# Any formulae for calculating dimensions of plywood surfaces ?

Discussion in 'Boat Design' started by rwatson, Mar 11, 2009.

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### rwatsonSenior Member

I was planning on building a small model of a stitch and glue boat to take scaled panel dimensions from, but was curious to know how easy it would be to calculate them mathematically

Its easy to do a design in three dimensions, but 'unrolling' the surface to get patterns for the plywood is a bit of a challenge without a 3d physical model.

I know it is can be done by various computer software, but I wondered if anyone had formulae or methods to do these calculations, thereby avoiding physical modelling.

Sounds fun ?

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if the model is to scale, then it is a straight forward geosim, yes?

3. ### Guest62110524Previous Member

before software came the dutch did this, they use the sheer and body plan to make patterns with sticks, they would not show me how it was done, there are trig functions, and once I had a math pro out to try solve this riddle, he never did,
but if you asked one of the older dutch yards to say how it was done, then sure they would help maybe send pm to Billy Doc, he's flamin maths genious

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### rwatsonSenior Member

geosim is what ?

The best method is described in the book from Sam Devlin aout doing the scale model thing, and using Mylar to "take off" the flat panel shapes from the chine "lifts".

I planned to divide the hull design into 100mm sections, and then calculate the true length of each side with SIN, COSINE knowing the elevation and depth of each point ... all ideas welcomed

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If you already have a model of some description, be-it large or small, if you wish to use the same geometric data from that to produce another that is identical but larger or smaller, it is all scale-able.

Geosim, if for example the hull model is say 200mm, and you wish to make a hull that is 1000mm, then the scale is 1000/2000= 5:1.

So any linear dimension is length 'times' the scale factor, in this example 5.

So if you measured a length of plank from your model, actual true girth length, then multiply it by the scale factor to get the same relative size and shape for your new 'model'.

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### ancient kayakeraka Terry Haines

It's not difficult to do using standard drawing projection methods if the plank angles are constant but not so easy if the planks are "twisted". Being a thoroughly lazy lout I just have Free!Ship do it for me.

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7. ### Guest625101138Previous Member

Most of the 3D modelling tools have a development module. They can provide you a cut file for router or laser cutting or simply hand lofting if that is what you want to do.

Freeship has this capability for example. It pays to ensure you have a developable shape of course.

Rick W

8. ### Guest62110524Previous Member

the Dutch could accurately make this template from a grid of sticks, COMPOUND shapes
taking the true length(from batten on loft) of say sheer and plate line, then taking sticks onto body plan, the result was a grid of sticks (squares) nailed together, a flattened plate, the ******** WOULD NEVER show even the apprentices, , I would still like to know how they did it

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### tom28571Senior Member

If you are doing S&G, then the shapes are developable by definition. The surfaces are sections of a cone and there are well described ways to verify this. Trying to develop a flat surface layout from the plan and profile can be done, I think, but will be very tedious. The "lift" model as described by Sam Devlin and used by many others for a long time is comparatively easy. The larger the model, the more accurate the results. I use 1/4 ply for the base, 1/8 ply for the lifts and 1/32 or 1/6 aircraft plywood for the surfaces. You could cut and try cardboard for the bottom and sides and not glue them on but use these to measure and draw the panel shapes from. I use like the 10 mil Mylar method best. http://www.bluejacketboats.com/scamp model.jpg.... http://www.bluejacketboats.com/Scamp 1 R.jpg

Making the half model in ply gives you a look at the final shape better and also gives you something to hang on the wall.

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### Earl BoebertSenior Member

I've used Hull Designer from Carlson Design with great success in doing hard chine models. It develops and lays out the sheets for you:

http://www.carlsondesign.com/hulls.zip

I'd strongly recommend getting the tutorial:

http://home.clara.net/gmatkin/hullstut.htm

As the user interface is, well, a bit challenging. I do initial design in Delftship and then transfer the dimensions to Carlson.

Cheers,

Earl

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### rwatsonSenior Member

All comments appreciated, and I do have a pre-exisiting design. It isnt a "developed" hull and I am just finishing a scale model using strip plank.I was planning on converting the lines to 'hard chine" (for stitch and glue") with a good old drafting board and pencil.

I must say I am very dissillusioned with the 'computerised' tool approach. I am a computer programmer by trade, and I found all the hull design programs I ever used that were supposed to be intuitive and 'easy' , were a severe pig of a job to learn, and all with serious 'gotchas' in them.

My impression of them is supported by the fact that every 'draftsman' I ever employed to do a boat design took six months and thousands of dollars to produce just line drawings of a hull that would take me three days with a drafting board to produce a hard chine version of. You cant find a CAD person under \$60 an hour - why? because the programs are so awfull to use, you have to be an expert in them. I am not complaining, just observing the facts. I charge that much for much less complex software development, and I spend the whole week fighting 'gotchas'

I am happy to use the 'Devlin' approach, but was curious to know if their was a mathematical methodology.

After a lot of thought, I am thinking that the whole exercise is simply a matter of finding the true length of each edge from the plan and elevation and forward views for panels between the frames, and calculating the correct angle of one of the corners to produce a "true shape". If I make the sections close together, any "raggedness" will be easily catered for.

I will experiment a bit more and see if I can nut it out unless anyone has more ideas.

The dutch GRID of Sticks is making a lot of sense to me now, I will have a play with that as well. Thansk for the idea whoosh.

Thanks for all the comments so far.

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12. Joined: Oct 2008
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rwatson:
"I found all the hull design programs I ever used that were supposed to be intuitive and 'easy'.....a boat design took six months and thousands of dollars to produce just line drawings of a hull that would take me three days with a drafting board to produce a hard chine version of..."

Man after my own heart.

The days of getting 'simple' drawings back from the draughtsman for checking and reviewing has gone. Simple in many senses such as quick, ie a day or 2, and basic data on the drawing so the plater/welder can fabricate it...all now gone. I have to wait weeks sometimes months for just one "cut part drawing", not a real drawing too....no details of joints or construction..all bloody hopeless. All the draughstman whinge, i cant do that until all the structure is done....and so one needs a real structural designer/naval architect to do the job properly.

The draughstman have become software 'experts' and no longer ship/boat-draughstman. This is exacerbated by the fact that many draughtman rarely if ever set foot in a shipyard..they all come straight from university, or college, and think because they can "draw" on a computer screen very quickly they can 'draw/design' boats!

anyway...good luck, sounds like fun.

13. ### Guest62110524Previous Member

thats ok, thansk for thanks, look I wish I could do that because it really was how they did it BEFORE likes of maxsurf, , I will call a Dutchie in NZ who used to do it, he now uses maxsurf so he will not be afraid to give up that trade secret

14. ### Guest625101138Previous Member

Give me some detail on the hull and I will do a Delftship 3D drawing in a few minutes. It will take ten minutes extra to produce the cut files.

Rick W

15. ### Guest62110524Previous Member

rick you are a kill joy

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