Navigation Depth Calculator

Inputs

Units

All inputs are interpreted in the selected unit.

Vessel draft

Keel to waterline at operating condition.

Under-keel clearance

Minimum clearance between keel and bottom.

Squat allowance

Set 0 if not used.

Wave allowance

Vertical motion due to waves and heave.

Tide allowance

Positive raises water; negative reduces water.

Siltation allowance

Expected bed build-up between cycles.

Survey uncertainty

Measurement and charting uncertainty.

Safety margin

Project-specific conservative buffer.

Existing water depth (optional)

Current depth below datum at location.

Seabed level vs datum (optional)

Example: -7.5 means seabed is 7.5 below datum.

Estimate dredge volume (needs seabed level)

Uses width, length, slope, and cut depth.

Channel bottom width

Bottom width at dredged level.

Channel length

Length of reach to dredge or maintain.

Side slope (H:1V)

0 = vertical sides; 3 = 3H:1V.

Bulking factor

Loose volume = in-situ × bulking factor.

Reset

Tip: Calculate first; downloads include your latest inputs and outputs.

Example data

Sample maintenance check scenario (meters shown).

Draft (m)	UKC (m)	Squat (m)	Wave (m)	Tide (m)	Silt (m)	Survey (m)	Safety (m)	Required depth (m)
7.2	0.8	0.3	0.2	0.5	0.4	0.2	0.3	8.9

With 8.9 m required, a location with 8.2 m existing depth needs 0.7 m additional dredging.

Formula used

Required Depth = Draft + UKC + Squat + Wave + Siltation + Survey Uncertainty + Safety Margin − Tide Allowance

Tide allowance is positive when higher water is expected.
If you enter existing depth: Additional Dredge = max(0, Required − Existing).
If you enter seabed level: Cut Depth = |Bottom Level − Seabed Level|.
Volume uses a trapezoid approximation when side slope is provided.

How to use this calculator

Always align allowances with local guidance and project specifications.