What is the best route for a fast passage?

What is the best route for a fast passage?

James Stevens answers your seamanship questions

Question:

Rob is the skipper of a 9.1m (30ft) cruiser in Cherbourg with crew Alan and Pete.

They are preparing to return to the Solent by the Canal des Aiguilles which is 60 miles to the north.

The weather is fine, the sea conditions are calm, but the wind direction is northerly at 10 knots, straight ahead and should remain so.

The Channel Light Vessel is also moving at 10 knots north.

The yacht should be doing 5 knots in these conditions and she is sailing about 45 ° to windward.

Continued below …

This is a high tide with maximum currents of over 4 knots on the French and English shores of the English Channel.

Currently, the tide is just starting to turn east.

Alan thinks they should go on starboard tack, turning around when the tide turns.

He thinks that by tilting the tide downwind the yacht will stay closer to the course line and get there more quickly.

Pete says if you draw the triangles for the next 12 hours with equal tides in both directions it doesn’t make any difference for the arrival time, you can go port tack, travel faster on the ground on a greater distance, tack on the reverse tide and come back faster.

Rob has always thought that yachts going upwind should tip the tide to leeward, but he’s puzzled because Pete’s calculations seem correct.

Are they? Why should tilting to the wind make a difference?

James Stevens responds:

The key to this question is the tidal wind.

If there was no real wind and an easterly tide of 4 knots, a yacht underway would experience an easterly wind of 4 knots.

Superimpose a north wind of 10 knots on the east tide of 4 knots and the trigonometry shows that the wind changes to 22 ° true and increases slightly to about 10.8 knots.

Credit: Maxine Heath

As the tide turns west and increases to 4 knots, the wind will be approximately 338 ° true and 10.8 knots.

It’s a huge lift on both sides if they go starboard and tack on the tide reversal, and a huge head if they do it upside down.

Starting on starboard tack, they will be about 6 miles from the Needles after 12 hours at 5 knots.

Credit: Maxine Heath

If they start on port tack at the same time, they will end up more than 30 miles south of the Needles.

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

This of course assumes that the wind direction and speed remain constant and that the 12 hour tidal effect is the same in the east as in the west.

In the real world, the wind is never so constant and a lot of lift could change the plan.

Navigation across the English Channel is also complicated by the slightly NE / SW tidal current rather than at right angles to a south / north course.

The leeward boat is not in a stronger wind. Boats close together on opposite edges experience the same tidal wind regardless of how strong or how weak the tide is.

I enjoyed reading What is the best course for a fast pass?

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