As rowboats go, the Chester Yawl is fast and efficient, but it's not a rowing shell.  It's probably good for 4 knots all day, a little faster in a sprint.  And a little faster still with a sliding seat, of course. Between 5-1/2 and 6 knots it will hit "hull speed."  

http://www.youtube.com/watch?v=QLMmm99QryA

You said that, as rowboats go, the Chester Yawl is fast and efficient.  You are an acknowledged expert in the subject, but even so, would it be fair to ask you why you think that, in simple terms that we as potential buyers of your (or your competitors') products can understand?  Fast by what metric?  Efficient by what metric? Faster then what competiive product at similar cost?  More efficient than what competitive product at a similar cost?

Camper wrote: "Fast by what metric?"

I row my Peeler skiff  at about 1 1/2 knots - sweating all the way vs the Chester Yawl at "4 knots all day".  I know you are concerned with some way to objectively measure the relative speeds of kayaks and other self propelled boats - but the human variables are such that an objective answer is difficult. Perhaps you might open a new quiry of anyone who has experience rowing the Chester Yawl vs. the Pygmy Wherry https://www.pygmyboats.com/boats/wineglass-wherry-rowboat-kit.html and then compare prices etc.

Better yet, try to get to one of the demos CLC puts on around the country each year and try actually rowing the Chester Yawl. The OkoumeFest is coming May 16-17 in Maryland and I'm sure John will have a Chester Yawl there to try out.

By the way, have you built the John's Sharpie yet? I'd be interested in knowing how the sail configuration we discussed worked out.

   My chester yawl is as fast as 5 to 8 km/h with fix seat, standard oars 2m40 and inexperience rower on a lake without wind nor swell

Here the report of our building session

 http://www.arwenmarine.com/NewsCY1308.html

Here a video of our first test on a lake (Saint Cassien)

http://www.dailymotion.com/video/x1443zz_yole-de-chester-chester-yawl_sport

We have then tested in a large river and in salt sea.

It passes well the swell, it is lightweight and give enough spaces for comfortable day trip and even more.

A boat's hull speed is the speed at which its length equals the wavelength of its bow wave. Hull speed is the theoretical maximum speed a displacement hull can go.

The calculation is as follows:

SQRT (LWL) * 1.34 in knots

Eg. Chester Yawl LWL is about 15ft

SQRT (15) = 3.9 rounded

3.9 * 1.34 = 5.2 knots = 4.5mph = 7.3kph

That is just a portion of the consideration. You need to apply exponentially more effort to make a boat go faster. I.e., to speed up a boat from 1 knot to 2 knots will take a lot less effort than to keep the boat at 5.2 knots.

With a sliding seat you will be able to convert your energy into forward motion more efficiently - you will be able to use your stronger leg muscles and will be able to row closer to hull speed.

The response from John (above) is thus spot on.

For reference and some nice drawings: http://www.cncphotoalbum.com/technical/hullspeed/hullspeed.htm

   5.2 knots = 6 mph = 9.7 kph

   @Birch2. You are correct. My error. Thank you.