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

Matt Broze
http://www.marinerkayaks.com
-----Original Message-----
From: 735769 <735769_at_ican.net>
To: paddlewise_at_lists.intelenet.net <paddlewise_at_lists.intelenet.net>
Date: Sunday, July 25, 1999 7:23 AM
Subject: Re: [Paddlewise] QCC boats and water line length ........



<BIG SNIP>
Jophn said:
>I don't see how this expands the discussion. Are not canoes open boats? If
>not, why not? A study of the boats will reveal that many canoes have
similar
>lines and proportions to many Umiaks, dories,and Viking ships.

Open Canadian canoes are a relatively specific type of craft without a lot
of flare and rake as opposed to an umiak or dorie (and I want to exlude the
Hiada Canoes from this Canadian canoe group too as they also have a large
amounts of rake and a high bow. I find them extremely seaworthy craft. Even
the forepiece that I had once assumed to be  decorative is hugely
functional. I saw some old film footage of a Hiada Canoe full of native
paddlers coming straight in through the surf. The bow tilted down until the
normally high raked "figurehead" rested on the green water surface in front
of the breaker. As the craft surfed the breaker the water divided like Moses
was standing on the bow. The water cleanly peeled up and out to each side of
the "canoe" falling back to the waters surface just outside the hull which
remained dry inside. I was impressed!
I objected to bringing the raked and flared open boats into a discussion
that was specifically discussing the dryness of a near vertical bow rake. If
the examples had been of craft that had similar shape as well as were "open"
(say a 327 or 432 canoe) I wouldn't have so much objection. I think the
seaworthiness you are claiming for dories and umiaks is because of the high
raked and flared ends in spite of them being open boats. In other word you
are trying to claim craft to make your point that are actually examples that
help make my point about rake and flare rather than yours about the
advantages of a vertical rake.
<SNIP>
I wrote:
>>This is partly because they are shorter and have
>>The problem with any boat that doesn't
>>have a lid on it is that the profile has to be high enough to avoid
>swamping
>>by waves. Unfortunately this extra freeboard adds to the windage so the
>wind
>>can blow it around a lot more.

John responded:
>Yes, open boats do have drawbacks (as do kayaks).  However, having cruised
>open water succesfully in canoes and learned to deal with those drawbacks
>(just as paddlers learn to deal with the drawbacks of kayaks ) I guess
can't
>appreciate your problems with canoes.

Just what drawbacks of  kayaks are you alluding to? Please be specific.
>
>(SNIP)
>
I wrote:
>>I still am not sure what "Pitch Gyradius" is.
>
John responded
>I thought I did define it by commenting that some people call it the radius
>of gyration, a term I thought (hoped) you would find familiar. Pitch, or
>pitching in the context of this discussion, is the angular component of the
>oscillatory motion of a hull about a transverse axis. The radius of
gyration
>is the square root of the ratio of the mass moment of inertia (referred to
>body axes) to the mass of the boat. Hope that helps. If not maybe some one
>with better teaching skills than I can take a try.

"Radius of gyration" gave me a pretty good idea of what you meant but
without an actual definition (I could understand) I couldn't be sure. Is the
definition you offered above (which I have trouble understanding--anyone
else care to try explaining it to me) the same as the one I found at
http://www.unb.ca/web/physics/1040/torque.htm ?
(The radius of gyration is the distance k from the axis of rotation at which
a single point mass equal to the object's mass M would be put to have the
same moment of inertia I as the object.) I think I understand that one so i
hope the result is the same.

<sNIP>
>All of our time. I have such poor teaching skills. Not only that but, for
>example, Gerritsma's paper is 13 pages of math. I can't do it justice here.
>Maybe you can. More importantly, you might read it and come to quite
>different conclusions from me or might see flaws in the paper(s) that you
>will want to bring to the attention of the author(s).

John you leave one with so little information to go on about what Gerritsma
did that now I don't even know if he did an actual experiment or a strickly
mathematical one. If I knew a little bit about what he did and why I would
be far more likely to accept his conclusions and have a much better idea if
your interpretation of them was relevant to the discussion and made sense.
You wrote: "Gerritsma in his highly regarded studies of sailboat resistance
determined that the three major factors for resisatnce in waves were the
significant
wave heigh, the wave period, and the pitch gyradius. Surprise! Not one word
about the length of the overhanging bow. A lot about gyradius, however,
which suffers with a long over hanging bow and stern." My bet is that the
reason he said nothing about overhang is that that was never a variable in
his "studies". I may find this out yet as Natalie has offered to help find
the study.
>
>
>
>
>>realize I am lazy and should have to muddle around in the library finding
>>this information for myself like you probably had to, but I'm not even
sure
>>the information is relevent and just writing (and rewriting when Windows
>ate
>>it) this post may mean I may not make my deadline for the next accident
>>report in Sea Kayaker.
>
>If you don't feel it is relevent then don't look for it. But don't you
think
>you can better judge its relevence after you have read it?

Of course, but you wouldnt have had to tell me much about the study for me
to have some idea if it was relevant to overhang. For instance had you said:
"The study towed six sailboats with varying degrees of overhang but the same
pitch gyradius in a towtank at three different wavelengths. It was found
that the less overhang the sailboat had the less resistance it had in each
of the tests." Would that be relevant? Most likely, but sailboats are not
kayaks so if the differences were quite small I might be less likely to
accept them as relevant than if the differences were great. If I needed or
wanted more details I could search for the study.

When you do direct us to the source I for one would appreciate something
like (hopefully) a web address or some way where it can be found in an
efficient manner.

Thanks for all your help and your understanding of my frustration here.
Matt Broze
http://www.marinerkayaks.com

>



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