Re: [Paddlewise] Pictures of my Northbay (Changing to : Lifting vs. Plunging Bow)

Joan wrote:

>>Which reminds me of a question I asked this weekend, and nobody really
had an answer: if the bow goes through the wave instead of up and over,
wouldn't you maintain speed better?  (Mine goes up & over, & it seems to
me that it slows me down, but I'm not really sure...)<<

When we get done arguing blade feather, wide vs. narrow (blades and kayaks),
paddlefloat vs. reenter and roll, Swede form vs. fishform and rudder or no
rudder we sometimes get down to this. So here is my take on it.

The rocking and slamming caused by heave/dip motions can add considerable
extra resistance to a hull.  Sea Kayaker Magazine tested five sea kayaks in
both calm water and directly into 8" high waves that were 16.6 feet long.
(Note: 16.6' long waves travel at about 5.5 knots -- the wave speed (in
knots) is equal to 1.34 times the square root of the wavelength (in feet)).
The kayaks traveled into the waves at 3 knots.  There was no wind.  The
waves increased the average resistance (the actual resistance varies as the
waveform passes) by about 1.5 times for the kayak that did the best and up
to 2.3 times for the kayak that did the worst. While these may seem like
small waves my videos show that most of the kayaks plunged enough to put
their bows under at times.
(Note: Randel Washburne in his book The Coastal Kayakers Manual (page 26)
does a good job discussing the pros and cons of a lifting vs. a knifing bow
when paddling into head seas.  Unfortunately after pointing out how both
extremes slow a kayak, he suggests the wrong conclusion when he says:
"Perhaps the worst is a compromise design that does neither well.")  I would
like to suggest instead that the best is probably a compromise that avoids
the problems at either extreme.
I once talked to a paddler who had just sold a kayak that both knifed into
the waves with its' fine bow and then lifted quickly due to a broad flat
midbody.  He usually paddled at the front of a group.  He complained that
whenever his group paddled into head seas everyone, right down to the
weakest paddler, would pass him as he struggled with his wet and
hobby-horsing kayak.  He was extremely frustrated by his kayak that:
1)Buried its bow into waves (adding to its wetted surface friction and
pushing a greater volume of water aside).  2)Tilted its' bow up steeply as
the wave crest passed (the more the kayak angles upwards--and the flatter
and wider the hull is--the blunter the angles at which the wave crest pushes
back against the hull and therefore the more the wave will slow the kayak).
3)Slammed down hard on its' wide flat bottom after the wave crest passed
(increasing friction with the added water pressure during the sudden--energy
dispersing--direction change, and jarring its' occupant into wanting to
decrease his speed even further to lessen the severity of the next slam).
Yes, perhaps the worst is not the compromise but the kayak that both knifes
into and then rises too quickly to the waves, thereby suffering the problems
of both extremes as this paddlers kayak apparently did.

Matt Broze
http://www.marinerkayaks.com


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