Shed lead , New tanks

[Diesel_Diver]

I have recently acquired a couple of Blue Steel (Faber) HP 133 tanks. Been diving Catalina AL 80’s . Question is where to start with my next weight check. I am thinking about 10 lbs off . Am I close? Or at least a good place to start?

 

[Andy in Gap]

That's too much, I would start with 4 lbs. Your new tank is just slightly positive when empty, maybe +1 lb. You will feel overweighted at the beginning of your dive with a full tank.

 

[Ontwreckdiver]

Here is the spec chart for your HP 133. Blue Steel Scuba - Cylinder Specs and the spec chart for your Aluminum 80. SCUBA | High Pressure Aluminum Gas Cylinders | Composite Cylinders

 

[BRT]

5-6 lb

 

[runsongas]

make sure to double check if your catalina tanks are c80 or s80

 

[scubadada]

DGX has a similar list of specs as is posted by @Ontwreckdiver. Looks like difference empty will be more like 2-3 lbs.

 

[rsingler]

Optimal Buoyancy Computer

 

[boulderjohn]

Don't just look at the total buoyancy swing. If you will be doing the same dives as before and breathing the same amount of gas as before, you will be not be going through the full buoyancy swing with the new tanks. If you start with a full tank it will be nearly half full when you are done.

 

[scubadada]

Don't just look at the total buoyancy swing. If you will be doing the same dives as before and breathing the same amount of gas as before, you will be not be going through the full buoyancy swing with the new tanks. If you start with a full tank it will be nearly half full when you are done.

Good point, but why would you switch from an AL80 to a steel 133 (mega of the usual HP steels), if you did not plan on using a lot more gas? There are smaller and/or lighter cylinders if you don't need that much gas. I guess he can add back 0.0807 lbs for every cubic foot not used

Quick estimate: breathe his Catalina AL 80 down to 500 psi, 12.95 cf of gas left, cylinder will be around 3 lbs positive. Breathe a HP 133 down 64.4 cf, you would have 55.6 cf left, cylinder will be about 3 lbs negative, a difference of 6 lbs.

So I revise my weight estimate for @Diesel_Diver He will be able to take off somewhere between 2 1/2 to 6 lbs, depending on how much gas he uses relative to his AL80.

 

[Diesel_Diver]

Good point, but why would you switch from an AL80 to a steel 133 (mega of the usual HP steels), if you did not plan on using a lot more gas? There are smaller and/or lighter cylinders if you don't need that much gas. I guess he can add back 0.0807 lbs for every cubic foot not used

Quick estimate: breathe his Catalina AL 80 down to 500 psi, 12.95 cf of gas left, cylinder will be around 3 lbs positive. Breathe a HP 133 down 64.4 cf, you would have 55.6 cf left, cylinder will be about 3 lbs negative, a difference of 6 lbs.

So I revise my weight estimate for @Diesel_Diver He will be able to take off somewhere between 2 1/2 to 6 lbs, depending on how much gas he uses relative to his AL80.

Bigger tanks for increased bottom time of course. With an AL 80 I routinely get in the 35-40 minutes range, shore diving with water temps in the mid 30’s . The majority of people around here run 117 or 133 some side mount 50’s . But end of the day I am normally the first one low.