I found what I was looking for at www.greenval.com/winters.html.
Writing about canoe design for frictional resistance John Winter says ...

"A 5% decrese in wetted surface is worth bragging about, but a
single year's scratches and banging can easily double coefficient
of friction from 0.004 on a new fibreglass canoe to 0.008. This
more than offsets the designer's efforts. The cavalier attitude of
most canoeists towards their boats is evidence that a 50%
resistance increase is not often noticed if only because the onset
of its effect is so gradual."

Earlier I wrote in this online discussion that paddling in a group
would require extra effort to keep up with other members who were
in similar boats with smooth hulls. I only assumed a 10% increase
in frictional resistance. Winters implies a 50% increase is not
unusual. I used performance data from Winters' former website. All
Winters data applies to canoes (at one point he mentions a
"typical" 16 foot canoe) and is provided to illustrate the
principles he is writing about. Its not specific to any boat,
particularly not kayaks.

I was kicked off the computer at the public library after an hour,
but not before taking a look at the kayak data provided by Mike
Daly at http://www.greatlakeskayaker.ca/spee...anceGraphs.htm. I
found the graph very interesting. I've copied down the numbers and
would like to replace the resistance in pounds by the effort in
horsepower when I get a free moment. Of the 5 kayaks, the
Endurance 18 and the Arctic Hawk are equivalent and fastest. I
don't know if they are the same length. However the Nordkapp H20
and the Solstice GT are equivalent and second fastest even though
the Nordkapp is 2 ft longer than the Endurance (if I'm
interpreting the names correctly). Up to a speed of 4 knots all
four of these kayaks are equivalent. The two pairs only begin to
diverge at speeds over 4 knots. The remaining kayak, Sonoma, is
the slowest. Its length is unknown. There is an error in the data
for the Sonoma at the fastest speed, revealed by a sudden change
in its graph. The slowest boat is one for which John Winters
suppled the data and I'm sure it is for a canoe, not a kayak, as
all the Winters data I've seen is for canoes.

Even though the boats I currently paddle are only cheap home made
experimental plywood boats I'm careful not to treat them roughly
and get the hulls scratched and gouged. That is why I was so
disgusted to see the condition of the used rental boats offered at
a recent sale here.

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