Under Keel Clearance Calculator

Input Pattern

Enter values in the left panel, keep units explicit, run the calculation, then copy or share the result. Invalid fields are highlighted immediately.

How to use this tool

1. Enter charted depth and expected tide height at transit time.
2. Add draft and dynamic allowances (squat, wave, safety margin).
3. Run the calculation and verify whether resulting UKC stays non-negative.

Worked example

Checking constrained-channel clearance

• Charted depth: 7.0 m
• Tide height: 1.2 m
• Draft: 6.5 m
• Squat: 0.3 m
• Wave allowance: 0.2 m
• Safety margin: 0.4 m

Result: Available water is compared with draft plus allowances to estimate remaining UKC.

A positive value does not automatically approve transit; local rules, pilot guidance, survey confidence, and vessel dynamics still matter.

How to interpret the result

• Positive UKC means the entered allowances fit within available water.
• A small positive UKC should be treated cautiously because measurement and environmental uncertainty can erase the margin.
• Squat, heel, trim, waves, siltation, density, and speed profile can change real clearance.
• Port, pilot, or company policy may require larger margins than the entered value.

Common mistakes

• Mixing chart datum and tide datum incorrectly.
• Forgetting squat, wave allowance, heel, trim, or density effects.
• Treating charted depth as current surveyed depth without checking updates.
• Using a single UKC value for an entire channel with changing depth and speed.

FAQ

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