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Nautical Publications
APPROACHES TO PORTLAND
1. This atlas contains a set of 13 charts showing tidal streams at hourly intervals commencing 6 hours before HW Devonport and ending 6 hours after HW Devonport. The times of HW at Devonport and Dover and other details of the prediction for this port are given in NP201, Admiralty Tide Tables Vol.1, which is published annually. NP201 also gives tidal predictions for Portland.
2. On the charts the directions of the tidal streams are shown by arrows which are graded in weight and, where possible, in length to indicate the approximate rate of the tidal stream. thus -> indicates a weak stream and --> indicates a strong stream.The figures against the arrows give the mean neap and spring rates in tenths of a knot, thus: 19,34 indicates a mean neap rate of 1.9 knots and a mean spring rate of 3.4 knots. The comma indicates the approximate position at which the observations were obtained.
3. The streams shown are the averages from the surface to 10m depth; that is to say, they show the effect of the streams on a vessel to 10m draught.
4. Streams in the entrances to Portland Harbour (the Ship Channels) are given in a table on the next page. Their approximate directions are also indicated in the tidal stream chart.
