On sailing a Folksong – of dolphins and speed

AA has come up with an answer to my ‘the speed of dolphins’ question via this link.

Under the title “Dolphins swim so fast it hurts” the author reports:

“What is the fastest a dolphin can swim? Near the surface, no more than 54 kilometres per hour. Why? Because it hurts it to swim faster.Those are the findings of a pair of researchers from the Israel Institute of Technology in Haifa.  But tuna, they say, do not suffer the same problem. Gil Iosilevskii and Danny Weihs carried out a series of calculations to model the tail and fins of fish such as tuna and mackerel, and cetaceans such as dolphins. The aim was to determine what limits the maximum speed at which these creatures can swim. The researchers found that although muscle power is the limiting factor for small fish, this is not the case for larger and more powerful swimmers such as tuna and dolphins. . . .”

Citing cavitation – (the same problem that causes erosion in propellers), as the painful limiting factor, they give 10-15 metres per second (36-54 kilometres per hour) as a maximum.

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So how does this tie in with man’s maximum speed on water without an engine?

For that, you have to look at Hydroptere achieving 51.3 knots over 500 metres

It seems they built an aeroplane and then found a way of gluing it to the surface of the water.

By the way, if you are a wooden-boat person, don’t for a moment think that boat-builders haven’t for ever been constantly developing their skills and technology to improve the speed and/or capacity of their craft, especially where commerce or glory were involved.

It’s not for nothing that the organisers of class-racing have had to place limits on boat specifications to make racing fairer – and don’t for a moment think that individual racers aren’t for ever looking for ways to quietly (very, very quietly) improve the performance of their own boats.

Hopefully, technology will come out of Hydroptere that will filter down to the rest of us.

(And let’s hope they continue to sail where there’s no traffic).

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Which brings me to Blue Mistrss and a more prosaic rate of travel!

When the Folksong were built, one of the accepted methods of calculating maximum boat speed was as follows:

“The speed that a yacht’s hull can be made to travel through water is related to waterline length.

The formula for an average sea-going yacht of conventional shape is:

Speed in knots = 1.4 x Square root of the L.W.L. in feet

The multiplier is altered according to the type of hull. It may range from 1.25 for a tubby hull to 1.5  for a large racing yacht.”

Therefore Blue Mistress’ theoretical maximum speed at L.W.L 19’ 8”: (I have made no allowance for hull shape)

= 1.4 x square root of 19.66 ft = 1.4 x 4.434 = 6.2 knots

I guess there are several other calculations now, but that was then.

The maximum speed (recorded on my handheld gps) on last Sunday’s sail was 6.8 knots.

The best ever is 10.4 knots, remembering that this is speed-over-the-ground rather than speed-through-the-water, i.e. there was an element of tide in the speed recorded – and in the case of 10.4 knots it was a spring tide plus surfing that helped, which makes it even slower than Hydroptere where, presumably, for their record to stand, the water was slack.

Oh, and also not forgetting that my numbers would have to be achieved for a mere nano-second to satisfy the gps, not a timed distance over 500 metres!

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But there’s one distinct advantage for Blue Mistress here  – I bet Hydroptere’s crew didn’t have time for the dolphins.

On sailing a Folksong – a Sunday sail in winter

1030, Sunday 13th December

My first sail since the end of October.

Blue Mistress has ridden the storms reasonably well.

The forehatch has sprung a small leak. The sail bags are wet.

We have lost not one but two shackle pins on the stern lines.

Poor mousing on my part – (yes, I did use wire), and not helped by the vastly increased run-off of water from Dartmoor into the Plym.

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The wind was easterly this morning and gusting. I left the Sound through the eastern entrance and sailed happily south – course 180 degrees (M), until Dodman Point opened up  in the west.

I turned for home about 1330.

There were one or two boats sailing and a number of small fishing boats. Mostly I had the sea to myself.

Looking towards Devon in the east to Great Mew Stone and the entrance to the Yealm

and towards Cornwall in the west – Rame Head with Kingsand and Cawsand on the right of the picture.

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The wind decided to back towards north which was exactly wrong for re-entering the Sound.

I was concentrating on clearing the eastern end of the Breakwater, when four dolphins appeared from nowhere . . .

They were intent on play, appearing randomly around the boat, racing passed or lazily rolling under the keel.

As they levelled with the cockpit, I could have touched them.

Delighted, excited and entranced, the tiller in one hand, the camera in the other, I took lots of images – mostly of freshly disturbed water.

They lead me on – (note the rapidly approaching conical mark on the end of the Breakwater), and, when I looked up, I had missed the entrance and had to tack very quickly.

My new friends immediately disappeared, and I was reminded of the Sirens of Greek Mythology.

“OK, guys, joke over.”

250 yards on, I tacked back and there they were again.

They escorted me to the entrance to the Sound, before swimming off – no doubt chuckling all the way back to sea!

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I was asked last week why I hadn’t taken my boat out of the water for the winter.

There’s your answer.