Brian Nystrom ) writes:
William R. Watt wrote:

That may not be a
problem for knocking about on your own but if you are on a trip with a
group and their hulls are smooth you are easily paddling 10% more to keep
up.

Exactly where did that figure come from? The tests I've seen indicate
that scratched hulls have ~2-5% more drag smooth hulls, with badly
scarred plastic hulls with lots of "hairies" being at the high end. The
difference with fiberglass boats is minuscule.

the reference is long gone. it said one season's scratches add 5% to
hull resistance.


That's like paddling 11 hours to their 10.

No, it's not like that at all. Even if your 10% figure is correct, it
pertains only to surface friction on the hull. That's only one component
of the total drag that must be overcome by the paddler. Wind resistance
and especially wave making resistance can be very substantial components
of total drag, depending on boat speed and weather conditions.
Realistically, a scratched hull will require you to paddle ~1-2% harder
than a smooth one. Unless you're racing, you'll never notice the difference.

where does that 1-2% figure come from?

at sustained (cruising) paddling speeds hull resistance is still the
biggest component of total hull drag when comparing identical boats. there
are some numbers in a file on my website under "Boats" on average hull,
wind, and wave resistance, and energy consumption. a paddler can't put out
the power needed to maintain high wave making resistance speeds for any
length of time. it's a concern for racers. your point about wind and wave
resistance is well taken. however, considering the money spent on paddles
to reduce effort, the scratches on the hull matter. I don't think 10% is
out of order in anything less than rough conditions. I was trying to be
conservative. I don't have figures for paddlers but cruising sailors
experince moderate conditions most of the time. Rough conditions most of
the time would pretty well eliminate such passtimes as paddling and
sailing.




--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned