Keel Clearance

MARITIME – TIDE & TIDAL TREAM CALCULATOR Keel Clearance A precise tool.
📖
What is the Keel Clearance & How does it work?

Tidal variations cause the water level at a port or channel to rise and fall, directly affecting the space available beneath a vessel’s keel. Maintaining a safe under‑keel clearance prevents grounding and structural damage, especially in shallow or rapidly changing waters.

The predicted water depth at a given time is obtained by adding the charted charted depth of the seabed to the expected tide height from tide tables or real‑time tidal predictions. This depth, together with the vessel’s draft, determines the margin of safety.

The under‑keel clearance (U) is simply the difference between the predicted water depth (Dpred) and the ship’s draft (d). A positive result indicates a safe margin, while a negative value signals an imminent grounding risk.

U = D_{text{pred}} – d_{text{draft}}
U = Under‑keel clearance (m)
⚙️
Parameters
Result —
❓
Frequently Asked Questions
What is under-keel clearance in maritime navigation?
Under-keel clearance is the vertical distance between a ship’s keel and the seabed, crucial for preventing grounding and structural damage.
How do I calculate predicted water depth at a given time?
Add the charted depth of the seabed to the expected tide height from tide tables or real-time tidal predictions.
Why is maintaining under-keel clearance important?
Maintaining sufficient under-keel clearance prevents a ship from grounding and protects its structure, especially in shallow waters with rapid tidal changes.
What factors affect the water level at a port or channel?
Tidal variations are the primary factor affecting water levels at ports or channels, causing them to rise and fall.
How do I determine the vessel’s draft?
The vessel’s draft is typically provided by the ship’s specifications or can be measured as the distance from the waterline to the keel.
Can I use real-time tidal predictions for this calculation?
Yes, using real-time tidal predictions is recommended for accurate calculations of predicted water depth and under-keel clearance.
What should I do if my calculated under-keel clearance is too low?
If the under-keel clearance is too low, you should adjust your course or schedule to avoid navigating through that area until conditions improve.

Results are for informational purposes only and do not constitute professional advice.