Newbie working with an existing design

salty__dog · Dec 23, 2003

I've found a design I like. Chapelle's 45' workboat from 'Boatbuilding'. I'd like to draw the boat in CAD and have access to a computer running Autocad 2004. After drawing the basic boat (single chine, deadrise) I'd like to pull off the panel shapes and put together a model. Can anyone point me to software for laying out the panels?

Afterwards I'd like to learn how to determine scantlings, plate thickness, longitudinal reinforcement etc. for a given material ie. aluminum, steel. If I can work my way through the above I'll takle hydrodynamics and propulsion.

I've been reading the forums and see there's a wealth of knowledge at hand. I'd like to learn some of this stuff and figure working through a project is the way forward. I'd appreciate any help to get me started.

Cheers, Greg

rjmac · Dec 24, 2003

Greg,

I am not sure where to begin, but if you are interested then these are the things that you will need to do:

Where to begin….?????

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I've found a design I like. Chapelle's 45' workboat from 'Boatbuilding'.
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If you found this in Boatbuilding then you need to contact the designer, he owns the design.

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I'd like to draw the boat in CAD and have access to a computer running Autocad 2004.
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I do not know what your background is…? I use AutoCAD 2000 and you will have to be at minimum a draftsman even with AutoCAD 2004, I was not aware that 2004 was out yet…..

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After drawing the basic boat (single chine, deadrise) I'd like to pull off the panel shapes and put together a model. Can anyone point me to software for laying out the panels?
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This is where the drafting/design skills come into play, these are things that you will have to develop, there are several CAD packages discussed in the software forum that could do this, pick one and go for it.

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Afterwards I'd like to learn how to determine scantlings, plate thickness, longitudinal reinforcement etc. for a given material ie. aluminum, steel. If I can work my way through the above I'll takle hydrodynamics and propulsion.
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This is an area where you need to have an understanding of engineering principals, plus there are several books out there that you should read. The ones that I reference to all the time are:

“Skene’s Elements of Yatch Design,” I have the 8th edition by Francis S. Kinney, this will walk you through a lot of the basic development processes. “Principles of Yatch Design,” I have the 2nd edition by Lars Larsson and Rolf E. Eliasson, this book will cover the same information but more polyester construction/design. If you are building a work boat then my dad swears by ferro-cement, I have not gone that way. Also the one book that I am looking forward to reading is, Dave Gerr's book "The elements of boat strength" Once you understand everything in these books, you will do well.

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I've been reading the forums and see there's a wealth of knowledge at hand. I'd like to learn some of this stuff and figure working through a project is the way forward. I'd appreciate any help to get me started.
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Last, there are a lot of guys on this forum that make their living in the marine industry and I feel very fortunate just to read about things that they are discussing. They seem to be very helpful but they also encourage one to do the work and they will guide you in that regard.

Regards,
Bob

SailDesign · Dec 24, 2003

Salty,
One of the most difficult things to do on a computer is to put together an _accurate_ model of a hand-drawn design. It is not so hard to draw something that has the same "feel", but to get it accurate to within a 1/4-inch or so is nearly impossible.
fortunately, that kind of accuracy is not usually necessary to produce a boat with all the characteristics of the original, so don't waste your time trying to match to the nearest 1/16th of an inch ;-)
Start the project slowly, one step at a time, and enjoy it.
Steve

salty__dog · Dec 24, 2003

Thanks for the fast response guys! It's appreciated.

Bob wrote:
>I do not know what your background is…? I use AutoCAD 2000 and you will have to be at minimum a draftsman...

I've tinkered with CAD (Autosketch, Generic Cad, Acad r13) but certainly have a ways to go.

I've recently looked at Hulls and Carene but am more comfortable drawing in Acad. Searched for "Unfold" but to no avail.

I ordered Rable's 'Ship and Aircraft Fairing and Development' based on recommendations of this text elsewhere on this board. Perhaps a manual method will seem more intuitive.

Regarding Skene's. I all but slept with that text while designing a kayak a number of years ago. I was pleased with the result and the book gets the credit. I'll look for the other you recommended.

And Steve, I've got nothing but time for this project ;-)

Cheers, Greg

SailDesign · Dec 24, 2003

Greg, "I've got nothing but time for this project...."
You STILL won't have enough ;-)
Steve

Unregistered · Jan 19, 2004

Boatbuilder/Designer

Is there a market for a simple hull design program including unfolding but no checking of "developabality" that runs inside AutoCAd or IntelliCAD?
We have used our own routines (small programs) for about 10 years now.

Raggi_Thor@hotmail.com

8knots · Jan 19, 2004

Salty,
I have "Boatbuilding" allso and have probably read the ink off the first copy (I'm on my second copy) As far as Getting a hull simular to those rather it be high or low chine, into CAD it should be very easy. The east coast hulls you refer to are I would say easily developable with the exception of the forfoot area. But I think with a competant fabricator you could use the "staving" method described in the book, The bottom plate would work out to no more than 3/16" at the most. When the run starts to twist up to meet the stem you could use 3-4" wide bar stock and twist each into the shape needed.
As far as books Yes... Do get Gerr's book!
Sail has a good point. I would not worry about Exact replication, rather get out the paper and a stick and work from the offsets most of those lines have. You could build one of those deadrises upside down in short order.
In my opinion I would not invest the time to develop plate patterns. I would tackle it like so
1 Draw up what you want... Weights and all the other calc's that go along with it!
2 Loft it full size and pick up the frames from the loft
3 frame it up upside down on a strongback
4 use masonite or other cheap sheet to pattern out your plate.
I have allways had it in my mind these hulls are one of the easiest to build.
You may consider having a professional review your work before you start the torch. Because of the easy hull form shouldent cost you a fortune.
Or consider posting your progress for input from the pro's here.
Best of luck 8Knots

salty__dog · Jan 19, 2004

8knots said:

>Getting a hull simular to those... into CAD should be very easy.

I'm crossing my fingers.

>The east coast hulls you refer to are I would say easily developable with the exception of the forfoot area.

And I'm not above changing that to make plating easier as long as I can live with the stem profile etc.

>Sail has a good point. I would not worry about Exact replication

I have several changes in mind. A round tugboat transom is one if it can be worked out. Raised bulwarks, extended wheelhouse, and longer trunk cabin are also on the list. And a sailplan (a pair of genoas on twin headstays? junk rig?) for downwind running - I've no pretense of trying to point.

This will be a live aboard for me. I have been living on a 34' Bill Rode sloop built of yellow cedar on oak frames in the J.T. Taylor yard in 1947 for the past 5 years and am enjoying this lifestyle more all the time. I intend to stay on the water and have a good idea what is important to me in a live aboard boat. My needs are simple but at the same time I'm very demanding. Things must funtion as intended with a minimum of fuss.

>In my opinion I would not invest the time to develop plate patterns.

This interests me. Having built several boats 'the other way' I thought I could speed construction and minimize handling of unwieldy plate by having it pre cut. I'm certainly more comfortable with a table of offsets and framing materials than manipulating b-splines. Perhaps some thought is in order.

>I would tackle it like so...
>2 Loft it full size and pick up the frames from the loft

Lacking a suitable space for lofting full size I had hoped the computer would prove useful. I'll admit to being somewhat uneasy about turning my back on full size layout.

Thanks for taking the time to post such a thoughtful, and helpful, response to my query.

>Best of luck

Thanks!

Greg
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Unregistered · Jan 20, 2004

Boatbuilder/Designer

salty__dog said:

8knots said:

>In my opinion I would not invest the time to develop plate patterns.
... I'm certainly more comfortable with a table of offsets and framing materials than manipulating b-splines. Perhaps some thought is in order.

Be careful with B-splines! Most Yacht Design Software uses B-splines because they are easy to work with for the programmer (inlcuded in many sw libraries). However, B-splines can be used to draw curves that are impossible to produce by bending a flexible batten (or stringer) in real life. I have seen designers "put on a (bending) moment in the end (of a stringer)", using those exact words. Now, take up a piece if "one by one" (inch) spruce or cedar and try to bend it in one of its ends...
In the days when all boats where lofted full size, the builder would correct the curvature in both ends of the hull. Colin Archer, for example, designed boats that would be impossible to build exactly as drawn. Obviusly there will be problems if you use old drawings without any lofting or "computer smooting".

The safest way to model a boat in a computer is to use "Natural Cubic Splines". They behave like the flexible batten used on the loft floor. They also give you (with very little extra math) the bending moments and the forces needed to keep them in place. So here's is a suggestion for AutoCAD (LT or IntelliCAD):

1) Scan some old drawings (assuming copyright has expired or is paid for).
2) Use the image as a background in AutoCAD, scale and stretch to size.
3) Looking along the x-axis, Draw some (not to many) defining frames, skip those close to the ends.
4) Change the view and move the frames to their correct position along the x-axis.
5) Draw the chines as splines with no "tangent direction" in the end points.
6) Compare the fullness of the hull defines by the chines and the old drawings near the ends...
7) Smoothen the curves visually or mathematically...
Build a model to check curvature in the chine stringers and developability in the bottom panels...

regards,
Raggi_Thor@hotmail.com
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8knots · Jan 20, 2004

Salty,
If you can get you hands on a copy GET this book! It has a fantastic collection of the sort of lines you are looking for. If you would like I could look up your boat in my copy of Chappelle and cross in to Suchers book and scan some options for you! This may give you a few more places to start.
Suchers book has lots of fantail launches from 26'-60' He has a 28' that I have allways thought would scale up nicely. Check out my gallery and see
"40' of slow" She is based loosly on this vessel.
As far as stick and sheet stuff I'm afraid I cant help you there!
Good luck 8

Thanks to our Guest on the insights into B-spline design!

8knots · Jan 20, 2004

Duh.....

Here is the link to the book
http://www.amazon.com/exec/obidos/ASIN/0393031802/kiwianadistribut/102-3605767-3607368

salty__dog · Jan 20, 2004

Guest said:

>Be careful with B-splines! ...The safest way to model a boat in a computer is to use "Natural Cubic Splines". So here's is a suggestion for AutoCAD (LT or IntelliCAD):

I'll be giving this a try. So much to learn! Good thing it's fun ;-)

8knots said:

>If you can get you hands on a copy GET this book!

Just checked the library system here and a copy is available so I'll be ordering it in tomorrow. Interestingly it was the stern of a sharpie schooner (~52') in Sucher's flat bottom book that initially got me thinking about that shape.

>Check out my gallery and see
"40' of slow" She is based loosly on this vessel.

We obviously have similar taste in boats. That's a gem! If the budget for this project were a little flusher... I hadn't perused any of the galleries before. More research to do ;-)

Thanks for your generous offer to scan pages. If the library falls through I'll take you up on it.

Cheers, Greg
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