CAD challenge

[Hector Bell]

Here's a challenge, theoretical or actual for you pootah fans.
Imagine a dinghy, say 14 ft long, suitable for rowing or sailing, but clinker built.  You chaps probably call it lapstrake.
Come up with the ACTUAL plank shape in the flat, which can be cut from wood, ply, whatever and built into a nice model, say 21" long.

Is this possible?

Martin

[davej]

http://www.eng-tips.com/viewthread.cfm?qid=229715&page=6

[Hector Bell]

A challenge, Dave, not advice!  Didn't understand a word of that!

Martin

[78ths]

Hi Martin
It is possible however from experience not so easy.
This may help

http://books.google.com/books?id=m-a8viwFFRsC&pg=PA105&lpg=PA105&dq=projecting+planking+lines&source=bl&ots=Dm874I84Pr&sig=AqakhDe_mO0mgit9G19iCb8hML0&hl=en&ei=2LzJTP_5H8iSnweo9uAZ&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCAQ6AEwAw#v=onepage&q=projecting%20planking%20lines&f=false

cheers Ferd

[marc_reusser]

You lost me at dinghy and sailing. 

Marc

[Gordon Ferguson]

Yes it is possible but each on one side is a different shape - top planks range from all most parallel sided at the gunwale to flat on one side with increasing curve on other. At the curve of the bilge and especially so if the transom is the typical wine glass shape the plank has two almost parallel sides but the whole plank becomes a very stretched S shape. Obviously the planks are mirror images of each other on each side.

Somewhere I have in my piles of plans the lines and individual planks shapes for a model 14 foot sailing dingy - will look tomorrow and show examples of what I mean.

If you are want to build a model the easiest and standard way is to carve a solid version of the hull then plot the individual stations (cross sections ) If the hull has say 8 planks per side you place a strip of paper on each station from the gunwale to the the keel line and divide that length by 8. You do this at each station and this will give you the width of the plank at each station. You can then plot these to give your individual plank shape  ......... this obviously a very rough and short description but hopefully gives the idea.

There are all sorts of quirks that you need to build in, how much overlap does the plank have, how thick is the plank ( in real life they are surprising thin) Then you need to think about how the planks fair into each other at the  stem (bow) again if you look at a full size clinker boat the planks are almost carvel (flush) with little or no overlap over last 6 to 9 inches.

It is this last detail and the fact that people try to plank a hull with parallel sided strips which are the real giveaway in most models.

If you have ever seen some of the early origonal half models of hulls these were not just carved as an ornament but were in fact so that they could see the lines of the hull in 3 d and they were also used to calculate the shape of the individual planks for the full size hull - this method was continued even when the switch to iron/steel happened, in most good maritime museums you will wooden hulls with all the plates drawn on with individual rivet lines , overlap points etc - this was then used to draw out on paper the "shell plan" which gave you the flat shapes that were then cut out on iron plates, then through various rollers etc to build in the required curves needed.

Sorry now rambling but you could say its a subject I love ( its my upbringing on the River Clyde , where they built a few ships , along with some wonderful J Class racing yachts)         

[Hector Bell]

Gordon has spelled it out pretty well there.
I don't want to know how to do it, just whether anyone would be prepared to take it on.
Where an ordinary little dinghy is concerned, most boatbuilders would just set up a mould (midship section)and the boat's backbone and off he'd go  I built my little diorama dinghy by setting up the transom, an eyeballed midship mould and the backbone.  It is a little over beamy, but that doesn't show, but then I built it in a day as a kind of tonic (I am an estuary man, missing my mud!)

Christopher Columbus Smith carved all new ChrisCraft designs on the back step of the boatyard at Algonac, when he wasn't carving decoys.  And they were relatively simple hard chine designs.

The recessings at the ends of the planks so that they seat nicely at stem and transom are called jerrolds over here, though rabbet is often used to describe the constantly varying shape required to allow two planks to fit each other. The bit between the jerrolds is called the land and is just wide enough to allow the planks or strakes to touch each other by the amount necessary for the nails to be clenched or roved.  The accuracy of cutting these lands and jerrolds is where the boat derives not only its strength, but its very shape.

Oh yes, we boaties can match you pootah boys for jargon!

So, nobody going to take it on then?<G>
Martin

[RoughboyModelworks]

Martin:

The CAD application would need to have a lofting function in order to do this and unless you've got a very powerful, full-featured program (perhaps something used in the aerospace industry) I don't think you're going to find it. I remember studying lofting years ago when I was working on ship models and somewhere I have a drawing (I believe a repro from the NMM) which shows a flat, lofted side view of the planking on an 18th century war ship... impressive drawing. As far as small clinker-built boats are concerned I don't recall every seeing a boat-builder draw out his plank shape beforehand. As such it's unlikely that there's a large enough market to warrant a software developer incorporating a lofting function specifically for small boat builders.

Paul

[78ths]

I used to know a boat builder in Toronto who ran a clinker dory building class. He shop was based in the Argonaut Rowing club and he used to repair all our damaged hulls. To make a long story short he used to draw out the profile of each board on large paper and match the boards to it before assembly. This would get him close leaving only fine tweaking. No software was used it was all projected manually. A lost art I am sure. I do remember watching him cut and draw out a lot of the boards and he did show me the process, this was now 15 years ago and two kids later so unfortunately I have no idea how he derived at the profile. I wish I did as it would make laser cutting the planks really easy.
http://www.boatbuilding.net/article.pl?sid=05/09/13/1254200
Will try to contact Peter to see if there is an easier way to come up with a profile. Most of these boats were designed and built long before cad.

Ferd

[Gordon Ferguson]

Martin,

my apologies, think the glass/bottle of red wine I was drinking at the time helped turn me into a politician ........

ignore the question and give you the answer I want tell you about!

[Hector Bell]

Gordon, no apologies necessary.  You obviously know your boats!
It is as I figured,that yes, it could be done. but it would ba very taxing job and obviously
there would never be a need for it amongst wooden boatbuilders, who know how to do it by hand/eye anyway.  It's a major part of their considerable skill, now taught at plenty of wooden boat schools.

Interesting idea though.

Cheers,
Martin

[RoughboyModelworks]

Martin:

I've been racking the grey cells a little on this and remember meeting a boat builder many years ago in Maine who specialized in small boats. He had standardized production on a couple of models and had made full-size wood patterns of each plank which he used to cut his planks for each build. He thus only had to loft the planks once as long as he didn't change any of the primary hull dimensions or contours.

I used to own a fairly extensive book on lofting and fairing hulls, along with many other boat-building volumes. Unfortunately I believe I sold it when a former Ex decided we didn't need all these boat building books hanging around the house when they could be converted to cash for more worthwhile purposes (new floor as I recall). Equally unfortunately, I agreed with her.... oh well, such is life and only after I came to my senses and escaped did I find out that her nickname was "The Claw." Thankfully I saved all the ship-modeling books.

Paul