Posted by MHK on November 14, 2000 at 09:55:15:
Further to the DIR thread below and Gerry's request to zero this issue in on the ditch -v- non ditch discussion I thought it would be worthwhile to dedicate a thread simply to this issue. We'll keep this thread focused on recreational diving and the notion of why it is important to distribute your weights proportionately and allow enough weight to be ditched so as to be able to get off the bottom should your inflation source fail but yet not enough that if you do ditch you will rocket to the surface..
Good discussion guys....
A properly weighted diver ( atleast here in SoCal )is generally diving with a 7 mil wetsuit or a drysuit.. As a GENERAL rule of thumb I always recommend 10% of your total body weight plus about 6 pounds.. After tweaking and adjusting the 6 may come down a pound or two but that's the starting point. ( If anyone's disagree's with the starting point, let it go for the minute and we'll discuss it after we sort out the ditch -v- non -ditch )..
So assuming you have a 200 lb diver, that diver is looking at needing 26 lbs in this stated fact pattern. FTR, all too many diver's think this means 26 lbs on teh weightbelt and then ignore all the other components of a weighting package taken as a whole ( ie; ankle weights, steel tanks, SS BP's and the like )..
So assuming the diver is using a AL 80, which swings from ~3 lbs
negative to ~3 lbs positive full -v- empty.. It's important to note that a diver should balance two components when approaching weight -v- lift capacity.. You want to weight yourself for the lightest point of your dive, this is generally at the end of your dive when the tank [s] are empty but you want enough lift capacity to lift yourself for the heaviest point of your dive, which is generally at the beginning when the tanks are full.. By correctly balancing these concepts you have enough lift at any point in your dive should you need it, but you have sufficient weight to hold your 15' safety stop..
To the extent that the diver in our example uses all 26 lbs on his weightbelt and needs to ditch for whatever reason it is likely that this diver would ascend much too quickly and could risk and AGE.. Gerry as I side note, I don't dispute that Navy diver's could ascend from 100' and control the exhale so as to limit the risk of an AGE, however I don't believe that John Q. Diver when faced with an emergency ( possibly an OOA )would have the presence of mind or the discipline to control the exhale..
That being said a few simple, and very common non-technical techniques to consider, are as follows:
You can re-distrbute the 26 lbs in several fashions by using a steel tank which ( depending on size and make ) generally run 4 lbs negative, you could use a SS BP ( 6 lbs negative ), you could use a light cannister ( granted this is more desirable for tech diver's but I'm throwing out options ), some diver's use ankle weights, some diver's use keel weights or V-weights..
By using any combination of the above it is critical that you allow enough ditchable weight so if you need to get to the surface you can.. I don't want anyone left with the impression that you should use any combination of the above to incorporate all non-ditchable weights.. That would be a receipe for disaster, particularly in the open ocean..
In terms of my discussion with Gerry, I'm troubled with the notion that it would be appropriate, much less encouraged, to put all the weights in one basket ( so to speak ) and then ditch the entire package to get to the surface.. If this is what is being taught we should continue this discussion because I don't believe this is a wise course of action... I think Gerry and I have a difference of opinion when it comes to the notion of a diver ascending slowly while holding his/her breathe.. I agree, of course, that every diver, TO THE EXTENT THAT THEY CAN, should breathe ( ie; not hold your breath) but in an OOA emergency panic sets in and most, if not the overwhelming majority of diver's are not skilled or practiced enough to ditch ALL of there weights, blow and go and then remain calm enough to exhale even in the face of an OOA.. By taking a few lbs off the weightbelt and distributing them wisely the diver still is able to get to the surface but can do so and reduce the risk of an AGE..
Later