achting
!Yg4titicker by sail?
d ver Stewart a prodigious banging of cannon the 0 fileht racing season has burst upon us. May's H^atUres have included the Seine Bay, Le Y , 1r0 re, Deauville and Cherbourg events and .e '11 now on not a day passes without its ri Thousands of helsmen will be obsessed with 4:41.11g to make their boats go faster. They will • 044grUd1ngly pour out money and time on tithing likely to give their, yacht an addito tia1 fraction of a knot. But they do not seem ,ticceed. ovine records do not show any marked 4:rall speed improvements. Our vaunted sv24namic knowledge; our marvellous Chinetic sail materials; our beautifully enhilered stainless steel fittings; our moulded al) I forms seem to have difficulty in catching „Yvith rope, canvas, wood and iron. aillls'there are the two kinds of sailing speed, 1" antaneous and sustained. Something has been done about the first. The existing sailing speed record for a single dash along a short, straight course was set last year at 29.3 knots or nearly 34 miles per hour. It was set by an astonishing contraption consisting of a long, slim hull with a small 'sidecar' boomed out to windward, pros-fashion, in which the crew rode high and dangerously.
It rubbed in the lesson, already taught by sand yachts, that a craft can sail much faster than the natural wind from which it derives its thrust. At the time of the record the wind was reported to be 20 knots. That is Force 5 or thereabouts on the Beaufort scale and far below gale strength.
But now look at sustained speed — speed, that is, kept up non-stop for days and weeks on end and on many different points of sailing, in many different kinds of sea. It is the kind of speed that a vessel does on a very long voyage. Achievements here do not give any great tribute to the marvels of modern scientific methods.
Homeward bound from Australia with a full load the Cutty Sark, in 1887, averaged an amazing 8 knots. Her captain reported having measured her speed over long stretches at somewhere near 18 knots. There are dozens of accounts of remarkable sustained speed performances by the big clippers, among them claims of 20 knot averages for two or three days running; but the Cutty Sark figures are probably the best authenticated.
They show the capabilities of sails or aerofoils at a time 'well before the powered aeroplane had flown which is to say well before aerodynamic theory had been explored. F. W. Lanchester's book Aerodynamics was first published in 1907.
It is most difficult to put fair: comparative speed figures on modern sailing craft. The fact that no payload is carried can be ignored but there remain many difficulties. Any voyage used as a measure of average speed must be non-stop. So the figures for the interesting and successful round-the-world race are not here of any help for the race was sailed in stages. And the same arrangement will apply to the round-Britain race in July.
My impression from such figures as have been given and from the achievements of modern yachtsmen — Chichester among them is that the large, modern, monohull yacht, built especially for speed, and benefitting from all scientific and technical aids that are applicable, can average about one knot better than the Cutty Sark when working under comparable conditions of voyage length and wind and weather. The difference seems remarkably small when the size of the world's aerodynamic effort during the past seventy years is taken into account.
The old full-rigged ships had a splendid appearance, but their rig and the cut of their sails look — to the aerodynamicist at any rate — horribly inefficient.
Admittedly there is the difference in water line length. But it has been amply demonstrated in recent years that any rigid association of speed with the square root of the water line length is unwise. Surfing and planing tend to throw out the calculations.
At the moment it looks as if any notable speed improvements are most likely to be made by the big sailing spiders, the weird looking catamarans and trimarans favoured by some of the French experts like Eric Tabarly and Alain Colas. These go like express trains when the conditions are right.
But the real test must always be the long voyage and the sharply computed average
speed over the whole distance. The short, straight speed dash is interesting and may point the way to future developments; but it is still speed on the long slog that counts most as a sailing efficiency indicator.
Oliver Stewart, the writer and broadcaster, is the author of, among other works, Bad Sailing Made Good (1971).
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