O Praticante de Prático

The main factors affecting ship squat are:
• The forward speed Vk which is the speed of the ship over the ground. This is the most important factor because ship squat varies directly as Vk² . If the speed is halved then the squat is quartered;
• The block coefficient Cb. Squat varies directly with the Cb. In other words, oil tankers and OBOs will have comparatively more squat than passenger liners and container ships;
• The relationship between the depth of water (H) and the static mean draught of the ship (T). As H/T decreases, squats increase;
• The presence of river or canal banks. The closer banks are to the sides of a moving vessel, the greater will be the squats; and
• The presence of another ship in a river in a crossing or passing manoeuvre. The presence of the second ship increases the squats on both vessels.

It has been found, based upon observations of both actual ships and models, that squat varies in proportion to the square of the speed. If ship's speed is doubled, squat increases by a factor of four. With today's large ships and minimal underkeel clearances it becomes immediately obvious why speed, which is the factor over which the mariner has the greatest control, and resulting squat must be very much on the shiphandler's mind. It should be noted that the ship's speed here refers to the speed of the ship through water and not the ground speed so, if the ship is moving against a current, the speed effect will be increased.