Tanks, Weights, Aluminum vs Steel

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I am a bit confused. Please give me your thoughts on this. Diving warm salt water in a full 3mm with AL80 and 10lbs. Now going to dive with same variables (salt/3mm full suit) except will use HP steel 100. Do I ditch 6lbs and dive only with 4lbs?
 
So I have a dive coming up and want to get reasonably close on my weight. Not sink like a rock or bob helplessly on the surface.
I use 10 lbs with aluminum 80s and a 3 mil suit in fresh water. I used 14 lbs with a 3 mil shorty and aluminum 80 in salt water.
I will be diving Steel 117s in salt water with a 5 mil suit. What should my starting weight be? It was suggested 8 lbs but I am newly back to diving and don’t have a lot of recent data on my weights for comparison.
I know the steel 117 will count for some weight added while the 5 mil suit will require some weight added. I am not sure where they might balance out. What say the experts?
Even after 40 years diving when I go to a new environment, like warm water (Thailand) from cool (UK) I always use the first dive to do a weight check.

There are too many valuables:
* The cylinder’s mass = even cylinders from the same manufacturer can vary. I’ve used 12Lt steels with 17Kg mass and others with 13Kg.
* Water density - can vary in monsoon season, the surface can be diluted with fresh water.
* Changes in dive kit - different fins or BC can change buoyancy.
* How much fat I’m carrying - normally changes during 2 week diving holidays.
 
Like Edward above, everytime I travel I weight check on the first dive - even though the items that will be different from my normal weekly diving are cylinder, and perhaps exposure suit. Like Edward my weightign decisions are instinctive based on experience, to teh following is used for conformation

My rule of thumb, is with a full tank, normal breath etc, having deflated my BCD, to "float" with the top of my head about a hands width under the surface. That gets me into the ballpark and I'll be beside the boat if I need to add or ditch

During the dive and especially near the end I'll mentally assess my buoyancy (often feeling the wing to see how much air its got (not really possible in a jacket) and then make any changes as required

Always remember that on the first dive the wetsuit will be dry thus slightly more buoyant, and newer/infrequent divers will need a few diver to relax and thus will be slightly more buoyant. So during a multi day trip you could expect to reduce yoru starting weight a little further.
 
I am a bit confused. Please give me your thoughts on this. Diving warm salt water in a full 3mm with AL80 and 10lbs. Now going to dive with same variables (salt/3mm full suit) except will use HP steel 100. Do I ditch 6lbs and dive only with 4lbs?

I dive in warm water.. for me that's from 24c and above temperature but not in a wet suit.... shorts and t shirt only...
 
I dive in warm water.. for me that's from 24c and above temperature but not in a wet suit.... shorts and t shirt only...

...and my weight question? Do you dive with steel tanks?

I freeze. I wish I had a 5mm for water temperatures below 26.6 C or 80F.
 
I am a bit confused. Please give me your thoughts on this. Diving warm salt water in a full 3mm with AL80 and 10lbs. Now going to dive with same variables (salt/3mm full suit) except will use HP steel 100. Do I ditch 6lbs and dive only with 4lbs?

When I do that, I ditch 6 lbs. :) 3mm with AL80 I use 6lbs. 3mm with HP100 I use 0 Lbs. :)
 
Just a mention from an experience I had many years ago. If you calculate your weight too light and you find yourself at the end of the dive trying to do a safety low on air, you really don't want to be struggling to stay down. The more air you suck, the lighter you become, the more air you suck. It can spiral out of control and force an ascent when you should have been able to relax and hold a full safety stop. Thus I learned to error on the side on of heavy when calculating ballast.
 
People often talk about doing weight checks and noting weight in the log book, as well as using the first dive in a new place to do the check. I did a weight check as a beginning diver 15 years ago for using my 7 mil farmer john wetsuit and steel 120 tank.
I sold that heavy SOB and wound up with 4 AL80s, so I of course did a new weight check (could've just dropped 5-6 pounds I guess). Then I did a weight check in my shorty for summer dives in the NYC area. Did one for my body suit when I traveled to Panama.
Wrote the 3 cases down on a sheet of paper. My body weight has varied by 20 pounds over the years--didn't do other weight checks for that.
Bought a new farmer john several years ago and had to adjust weights for that, but didn't do a formal check.
Don't figure I'll ever do one again, or not for years (if I'm still diving....).
No need to be doing weight checks every time you go somewhere new. I suppose maybe with rental gear, but you do know what sort of gear it is--ie. wetsute thickness, tank type.
 
https://www.shearwater.com/products/peregrine/

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