deepdiverbc
Contributor
For drysuit diving the ditchable weight is different for trilam/shell suits than it is for neoprene.
With my 7mil neoprene drysuit my biggest consideration is suit compression so I did a test. Using a fishing scale that went to 40 pounds I measured my negative buoyancy at different depths with no air in my lungs, BCD or drysuit. Here are the results.
With 31lbs of total ballast.
25ft = 9lb negative
45ft = 11lb negative
70ft = 16lb negative
85ft = 17lb negative
105ft= 19lb negative
Note
The above measurements initiate pounds of negative buoyancy and since lead looses 10% of its weight submerged you need to add 10% to the amount of submerged lead used to compensate for the above measurements.
My suit is 26lbs positive if you use it for snorkeling so at 105ft I only have 7lbs of buoyancy left in it which is lost very gradually past 100 feet.
How much weight do you need to be ditchable?
If you have a first stage failure at depth you will mostly likely be neutrally buoyant when it happens or just slightly negative if you were descending at the time of the failure, so in this case you would not have to ditch much weight if any.
If you rip your drysuit you will have your BCD to compensate for lost buoyancy and vice versa so not much ditchable weight needed if any.
If for some reason you end up at 200 feet plus and out of air I can't see how you would end up there without having air in either your BCD or drysuit.
The worst scenario I could imagine was during the descent when you have vented all air from your lungs, BCD and drysuit, and then have a first stage failure, I suppose you could also be caught in a downwelling. In this case you would drop until you dumped weight during the depths at which your suit looses the most buoyancy. So the question becomes how far would you drop before you could dump weight also considering that you should be able to kick for the surface with at least 10lbs of thrust.
The final decision on the amount you need for ditchable weight is yours to make but with the scenarios I have considered I am personally comfortable with between 16lbs-20lbs in ditchable weight. Preferably split up into two integrated pockets since the amount you would want to ditch in a worst case scenario is all of it but it is more likely you would only want to ditch half of it.
With my 7mil neoprene drysuit my biggest consideration is suit compression so I did a test. Using a fishing scale that went to 40 pounds I measured my negative buoyancy at different depths with no air in my lungs, BCD or drysuit. Here are the results.
With 31lbs of total ballast.
25ft = 9lb negative
45ft = 11lb negative
70ft = 16lb negative
85ft = 17lb negative
105ft= 19lb negative
Note
The above measurements initiate pounds of negative buoyancy and since lead looses 10% of its weight submerged you need to add 10% to the amount of submerged lead used to compensate for the above measurements.
My suit is 26lbs positive if you use it for snorkeling so at 105ft I only have 7lbs of buoyancy left in it which is lost very gradually past 100 feet.
How much weight do you need to be ditchable?
If you have a first stage failure at depth you will mostly likely be neutrally buoyant when it happens or just slightly negative if you were descending at the time of the failure, so in this case you would not have to ditch much weight if any.
If you rip your drysuit you will have your BCD to compensate for lost buoyancy and vice versa so not much ditchable weight needed if any.
If for some reason you end up at 200 feet plus and out of air I can't see how you would end up there without having air in either your BCD or drysuit.
The worst scenario I could imagine was during the descent when you have vented all air from your lungs, BCD and drysuit, and then have a first stage failure, I suppose you could also be caught in a downwelling. In this case you would drop until you dumped weight during the depths at which your suit looses the most buoyancy. So the question becomes how far would you drop before you could dump weight also considering that you should be able to kick for the surface with at least 10lbs of thrust.
The final decision on the amount you need for ditchable weight is yours to make but with the scenarios I have considered I am personally comfortable with between 16lbs-20lbs in ditchable weight. Preferably split up into two integrated pockets since the amount you would want to ditch in a worst case scenario is all of it but it is more likely you would only want to ditch half of it.
