"Michael Daly" ) writes:
On 28-May-2004, (William R. Watt) wrote:


Sorry it's not an inverse relation.

??? The more you say about small craft hydrodynamics, the more I realize
how little you understand.

Skin friction increases with length, while wave-making resistance decreases
with length. Minimum total resistance is where the sum of the two is minimum.

Skin friction does not increase monotonically with length. It does
increase monotonically with the product of surface smoothness and wetted
surface area. Wetted surface area in a dead calm is a function of
displacement and hull shape but not a well-defined mathematical function,
and it is complicated by waves. There are quite a few indicators of hull
shape such as length-to-beam ratio, block coefficient, prismatic
coefficient, and girth.

Brian didn't provide any data.

He said 2% or so.

A percentage is not data. A percentage is a calculated number.

You have no such data that I've seen. Where do you have the data that indicates
how much resistance is due to scratches?


And where do you get that data, in your dreams?

"The Shape of the Canoe" by John Winters.

the hull resistance data on my website is from Winters' website. where he
got the data I do not know. at one time he was collaborating with a
university in Australia. the fellow at the university has posted in this
newsgroup. Its been a few years and I can't recall the university. the
"Winters" data is very general. I would like to see data specific to sea
kayaks. the wind and wave resistance data is from a book on sea kayak
cruising. it also appears to me to be pretty general.

you are not basing your arugment on data, but on your impressions.
I am basing my argument on actual data which I admit is pretty general.

I know what you are trying to express, that within a narrow range
there is a local optimum.
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