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Speed to order to make the tidal gate with the pilot aboard

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Passage planning graph: steam to the boarding ground early enough to embark the pilot before the tidal gate closesTime from now along the bottom, distance to the pilot boarding ground up the side, both to scale. The tidal gate closes in 16.5 h. 1.2 h at the end of the window goes to embarking the pilot and manoeuvring, so she must cover the 196 nm in 16.5 − 1.2 = 15.3 h: speed to order 196 ÷ 15.3 = 12.8 kn. Using the whole window gives 11.9 kn and leaves no time for the pilot. The 14 nm from the boarding ground to the berth is not in the sum.PASSAGE PLAN · TIME AGAINST DISTANCEberth + 14 nm after the gate: not in the sumtidal gate closes16.5 hboarding ground196 nmpilot + manoeuvring 1.2 hspeed to order196 ÷ 15.3 = 12.8 kn11.9 kn: whole windowno time left for the pilotnow481216hsteaming 15.3 h1.2 h

The rule

  • The window runs from now until the tidal gate closes.
  • She is not steaming while she stops for the pilot and manoeuvres, so take that allowance out of the window: what is left is the steaming time.
  • Steam only the distance to the boarding ground; the miles to the berth are made with the pilot at manoeuvring speed.
  • Speed to order = distance to the boarding ground ÷ steaming time. If it is close to her full sea speed, tell the agent now and book the next tide.

Formula

  • Steaming time = time until the gate closes − pilot and manoeuvring allowance
  • Speed to order = distance to the boarding ground ÷ steaming time

Worked example

Distance from the present position to the pilot boarding ground196 nm
Further distance from the boarding ground to the berth14 nm
Time from now until the tidal gate closes16.5 h
Time to be allowed for embarking the pilot and manoeuvring1.2 h
  1. Steaming time = 16.5 − 1.2 = 15.3 h
  2. Distance to steam = 196 nm to the boarding ground (the 14 nm to the berth is not in it)
  3. Speed to order = 196 ÷ 15.3 = 12.8 kn

Answer12.8 kn

Common mistake

Dividing by the whole 16.5 h window.

At 11.9 kn she reaches the boarding ground just as the gate closes, with the 1.2 h for the pilot still to come; the allowance has been counted as steaming time and as pilot time at once.