How to Calculate a Course to Steer

The tides (UT) for the Port of Trumpton in June and tidal stream information for Trumpton roads

It is Saturday June 7th.  Trumpholm Island lies 4 Nm from the harbour on a bearing of 140(T). The boat is capable of 6kn through the water in a SW breeze F5, leeway 6 degrees. Departure is set for 1200 DST(1100 UT).

What is the compass course to steer for  Trumpholm island and what is the estimated time of arrival?


 Time after HW = (1100 - 0929) = 0131; use the  tidal diamond for HW+2 as this is valid from HW +01:30 to HW +02:30.  The tidal range is (12.2 - 2.2) = 10m. The tidal diamond spreadsheet  predicts 2.8kn tidal stream at 230(T)

The CTS spreadsheet predicts 112T as the course to steer and an ETA of 1200 + 0045 = 1245 DST. To prevent the boat being  pushed off the desired ground track we adjust course by +6 degrees into the wind, to 118T. Magnetic variation is 4 degrees West, so the course is 118+4 = 122 (M). On this heading the boat has magnetic deviation of 5E so the final compass course is 117(C)

The compass course is 117(C) ETA 1245 DST.