With the development of ship sizes, available space for ships to navigate in restricted waterway gradually decreases. Therefore it is vital to give an accurate prediction of squat in restricted waterway for the sake of safety. Objective of this paper is to present method to apply appropriate formulae to specific channels and ships for prediction of squat. In this study, popular formulae for squat prediction are compared and validated to measured data of several model tests with similar feature of target condition. Formulae for further investigation are selected based on comparison results. Then these formulae are applied to object channel with three typical sizes of ships. Moreover, maximum speed in restricted waterway due to effect of squat is predicted and analyzed. The result demonstrates that larger ships tend to occur more significant squat in restricted waterway and consequently should sail with more limited draught considering safety. It is recommended to validate applicability of formulae for object condition with similar tests before application to specific cases.
With the upgrading of the ship fleet, recent years have witnessed increasing trend of dimensions of ships. Meanwhile port or waterway authorities are usually unable to expand the waterway dimensions with the synchronous pace. Therefore, available space for ships to navigate in restricted waterway have gradually decreased. The restricted room underneath and alongside ships has noticeable influence on the increase of the ship draught and consequent reduction of distance between the ship bottom and the sea or river bed when moving forward. This phenomenon is known as ‘ship squat’ (Constantine, 1960).
Squat is a strong risk factor for grounding that potentially results in severe damage to the ship and in extreme cases may give rise to complete loss of ships as well as channels and ports. It is never excessive concern because more than 40 ships have suffered grounding in recent years (Barrass, 2012). Grounding of passenger liner Queen Elisabeth II is one of the most striking cases, which produced repair bill of 13 million dollars, plus an estimation for lost passenger booking of 50 million dollars (Pasquay, 2001).