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Once again we seem to be flogging the greasy spot in the road where the horse used to be... "Buoyancy" refers to whether you are lighter or heavier than water. If you are lighter than water, you displace a volume of water equal to your mass. If you are heavier than water, you displace a volume of water equal to your volume. Remember Archimedes? If you're negative, it doesn't matter much if it's a pound or a hundred, you'll sink. If you're positive, similar analogy but you float. To dive, you must be negative. With [most if not all] steels you are negative empty or full; with [some if not all] aluminums you can be positive when empty. The weight of the "air" is fixed. You want to be slightly negative with an empty tank and empty BC; with Al this takes more weight than steel [generally speaking]. So you carry more lead for Al or less for steel; big deal. That figures on your finishing weighting requirements. HP/LP low/high capacity tanks only increase the difference in weighting between full/empty, independent of tanks. But since Al is generally positive, it takes more weight to offset the buoyancy characteristics to start with than steel which may have you more or less negative to start with. Yeah, they are generalizations, and I'm sure some nit-picking is to follow. But air is air, not that much magic involved other than Al takes more weight to offset the *initial* empty positive buoyancy. After that, all sides are essentially equal for a given volume of gas at any pressure. Jeff Kell <jeff-kell@ut*.ed*> -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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