Re: [Paddlewise] Greenland paddle - Throw-weight

Paddlewisers:

Phil Baumgaertner (pbaum_at_ix.netcom.com) wrote:

>I'd like to address the question about throw-weight or paddle inertia.  Its 
>an important question and a potential energy sapper.  Physics states that an 
>object moving thru the space will continue in a straight line until a force 
>acts on that object.  One of the replies to this question suggested that 
>since the paddle is moving more or less in a circular or elliptical manner 
>without stops, that this "throw-weight" is not important.  This is not 
>accurate, paddle inertia is very important.  

It sure is, in my opinion, also, but maybe for different reasons than some
have thought about.  The paddle seems to be moving in circles (elipses,
whatever), but the forces the paddler applies are mostly forward and back,
like the piston in a car's engine.  I think the start and stop force for
overcoming inertia is much greater than most people believe.  Momentum
*may* get the blades up and down to some extent to start the next stroke
(though not much in my opinion), but you do have to exert force to keep the
paddle moving and accelerate the blade.  

The bottom blade actually does essentially stop in the water -  the boat
moves on past it (hopefully or you are going nowhere fast!) - and the upper
blade travels faster to make up for it.  Yup, start, stop, start, stop.....
 The center of the shaft travels the same speed as the boat.  If the bottom
blade stops, the upper blade has to be traveling at an average of twice the
speed of the boat to get ahead for the next stroke.  You are accelerating
the upper blade of the paddle from a dead stop to twice as fast as the boat
(or more for a short period of time).  And if you paddle unfeathered, think
of the wind resistance!  

Phil's back onstage:
>If you tie a string to an object and swing that object around your hand, the 
>centripetal (center-seeking) force provided by your hand to the string (to 
>keep the object from flying out straight is given by Force=(mass)X(velocity 
>squared)/(radius squared).  This equation tells us the faster we swing the 
>paddle, the force necessary to hold the paddle will increase rapidly, such 
>as doubling the stroke speed will increase the force required to keep the 
>paddle in its path by a factor of 4.  

Yup, acceleration is expensive in energy costs.  But, does this matter as
much as you think?  The paddle shaft has a counterweight at the other end,
the string does not.  One paddle blade cannot go flying off on the tangent
into orbit because of the shaft and the blade on the other end.  Drill a
hole through the center of the shaft, insert an axle, mount the axle in
bearings and give the paddle a spin.  It will go in circles until air
resistance stops it (meaning pretty soon).  Forces keeping the blades
together balance so no energy expended in that regard.  People don't paddle
like this when in a boat, just when standing on the ground.    

>Some good things about the wood paddle, it was noticeably warmer than my 
>fiberglass shafted paddle and the varnished finish seemed stickier and much 
>easier to grip than my paddle (can you varnish over fiberglass?)

Yes the cedar strip and stitch and glue canoe/kayak makers do it all the
time (several coats, even).  

John W and others - input on the above physics, please.  

Thanks, 

Hank Hays
Lightning Paddles


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