Friday, 20 July 2018

Tide & Current Infomation

Web sites we use for tide information:

Tides and currents:
Web sites we find very helpful.
Tide forecast, a world wide tide forecasting site. We have found them to be fairly accurate in Asia.

Department of Survey and Mapping Malaysia, reports the major Malaysian ports.

Tidetech is a very informative web site detailing ocean currents world wide. If you have ever tried to get your head around the currents in the Malacca Strait this will shed light on this and many more.

Tide Program for your PC:
WXTide32 we use this and while its not always exact, however it is in the ball park as far as time and heights are concerned.

XTide was designed for Unix and X11, not Microsoft Windows, so if your savy with Unix, here is the original version.
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Tidal Stream – Computation of rate

Range of tide for day
_________________         x Spring tide rate of tidal stream
Spring tide range

Why do we need to know this? It’s for working out tidal drift.  If the chart has a tidal arrow its value should have been referenced to the spring tide rate. So if you are there in a neap tide and require the tidal rate this is the formula to use for the job.

Or the easy way, if you have integrated instruments connected to the chart plotter, in most cases the drift/tidal rate can be displayed, the chart plotter uses data from several inputs to calculate tidal drift when on passage.  However this doesn’t work when passage planning. If the chart has tidal diamonds then you will have a good source of rate and direction. Not all charts have these tidal diamonds but have tidal arrows so if you can remember the formula for the computation of tidal rate it may help get you out of a slow trip. 


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Assuming that the tide in your area has a normal semi-diurnal cycle, The rules of 12ths can be used to provide a quick estimate of the height and flow of the tide for times in between high and low water.

For the first hour of tide one 12th of the tide will move
For the second hour of tide two 12th of the tide will move
For the third hour of tide three 12th of the tide will move
For the forth hour of tide three 12th of the tide will move
For the fifth hour of tide two 12th of the tide will move
For the sixth hour of tide one 12th of the tide will move

1+2+3+3+2+1=12

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