The calculated buoyancy value of 260N for a 17” with 14mm wall size (and all other buoyancy information respectively) is based on the dimensions and the density of VITROVEX glass and the density of sea water. Since the density of sea water varies (1.02 to 1.03) and production tolerances for a particular enclosure may apply, this value is a good approximate; in particular, if VITROVEX spheres are used together with its protective shells. Since protective shell sets are slightly positive, one can safely assume 260N for doing any buoyancy calculations. However, without protective shells one may reduce the given buoyancy value by 5N.
Nevertheless, Nautilus Marine Service always advise to consider a safety margin in your buoyancy calculations to reflect other influences such as current or temperature changes or miscalculations on the actual weight of the equipment.
