James Stevens answers your Questions of Seamanship. In this article, is it worth moving to a new anchorage it if meant sailing through shoal water in approaching bad weather?

Would you decide to move to a new anchorage if it meant sailing through shoal water in approaching bad weather? James Stevens looks at the problem and provides the solution.

Question: Is it worth moving to a new anchorage if it meant sailing through shoal water in approaching bad weather?

Rachel is on board her yacht Pampero, an 11m Sadler 34, secured to a visitors’ mooring in Hugh Town, a port on St Mary’s, one of the Isles of Scilly.

Pampero has a draught of 1.7m and is well equipped for offshore cruising.

Rachel has always wanted to visit the Islands and a two-week break in May has given her the chance to sail there with her family.

The weather has been good so far but the high clouds coming in from the west are indicating fresh winds to come.

Rachel checks the forecast.

The wind, currently southerly Force 3 to 4, is going to veer southwest and increase to 6 to 7 by nightfall.

Chart of St Mary's

It is 1400, two hours after low water springs.

The yacht is beginning to roll on her mooring and although rolling is part of cruising in this area Rachel would rather be somewhere more protected.

The most sheltered moorings in the forecast wind would be New Grimsby Sound between Bryher and Tresco.

It is a passage of less than three miles and the route runs across a shoal between the Islands called the Tresco Flats.

The flats are impassable for Pampero at low water.

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Rachel has worked out that in a couple of hours there should be a clearance of 1m, or if she left it until high water, clearance would be 2m.

The alternatives are: a tricky passage of about six miles around Bryher, a shoal passage to the east of Tresco, or stay on the mooring.

Porthcressa, a bay to the south of Hugh Town, looks equally exposed.

Should she risk moving to a new anchorage?

James Stevens answers:

In the absence of local knowledge, yacht skippers have to be very cautious about shoal water in approaching bad weather.


James Stevens, author of the Yachtmaster Handbook, spent 10 of his 23 years at the RYA as Training Manager and Yachtmaster Chief Examiner

Striking the sand with the keel in a swell can cause severe damage and loss of the yacht.

On the other hand the shoals in this case are protected from the Atlantic swell by islands which are going to reduce the power of the sea.

Yachting would be a lot easier if the answer to this question was an exact number of knots of wind beyond which the passage over the flats is impossible.

It depends on the ground swell.

My view would be first to ask the harbour master and second to go out and have a look.

Providing the swell is not too great, the flats should be passable towards high water in Force 4 to 5 in good visibility with a detailed chart.

Once in the lee of Bryher the passage will be sheltered and straightforward.

There are plenty of rocks about so careful pilotage preparation is needed.

Rachel needs to have made her decision and be secured to her overnight mooring or anchored before the wind freshens to Force 7.

Most yacht skippers will be familiar with that feeling that the passage should have been made yesterday.