Baby's First-And-A-Half Portrait

[catsittingstill]

I had Binturong all drawn out, and then I was reading a kayak book last night and it mentioned that the center of lateral area (the underwater cross sectional area of the boat seen from the side) should be behind the paddler (thus, behind the center of buoyancy).

When I fired up Bearboat and checked Binturong--oops, it wasn't.  I thought the kayak book had a good, plausible argument for why this should be so, so I tweaked the Binturong design some more to move the CLA behind the center of buoyancy. 

Meaning, of course, the station drawings I had just spent six hours producing from offsets were, ah, out of date.  Well, better six hours wasted than six months if I actually build the design and then don't like it.  New offsets, and off to Carson-Newman to say "I know I said I was done using the table but..." (except not really, they let me just come in and use it; I don't have to ask every time.)

New portrait half-finished.  I'm getting better with practice.  Go me.

Comments

[peteralway.livejournal.com]

Hey, the argument for placing the center of lateral area behind the center of gravity is convincing for model rockets, so why not for boats. However, CLA is just an approximation for center of pressure--if the contour ahead of the CLA is significantly different than the countours behind the CLA, (say, rounded ahead of the CLA and with flat fins behind the CLA), the center of pressure won't be at the CLA.

All this is related to Bob's and my patent, by the way.

[catsittingstill.livejournal.com]

:-) cool.

Its true that another way to get the effect is ti have rounded contours ahead and v-shaped contours behind, but the program I'm using doesn't have any way to achieve that that I can find. Well, it kind of does--I could move more of the carrying capacity forward, and if I held the draft steady that would tend to bulge out the parts of the forward stations that are under the water, but I want the center of buoyancy aft of the center of the boat because that's supposed to be faster.

Anyway, I ended up putting more rocker in the front, which had a similar effect except now I have about an inch and a half of rocker, which is more than I intended, but which was what it took to shift the CLA.

And I only have the CLA 2 inches behind the center of buoyancy and I wonder if that is enough.

[bigbumble.livejournal.com]

I expect the optimum location for CLA vs. center of buoyancy depends on if you want a highly maneuverable canoe or one that tends to travel in a straight line even with less than skillful paddling.

I'm guessing the two inch difference would be at the maneuverable end of things and half the width of the boat or more would bring you into the straight forward range.

[catsittingstill.livejournal.com]

Actually, usually "little rocker" (rocker is where the boat goes less deeply into the water at the ends) means a boat that goes straight and "lots of rocker" means a boat that turns easily. "More rocker in the front than in the back" is supposedly a boat that goes straight when you want and turns easily (easier than "no rocker" anyway) when you want.

At the time I had no idea how far back it should go. "Behind" was all I knew. After much thrashing around with search engines and bulletin boards I finally found someone who said "1/2 inch to 2 inches" was a normal range.

So I'm wondering whether 2 inches was too much. It falls in the normal range but I'm not sure I trust the extremes. I want a boat that is more weighted to the tracking than the turning. On the other hand, it's not just rocker and CLA vs CB that matters--it's also the shape of the hull and this one is definitely shallow V, which tracks better than shallow arch and much better than flat. So maybe it's all cool.

[boywizard.livejournal.com]

I actually have no idea where, in either of my self-built boats, the CLA fell relative to the CB. Two inches might have a noticeable effect; I rather doubt that half an inch would, unless maybe the paddler is Olympic class and spends many many hours each week in boats. As for rocker, my Grumman has very little; if I want to make a serious turn, I just lean the boat - the more lean, the more rocker. If the gunwale is touching the water, it probably has four or five inches of rocker, and spins on a dime. One does need a good brace if one hopes to stay dry when attempting this. I used to do it often when I first got the boat about twenty-five or so years ago, but I am much more sedate now, having deteriorated physically in the interim. (I wish I had thought to name my boats; boat 1, boat 2, and the Grumman just don't have much cachet)

[catsittingstill.livejournal.com]

I have heard of leaning to turn. I should probably give this a try in Constance, actually.

I agree that boat 1, boat 2 and the Grumman leaves a little something to be desired in the name department. You could always name them now, I suppose. Unless you don't have them anymore (well, I guess you could still do it, but that would seem a little flat to me.)

Binturong is the design name; I will probably call the next canoe "Moxie" unless I think of something better. Although "Happy Place" would be a good name for a canoe. "Audacity" is arguably more of a kayak name. Or a whitewater canoe, but I don't see myself ever wanting one of those. Which is a pity because Audacity would be a great name.

[maiac.livejournal.com]

I love that you're calling the boat Binturong. We have binturongs at the Detroit Zoo, and while they're not as cute as red pandas, they are pretty adorable.

[catsittingstill.livejournal.com]

:-) I got the idea because the program is called Bearboat. Bear + Cat = Binturong, which is the only mammal with a prehensile tail and which one source said actually swims well enough to catch fish, though apparently it spends most of its time in the trees.

[maiac.livejournal.com]

Judging by the binturongs in the Detroit Zoo, they spend enough time curled up asleep to qualify as cats.

[catsittingstill.livejournal.com]

:-) Hopefully someday you'll get to see them when they're active.

[maiac.livejournal.com]

I do, occasionally:

(http://www.flickr.com/photos/maiac/4994016413/)

[catsittingstill.livejournal.com]

:-) Cool.