cavelamb himself wrote:
Matt Colie wrote:
cavelamb himself wrote:
Matt Colie wrote:
cavelamb himself wrote:

I thought I was a pretty good draftsman.
At least until I tried lofting hull shapes...
Buildings, machine parts, entire aircraft - no problems.

But fairing a hull can be a humbling experience.

Well, for grins and giggles, here are a few of my efforts so far.

http://www.home.earthlink.net/~cavelamb/draft.htm

Richard

Well Richard,

This is no surprise to a third generation boat builder.
The pictures look pretty good.
It that first one your design?
I don't like working with a baseline other than zero draft because I
always get screwed up doing the TPI, trim and stability calculations.
It does get a little easier when working on the lofting floor at
full scale. The you can go back and correct the offset table.

Matt Colie

It's (supposed to be) a Catalina 27.

Gee, I though it looked real familiar.
Matt


I had this lame idea I was going to try when I pull my boat out
for the winter. But I can't bring it home because it's too
tall for the city standards, so I dunno now.

Anyway, the idea was to level the boat and use a few laser levels
to pick off the frames shapes.

Set up the lasers so as to draw a vertical line every 2 or 3 feet and
one horizontally at the water line.

Add a couple of vertical lines to pick off the buttlines too (side shot).

Take a digital photo - one front - one aft with the "waterline"
reference at the same height on my tripod...

Load the photos into CAD and trace off the frames.

I can't capture the waterlines that way, but the buttlines and frames
should be enough to get a fairly accurate start....

Should work ok, don't ya think?

Richard

Richard,

Did you thing to try to get a trailer made that would allow the foil
(keel) to drop between the axles and only clear the pavement by a few
inches?

Next....
Did you just guess at the offsets you used to generate that set of lines?

If you did, why didn't you just get a hold of either the class
association or Frank Butler (I think he still runs that show) and get
the offsets? (If Catalina says that this is proprietary and they don't
want to release them, then go ahead and develop an offset table and sell
it to owners yourself. This is not illegal because you are making
available the observations of a lawfully purchased physical object.)

Real world efforts to capture 3 dimensional data have never been simple.
We (the family) once did this to reconstruct a much loved dinghy and
it was a major undertaking with strings and levels and plumbbobs (lasers
would not be available for another few decades).

How would you get the image of the frame stations or buttlines with the
cradle structures in the way?

One of the little "gotchas" out there is the actual accuracy required is
quite high. I do the odd keel refairing job from time to time and that
is simple compared to this because the measurement survey is largely
done against and almost vertical surface. It is still really hard to
get better than +/-1/8" and that is just not very usable data.

I was struggling with this issue myself for a number of years. I owned
and S2-7.9. No lines or offsets are available. I got real close to
being able to barrow a large scale coordinate measuring system. I was
going to either hang the boat by the chainplates or roll it over, but
the entire plan collapsed before that became the big issue.

Keep working on the plan and let me know how you make out.
I'm here a lot.

Matt Colie