Thursday, May 5, 2011

Water Rat

Edward has written in regard to the discussion about flat-bottomed hulls: -

Hello, There was a flat bottom sharpie built in England in 1898. Very unusual at the time. She was 14ft and had a sprit main and jib. Mr. Lillistone could you look at this picture of her from Dixon Kemp, and comment on what you think? I'd quite like to build an historical replica to see how she went (fast by all accounts at the time as she was banned from racing). Regards Edward

Thanks for the comment and the drawing, Edward. I am flattered that you are interested in what I have to say, but I am mildly worried that people may think that I know more than I actually do!

Anyway, here is my opinion, and I'd welcome input from others who may have a deeper understanding of the subject.

I view this boat in two separate parts - the forward sections and the aft sections. She is quite wide for her length, which immediately introduces problems with eddying around the chine. The line of the chine is very flat up for'ard, which also increases the problem of wild eddys forming around the chine, causing drag and wild steering.

However, the chine line in the aft sections shows a nice lift when viewed in the body plan, and I think it comes close to the optimum when hoping to prevent eddying. If you look closely in the body plan (i.e. the end elevation) you can see that the line of the chine more-or-less bisects the angle between the bottom and the topside panels.

So, I think that this boat would perform well as long as she was sailed flat with the fore-foot lifted clear of the water - which she would naturally do considering her large sail area and tucked-up transom. Her shape looks similar to plenty of racing dinghies from the last forty or fifty years. If built lightly, I think she would go rapidly, but I also think she would be a handful in a decent breeze.

The potential for the chine at the bow to produce turbulence would not be a problem when running fast and level in flat water, but if she stuck her bow into the back of a wave (especially running down-wind) I think she could sheer off wildly and suddenly.

That is my opinion, but just remember that there is no guarantee that I have any idea about what I'm saying!

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