Thorvald Natvig
Registered
I just finished my open water. It was a ton of fun, but I was surprised at how heavy the dive gear was when walking across all that sand on the beach. Not a problem, but I suffer from excessive curiosity, so I started pondering -- how do I optimize my on-land weight without sacrificing underwater buoyancy?
First thought was to look at tanks. Let's assume that between the tank and the weight on my belt, I need -15lbs of buoyancy to stay neutral at my safety stop, and let's assume that at the end of the safety stop, I've used 60cf of air for the dive.
We dove a LP85, which (from datasheets) when empty has +2.3 lb buoyancy. Capacity is 81.1cf, so after using 60cf, there's still 21.1cf left, which subtracts about 1.7lb. Hence, to achieve the goal of -15 lb buoyancy, I'll need 15.6 lb of lead. On land, the tank weighs 31.2 lb empty, so with the lead and 81.1 cf of air, I'm carrying 53.3 lb across the beach on my way into the water.
What would happen if I used a HP80, which (from datasheets) when empty has -1.7 lb buoyancy? After using 60cf of air, the remaining air is about 1.6 lb. Hence, to achieve the goal of -15 lb buoyancy, I'll need just 11.7 lb of lead. On the land, that tank weighs 28.3 lb, so with the lead and 80 cf of air I'm carrying just 46.4 lb across the beach.
I did the same calculation with a few other tank sizes, and HP80 wins when optimizing for "beach carry weight".
I'm new to diving. The weight didn't bother me, but the feeling that I'm missing something here is really bothering me. Are my calculations way off? Does the HP80, being shorter, cause the center of mass to be higher up your body, and that is undesirable? Are LP tanks easier to fill than HP tanks?
(I needed quite a bit more than -15lbs to stay down without holding on to the rope, but the additional weight applies the same regardless of tank.. Unless that's where I'm missing something?)
First thought was to look at tanks. Let's assume that between the tank and the weight on my belt, I need -15lbs of buoyancy to stay neutral at my safety stop, and let's assume that at the end of the safety stop, I've used 60cf of air for the dive.
We dove a LP85, which (from datasheets) when empty has +2.3 lb buoyancy. Capacity is 81.1cf, so after using 60cf, there's still 21.1cf left, which subtracts about 1.7lb. Hence, to achieve the goal of -15 lb buoyancy, I'll need 15.6 lb of lead. On land, the tank weighs 31.2 lb empty, so with the lead and 81.1 cf of air, I'm carrying 53.3 lb across the beach on my way into the water.
What would happen if I used a HP80, which (from datasheets) when empty has -1.7 lb buoyancy? After using 60cf of air, the remaining air is about 1.6 lb. Hence, to achieve the goal of -15 lb buoyancy, I'll need just 11.7 lb of lead. On the land, that tank weighs 28.3 lb, so with the lead and 80 cf of air I'm carrying just 46.4 lb across the beach.
I did the same calculation with a few other tank sizes, and HP80 wins when optimizing for "beach carry weight".
I'm new to diving. The weight didn't bother me, but the feeling that I'm missing something here is really bothering me. Are my calculations way off? Does the HP80, being shorter, cause the center of mass to be higher up your body, and that is undesirable? Are LP tanks easier to fill than HP tanks?
(I needed quite a bit more than -15lbs to stay down without holding on to the rope, but the additional weight applies the same regardless of tank.. Unless that's where I'm missing something?)
