Scott M:
OK, I've read until I am blue in the face (or maybe it was the scotch) anyway. After reading all the threads I am trying to figure out what makes the way you weight at the start work of the dive work at the end?
From what I understand if properly weighted you will float at eye level at the start of a dive and have to exhale to sink when properly weighted. How does that correlate to the end with 500lbs and being neutral?
I know ideally you should weight test your weight with 500 lbs in the tank and then work from there but if that is not an option. And I have done the math for a proper weighting to start the dive. I am more looking for how one effects the other.
Thanks for any insight
There are several schools of thought on what is proper, for proper weighting.
Generally speaking, the less weight you have on, the better your buoyancy and trim will be, and the less air you will consume. Therefore most divers try for minimal weighting.
Since compressed air weights about 0.08 lbs per cubic foot, you will be losing weight throughout your dive by exhaling (unless you are diving with a CCR). That equals about a 5 lb swing for an 80 cu ft tank. Since you cannot easily split 5 lbs into halves, we usually round up to 6 lbs, and therefore add 3 lbs to each side of your weight belt or integrated weight pouches to compensate for the weight loss from the gas you will exhale during your dive, if we are adjusting your weighting as of the beginning of the dive.
If you adjust your weighting so that you float vertically at eye level, at the beginning of your dive, without being able to submerge unless you exhale completely, then by adding another 6 lbs, you will be perfectly neutrally buoyant at the end of your dive, when your tank is lighter from being down to 500 psi.
Some divers take it a step further, and they make the weight adjustment while submerged at 15 ft with 500 psi in their tank. This will then also take into account suit compression at the final safety stop. It tends to trim a few more pounds off the weight belt, but the trick is that you cannot let yourself surface until your 3 min safety stop has been completed.
One you get your weighting optimized, then you will find that at the beginning of your dive, that you will need to exhale completely to slowly descend. This is especially true if you did the 15 ft submerged at end of dive adjustment.
Where you then move your optimized weighting to, around your body, will determine your trim in the water. Horizontal is preferred, for most advanced divers. However some divers who have ear clearing problems may need to be more verticle in order to descend and be able to clear their ears.
The difference in your weighting from the beginning of your dive to the end of it will be 0.08 lbs per cu ft of air that you breathe during the dive.
