Discussion in 'Boat Design' started by frank smith, Jun 16, 2011.

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### frank smithSenior Member

Daniel Z. Bombigher used the term radial diagonals in describing the lines of one of his designs . I have not heard this term before . Would someone please explain what this term means .

Thanks , Frank

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### tom28571Senior Member

I expect he meant the same thing as diagonals. They are radial about a longitudinal axis.

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### ancient kayakeraka Terry Haines

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### frank smithSenior Member

The question is about the term "radial diagonals " . It may have to do with the way in which the diagonals are arranged . I understand the conventional methods that are used for laying out diagonals, and the usage of diagonals . But have never heard the term " radial diagonals ".Maybe it is a French thing.

I understand that diagonals are not used that much today with Cad design being so prevalent . But i use them all the time , and they give me a much better understanding of the form .

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### frank smithSenior Member

Well i went back and looked at some of Bombigher's line plans and can see what he is talking about.

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### PARYacht Designer/Builder

I suspect what he's trying to say with radial diagonals is they fan out from a single point on the centerline. This isn't as effective as placing each to bisect the stations at close to a right angle as practical, which usually requires you to have multiple starting points from the diagonals.

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### timothy22Junior Member

Bombigher's line drawing

shows the diagonals emanating from two points in space, at max beam and, well, see for yourselves. The result is not unlike what we see on many older Murray Peterson designs among others. Bombigher just shows us the origin points. I think it may have been intended to help the lofter locate the diagonals on the floor.

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In most of the larger lofting projects I've done those diagonal origins would be outside the building....not too practical but nice art.

I usually use intersections of the lofting grid to locate diagonals....keep it simple and compact.

In the design shown "Dream", I would rather see a diagonal run more vertically (body plan view) between the two lower diagonals shown. This will be a fair line from the bottom vee surface up through the reverse tuck along the garboard aft.

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### ancient kayakeraka Terry Haines

Unless there is a structural member in the plan eof a diagonal I don't see how it can be of much use for lofting or building, although I did come across this -

"Diagonals informed the shipbuilders of how to arrange the huge wooden components of the ship's ribs on the assembly platforms prior to the connection of the components and subsequent raising of the ribs into place.".

It has also been suggested they help for fairing purposes, clarity, improved precision, a guide to planking curves, as an aid to the designer, or any time the regular orthogonal views fall short of displaying the designer's intent. Hmm - that one covers a lot of ground!

Here's my theory: perhaps they act an aid in visualising the underwater shape of the hull when heeled. Which begs the question, is the use of diagonals unique to sailboat design?

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Long ago before the internet....before personal computers even......Lines drawings were made by hand, with a pencil on a piece of paper.......It was tedious work making all intersections in the exact same place in all three views of the drawing......so some quick and useful aids were invented......DIAGONALS!.......

You can run in a diagonal after laying out only a couple of sections, this greatly speeds the fairing process.....note how I used them in the powerboat below to fair the forebody into an almost monohedron planing surface aft.....Also note how the diagonal is run through the tumblehome aft where no other lines occur.....

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