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

Matt Broze
http://www.marinerkayaks.com
-----Original Message-----
From: 735769 <735769_at_ican.net>
To: paddlewise <paddlewise_at_lists.intelenet.net>
Date: Friday, July 23, 1999 10:42 AM
Subject: Re: [Paddlewise] QCC boats and water line length ........


John Winters wrote:
>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.

I agree with most of this but I think you are reaching by bringing in naval
ships.
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.
I think John is stretching here by using the shape of Navy ships to make a
point about kayaks. First kayaks often operate in far rougher relative wave
conditions than Naval ships ever see, steep 16 to 20 foot long wind waves
are common to kayaking but the equivalent seas to a 500 foot long naval ship
probably do not exist in our oceans, and therefore the Navy does not need to
design for them. Looking at the QCC kayak pictures on their website the bows
I see bear very little resemblence to that of a Navy ship either so I don't
see how that comparison is valid to the kayaks that were under discussion.
Navy ships have far more rake and flare.

<Snip>
> 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.

As a group I have never thought of open canoes as seaworthy (well maybe a
short rockered whitewater "open" canoe packed full of flotation). As I said
above ships operate in a different environment than kayaks relative to wave
sizes and steepnesses, although I'll agree naval ships offer the closest
comparisons to long narrow kayaks that exist in the ship world. After
designing our first Mariner (18'-5"x 20.5") I was surprised that most of the
relationships between the dimensions were almost identical to those of a
naval destroyer.
There are many ways to skin a cat so I am sure kayaks without rake can be
made to not pearl their bows. The only question I'd have is what else did
you have to give up to do it? Fuller bow sections below the waterline are
likely to mean more harsh pounding in waves and more of the "kayak on a
spit" effect as two waves lift the narrow ends and suspend the middle in the
trough between them.
The proof is really in the paddling and all this theoretical talk pales next
to a test paddle of many different kayaks in rough conditions. I have
paddled dozens and dozens of single kayaks in rough conditions and as a
general rule: longer kayaks, finer ended kayaks, lower bowed (and over all
lower) kayaks, those with less overhang, those with less flare forward,
those with lower or flater foredecks, and those decks that sloped inward
down too close to the waterline in the foot and knee area (even though high
and v-ed--the waves glance up off the slope into the cockpit), were more
likely to have green water over the cockpit. Those with less rocker and rake
in the bow also tended to get their generally more vertically sided bows
trapped underwater in following seas and then broached more readily around
the pinned bow. That said sometimes kayaks surprise me and do not perform as
I have predicted based on my past experience. I always love it when that
happens because that's when I get to learn something new.
I know someone on this list has one of John's kayaks out here in Seattle
because I have seen it. If you are reading this post lets go paddling on a
rougher day (or through the Montlake Cut on a busy summer Sunday) so I can
see for myself if John's design is an exception to my experience with bows
with little or no rake.
>
<SNIP>
>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.

GYRADIUS? If you insist on using words I can't find in a nautical,
scientific or Webster's dictionary please define them for us. Is pitch
gyradius related to the moment of inertia as I'm imagining? I think you
might be reaching here as well. I'm having trouble even picturing a
displacement sailboat without a lot of overhang at the bow (and sailboats
have a much different shape from a kayak, so I question the relevence). I
don't know but I'll bet Gerritsma advocated keeping the ends of the sailboat
light to reduce the "pitch gyradius" and didn't mention overhang at the ends
at all because that wasn't something he experimented with.

<SNIP>
>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).

Big waves do not get as steep as small waves so kayaks operate in rougher
conditions than ships, same physics, different scale. Salt water waves
(where most Navy vessels operate) do not get as steep as fresh water waves
(where a lot of sea kayaks operate). Deep water waves (where ships operate)
are not as steep as waves steepened by shallow water (surf) where sea kayaks
sometime operate. I'm the first to admit that much can be learned from the
study of "Ships in Rough Water". (In fact the book by that name--by
Kent--was very influential in the design of our first kayak.) However, the
situations are not totally analagous.

<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.

Yes, it always gauls me too when I hear sweeping generalizations made from
one or two examples. However, I have paddled over 500 single sea kayaks.
While most of the paddles were for 1/2 hour or less in relatively mild
conditions I have tried a lot of kayaks in rough sea conditions and many
more times I have used the steep waves in boat wakes (and often their
reflections in a narrow vertically sided channel) and steep fresh water wind
waves bouncing off the floating bridge during storms to simulate rough wave
conditions. I have done this partly because I find paddling in rough
conditions great fun but I use an untried kayak when I can for the purpose
of trying to find out what features of a kayak create which results.
So if you think my opinions are all wet, I guess I'd have to agree. ;-)

Colin wrote:
>>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.

John responded:
>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.

I think you are both missing the point here although both are right in what
you said. We do design for collisions but not just with other kayaks. I
often purposely collide with the shoreline at full speed. I skid right up on
it (if the beach is sand or rounded rocks and the barnacles aren't too
thick). That way I can step out on dry land with dry feet. Most kayaks I
have seen with little rake at the bow tend to stick into the beach and stop
dead within a few feet. Often the designers of boats like this tell the
public the proper way to land on a beach is at a shallow angle. The
absurdity of this approach is very apparent on the TASK (now TAPS) beginners
paddling video where the "proper" landing technique is being demonstrated.
The paddler is having a devil of a time getting out of his kayak what with
the four to six inch high waves slapping against the side of his boat. When
he does step out the little waves knock the boat into his legs. Imagine
bigger waves and breaking ones on steeper beaches.
One pitch black Baja evening I was paddling back to our campsite from a nice
dinner in a little cantina. Out of the darkness loomed a large spit blocking
our way. It was made up of large volcanic boulders so fine grained they
tinkled like glass. Imagine a bank of channelized river rip-rap made from
sharp edged obsidian. I turned to parallel the bank to go around it. The
phosphoresence there was incredible in the pitch black night. it was so
bright it hurt my dark adapted eyes. I became immersed in being able to see
how the water flowed and swirled around my paddle blade. I watched the
phosphoresent flow around the blade as I increased my speed because it could
reveal a lot about how a paddle works that is usually hidden from view. Upon
reaching top speed I heard and awful bang, crash and clatter as my highly
raked bow lept skyward over the rip-rap (that had curved around in front of
me in the blackness so I hit it head-on) and it came to a stop about three
feet higher than the water with me teetering in the air while trying to
reach way down to the water and brace to keep my balance and not tumble
over. I slid (bang, bang, splash) backwards down into the water, luckily
still dry and upright. Had I not had a raked bow I might have broken off the
footpedals or had they been strong enough maybe broken my ankles. Maybe I
would have punched in the bow or knocked a hole in it. This kayak is still
our demo after13 years of regular use and the scratches from the sharp edged
volcanic boulders (still clearly visible) were the only damage sustained.
Unlikely you readers will be as stupid as me but I'd rather glance up over
the unseen deadhead, below surface rock hidden by the suns reflection, or
the underwater log in the waterway (all of which I have hit while moving at
a good clip) than come to a sudden bone grinding halt.
Once my brother glanced off my (quickly) overturned hull in big surf too and
I was glad there was rocker and rake in his hull so no damage was done. I'll
admit that for most paddlers this is an extremely rare.
I know your may be thinking these are all fun little stories but certainly
not everyday occurances for you or most other sea kayakers. You are right,
so I will get to my real point (the one I think has been missed). Without
enough rake and rocker a SEA kayak will push kelp or seaweed in front of it
until it is forced to a stop rather than be able to slide easily over its
slippery surface. On the West Coast the sea can be choked with kelp for
miles. Even when it isn't, paddling in the kelp that does exists is often
the most effective way to avoid BOOMERS. Breakers will tear kelp loose from
the bottom so if you are in the kelp you know that not too many waves have
been breaking there (not impossible just unlikely). We are so cognizant of
this benifit of rake most of our kayaks are also raked at the stern so they
can back up over kelp as well as slide over it forward.
In steep waves too low or too fine a bow can bury itself under a mass of
kelp and be very difficult to extract, especially from the stern if a rudder
also makes pushing it off with the paddle difficult.

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

In a loaded sea kayak (which is the time it is most likely to put its bow
under) this increase in inertia would be insignificant. Even in an empty sea
kayak it would be quite small. Your argument is also assuming the same
waterline length. I would argue with the primacy of waterline length here
because, as the QCC website so rightly points out, more waterline length
increases wetted surface and other things being equal that increases drag.
A long waterline is essential to a racing kayak being operated at top speed
but that extra waterline length is often a detriment to a sea kayak where it
likely increases cruising resistence but more importantly often decreases
controlability and responsiveness.
>
>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.

All the studies in the world don't mean much to me compared with test
paddles of real kayaks in real conditions. My advice to kayak buyers is to
paddle as many kayaks as you can and then take your favorites out into wind
and waves and compare them head to head. You will know what is right for you
without having to listen to all the confusing arguments for and against this
feature or that and what study of ships or sailboats proved what.
If at all possible don't buy a kayak without trying it out, preferably in
some wind and waves!

Matt Broze
http://www.marinerkayaks.com



***************************************************************************
PaddleWise Paddling Mailing List
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.paddlewise.net/
***************************************************************************