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.


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).


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!


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

2 thoughts on “On sailing a Folksong – of dolphins and speed

  1. What an……airplane (!)

    I can’t see the “sailing ship” anywhere on this hull but then again i understand that finding a way to reduce displacement as velocity increases is a good solution to get performance. Just as when the crew hangs overboard to reduce rolling and squeeze more power out of the sails.

    There must be an element of aerodynamics involved in this design, more than it is in the classic ships. I have the suspicion that the deck must be acting as a foil to some extent….So it resembles an ekranoplan, an aerofoil always kept under the “ground effect”.

    These little, “demons” have become popular lately perhaps because of progress in material technology.

    Imagine having to balance, length-wise, such a small boat on practically a point below the surface, keeping your mind on gusts and waves and wind direction…..That’s going to take some trimming skills 😀

    Best wishes for this holiday season and all the best for 2010 🙂

  2. Hi Bill, When sailing back from Fowey,with Lindsey,on a broad reach we achievd 7.5 kts several times on the Log,not GPS, while coming off waves, slowed to 6.5 kts and then picked up to 7.5 kts on occasion. However we were hit hard by a squall and couldn’t hold her on course and headed rapidly for Looe Island while I tried to shorten sail with wildly flogging canvas!
    The moral of the story is not to look ahead, bug eyed, shouting with excitement as we surf off waves but to look astern but in this instance for the weather & not for boats!!
    Jonathan (ex Blue Mistress)

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