No
headache here
In
the last post I said that I couldn't remember how to develop twisted
panels then I remembered an article I wrote for Duckworks, here
and here's the quote that put me back on track,
I
finally figured out that the reason that the panel development worked
on Ode II was that the bottom was flat and that the waterline through
the sides was at right angles to the surface of the panel. Problem
solved. Go get another sheet of 1/4 ply.
You
will also remember that, when developing V bottom panels, I said that
the diagonal was at 90 degrees to station 5. Well the same is true of
twisted panels but with one important difference there needs to be
two lines parallel to each other not just one.
So
the design I'm using for this post is 3S. I had designed a boat based
upon the Whitehall skiff which I named Sally Blank. White = blanc =
blank, hall = room = salle = Sally. 3S is Sally's slimmer sister.
Here are the lines.
A
slimmer sister indeed!
The
panel we're going to develop is the bottom panel which has quite a
twist in it. First we'll draw a line from where the chine meets the
stem at right angles to station 5.
and
then a second line parallel to the first from the transom chine
junction. However that won't work as the line exits the panel through
the chine and that won't define the length of the panel. Back to the
drawing board. The only way to have a parallel line which doesn't
exit the panel through the chine is to have that line between the
keel and the first line like so.
This
line is from the stem knuckle and remains inside the panel. Next we
transfer those line to the profile drawing and, as we did previously,
draw a baseline with a perpendicular at the middle and transfer the
parallel lines to the upright as we did on the previous post. Once
that is complete then we can transfer the length of the lines from
the profile to the baseline drawing.
One
crucial point, the reason the transfer of length works is that we are
actually transferring a chord of an arc however if the arc is too
tight or the stations are too far apart then the chord does not
approximate the length of the arc and is very much shorter.
Here
the chord between two stations is very near the length of the arc
whereas the chord spanning two stations can be seen to be much
shorter. I mention this because one the transferred lines on the
profile has quite a tight arc near the bow and so an extra station
needs to be put in.
Once
the length has been transferred then we can join the station marks
and extend them and draw in the ends of the panel.
Now
we transfer the station lengths from the section drawing to the
station lines as we did previously.
As
we did in the last post, draw in the upper curve and take out the big
circles and the base line. Extend the station lines downward and draw
in the lower curve being careful to get the minute differences as
before.
Clean
it up and there's your panel.
This
does work, I made a model of 3S and here it is.
The
reason it's all lumpy is because I sank it testing for max
displacement using the Weston Farmer method of which more later
