Al40 vs lp50

[Asheron]

Okay everyone, please review what I am thinking and let me know if I am messed up because I am having a hard time figuring out that AL40 are actually a better weight investment than LP50's.

My thought process:
Empty Weight + Empty Bouyancy= Weight to make neutral

The lower the overall weight to make neutral means less weight ill have to haul down the beach.

LP50
18.9lb + 1.24lb = 20.14lb of total weight for neutral

Luxfer SO40
14.9lb + 2.4lb = 17.3lb

Metal Impact AL40
15.3lb + 1.4lb = 16.7lb

Catalina S40
16.2lb + 1.4lb = 17.6lb

So it is approximately 3 to 4 lbs in weight saving to haul an Aluminum 40 down the beach over the steel lp50 and they are cheaper?

 

[Marie13]

Get the 50s, especially if you can get overfills on them. Steel is better for cold water.

If I can walk out of the water with two 50s clipped to me (SM) with my bad knees and not in as good of shape as I could be, then a guy can handle the extra weight of 50s.

 

[Asheron]

But why? If I am thinking about this correctly, I could potentially save almost 8 lbs walking down the beach on my SCR rebreather I am piecing together. The additional capacity is probably not needed.

Edit: this post is to figure out if my thought process is correct.

 

[happy-diver]

What weight will permit you to submerge when you complete the SCR rebreather you are piecing together

Do you know how much gas you will be belching out into the ocean

 

[Asheron]

I am unsure of weight the submerge the unit right now. I am trying to shed all reasonable weight and was just looking through cylinder weights since my buddy loaned me LP50's.

It should be 1/3 ratio to start since I'll be using a GEM mouthpiece and ill probably dial it back to 1/5 expelled ratio per a breath. My OC RMV is around 0.4cuft/min so I expect around 0.167 cuft/min/ATA expelled. The Gem mouthpiece is not depth compensated like the RB80.

Edit: Corrected expelled gas to reflect 1/3 ratio

 

[happy-diver]

As it has taken me one year to assemble my Freedom Plate, formed by a Mr Eric Sedletzky, respected SB member

So when you affix your friends lp50s to your wonderful unit Asheron, all your answers will be burst forth upon you

Do you like my Freedom rig, it's nice isn't it.

Happy building

 

[rjack321]

I am unsure of weight the submerge the unit right now. I am trying to shed all reasonable weight and was just looking through cylinder weights since my buddy loaned me LP50's.

It should be 1/3 ratio to start since I'll be using a GEM mouthpiece and ill probably dial it back to 1/5 expelled ratio per a breath. My OC RMV is around 0.4cuft/min so I expect around 0.167 cuft/min/ATA expelled. The Gem mouthpiece is not depth compensated like the RB80.

Edit: Corrected expelled gas to reflect 1/3 ratio

what gas(es) are you planning on diving?

 

[Asheron]

Probably 32 to 40 nitrox, usually 36 to match the guys who are running Mares Horizons. This isn't a "serious"(all rebreathers are serious!!) tool since I will be cruising around with the horizon guys who are restricted by the computer system to 132ft.

 

[Cio]

I think this isn't really an apples to apples comparison, there are tiny Steel 40s that are better than alu 40s from a weight comparison

HP Steel 40 14.8 lbs - 1.48lbs = 13.32# Not too expensive, $184 much lighter and shorter.

The LP50 holds 25% more than an AL40 and that a worst case. The #/CF is better on an LP50 so it is a more efficient form to carry gas, but its wasted weight if you simply don't need it.

If lightweight and 40CF are your requirements, Steel HP40 is the winner.

 

[grantctobin]

I think this isn't really an apples to apples comparison, there are tiny Steel 40s that are better than alu 40s from a weight comparison

HP Steel 40 14.8 lbs - 1.48lbs = 13.32# Not too expensive, $184 much lighter and shorter.

The LP50 holds 25% more than an AL40 and that a worst case. The #/CF is better on an LP50 so it is a more efficient form to carry gas, but its wasted weight if you simply don't need it.

If lightweight and 40CF are your requirements, Steel HP40 is the winner.

Except that HP40s are:
1) less likely to be fully filled
2) too short to sidemount as bailout (<18”)
3) have nearly no resale value