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Navigation

Speed, distance, tide and keel clearance, from the watch to the master's passage plan.

15 pagesThird Officer – Master

  1. Third Officer

    1.Speed made good over the watch: the ground, not the logSpeed made good is the distance between the plotted positions ÷ the whole length of the watch; the stoppage stays in, because your next ETA is worked from it.
  2. 2.Distance still to run when you hand over the watchWhat your watch covers is speed × the hours it really runs; take that off the distance you were handed, and nothing from an earlier watch comes off again.
  3. 3.Distance run, corrected for log errorAn under-reading log shows fewer miles than she ran; so add the percentage of what it shows, and the corrected distance is bigger.
  4. 4.Gyro error from a sun azimuthGyro azimuth − true azimuth gives the error; take it off every gyro bearing if the gyro reads high, and add it if it reads low.
  5. 5.Height of high water at a secondary portApply the difference for the same tide: high water for high water, low water for low water; the range changes, not only the level.
  6. 6.Steady bearing: what the range will be at the next plotWhile the bearing stays steady, the next range is the present range minus relative speed × the interval; first check that the two plots agree with that speed.
  7. 7.How long before she reaches your passing distance?While her bearing stays steady, your time to act is the range minus the passing distance, divided by the relative speed.

  8. Second Officer

    8.Noon speed when the clocks went backRunning west, the day from noon to noon is longer than 24 hours; divide the distance made good by 24 plus the hours the clocks went back.
  9. 9.What going round a traffic separation scheme costs in timeWork two whole passages and take one from the other; the route through the scheme is shorter but slower in the lane; the extra miles alone overstate the cost.
  10. 10.Height of tide needed to berth with the company's under-keel clearanceDeepest draught plus the required clearance, minus the charted depth, is the height of tide the berth needs; the tide must supply what the chart does not.

  11. Master

    11.Squat in shallow water: Barrass's formulas and the under-keel clearanceSquat grows with the square of speed: Cb × V² ÷ 100 in open water, ÷ 50 in a confined channel; take it off the static clearance before calling the UKC enough.
  12. 12.Under-keel clearance over the shoal patchWater over the patch is charted depth plus height of tide; the ship in it is deepest draught plus squat; the clearance is the difference.
  13. 13.Speed to order to make the tidal gate with the pilot aboardTake the pilot and manoeuvring allowance out of the window first; then divide the distance to the boarding ground by the steaming time left.
  14. 14.Which advance for tonight's wheel-over?The booklet gives the advance only for ballast and loaded; interpolate it by tonight's displacement, from the advance column, not the transfer.
  15. 15.How big is your swinging circle?Your swinging radius is the cable veered plus your whole length overall, never half of it; the circle you swing in is twice that radius.