Interested in comments.....

Some pretty ingenious people have tried their hand at novel ways to ease the labor-intensive process to design, loft, and build speedy hull shapes. Examples include tortured plywood, constant camber, cylinder molded, the Kelsall KISS method…. And so forth. All these efforts try to balance fast hull shapes with less man-hours to build them. I hesitate to propose yet another approach but I recently used one to design and construct both the amas and main hull of a 34 foot trimaran. It did save a lot of time, produced a fast shape, and it was compatible with vacuum bagging carbon fiber/nomex honeycomb hull sides. I will try to explain….
Say you want to design an easy to build hull shape. If you look at across sections of good hull designs they often look a lot like a segment of an ellipse or sometimes a parabola. So, we could start by cutting a quarter ellipse out of stiff paper. Make it the right size to form a mid ships hull section. To use this same ellipse cut out to make other hull sections, you need to carry the ends of the ellipse segment somewhat past the keel and sheer positions of the midship section. Call this the “master template” Now, imagine the range of adjustments you can make as you sweep the master template along the length of the hull: you can adjust the position thwartships, move it up or down, and rotate it about the centerline. You can also choose which part of the elliptical segment you want to use at any given hull station. For instance, at the bow where there is very little volume, you would want to use the flattest part of the ellipse section and orient it vertical and close to the centerline. At the stern you may want to use the “curviest” part and rotate it outboard somewhat to increase volume and make a flatter run. After some trial and error on a sheet of drafting paper you can end up with a very attractive set of hull lines that are about 99% as good as drawing the traditional orthogonal set of waterlines, buttock lines, and sections.
So far you might say, “this is no big deal, I saved only 5 hours of drafting time”. But now it’s time to build a male mold and the real savings become apparent. Imagine a hard chine catamaran hull. It has three lines that have to be lofted; the keel, the chine, and the shear. Going to our lines drawing that consists of a family of elliptical sections, what if we superimposed a hard chine hull into elliptical sections so the shear and keel of the two hulls coincide and the chine is located to be tangent to all the elliptical sections in the bilge area. Now for the mold…. We first build the hard chine hull full scale with all the correct tangent points to the elliptical hull sections. It is planked with thin plywood and over planked with 2 inch Styrofoam insulation board. Next make a fairing tool with the exact shape of the ‘master” ellipse scaled up to full size. It needs to be about 8 inches wide and just like the original paper cutout it needs to extend several inches beyond the keel and shear of the hull sections. Now glue some sheets of 40 grit sandpaper to the fairing tool and start rubbing it lengthwise (fore and aft) up and down the hard chine mold. The foam will quickly sand away until you contact the tangent points. There is only one orientation of the tool at any given section that contacts sheer, keel, and chine at the same time. In spite of your best efforts to screw this up, you will produce a perfectly faired round bilge hull shape that is about as good as any you can draft the traditional way. Add a layer of glass to the foam and an epoxy tooling compound and you are ready to go into production – saved perhaps two hundred hours!
The next part of the story is how to mold the hull sides but that is a different subject. I can send pictures of all this once I figure out to post them!

I would like some pictures with that text <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> Please?

Seriously. If you are going to upload rather a lot of pictures, you should consider a picasa account: http://picasa.google.com

So what is trying to be achieved?

An easier way to draw and shape a catamaran or trimaran hull. It dispenses with most of the labor involved with lofting and fairing hull lines. Instead of laying down a full set of waterlines, half breadths, sections and diagonals on the lofting floor, this method uses only three lines - keel, sheer, and a single chine. Also, producing the full size hull shape by carving foam is fool proof because the keel, shear, and chine serve as guides.

I'm still trying to get a handle on exactly how this works...it sounds very interesting. Could another few hours be saved if one could figure out how to make an elliptically curved hot wire cutter?

One concern I would have is that the rapid proliferation of CAD software and NC machinery will somewhat decrease the impact of such a technique in the next few years. But that takes nothing away from the elegance of the technique, nor its relevance to folks who don't have Shopbots all over town...

try this URL for pictures: http://www2.snapfish.com/photolibrary/t_=130509924

Slosail,
Your points are valid. If someone is building from a stock design where they provide full scale section templates, all this lofting work has been done ahead of time and these approacxhes are not needed. Also, if a tortured ply design fits your needs, then as a home builder, that is easier to build.
So what is the method good for? If you want to design your own hull shapes and if you want build of higher performance materials that require either male of female tooling (and you don't have a shopbot!).
I think a hot wire rig is an interesting idea. Might be another way to do the same thing.
I apologize for having so many troubles posting pictures. This kind of thing is very hard to explain without them. But, I think I have a few posted now and I will add some shots of the finished mold and the "shaping tool"

How do you perform hydrostatic calcs without atleast a set of offsets? How do you know where it will float (draft and trim)? Boat building is an expensive project to undertake without knowing that the end result will float properly.

There are some good, free programs about that take care of this. An accurate weight estimate (including centre of gravity) and some simple hydrostatics go a long way towards achieving a desirable outcome and minimising the risk.

A couple of frame sections combined with your foam fairing is a possible method of mould construction. Although you should look at what the professionals do, they will always choose a commercially sensible option. Generally speaking, a set of mdf frames will be cut and stood up then covered with a skin (mdf or strip planked).
Building yacht

Gero,
Wow! that is a cool video. The big guys have the resources needed to do this type of thing - a software suite, large scale ploting table, CNC routers... and so forth. I on the other hand have some sandpaper and a limited amount of time.
Concerning hydrostatic calculations, I am old school and do this with a planimiter and using simpson's rule or trapezodial rule. One advantage of developing hull lines as a family of ellipse sections is that unlike tortured plywood or constant camber, you do end up with true lofted surface. This helps greatly in prefabricating bulkheads and interior structural joinery. Try this for pictures:

http://www2.snapfish.com/photolibrary/t_=130509924
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