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

Colin wrote;

(SNIP)


>John has designed some whizzy boats, and I'm aware that he also  knows a
fair bit
>more than I do about the design of traditional kayaks, but I would
challenge that
>the pointy bows of 'traditional' designs are functional as well as
aesthetically
>pleasing. It is very rare that I find myself paddling my sea kayak in
anything
>approaching flat water, and thus it is also very rare for the bow of my
boat to be
>just "hanging out over the ocean looking pretty". Paddling in any sort of
sea the
>whole of the bow is frequently immersed, infact paddling in whitecaps or a
steep
>oncoming sea so is pretty much the whole boat.

First let me say that I cannot give a full course in naval architecture on
this list so of necessity I must condense what would normally take chapters
to explain. Also, I have never said that long overhanging bows do not have a
functional purpose on traditional boats that may have lacked adequate
reserve buoyancy in the hull through higher topside heights, deck crown,  or
greater flare.

Many people make the mistake of assuming that their boat or the boats they
know represent the characteristics of all boats. Just because one boat
buries its bow one should not assume all boats bury their bows. Likewise,
just because some boats use long overhanging ends to provide reserve
buoyancy one should not assume that no other way of providing reserve
buoyancy exists. One can easily design boats with short  overhangs that do
not bury their bows. Our friends in the US NAVY and various other design
bodies have studied heavy weather performance and have determined what bow
shapes work best. It is no surprise that Naval ships that must, of
neccessity, stay at sea regardless of conditions do not have log overhanging
bows ala traditional sea kayaks. Being practical peple they design to do the
job not to please some aesthetic standard or historical precedent. Even I
shape my bows with an aesthetic influence for no matter how much I would
like it otherwise, buyers place high value on how a boat looks. I will only
go so far.

I am very much aware that waves impact on performance and design my boats
around that environment. Years of ocean racing and paddling in open water
have had their influence on me as well as other designers of short ended
boats. Indeed, my boats have a fine reputation for their heavy weather
performance (If you can believe the people who paddle them). All theories
must come with a test that can prove the theory wrong. In this case, the
theory that short ends lack seaworthiness is easily disproved by looking at
well designed ships, short ended sea kayaks, short ended canoes and, yes,
short ended power boats.

> How relevant are the wave making
>characteristics of the hull in flat water when the whole boat is being
bumped
>around by waves orders of magnitude larger?

Naval architects have puzzled over this. They puzzled so much that they
built wave tanks in which to determine the effects of waves and even
measured performance of full size ships.  What did they discover? They
discovered that fast boats in smooth water tended to be fast boats in rough
water. Obviously they qualified that by insisting that adequate volume be
built into the topsides and that the topsides get appropriately shaped.  J.
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. Gerritsma's paper was
deliverd at the 11th Chesapeake Sailing Yacht Symposium sponsored by the
friendly people at the Society of Naval Architects and Marine Engineers for
those who want to get the paper and read it for themselves.

> Has anyone thought about analysing the
>shape of the deck, often frequently awash ?

Absolutely. However, some design boats to keep the decks dry in all but
extraordinary conditions. If a boat spends a lot of time with its deck awash
you might want to ask the question, Why? And, then consider if there is no
other way to design a boat.


>Which has more windage a low flat deck with balanced raised bows and stern
with
>buyancy far forward, or a high angled deck with square bow and stern ?

This is an easy one. The short ends with the more streamlined rounded deck.
Lots of wind tunnel tests to support this. You might rephrase the question
thusly.  Which has more windage the unstreamlined flat deck with its
attendant turbulence when exposed to the wind and its high unstreamlined
ends waving about in the wind or the short ended streamlined deck
configuration that minimizes turbulence?


>Which is
>dryer ? Which is faster in sea conditions ?

Once again an easy one. The good old US Navy has guidelines for dry decks
(more important on a ship at sea with sailors walking about than on a kayak
with the paddler tucked into his cockpit). I will not use space here
repeating readily available research but can recommend the whole list of
papers by N.K. Bales on seakeeping and seakeeping standards. Fortunately for
us the laws of physics remain fairly constant and we can apply what we learn
from ships to sea kayaks (always assuming one applies the laws strictly and
without twisting them around to suit preconceptions)

>I would also argue that flat water speed of a boat is a very poor measure
of miles
>you can paddle a day at sea, and optimising a boat for wave making
resistance
>doesn't necessarily make a good sea kayak.

You can argue it but you can't prove it :)

One does not optimize only for flatwater speed or even wave making
resistance. Speed forms one part of the equation. I doubt if Matt Broze or
Steve Killing (and certainly not myself) design for flatwater only and yet I
am sure all of us try to obtain the lowest resistance possible given the
boat's objectives. It helps to have some familiarity with the design
process. I recommend Steven Hollisters ppaer on the "Design Spiral" as good
reading for those of you who do not design boats and want to get a good idea
of what teh designer goes trhough to put a smile of your face.  You can find
his paper on the New Wave web site (link on my resources page).

> I demo'd a P&H spitzbergen at a
>symposium in May (an example of a boat designed to be 'fast' with a high
waterline
>to overall length ratio). (SNIP)

One should not asume that a poorly designed boat or one not designed for
open water use provides and example of all short ended boats anymore that
one should assume that a really poor example of a traditionally shaped boat
is an example of all traditionally shaped boats. If the readers on Paddle
wise will refrain from telling me their horror stories about poorly designed
short ended boats I will refrain from telling my horror stories about long
ended boats.


>They have the added benefit that the shape will ride up over objects in
their
>path - apparently important for the traditional hunter landing and
launching from
>ice floes, but more importantly for the paddler today essential for a
number of
>rescues. Maybe of minor concern  but there is also a useful safety bonus of
raised
>bows in collisions. I watched a potentially nasty coming together between a
>knordkapp and a sirrius last week in surf. Experienced Paddler in the
sirrius was
>confronted by an inexperienced surfer in a knordkapp surfing very rapidly
offline
>towards him. He capsized his sirrius, and you can bet he was glad the
knorddapps
>bows were the shape they were as it rode up and over his hull. He rolled up
with
>no damage to either boat or persons - due in great part to the bow shape of
the
>knordkapp.

Well I can't argue that. If I were designing my boats for collisions I would
certainly give them more sloping bows and maybe even knife sharp tips so
that I would win the fight after the collision. I, and a lot of other
designers, design for paddling not colliding. But if surfing bumper cars
turns you on, by all means buy a Nordkapp. Of course, my boats would ride up
over a capsized Sirius too, so I fail to see the point. I guess I have no
sympathy for paddlers who cannot understand the simple rules of surfing and
it is no wonder that so many surfers like my nephew (a pretty good
competitive surfer in his younger days) consider kayakers a menace on the
waves.
,
>For *** FLAT *** water use, I think that John's arguments about waterline
length
>make a lot of sense. The QCC boats look not dissimilar in bow and stern
shape to
>an old flat water touring boat I have sitting in my yard, which at 15 or so
feet
>long with a water line length of 15 or so feet, is indeed noticeably
quicker on
>flat water than my sea kayak, with an overall length a couple of feet
longer. But
>I wouldn't want to paddle it in any sort of sea state.

Well, maybe had it been designed by a more competent designer it could have
done both or maybe it was designed by a competent designer who, if asked to
make the boat suitable for open water would have done so and still kept his
short ends.

In any case, the long overhanging bows increase the moment of inertia and
add weight in the least desireable place.

I respect Colin's opinions. I have a few that I cherish myself.  In this
case, however,  we have a wealth of information derived from many studies
into the performance of boats in rough water spanning many years. With this
at our hands we can temper our opinions with more objective information.

I will submit that my statements on the QCC web site have support from a
number of highly respected sources which I have listed in this message and
in my web site on my "resources" page. Rather than get into an interminable
argument over "my opinion" versus "your opinion" I suggest that interested
parties read the literature first and then debate it with the naval
architect or scientist who wrote it.

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



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