[Paddlewise] Kayak speed vs length

I've often heard (and intuitively accept) that all other factors being equal, a
longer kayak will be faster than a shorter one.  I've got a friend who disagrees
with this, but I've had a hard time explaining why this would be true.  I would
speculate (fancy word for "guess") the following possible reasons:

1.  Paddling on the ocean, there are generally little (or big, for that matter)
waves and chop that push against the kayak from different angles.  The longer
the kayak, the more these "local" disturbances would tend to cancel out and thus
interfere less with the boat's movement through the water.  If this is true,
then would this advantage disappear when paddling in very smooth, flat water?
Or would the longer kayak continue to be faster?

2.  A longer kayak has more floatation than a shorter boat (again assuming other
factors are equal), so it would float a little higher in the water, thus
reducing drag.  I assume that most of the friction comes from the movement of
the bow cutting through the water and that the additional length contributes
very little additional drag.  (I expect I'm going out on a limb on this one,
having once gazed at Matt's speadsheet on this subject (phew!)) I know enough to
know it's ultimately more complicated than that).

My friend countered my comments by saying if that were true, then paddling a
boat a mile long would be faster than a 17 footer.  Obviously a REALLY long boat
like that would weigh a lot and thus have a lot of inertia to overcome getting
it moving, but once up to speed -- would it be faster than the 17 footer?  Or
perhaps another way to ask it:  would it require less paddle effort to maintain
a given speed than a 17 footer??  What if it were so loaded with weight that it
floated the same height in the water as the shorter kayak -- would it still be
faster?

Lastly, is there a simplified formula for estimating the speed, given a certain
beam and length (holding other factors constant)?

Evan Dallas
Woodinville, WA.



***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************