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

Matt wrote;

(Large SNIP)

Matt, when you have read the papers you can tell me if I have interpreted
them incorrectly.


The Navy has never had much concern for costs where performance of ships at
sea is concerned. How do I know? From my years building Navy ships and
sailing with a senior officer from the Bureau of Ships. Perhaps Matt has
better background than that. I would like to hear why they would place cost
above performance when Matt is paying the bills via his taxes. :)



>As a group I have never thought of open canoes as seaworthy (well maybe a
>short rockered whitewater "open" canoe packed full of flotation).


I guess you had to have been there to appreciate the seaworthiness of open
canoes. or even open boats in general. Like Viking ships, the open boat that
Bligh sailed, or the Umiaks, etc. Some some experience with them helps.

.

>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.

Ain't that neat?


>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.

Boy, I can apperciate how unbaised that will be. :)



>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.

Sorry for using a word you don't find familiar. I don't now wat you have
read so you have the advantage of me here. I suggest you read the paper and
discuss this with Gerritsma.


>
>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.

Yes, they are. The Navy and Coast Guard also operate in fresh water.

>So if you think my opinions are all wet, I guess I'd have to agree. ;-)

I failed to keep track of the boats I have paddled or sailed.


>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).

Gee I do that too with my boats. Maybe I am just a lucky guy sinvce my
boatrs are designed all wrong.
.


>
><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.


Do you have teh proff of this?  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.

Called design optimization
>>
>>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
>
>
>
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