Calculate a simplified under-keel clearance with explicit assumptions.
What you’ll practise
- Combining compatible soundings and tidal heights
- Calculating static under-keel clearance
- Testing falling-water assumptions and practical margins
Each question includes a custom diagram, the reasoning behind the answer, an explanation of the other choices and a follow-up exercise. Try the quiz first, or use the study view to read every answer.
01 / Learn
Keep a common reference
For these fictional exercises, charted depth and tide height share the same vertical datum and all values are metres. Estimated water depth = charted depth + height of tide. Static under-keel clearance = estimated water depth − vessel draught. Check actual chart and tide-table references before using real data.
02 / Learn
A worked example
A fictional sounding is 2.4 m, the predicted tide height is 1.1 m and draught is 1.8 m. Estimated water depth is 3.5 m. Static clearance is 3.5 − 1.8 = 1.7 m. That is a calculation, not a declaration that a route is safe.
03 / Learn
Allow for the real world
Predicted tide levels can differ from observations, including because of weather. A practical clearance assessment must also consider waves, vessel movement, squat where relevant, survey uncertainty and the skipper’s required margin. Do not apply this addition rule to bridge clearance: overhead structures can use a different reference.
Your two-minute exercise
With the same fictional 2.4 m sounding and 1.8 m draught, calculate static clearance at tide heights of 0.3 m and 1.3 m. List what you still need to know.
Keep learning from the source
Source check: . Scenarios and quiz questions are original YouSail practice material. Editorial policy.