Tidal streams

[lupins]

Having only just completed my day skipper I thought I'd put into practice what I'd learnt by making a real passage plan. When plotting the tide from the tidal streams atlas I'm aware that I have to split it into what was only taught to me as crocodile teeth (If I'd like to work out the tidal stream between 1045 and 1145 and high water is at 0915, then I know to plot the tidal stream for 2 hours after HW based on the fact that I have split the timings by half an hour. However lets say I wanted to plot the tidal stream for a passage between 1015 and 1115, surely I'd have to plot half an hours worth of tide from 1 hour after HW and half an hours worth of tide from 2 hours after high water? Please correct me if I'm wrong, just stumbling over this part.

 

[superheat6k]

As no one else has responded, I will try to help you.

Firstly remember all tidal data references are predictions, and are subject to numerous vagaries. So it is prudent to take timings as +- 1/2 hour anyway. Then you are looking at what the tide is doing between HW +1 & +2. I would simply review the tidal stream atlas or tidal diamonds for the sea area concerned and estimate the average for the two hourly periods.

Also remember tidal streams are not the same as tidal heights. The tide doesn't turn at HW everywhere, and indeed every different place will see tidal streams change differently relative to any particular standard port.

The prudence I was taught years ago was to take a view of tidal stream rates and heights as the aspect least favourable to your progress or safety, that way you are erring on the side of caution. If the tide height or stream turns out in your favour then all the better, but it is less likely to be far wrong against you.