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

Matt wrote;

(SNIP)

>I'll agree that compared to a business the navy is far more performance
>oriented than dollar oriented,
>but cost is always a consideration although not as important as the lives
of
>the crew and the safety of the ship. If the goals can be achieved with less
>cost then that is likely the way it will be done. If a benifit is minor and
>costly and only applicable in rare circumstances then a lot of money will
>not be spent that could be used to better effect elsewhere.

Absolutely.  If you can achieve dry decks in storm conditions with short
ends then why shouldn't you? As for rare and minor, well, maybe more time at
sea in ships or yachts will affect your opinion or what constitutes rare and
minor.

>
>Yes, I was considering the navy ships that would be relevent to this
>discussion.

>Those with roughly the same dimension and performance
>relationships as kayaks. These would be displacement hulled ships, not
>planing PT boats or stubby little surf lifeboats (although the picture I
>have of one (plate 39 in the 1980 edition of "Waves and Beaches" by Bascom
>shows substantial rocker and rake--I est. 60 degrees-- and lots of flare).

Absolutely. By the way,  what do you consider a lot of rake and a lot of
flare? Might be helpful to define "a lot" .

(SNIP about wave sizes applicable to ships longer than breaking storm waves)

>I believe I said open canoes not open boats.

I particularly disagree with what you said about open canoes too (see
below).

(SNIP)
.
>
>Although I fail to see why John has expanded the discussion to these other
>open boats, I believe that in general umiaks and dories are more seaworthy
>than open canoes too.

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.


>This is partly because they are shorter and have
>higher freeboard and more flare and yes more rake to the bows and sterns.
>However if forced to chose a craft that I had to paddle or row for a few
>hours in any direction you want to chose in a 35 knot wind the kayak would
>be my first choice hands down and the canoe would be my last (even if I sat
>in the bottom to lower the center of gravity and used a kayak paddle so I
>could quickly brace on either side). 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.

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.

(SNIP)


>I still am not sure what "Pitch Gyradius" is.

>"Seaworthiness,..." a few years ago and much earlier read the relevent
parts
>(and some not so relavent parts) of "Introduction..." and Skene's
>"Principles..." they were borrowed from a friend or the library so I don't
>have them handy like you apparently do. Since you are the one who used the
>word to make your point I fail to see why you haven't made it easy for the
>rest of us and simply defined the term rather than sending us off to the
>library to look for it?

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.

>Also, since
>you think we should read the studies you suggest, at least if we question
>any of your conclusions, I for one would appreciate learning more about how
>to find those sources.

Glad to help with this. Many libraries, universities, professional
organizations etc. can supply copies or will search for them. Often on the
Internet or by telphone so you can do it from the comfort of your own home.
I can't tell you which will work best in the US as I live in Canada and rely
upon CISTI, the Canada Institute for Scientific and Technical Information. I
think Americans can use it too. I don't recall their web address (I bet a
search engine will turn it up without a lot of effort) as I prefer to do it
by telephone which is 613-993-9251. You will need an account number and
should get their booklet on document searches. Maybe one of you Americans
will tell me the best service in the US. Of course, you can also use SNAME
for those papers published  by them. I think I provided their address in my
web page on resources (As I mentioned in my post). Bet they have a  web
address too but I have never used it.

I don't think anyone has to read the papers to question my conclusions.  It
just helps in the discussion if they do. (see below)

>I assume when you said reading the papers you
>mentioned will save a lot of time you were refering to your time not ours.

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).




>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?

>Sorry about the rant but you can be very frustrating to somebody trying to
>understand what you are saying and I'll bet I am not alone in feeling this
>way.

Don't rant, just ask politely.

Matt (and readers), my experience, measurements, and testing of boats with
long traditionally styled ends suggests that most of the length is wasted
weight and length that acts detrimentally to performance. I support these
conclusions with what I have read and learned from other boat designers and
naval architects. I don't mind changing my mind but I like something more
than opinion to change it.

I don't think the Internet serves well for in depth debate on complex
topics. No one can write fully on much of anything here. For that reason I
refer interested readers to sources of more detailed information from whence
they can draw their own conclusions.  I try to make my point as clearly as I
can and as simply as I can and I hope everyone recognises that I and others
could say more.


Cheers,
John Winters
Redwing Designs
Web site address, http://home.ican.net/~735769

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