Re: [Paddlewise] Hard chined hulls

From: "Robert Warren" <rdwar_at_earthlink.net>
 
> "The V-shaped or chine hull, the traditional shape of many
> Eskimo kayaks, gives directional stability as long as the amount
> of rocker is not excessive. However, with such a hull it is
> unfortunately almost impossible to maintain fast forward speeds
> because as the speed increases the boat tends to plane on the
> flat chines. The kayak thus retards itself on its own bow wave".

This seems to be more a function of the flatness of the bottom 
than the existance of hard chines as inferred by the subject line.
Note that a chine refers to the the point where the bottom of
a hull meets the sides, not the V at the center (though some
use the term that way, as Uncle Derek seems to be doing.)  
It would seem that a V-bottomed, round chine hull should exhibit 
similar behavior and a flat bottom with any chine shape should, 
even more so.

I wonder about the ability to get significant semi-planing out 
of such sloped surfaces.  Planing usually requires a fairly 
flat hull.  In planing hulls, the transition from V to flat 
along the length of the hull has to be rather significant with
the flatness dominant in the rear of the hull; in kayaks the V 
continues the length of the craft with the WL beam decreasing 
greatly in the stern.

A more conventional explanation of the reason for a tad more 
resistance in hard chine hulls is that they have a greater wetted 
surface than rounded or soft chine hulls with the same displacement.

And of course, there are always exceptions to this.  Boreal
Designs got around the problem somewhat by combining a rounded
bottom with hard chines and flared sides in the Ellesmere.  
This gives hard chines without the extra surface area of 
a V bottom.  The flat sides still contribute more surface
area than a fully rounded hull, though.

Someone once commented to me that hard chined hulls seem to hit 
their speed limit rather "solidly" and they are hard to push
further.  My limited experience is that this seems to be true.
Round chine hulls feel like they can always be pushed a little 
more, but the hard chines seem to stall out. Given the limits 
of a paddler's perception, this may not be true.  My experiences 
may be coloured by this expectation.  

Mike

PS - an International Sailing Canoe (sailboat) _starts_ to semi-plane
at a driving force to displacement ratio (Fr/W) of 0.1 (Marchaj).  Using
a kayaker (175lb) + kayak (50lb) = 225, that would be 22.5 lb of 
thrust on the paddle continuously.  Given the intermittent nature
of paddling, that would put the actual paddle forces well up into
the top of Matt's very useful table of paddling force & hp 
requirements in the Aug '98 edition of SK.  I wonder what the 
appropriate Fr/W ratio for a kayak is?





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