Tide Window Planner estimates how long draft-limited transit is likely available around high tide using charted depth, vessel draft, safety margin, and high/low tide heights. It is useful for bar crossings, marina entrances, and shallow-channel planning when timing is critical. The model treats the tide cycle as a semidiurnal sinusoid, so it is best for first-pass planning rather than final pilotage decisions. Use local tide tables and real-time observations before committing to transit.
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
Enter charted depth, vessel draft, and desired safety margin.
Add high and low tide heights for the expected cycle and run the calculation.
Use the estimated window duration and ±hours around high tide as planning guidance.
Tide Window Inputs
Estimate transit window around high tide using a semidiurnal sinusoid approximation.
Result
Required depth: 3.000 m
Required tide above datum: 0.900 m
Clearance at low tide: -0.300 m
Clearance at high tide: 2.500 m
Window available: Yes
Estimated window duration: 9.78 h
Around high tide: ±4.89 h
Worked example
Planning a shallow-channel transit
Charted depth: 1.8 m
Vessel draft: 1.5 m
Safety margin: 0.3 m
High tide: 2.1 m
Low tide: 0.2 m
Result: The planner estimates how much of the tide cycle provides enough water and reports the approximate window around high tide.
Use the window for early planning only. Confirm the actual tide station, chart datum, weather effects, local notices, and pilot guidance before transit.
How to interpret the result
A longer window gives more timing flexibility, but it does not remove local hazards.
A short or marginal window should trigger a more conservative transit plan or a delay.
Tide height should use the correct station, time zone, and chart datum for the transit area.
Surge, wind setup, river flow, waves, and bar conditions can make the real window narrower than the estimate.
Common mistakes
Treating a smooth tide approximation as a local tide table.
Forgetting chart datum, time zone, or daylight-saving adjustments.
Ignoring wave troughs, squat, siltation, or local depth restrictions.
Planning to arrive at the edge of the window without operational margin.
Review note and limitations
Method - semidiurnal sinusoid tide-window approximation using required tide height.
Navigation planning support only. Do not use this page as a substitute for official charts, tide/current sources, local rules, bridge procedures, or qualified navigation judgment.
FAQ
Is this tide window exact?
No. It is a planning approximation. Use official tide predictions, local observations, weather, and pilot guidance for actual transit decisions.
Why does chart datum matter?
Charted depths and tide heights must refer to the same datum. Mixing datums can overstate or understate available water.
What should I check before a shallow transit?
Check tide station relevance, weather, wave conditions, chart updates, local notices, draft, squat, safety margin, and any port or pilot requirements.
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