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09:00 Friday 24 Jul 2015 Rupert HolmesTidal heights and streams during Aberdeen Asset Management Cowes Week 2015

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Rupert Holmes shares his thoughts on the tides during Cowes Week this year.

This year’s Aberdeen Asset Management Cowes Week is a week later than the traditional date in order to avoid spring tides. However, even though the tides will be less fierce during the event, good tidal planning will still be critical to good results. On the opening day high water Portsmouth is at around 0730, so the starting sequence will get under way with a strong west going stream on both the Royal Yacht Squadron (RYS) and Bramble start lines.

However, the rate of the stream will diminish during the start sequence, with an inshore easterly eddy forming close inshore under the RYS around midday. As the time of low water moves later during the latter part of the week, then starts will all be subject to a strong west-going stream, until the final couple of days, when the early classes will experience the last part of the east-going flood tide – high water Cowes on Friday is at midday.

Since the construction of the base of the Cowes harbour outer breakwater, the west-going eddy close inshore of the RYS and the Green sets up earlier than in the past and also appears to be stronger. Boats entering and leaving Cowes harbour in the main channel also need to be aware of a strong west going cross tide in the area just to the north of the Yacht Haven, especially between two and a half hours before high water to an hour before high tide.This tends to set vessels towards the western shore of the channel. More information can be found here.

For most of the week racing will be take place over low water, with minimum tidal heights ranging from 1.5m above chart datum on the first Saturday, diminishing to just 0.9m on the Friday. Fortunately, when starting to the west from the RYS line, most classes will have a favourable stream, so at that stage of the race there’s no need to be tempted to take a chance on skimming close to the Grantham Rocks, between the RYS and the Green, or Gurnard and Quarry Ledges to the west. However, the later part of the week will give course setters the opportunity to provide a classic Cowes Week finish approaching the RYS line from the west against the ebb tide.

When closing the shore to gain tidal relief, make sure you keep a close eye on the depth, the obstructions ahead of your track, and call other boats for room clearly and in good time when necessary. Similarly, it’s important to be aware of shoal areas in the middle of the race area such as the Bramble Bank, Stansore Point and for larger yachts in Black Group the Knoll Bank to the east of the Bramble, where charted depths are as little as 0.7m.