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Originally Posted by Rookie Sorry. Just re-read that. It sounded like a slag on the design of the Eureka. It wasn't. I doubt very much that the Eureka is an "unstable" canoe. I have never built one and am in no position to give a first hand opinion. I merely wanted to point out the difference in stability between designs. If you place the seats as low as possible the centre of gravity goes further down towrd the centre of bouyancy, and it will be more stable.
Michael, I hope I described that properly. |
Looks fine to me Rookie!
I do all the hydrostatic stuff with even the simplest boats I design - it is so simple nowadays - just press a button - but some background is needed to interpret what is happening.
But the basic problem with Doug's test paddlings were that the beam had come out a lot less than designed. Midge's boat was much closer, but still too far away for my liking - so it was clear that there was a deficiency in the plan instruction pack.
Basically the strongest determinant of stability is - wait for it - beam. ie the width of the boat. The hullshape determines the "feel" of that stability.
Doug's boat was deficient on beam before he pushed the sides out.
For example a conventional canoe will gain stability as it heels, In a gradual way (as will a 5 panel boat like the Eureka), whereas a square section canoe (with no ballast and little weight in the hull) will have a high level of initial stability but around the 45 degree mark will suddenly lose everything (for a square hull it is symmetrical to the water when it heels to 45.).
Anyway, the thing to realise is that beam works to the 3rd power in rough stability terms
ie stability = beam^3 X length. (for the maths experts, read the = as "is proportional to")
so if you double the size of a boat in all dimensions it will have 16 times the stability.
Or if you halve it - theres 1/16 the stability - notice how radio control yachts always have REALLY deep and REALLY heavy keels. It is because the small hull has very little stability.
Doug's beam was at about 88 percent of the design beam which means the worst case scenario is that stability was 0.88^3 = 0.70
Stability was down 30 percent.
And that's what he may have got back by pushing the sides out.
It is a bit more complicated than that because increasing the beam by pushing the sides out doesn't change the bottom shape much.
So my feeling for it is that the initial stability won't be much different - ie the stability when the boat wobbles through about 3 or 4 degrees won't change.
But as it heels further it will feel much better than before as the wider topsides start meeting the water.
BUT - the big test is to get it into the water - which is why I am hassling Midge, who I am staying with, to get his Eureka in the water.
The other factor is that the big Eureka plan has been around for some time and I have only heard good things about it. As a designer, you don't get much feedback if things go OK - just the same as with Social Workers and Doctors.
But back in the days when the plan required the boat to be built over a strongback and molds (between 1993 and two years ago) there were a fair few plans sold and three people did get back and say they loved the boat. Strongback and molds ENSURES the boat will end up the designed shape - so it does appear that the designed shape works.
The revised plans for the stitch and glue version have been modified so that the width of the boat will come out very close to the designed beam.
But, even though there is evidence that the boat works fine I find I am waiting with some nervousness to paddle Pete's boat around. I make lots of effort to make sure my boats work well and the plans take good care of first time builder and want everyone to really like them too.
There is no great financial reward from designing boats - but I know the difference between the standard things that most people use and a boat that really fits its purpose. Paddling boats that REALLY paddle, Sailing boats that REALLY sail etc. That's the payoff for me - that people become educated to know what a good boat is really like and can experience the pleasure as the beastie does what it is supposed to with very little fuss.
Which is why, like Daddles, my favourite Australian Designers are David Payne and Ian Oughtred (he lives in Scotland, but he was entirely educated about boats living in Australia - his boats LOOK like traditional forms, but everything about them, their lightness simplicity and speed is pure Australian - the Brits and Yanks just don't get it the same way). They just don't put a foot wrong. Or hardly ever.
By the way, David Payne has just won the Classic Boat Magazine International Design Competition for a RAID boat.
Anyway I have some Paddle Ducks to cook and we are still kidding ourselves that we will get them into the water on Sunday. Maybe we will.
Best Regards
Michael Storer
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the finished canoe. 
