Minimum safe depth 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 how much a vessel draws are shown below:
Vessel displacement (weight) — A vessel’s draft will increase when it is fully laden when compared with its unladen displacement.
Water type — A vessel’s draft will increase 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 draft increases due to squat, trim, roll, pitch and heave.
Chart accuracy — The electronic chart depth may not be accurate or the true depth may have changed since the last survey.
Weather conditions — High air pressure, and prevailing wind strength and direction can affect wave height.