Re: [Paddlewise] QCC boats and water line length ........

At 3:45 PM +0100 7/23/99, Colin Calder wrote:
>With the recent Maligiaq traffic I followed the links to the QCC web site (re
>Maligiaq and the boat he will race) and was very interested in the articles by
>John Winters on the site about his kayak designs.
>
>http://www.qualitycomposites.com/speakboat.htm
>
>The list comparing overall length vs water line length of many popular sea
>kayaks
>at:
>
>http://www.qualitycomposites.com/howlong.htm
>
>makes interesting reading.
>
>The general gist of the argument is that any part of the boat which
>overhangs the
>water line length at bow and stern is a waste of materials, adds weight
>etc, and
>does nothing for the boats handling or speed. John puts forward:
>
>	"Some traditional designs have as much as two feet of skinny boat
>hanging out
>over the ocean. It looks pretty but it doesn't do much"


John is probably overstating the case when he says: "It looks pretty but it
doesn't do much". Simple through-the-water efficiency is not the end all of
kayak design. For many kayaks it is probably the last thing the designer
looks at after maneuverability, and other handling properties at sea. The
goal, generally, is to make as efficient a boat as possible given the other
design constraints. This equation is probably reversed for racing kayaks,
but most of us are not that interested in racing.

We don't know the design constraints of the traditional designers, so we
don't know what those overhangs were for. Therefore, we can't really
comment about whether they did anything or not.

There are generally several ways of solving boat design problems. Long
overhangs and plumb-bows with flare, both solve the same problem of keeping
the bow above the water in waves. With careful designing it is probably
possible to create the exact same lifting response using either solution.
However, each solution will have consequences on other aspects of the boat
handling characteristics.

For example, Navy designers must consider where they will mount the sonar
system, or whether the ship will need to be able to get through the Panama
Canal. These considerations can not help but impact overall efficiency and
sea-handling characteristics. It is an oversimplification to say that the
bow of a destroyer is shaped a particular way because that is the _best_
shape for going fast through waves, period. You may be able to say that it
is the best shape for going fast through waves for a boat that will fit in
a lock and have a sonar system slung under the bow and other considerations
I don't know about.

For any plumb-bow shape you can imagine, you can always design a higher
volume bow with better ability to rise over waves by pulling out the top of
the stem to give it more overhang. Making this modification will have
consequences on how the boat surfs, how much storage room it has, how
fiberglass lies into the mold, and strength running into an obstacle.

What the best design is depends wholely on what you are trying to
accomplish. I am under the impression that John likes keeping the overall
length of his boats short (a good idea for a variety of reasons) and he
wants them efficient (always a worthy goal). Combined with other design
considerations he chooses a relatively plumb bow. His cat is skinned.

Early British sea kayaks were essentially knock-offs of Inuit designs. They
buggered with these designs slightly to acheive slightly different
properties, but essentially they let someone else skin the cat. Nobody
(accept maybe the good Professor) really knows what the Inuits liked about
their cats so their method of skinning is not neccesarily the best for us
today. For example the early British boats have long overhangs with very
little volume in the ends. Looking straight down on some boats, the
sheerline is concave on some boats. The leaves very little volume in the
overhang for helping the bow over waves. With some of these designs, the
first 6" to 12" could be sawed off without affecting the volume much. I
don't know what this extra length is good for, but the Inuits probably had
a good reason for it. That does not mean it has any usefulness now. Many
newer British designs have much fuller overhangs. The designers of these
new boats decided more volume in the ends better served their needs.

It is possible that British boats will evolve a more plumb bow, but once
you are used to the performance characteristics of one style of boat,
chances are you will like those characteristics and not want to deviate
much in your design choices.

Nick





Nick Schade
Guillemot Kayaks
10 Ash Swamp Rd
Glastonbury, CT 06033
(860) 659-8847

Schade_at_guillemot-kayaks.com
http://www.guillemot-kayaks.com/

>>>>"It's not just Art, It's a Craft!"<<<<


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