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: Saturday, July 24, 1999 6:59 AM
Subject: Re: [Paddlewise] QCC boats and water line length ........


>Matt wrote;
>(SNIP)
>
>
>>Being practical the navy isn't going to add a whole lot of cost to the
ship
>>by creating expensive overhang (even though it might well make the ship
>>drier during a hurricaine) especially if an adequate hull for most rough
>>conditions can be built much more cheaply using some rake and a lot of
>flare
>>above the bow. This may create more spray in huge seas than the finer
>longer
>>bow would but in a ship spray is far preferable to green water washing
over
>>the bow.
>
>(Large SNIP)
>
>Matt's experience with the Navy differs from mine and certainly differs
from
>the Navy design standards. My experience working on their ships suggests
>that the Navy has more concern over performance and safety than cost.
Rather
>remarkably they prefer not to have their sailors washed overboard. >I
sailed
>with a senior officer from the Bureau of Ships for a few years and he
>confirmed this.

One of the very reasons I suggested they would probably trade more spray for
less green water on deck. Washing away the superstructure is another.

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.
>
>Of what importance is cost when you are spending Matt's tax money to build
>the ship. :-)

My pockets are only so deep so cost eventually will rear its ugly head.
>
>Matt says Navy ships do not encounter the kinds of conditions that sea
>kayaks encounter. I guess the Victory at Sea series was doctored and my
time
>aboard ships a foggy haze of imagination (not to mention my ocean racing in
>large yachts).  Perhaps Matt is thinking only of the largest ships of the
>Navy and Coast Guard.  In any case you will find a particularly fascinating
>picture - possibly a fabrication - of a Coast Guard lifeboat (short ended
to
>keep cost down) running the breakers at Yaquina Bay Oregon in Skenes
>Elements of Yacht Design.  My brother served in the Coast Guard and he has
>some interesting tales of "little" waves and "big" ships. Maybe he was
>smoking too much wacky tobaccy and imagined it all.

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).
My point was that a kayak operates quite often in wave conditions that if
they were to be scaled up to the size of a similar shaped ship would quickly
destroy it. The reason that ships have not all been destroyed by conditions
like this already is because these conditions are extremely rare to
non-existant. My understanding (I believe this came from "Ships in Rough
Water" by Kent) is that the most difficult waves for a long vessel are those
with roughly the same wavelength as the vessel is long. Wind waves in deep
water topple into whitecaps when their height is about 1/7th their
wavelength. This means that they cannot get steeper than this except under
special circumstances such as clapotis. For instance, a 14 foot long kayak
will be operating in its most trying condition with waves that are about 2
feet high and 14 feet long. It doesn't take much time to create seas like
this with any wind of 20 knots or more. Eventually the wind will create
waves that pass through a stage where they reach this steepness (2 foot
whitcaps--- and here the angle of the wave crest will be about 120 degrees).
Now lets up the scale about 50 times. A 700 foot ship would be operating in
100 foot high waves that are about 700 feet between crests to get the
equivalent roughness of seas relative to its size.
According to Bascom (page 51) a 50 knot wind blowing steadily over 1420
miles of fetch for 69 hours will create a sea where the average wave is 48
feet tall. Most of the wave energy will be in waves of about 1400 feet long.
These waves will be less than 1/2 as tall and twice as long, or only 1/4 AS
STEEP, as the 2 foot high whitecapping waves are on a 14 foot kayak.
Furthermore even waves this big are only going to happen under the most
freakish of conditions. 1420 miles is a long way to have to blow a 50 knot
wind over for 69 hours to get seas as rough 1/4 as rough as a kayak
regularily operates in. I don't know what it would take to have the average
wave reach 100 feet with an average wavelength of 700 feet but I don't think
I will live to see it. The fact that the far milder waves which were chosen
to exite us about "Victory at Sea" or were big enough to impress the
relatives with only demonstrates their rarity. Waves of the same relative
size and steepness as create problems for a kayak would quickly destroy the
far more delicate ships that suffer with the change in scale because mass
increases by the cube but strength only increases by the square. My point is
that a bow shape perfectly adequate for a ship may be very wet when scaled
down to kayak size.
>
>I particularly disagree with Matt's comments about open boats.

I believe I said open canoes not open boats.

>Matt makes
>much of paddling experience and having paddled open canoes extensively on
>the Great Lakes and having paddled around the northern tip of Labrador in
>open canoes I would suggest that I have some experience with their
>seaworthiness. One could also learn a bit about seaworthiness from open
>Viking ships, Umiaks, dories, and even Captain Bligh's open boat.  HMMM.
All
>short ended (relative to sea kayaks) too.

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. 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.

>
>Regarding the remainder of Matt's post, my suggestion that one read the
>papers I mentioned in my post will save a lot of time. If one disagrees
>strongly, one can skirt the middleman and argue with the author(s). I have
>passed along what I have learned from my studies, my instructors, my
>reading, my experience paddling and working in yacht design offices.
>Unfortunately I failed to keep count of the kayaks I have paddled so if the
>reader considers spending a little time in a lot of kayaks valuable then I
>recommend you embrace Matt's opinions.


Because I keep track of the handling and performance of most of the kayaks I
test on a spreadsheet in order to remind myself of the kayaks
characteristics later, it is a simple matter to count the number of dates in
the "month/year tested field to know how many I have tried. Pretty
compulsive I know, but we all have our hobbies and one of mine is collecting
experiences in a wide variety of watercraft. On the Fourth of July I even
got to pedal a wavebike.

>Finally, I apologise for the term "gyradius". Many people use "radius of
>gyration". Matt has the advantage of me here as he knows what words he and
>others know. I use them as I was taught. One can find the term used in such
>books as Introduction to Naval Architecture, The Symmetry of Sailing,
>Seaworthiness, the Forgotten Factor, Principles of Yacht Design, and maybe
>some others. I also use English spellings such as "colour" for the American
>"color". I hope this does not cause any  problems  for those who have no
>familiarity with English as written by the English.

I still am not sure what "Pitch Gyradius" is. While I read
"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? Wouldn't it have been just as easy for you to type
the definition as to list the sources where we might find it? 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. I assume when you said reading the papers you
mentioned will save a lot of time you were refering to your time not ours. I
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. How about doing us curious but lazy folks a favor and
either tell us more details about the research you think is relevent or
direct us on how to find the source in an efficient way.
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.
I hope to get to test paddle your kayaks one day and I hope they make me
reformulate my opinions. When I'm surprised by a kayak is the time I get the
chance to learn something new. You needn't worry about me reviewing yours or
any other kayak or giving my admittedly subjective opinions about any
specific kayak to this group as a whole. Were I not a competitor I might
feel freer about doing so, but I will restrain myself and leave the
published subjective opinions about kayaks to the subjective reviewers at
Sea Kayaker magazine whose axes to grind are probably real but far less
obvious than mine.
Matt Broze
http://www.marinerkayaks.com





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