Posted by Kendall Raine on November 13, 2000 at 13:18:56:
In Reply to: steel vs. alum.: where's the logic? posted by JRM on November 13, 2000 at 12:06:07:
JRM;
With a wet suit in OW you have no redundant buoyancy. You therefore want to have ditchable weight. Whether you use a keel weight or other form of non-ditchable weight, you should still be able to dump enough ballast to become slightly positive at depth-emphasis on slightly since turning yourself into a Polaris missile is counterproductive. Since steel tanks generally have much greater negative buoyancy when they're full than do most AL's, you have a greater proportion of your total weighting in the tank which is non-ditchable. The buoyancy shift from full to empty is not the question-it's what can you do to get off the bottom, or out of free-fall, if you sustain a total BC failure at your most negative point in the dive.
You also mention grit in your dump valve this past weekend. That's the problem with dump valves. I would strongly recommend you change it for an elbow. Consider last weekend's failure a warning of possible disasters to come.
I used to use Poseidon seconds. I agree they're nice to have since the don't have an up or down. They do have a really serious flaw, however, in that you can't get the grit out of them without a screw driver. This point came home to me in a cave in Mexico when, after negotiating a tight restriction, my Jetstream was completely full of crap. They breath really wet when the diaphram gets gunked up. A G250 or similar reg I could have opened and cleaned on the fly. If you don't believe me I have two Jetstreams I'll sell you for a good price.