From: Guillemot@aol.com
Date: Thu, 16 Mar 1995 20:29:19 -0500
Message-Id: <950316202918_51878177@aol.com>
To: kork@imagelan.com, baidarka@imagelan.com
Subject: Re: Traditional Paddles new thoughts
> With regard to the stroke, energy is lost when the blade is cavitating.
> Because the paddle is moving backward relative to the water and thus
> 1 unit on input energy does equal 1 unit of propulsion. But some of the
> propulsion energy is in the blade moving backward through the water and
> not in the boat itself moving forward.
I guess for every paddle stroke of a given force you will create a equal
increase in energy. This energy can be kinetic energy of the boat or of the
water. The more you make the water move the less energy available to propel
the boat. I'm not sure how much energy will actually be lost in cavitation.
The water moves out of the way, then back. The net change in energy is
relatively small. Some energy lost in heat. Hmmm...
Last weekend I went xcountry-skiing. It was pretty icy and my skis were not
gripping well on hills. When I pushed off the skis would slip backwards. I
would not be pushed forward very far. Were my skis being inefficient. Well,
they certainly weren't being much fun. I was getting all kinds of tired and
going nowhere, but it was the front of my legs getting sore from trying to
catch myself from falling. Almost no effort was require to push my skis
backward and what little force I could apply result in forward motion with
little loss. My skis were not effective, but my fatigue came from my desire
to keep my face out of the snow. My body didn't actually slide backwards,
only my means of propulsion slid. I think my skis were more frustrating than
truly inefficient. It was me that was inefficient. Much more efficient would
have been to fall flat on my face then use my hands to pull on shrubs
(kedging?).
This is not completely analogous to paddling but, some of the same principles
apply. I guess the point I'm trying to make is that the paddle slipping
through the water is not, in itself, a sign of inefficiency. Riled up water
and a lot of splashing does indicate waste.