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April 11, 2008
Weight: Fresh Water versus Salt Water
Recently, a site visitor emailed me and asked about the difference between weight in salt water and weight in fresh water. Weighing 175 pounds and usually carrying 12 pounds of weight, he wondered how much he should be using for fresh water diving.
Well, there are a lot of variables in determining the amount of weight you need in fresh water versus saltwater. Generally, people need approximately five pounds less in freshwater than they'd use in saltwater IF they are using the same gear configuration. Major considerations are exposure wear (type, thickness, and age) and the type of tank.
As an Instructor, I usually tell people wearing 7mm rental wetsuits and an 80 cubic foot aluminum tank to begin with 10% of their body weight. For a person weighing 175 pounds, I'd suggest starting with 18 pounds, to keep it even. If you're too negatively buoyant or wearing less neoprene, obviously you'd drop weights until you can sink with an empty BC after exhaling, but float at eye level with a full breath of air in your lungs.
If you will be using a steel tank, depending on the size and brand, you will wear less weights. As an example, a low pressure (2400psi) 80 cf tank is approximately six pounds negative, so a diver can automatically make an adjustment of six pounds of lead from his/her weightbelt.
When I dive in the ocean wearing a skin 2mm wetsuit, I generally wear 6 - 8 pounds of lead. However, when I am wearing a 2mm wetsuit in fresh water with a steel 80cf tank, I don't wear any weights at all. Last August when Conrad and I dived Lake Tahoe I wore a 4/3 wetsuit. On the first day I used a low pressure (2400 psi) 95 cubic foot tank with no weights, hood or gloves and I was just about perfect. On the second day I added a hood and gloves and switched to a high pressure 130 cubic foot tank and was extremely negatively buoyant. I had no choice in that situation other than to switch tanks, but none were available. So, I made the best of the situation, went on the dive, added air to my BC, and had a wonderful dive! :-)
Bottom line is that you need about five pounds less in fresh water than in salt water. The exact gear configuration (wetsuit, tank, BC, etc.) also makes a difference. All too often, divers are over-weighted in most diving conditions. In turn, this affects their buoyancy and can greatly increase their air consumption.
Posted by Carol at April 11, 2008 04:39 PM