Your point is well taken. To be fair though, the beam of the boat should be altered as well as length in your simulation. Something like displacement should be chosen as a constant.

: Yup, I was thinking that and just wasn't sure if I wanted to bring it up. But
: since someone did. Here is an exert from something I am working on for my
: web site. Still needs some editing.
: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`

: Everyone knows that a longer boat is faster than a short boat, right? That is
: what I was always lead to believe. When I started to design boats and
: learned more about hull design I started to question this. I also realized
: you have to define what fast means because it means different things to
: different people. Fast to a Racer is fairly obvious, top speed. But what
: about the paddler that never paddles at racing speeds for more than a few
: seconds at time? Does fast really mean top speed potential?

: Since speed is relative to the paddlers strength a much better way to look at
: it is how much effort it takes to propel a boat at a given speed. Using
: hull resistance numbers you can compare one boat to another with hard
: numbers instead of opinion.

: The method I used was to take an existing design in my computer and let the
: software stretch and shrink the length of the hull, nothing else. What I
: found was interesting and not what exactly what I had been lead to
: believe.

: Clearly the longer hulls are faster. At 8 lbs of resistance the 21 ft boat
: would be at least .5 mph faster than the 15 foot version. Meaning for the
: same amount of effort from the paddler would go faster in the long boat.
: So long boats are faster. Well, actually they have more speed potential if
: you have the horsepower to power the boat.

: How many recreation paddlers can keep up these speeds for more than a couple
: of minutes? From what I have read and seen not many, the average
: recreational paddler travels at around 3mph with the more experienced
: probably closer to 4 mph. The number of paddlers that maintain a higher
: than 4 mph average are a fairly small group. With this in mind the chart
: looks a little different.

: Dropping down to the more typical speeds of 3mph you see something
: interesting, the 15 foot boat has the advantage. Under approximately 4.5
: mph the shorter 15 ft. boat is actually faster (has less resistance) given
: the same amount of effort. The paddler in the longer boat has to exert
: more effort to maintain the same speed.

: At 2 lb of resistance the 15' boat is approximately .4 mph faster than the
: 21' boat. Meaning if you paddled for 2 hours that would put you almost a
: mile further down the river for the same amount of effort.