Chris Ross
Contributor
BTW, the mass of lead you need will be quite close to the same as the mass of copper, just the volume will be smaller because the density of lead is higher, the buoyancy difference will be about 20g less buoyant than copper and putting it in the housing will make a small amount of difference (by the amount of water the lead displaces) but it won't be much, maybe 30g. The weight you estimated is just under one pound so a 1 lb dive weight would be about perfect, if you get one that has belt loops cable tie it on to the base of the housing. If the 1 lb weight is exactly 1 pound then strapping that on should make is about 40 gram negative in fresh water.
If you take the total weight of the housing in water that displaces the same weight of water when neutral, salt water is 1.025 x heavier than fresh so a 3 kg housing would 3 x 1.025 = 3.075 - 3 = .075 kg or 75 g more buoyant, so if it was 40 gr negative in fresh it will 75-40 = 35g positive in salt. To be precise you should subtract the amount of negative weight off the weight of the housing in air and the that is the weight of water displaced by the housing. Buoyancy is the weight of the volume of water displaced by the housing arms etc.
If you take the total weight of the housing in water that displaces the same weight of water when neutral, salt water is 1.025 x heavier than fresh so a 3 kg housing would 3 x 1.025 = 3.075 - 3 = .075 kg or 75 g more buoyant, so if it was 40 gr negative in fresh it will 75-40 = 35g positive in salt. To be precise you should subtract the amount of negative weight off the weight of the housing in air and the that is the weight of water displaced by the housing. Buoyancy is the weight of the volume of water displaced by the housing arms etc.
