Designing developable surfaces in Rhino

So I'm having some problems designing a hull in rhino. I would like to design the boat to be made cold-molded with plywood and veneer strips. The bow section has some twisting and flare and I don't believe can be made with a single sheet. I have attached a couple of images of a similar hull shape being made in the manner that I would like to construct. They are of a friends boat, of which he bought plans for.

I have tried DevSurf, Loft developable surface, and flatten in rhino, but none allow me to adjust cuts for the strips as in the hull pictured.

I basically have two questions:
One, can any shape (closely similar to the hull shape pictured) be made by strip planking as pictured?
And Two, If not, is there a program that can cycle through the following steps?
1) Cut my hull design into strips of appropriate size based on a maximum bending input, and location tolerances.
2) Flatten those strips.
3) Approximate those strips as a rectangle. (As an improvement trapezoidal strips)
4) Re-build the hull surface using these rectangular strips so that it can be compared to the original hull, and maximum gap sizing can be measured.

I'm guessing this surface is not considered a truly developable surface...?

I would like to use rhino. I suspect that programs like Grasshopper and Galapago hold the answer, but I have trouble even starting to understand these programs.

 

For the build method pictured, there is no necessity to develop panels. Each strip is shaped directly in-place.

 

fpjeepy05,

For the boat you show in the photos, it appears that there is a developable surface which fits the chines and keel. However it may be slightly different in shape to the shape of the bottom in the photo. For the developable surface the transverse frames would have curved, not straight edges in contact with the bottom.

The shape of the topsides is fundamentally not a developable surface due to being curved in two different directions.

 

I second this.

 

There is a build method called Constant Camber that is similar to what you propose, but it is not suitable for the hull you show.

 

The brief answer is yes, almost any hull shape can be built using the method shown. But that method is not usually called strip planking. Strip planking usually refers to planking with narrow strips which run more or less fore and aft.

An excellent reference on plywood and glued boat building techniques is The Gougeon Brothers on Boat Construction which is available for free download at http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook 061205.pdf

Are you hoping to design a hull which can be planked using rectangular strips? If so the hull shape will be severely restricted and basically the same as a shape which can be planked with a sheet of plywood. As others have mentioned the method shown in the photos requires shaping of the individual strips.

 

Strip planking a modern form of diagonal planking I suppose or are there distinct diferences?

 

From what I've seen diagonal planking uses multiple layers, usually glued together, and the layers are frequently at angles to each other. At least one layer runs at a large angle (45 degrees or more) to the keel and rails. The "planks" in diagonal planking are usually thin, a small fraction of their maximum width.

The basic form of strip planking uses only one layer of strips, and the strips run longitudinal. The strips range from square cross-section with the width equal to the thickness, to widths of three or four times the thickness. The strips are fastened to each other with glue and/or mechanical fasteners.

Both diagonal planking and strip planking have been used for over a hundred years although variations and refinements continue to be developed.

A popular method for larger boats uses both strips and diagonal laminations. The hull is first planked with longitudinal strips, and then "planks of veneer or thin plywood are applied diagonally to the exterior and possibly interior.

 

I understand this is how it can be done, and quite possibly would be the most efficient method. However I feel like CAD is such a powerful tool that it should be relatively easy to make some things a little easier. Even if it is only calculating strip width or shape to maximize strength, or minimize fairing.

Attached are some pictures of a build that was documented over on THT. All of their strips were cut on a cnc with a curved shape. It appears that very little fairing was required on this hull. How was this done? Why wouldn't someone want to do something like this?

 

Working on the reading now. I guess my last question would be what you mean by "shaping of the individual strips" I'm sure the reading will answer this, but does that only mean the cutting of the two ends? or scribing lengthwise of the strips? One seems simple and the other time consuming.

 

Thanks David, was thinking of motor torpedo boats of the second world war. Seemed they were easy replanked, had sometimes canvas between the layers. Strip glued minesweeper i looked at once felt more like a solid polyhull.
Will read up the Gougeon bros as well

 

Fpjeepy05 there is away you could get some of the things you want out of rhino. Once you have your model in rhino you draw some lines in plan view that represent the edges of the planks and possible spacing for the surface in question (black lines in example). Now if you turn on record history and use the “project to surface command”, pick the lines you have drawn and the surface you want. You now have lines drawn on the surface (blue in example). These will be the edges of the planks on the surface; the good thing about the history being turned on is you can now edit these lines by moving the originals either individually or on mass (moving or rotating) to get what you want. Now if you turn on the record history again and use the “loft command”, pick the two edge lines and create a surface. This surface is now also connected to the original lines so can be edited. You repeat for each plank. You can now use either unroll, smash or squish to get a flattened plank surfaces.

 

Three different construction techniques in two different hulls/plugs. (The second one with the wide flange at the sheer appears to be a plug for making a female mold.)

This hull in the first photo uses several layers of veneers or thin plywood with each layer at a different angle. The layers would be glued together. Each piece of veneer or plywood would need to be fitted. While it is possible to develop the shapes on a computer my understanding is that experienced builders can quickly fit the adjoining pieces. Earlier versions of this system used a layer of thin fabric between the layers.


The transverse molds used on the plug in the second and third photos were probably cut with a CNC machine. The sides are strip planked. The strips are usually straight after milling and then sprung into position. Typically no shaping is done other than sometimes tapering a portion of the strips to change the angle of the intersection of the strips with the the keel or sheer. The third photo shows what appear to be curved strips nested together flat on the floor. No idea what they are for and evidently they were not used for the bottom or side of the plug.

The bottom in the second and third photos appears to be made using three strakes of plywood or similar. The shape for these strakes could have been determined using software such as Rhino and then the strakes cut with a CNC machine. Or the shape could have been determined directly.

 

Four hours on an airplane today... I made it to chapter 12... great read.

That would do it. Seems like a bit of work but would definitely work. Might have taken me a while to figure that out.

So one more question... A 6" strip in the bow section of this boat, when forced into position is the veneer going to do which of the following:
Bend in one dimension and lie straight in the other.
Make a compound curve, and bend in both dimensions.
Or a combination of both.
Depending on the answer to this question, it should be possible to develop a script that determines the width of the strips based on veneer thickness and radius of curvature in both directions, and tolerance.

How about a script that calculates hull springback?

 

The reason that the strips are at angles, is that they are laid in one developable direction of the two possible in a compound curve. Thats one of the reasons why there are two layers of strips going almost at right angles to each other.

The reason the strips are narrow, is because they wont bend in two dimensions, so lots of 'little steps' are required to get around the 'other' axis.

In practice, the problem isnt a design one. You will be surprised how easy is to start planking or stripping on the actual hull. Even is there was software to calculate it, it would be a waste of time using it. As long as you keep the strips as close to the same shape as the corresponding one on the other side, you will end up with a good result.