Message-Id: <97Oct7.195455edt.14779-3@prufire1.prusec.com>
Date: Tue, 7 Oct 1997 22:38:57 -0400
From: carl_vonkleistiii <carl_vonkleistiii@PRUSEC.COM>
To: baidarka@lists.intelenet.net
Subject: Re: design+building -- Longish
t simpson wrote:
>
> In my replica of the 1934 Atka baidarka after making a wet exit and
> using a paddle float to stabilize myself I was able to re-enter the boat
> with no trouble which rather surprised me. This boat is only 20.4" wide
> with about 18 degrees of V in the cockpit area.
I have seen several people mention the degrees of V in their boats, but I am
not sure I understand what reference point the degrees are measured from or
how far they are measured to. Is there a standard? What I have been
guessing is that it is the angle at which the hull curves upward away from a
plane on which the keelson is resting (with the boat held upright.) Is the V
measured only out to the first stringer from the keelson (i.e. to the first
chine up from the bottom) or is it measured out farther? The former makes
more sense to me...but then I thought hot water would make ice-cubes faster
when I was young.
> It seems to me that the
> fullness in the aft hull contributes to the stability.
The range of hull forms available to the baidarka builder has really been
intriguing to me, and I confess that I have done some little experimenting.
All of the boats I am building have different hull shapes (ON PURPOSE - no,
really.) The major differences in the shapes have been accomplished by
varying the length of the frames and by altering the shape of the ribs to
provide a fuller or deeper or hull. In the current construction phase of
attaching the rib stringers to the hulls, I am finding that quite a bit of
subtle form shaping can be done through the lashing of the rib stringers.
The first rib stringers that I installed (my boat - hull #1) were located
pretty much according to the instructions in Wolfgang Brinck's book, that is
to say, that they were lashed with fairly even spacing down the length of the
hull. The result of this lashing method is a hull form that is pretty much
rounded at any given point from the stern forward to about the front half of
the bow portion of the keelson (with some V from the keelson out to the first
stringer/chine of the hull, but round after that.) On the second boat (my
sister's - hull #2) I became interested with refining the hull shape and
lashed the stringers on with even spacing, but modified the curve of the
stringers as I lashed them on. This is kind of hard to describe, but if you
think of the curve that the stringers take as you lash them to the hull, it
is basically a two dimensional curve: you could take a plane and lay it flat
across the stringer from end to end, each stringer's plane intersecting the
center of the kayak and angled vertically toward the keelson(roughly.)
As I lashed the stringers on her kayak, I kept adjusting them and gauging the
effects of their positioning by holding a sheet of cloth tight over the area
I was working on. Near the cockpit the stringers are lashed on pretty
normally (as per the book), but as I entered the area around the footbrace I
started pushing the stringers in closer toward the keelson than they would
otherwise lie. The effect of this is to create more of a V shape forward of
the cockpit. Nearer to the bow I shifted the stringers back away from the
keelson a bit more toward the gun'l's, which also created the effect of
deepening the V at the bow. Toward the stern, I did much the same, and the
end result is that the stringers now have a three dimensional curve in them:
in addition to being bent away from the centerline of the boat, they are
also bent in toward the centerline around the footbrace (which is down
relative to the original 2-d plane) and out from the centerline near the bow
(which is up relative to the original 2-d plane.) Viewed from the side and
above (below, really since it's upsidedown on sawhorses), the stringers take
on a very (VERY) slight serpentine shape from bow to stern, yet because of
the rocker in the boat that curvature along the hull lies almost flat in the
plane of the gun'l's.
This gave me lots of control (I HOPE) over the paddling characteristics of
the hull. The bow will (should) have a very fine entry (especially right
along the forward keelson), even as it begins to flare out behind the
bowpiece, although I don't think it is so dramatically fine as to reduce the
bouyancy of that area significantly, as the fullness of the upper portion is
unaffected overall. The forward section of the boat between the bow and the
cockpit will also have a pronounced V shape along the keelson. The stern has
been manipulated similarly, but the V shape isn't as pronounced at the stern
since that area has a rounder profile anyway (but it is a fairly fine stern.)
Sound confusing? Well, when I look at the two boats and try to imagine how
they will paddle, I look for indications of primary and secondary stability.
I imagine leaning the boat and how it will feel. What I have accomplished
on hull #2 (I HOPE) is that there is a very gradual transition from being a
fine, sharp hull (read tippy) in an upright position to being a very solid
rounded hull (read solid) when leaned over, and that the transition is a
smooth one, that will be mostly transparent to the paddler, instead of that
kind of transition where you feel tippy and then flop over on the side and
feel stable. I think (HOPE) this boat will just lean over gently, getting
firmer and firmer all the time.
(The descriptions may not be very accurate as I am doing this from memory and
don't have the boats in front of me, and I am not good at 3-D descriptive
narration.)
TO CONTINUE WITH MY BABBLING....
In addition to messing with the stringers to control hull shape, I have been
viewing them structurally. This is kind of hard to do until you see them
lashed onto the frame because individually they are rather silly looking and
behaving pieces of wood, long, thin and floppy. Once you lash them to the
frame, however, they work in a unified fashion to help stiffen the structure.
On hull #1 I had the stringers evenly spaced, and on hull #2 I "tweaked"
their placement to control hull contour. I have been studying them as
structural members, too, and on hull #3 (the next boat to get stringers --
this week) I am going to incorporate the tweaking that I used on hull #2 with
a modified spacing arrangement that, while I don't think it will increase the
strength of the frame, will allow for perhaps some additional hull-form
control without weakening the structure.
My idea is this, to seperate the set of four stringers into two sets of two
stringers on each side of the hull. The lower set of stringers (closest to
the keelson) will serve to control the shape of the most frequently wetted
areas of the boat, say between the waterline and the keelson, and the upper
set of stringers will be used more to stiffen the area directly below the
gun'l's.
In seperating the set of stringers into two groups, I am not talking about a
large seperation or great divergence from the standard layout. The total
amount of "seperation" between the two groups only amounts to putting a
little (perhaps 1" at the very most) extra distance between the two sets
instead of spacing the stringers evenly. The upper stringers will be moved
closer up the hull toward the gun'l's and pretty much follow their line down
the frame. The lower set will be treated as in my description of hull #2
above. Alternatively, I may let one stringer follow the gun'l' and group the
other three together to provide more control over hull shape. I think that
to get too liberal with the spacing would result in greater stresses being
placed on the portions of the ribs that were unsupported over the greater
distance. According to Wolfgang Brinck, part of the reason that this whole
stick-frame works is that the stresses are spread out evenly over equally
strong frame-members.
Please note that in all the above where I am talking about making changes to
the location of the stringers, I am not talking about large variations from
"normal" construction, merely about shifting the lie of a stringer 3/8" or
1/2" this way or that over a distance of several feet. Really more a matter
of "optimizing" the way the hull is shaped. "Optimizing" may well be the
wrong word -- I'm using wholly uneducated guesses to make it look the way I
think it will behave best in the water. Given that I can only make fairly
crude estimates of the behaviour of the canvas over the frame (and given that
I have no idea exactly where the waterlines on these boats will end up) I may
be doing more harm than good. But since I have (seemingly) forsworn paddling
until these boats are done, at least I get some amusement out of the project!
> This boat really
> is a great design and any newbee would not be sorry building one.
> Wolfgang Brinck's " The Aleutian Kayak" is the book to get for baidarka
> building.
Hear, hear! :)
> For Greenland kayaks and canvas covered kayaks in general
> Bob Boucher's video "Build Your Own Sea Kayak" is excellent, it details
> building a West Greenland kayak,the Boucher Kayak Company can be reached
> at 414-476-3787. This video got me started. regards
> Tom
Greenland Kayak = proto-Jetski according to WB! ;)
Perhaps after I finish these boats, I can make and distribute Greenland
Kayaks gratis to Jetskiers and try to get them to devolve to a more human
form! They sure look like they would be fun to try (G. Kayaks, that is, not
Jetskis.)
--
Eric von Kleist We pray for one last landing
Hilton Head Island, SC On the globe that gave us birth,
USA To rest our eyes on the fleecy skies
And the cool green hills of Earth.
Carlyle said, "A lie cannot live"; it shows he did not now how to
tell them. Mark Twain
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