 The preparation phase usually removes a significant amount of weight, so the ship floats higher in the water than normal.This may make it necessary to stabilise the vessel by filling some compartments with water as makeshift ballast tanks to prevent excessive rolling in port or during towing.The ship is towed to the sinking location, usually in waters shallow enough to allow access by a large number of divers, but deep enough to be relatively unaffected by surface weather conditions.