi + 3.4 lbs.

HP100
Buoyancy*FULL - 10.0 lbs.
Buoyancy*EMPTY - 2.5 lbs.
 
To figure out your proper weighting going from your Al80 to your HP100, you need to compare the difference in empty buoyancy of the tanks. An empty Al80 is +4.4lb, while your HP100 is -2.5lb. This is a difference of about 7lb. This means you can take 7 pounds off your weight belt when going from an Al80 to an HP100.

It should be pretty much the same regardless of salt vs fresh (i.e. you'd need 3lb in fresh water and 15lb in salt). However, the difference between your salt and fresh water weighting seems to be pretty big. Have you done a proper weight check? Granted I've never dived in fresh water, but I wouldn't expect your proper weighting difference to be that big (maybe it is though....).
 
Do you also change exposure protection between fresh and salt water? That's a huge difference in weight if it's just from salinity.

Basically, you are going to take off about six pounds by going from Al to steel (I'm conservative, and would use 5). So if you have your weight correctly determined in salt water, simply subtract 5 lbs and start from there. No need to redo the ratio (which is add 2.5% of the total weight of you and your gear to go from fresh water to salt -- which would imply you and your gear are in the 450 lb range to account for a ten pound difference!)
 
I always found trial and error to work great. On the second dive I usually have it dialed in...
 
All the advice given above is good but when you say the difference between salt and fresh water for you is 12 pounds that can't be correct. Which means you either haven't done a proper weight check in fresh water or in salt water.

The salinity doesn't vary that much so unless you weigh 250 lbs and carry 200lbs of gear the difference can't be 12 lbs.
 
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For me, the difference is about 6 pounds. Two in each of the integrated pockets and one in each trim pocket higher up. That keeps my position about the same.
 
I was at work when I posted and did not have my logbook in front of me. I checked and it shows I posted incorrectly. It appears looking through my boook that I have never worn the same combination in fresh and salt. Saltwater was 22lbs with the configuration I was using. I am now swapping from the AL80 to the HP100 and based on what everyone has said so far. Appears I can remove between 5 - 7 lbs. That gives me some good numbers to start with. I work with ShagMan and purchased his old dive rite steel backplate and venture single wing but have never used it, so it next I will begin using it and getting my weight down some more. Thanks for the advise everyone.
 
pro99line:
It appears looking through my book that I have never worn the same combination in fresh and salt.

I'm glad to hear it because if it were with the same set up and assuming you are weighted correctly, you and your gear (dry) weigh in at 480 lbs.
 
I'm glad to hear it because if it were with the same set up and assuming you are weighted correctly, you and your gear (dry) weigh in at 480 lbs.

Haha. Yeah I am only 175. In fresh I was wearing a farmer john, 3mm top with 5mm bottom and skin. In salt I only wore the 3mm top and a skin. Both I used an AL80 tank and Seaquest Pro Unlimited BC.
 
Haha. Yeah I am only 175. In fresh I was wearing a farmer john, 3mm top with 5mm bottom and skin. In salt I only wore the 3mm top and a skin. Both I used an AL80 tank and Seaquest Pro Unlimited BC.

I used 18lbs fresh with the full suit. With just skin and AL80 I used 4lbs fresh. I have no clue why I thought 10lbs this morning when I posted. :confused:
 
https://www.shearwater.com/products/perdix-ai/

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