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

Matt Colie wrote:



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).

The top pic, the basic lines layout was found on the web.
The others I've either taken from books and traced, or used the
published offsets.

But I'm not intending to sell anything.
At least not at this stage.
Just trying to learn how to do the work.

Tracing sucks.
Terribly inaccurate since he lines look like they were drawn with a 3"
paint brush.

Makes fairing a lot harder than necessary.
And once faired, there is no telling how accurate the generated shape is
compared to the original.



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

My trailer has very little to interfere with the laser.
This CAD package used a splined curve.
Outta fill in the small gaps ok.

At least it would be cheap and easy enough to try.


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

Steve Lusardi wrote:

Richard,
You have done a very good job of recreating a lines drawing on a computer,
but your effort has nothing to do with lofting. Lofting is laying out on a
wooden floor the full lines drawings full scale for the purpose of template
generation, one on top of the other using the table of offsets as an initial
starting point. Fairing the lines occurs during this process by driving
nails in the floor at line intersections and subsequently bending an
appropriate batten around the nails to scribe the line. When the battens
fails to bear on a nail, the nail is then removed and redriven at the
correct point. The offset from the table is then remeasured and entered into
a new table that is called the "corrected table of offsets". Only then can
templates be taken off the lofting for the manufacture of the individual
components to stand up the actual hull. This is not done with a mouse while
sitting comfortably in a chair. It is extremely hard work done on your hands
and knees for many days on end. No computer will ever replace this task,
even big ship yards still must bulletproof the table of offsets for CNC
cutting machines to be accurate.
Steve

"cavelamb himself" wrote in message
...

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 glggles, here are a few of my efforts so far.

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

Richard




Hi Steve,

Actually, I erased all the nail holes - trying to be neat.

Richard

Steve Lusardi wrote:

No computer will ever replace this task,
even big ship yards still must bulletproof the table of offsets for CNC
cutting machines to be accurate.
Steve

Steve,

Maybe a decade ago this was true, but in the real world of today's
shipyard, the cut files are all done on computer, the plate is burned,
and erection starts the next week. The loftsman is a dying breed.

We (commercial naval architects) seldom provide tables of offsets any
more; just send 'em an IGES file of the 3D hull surface, or we produce
all the steel parts in house. No lofting required.

Evan Gatehouse

On Fri, 30 Nov 2007 06:16:55 GMT, Evan Gatehouse
wrote:

Steve Lusardi wrote:

No computer will ever replace this task,
even big ship yards still must bulletproof the table of offsets for CNC
cutting machines to be accurate.
Steve

Steve,

Maybe a decade ago this was true, but in the real world of today's
shipyard, the cut files are all done on computer, the plate is burned,
and erection starts the next week. The loftsman is a dying breed.

We (commercial naval architects) seldom provide tables of offsets any
more; just send 'em an IGES file of the 3D hull surface, or we produce
all the steel parts in house. No lofting required.

Evan Gatehouse

Aw shucks! You didn't even mention being able to run a ball bearing
along the panel seams before weldup! :-)

Brian Whatcott Altus OK

Evan Gatehouse wrote:

Steve Lusardi wrote:

No computer will ever replace this task,

even big ship yards still must bulletproof the table of offsets for
CNC cutting machines to be accurate.
Steve


Steve,

Maybe a decade ago this was true, but in the real world of today's
shipyard, the cut files are all done on computer, the plate is burned,
and erection starts the next week. The loftsman is a dying breed.

We (commercial naval architects) seldom provide tables of offsets any
more; just send 'em an IGES file of the 3D hull surface, or we produce
all the steel parts in house. No lofting required.

Evan Gatehouse


While the drawings look small, they are drawn in full scale.

Actually, sometimes much larger than full scale.
When zooming in to locate a point between a waterline and section
I may be as much as 100 x magnification.
Trying for .01 inch resolution.

Can't do that on the floor.

But that's the way it's done these days - and why the parts fit
so well (hopefully!).

Richard

Evan,
I did a bit of research and you are correct, it is now done that way. I
guess I am a dinosaur. God bless computers, lofting is a horrible task. I
know, I have done a lot of it in my life. However, I hesitate calling mouse
work lofting in deference at least to the way it was.
Steve

"Evan Gatehouse" wrote in message
news:rVN3j.3921$UQ1.364@pd7urf1no...
Steve Lusardi wrote:

No computer will ever replace this task,
even big ship yards still must bulletproof the table of offsets for CNC
cutting machines to be accurate.
Steve

Steve,

Maybe a decade ago this was true, but in the real world of today's
shipyard, the cut files are all done on computer, the plate is burned, and
erection starts the next week. The loftsman is a dying breed.

We (commercial naval architects) seldom provide tables of offsets any
more; just send 'em an IGES file of the 3D hull surface, or we produce all
the steel parts in house. No lofting required.

Evan Gatehouse

cavelamb himself wrote:

The top pic, the basic lines layout was found on the web.
The others I've either taken from books and traced, or used the
published offsets.
Sounds Like you have found effective sources.


But I'm not intending to sell anything.
At least not at this stage.
Just trying to learn how to do the work.
Learning is always good,

Tracing sucks.
Terribly inaccurate since he lines look like they were drawn with a 3"
paint brush.

Makes fairing a lot harder than necessary.
And once faired, there is no telling how accurate the generated shape is
compared to the original.
Just so you know.... The final hull and foil shapes of a number of boats
out there don't always have a lot in common with the designed lines.
(That's what I often have to fix.)


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

My trailer has very little to interfere with the laser.
This CAD package used a splined curve.
Outta fill in the small gaps ok.
Prolly work, just watch out, computers can be real stupid sometimes.

At least it would be cheap and easy enough to try.
Actually, it sounds like it could just be a lot of fun.
If you could get about a box full of those line creating lasers and set
some up as waterplane, some as station and some as butts - you might be
able to reverse engineer a hull shape pretty effectively.

I'm interested to see how it works out.

Matt Colie