Minimum safe height calculation guidance

The information below is provided for guidance only and is not exhaustive. Some influencing factors can be unique to certain vessels and / or areas of water and may not be listed below. You should ensure you account for ALL factors that apply to your current situation when making calculations.

Some of the factors that can influence vessel height are shown below:

Vessel displacement (weight) — A vessel’s height (from the waterline) will decrease when it is fully laden compared with its unladen displacement.
Water type — A vessel’s height will decrease by approximately 2% to 3% in fresh water compared to seawater.

Some of the factors that should be taken into account when calculating a safety margin are:

Vessel maneuvering characteristics — A vessel’s height changes due to squat, trim, roll, pitch and heave.
Chart accuracy — The electronic chart data may not be accurate or may have changed since the last survey.
Weather conditions — Low air pressure, and prevailing wind strength and direction can affect water level.