SailorNotebook
All lessons

NavigationPage 4 of 12

Height of high water at a secondary port

Bu sayfanın Türkçesi

Tide staffs on one chart datum: the standard port's heights carried to the secondary port by the height differencesTwo tide staffs on one vertical scale from the same chart datum. Standard port: high water 5.4 m, low water 1.1 m. At the secondary port high water is 5.4 + 0.62 = 6.02 m and low water 1.1 + 0.18 = 1.28 m. The two differences are not equal, so the range changes too: 4.3 m at the standard port, 4.74 m at the berth.STANDARD PORTSECONDARY PORTHW 5.4 mLW 1.1 mHW 6.02 mnot 5.58 mLW 1.28 m+ 0.62 mHW difference+ 0.18 mLW differencechart datumrange: standard port 4.3 m · berth 4.74 mEach tide takes its own difference.

The rule

  • Find the standard port for the berth in the tide tables and take its predicted height of high water.
  • Apply the secondary port's height difference at high water, with the sign the table gives (here: to be added).
  • Keep the low water difference for low water: the two differ because the range at the berth is not the range at the standard port.
  • It is still a prediction: a high barometer or an offshore wind leaves less water than the table says.

Formula

  • HW at the secondary port = HW at the standard port + height difference at HW
  • LW at the secondary port = LW at the standard port + height difference at LW

Worked example

Predicted height of high water at the standard port5.4 m
Height difference at high water, to be added0.62 m
Predicted height of low water at the standard port1.1 m
Height difference at low water, to be added0.18 m
  1. Standard port, high water = 5.4 m
  2. For comparison, low water at the berth = 1.1 + 0.18 = 1.28 m (range 4.74 m against 4.3 m at the standard port)
  3. High water at the secondary port = 5.4 + 0.62 = 6.02 m

Answer6.02 m

Common mistake

Adding the low water difference (0.18 m) to the high water height.

Each tide has its own column because the secondary port's tide is a different shape, not the same tide shifted: 5.4 + 0.18 gives 5.58 m, 0.44 m short of the 6.02 m at the berth.