developable panels

New to the forum.
Easy first question:
How do I develop a panel for the underside of a boat, to be cut from a sheet of plywood?

 

A developed panel must be a section of a cone or cylinder with not necessarily a round cross-section. Therefore, you can define one edge of this developed panel, usually using either a preselected keel or chine shape (using the chine is easier), then pick a point in space for the apex of your cone, or pick a constant 3-D slope if you decide on a cylindrical development. Either visually, using a string, or a laser beam you could line up your apex, or slope, with a point on the defined/preselected edge and find a third point to help create the other edge of your developed panel. After finding multiple points along both panel edges and the ruling lines connecting them, you can determine your panel shape.

I have also read of building a half model and experimenting to see how stiff paper or thin plywood wraps around various points. Graphing would provide another method, similar to what is done for sheet metal development.

I use a mathematical method instead of any of these which was explained in a previous post and is too long to restate here.

 

Hi Dries, welcome to the forum.
It helps if the surface you want to develope, can be. If you do it with software its best to draw that surface with the same software. There are some free and low cost software that will draw hulls that have developeable panels. This can also be done on the drawing table, I have an old book that shows the process. There is some expensive software that will flatten almost any surface but they require more data than just the shape to get good results. I think you will find a lot of informatin on this subject in the software section of this forum. Use the search function it will get you there.
Gary

 

This thread will provide some possibilities:
http://www.boatdesign.net/forums/bo...ting-dimensions-plywood-surfaces-26434-2.html

Using Delftship is probably the best if you want to compare different hulls:
http://www.delftship.net/
There is a free version and it is fundamentally the same as Freeship. Just register and download - hope you have windows and not a Mac.

Be prepared to to put in 30 to 40 hours to come to grips with the program. It is a surface modelling tool not solid modelling or normal line drawing as in typical CAD. You extend surfaces. If you get problems then post a specific question.

If you are good with a speadsheet you can do the development mathematically but this is tedious.

The fun with using Delftship is that you can gat to see what it will look like before you build it.

Rick W

 

An even easier program to learn, that also provides developed 2D patterns is Carlson's Hulls. You can find it on the Carlson Design website as a free download. Do get the tutorial that is also available and start by working with the hordes of free, already drawn, hull shapes that are also provided.

Simply pick one that closely resembles the hull you are thinking of building and fiddle with it until you understand the process. You can then produce a 2D .dxf file that can be opened in any of a number of free CAD packages from which you can print them out full size as templates, or give them to a CNC service for cutting of the panels.

Most of all, have fun.

 

Eventually thinking about boats again, hectic times moving behind me!
The IOU's in the blue boatfund box are starting to add up, and I still don't know what to build.
I downloaded and had a close look at delftship, and now understand what they mean when they say that the developed panels may be viewed. I can see them, but I can't export them to a usable format such as dxf or igs/step. That is no use....I love the software though, real classy aesthetics and interface etc.
So where to next for that tricky darn bow area development of the lower panel?

 

Dries,

I don't know about Delftship output, but in Freeship you can out put the developed panels through the following procedure...

1.) Open your design in the software.

2.) Go to the TOOLS heading and pull down to the DEVELOP PLATES line and click there.

3.) You will see all of the panels for the hull you have designed as individual parts.

4.) Along the top line of the graphic symbols, you will see a compass over a grid background. When you hover over that symbol, you will see a pop-up that says EXPORT THE VISIBLE PLATE TO A .dxf FILE Simply click the compass symbol and you will be prompted to save the .dxf file to a location of your choosing.

5.) Open the saved file in the CAD program of your choosing, or take the file to a printing service location where the full sized panels can be printed and then used as templates for cutting your panels.

6.) Once in the CAd environment, you can arrange the panels to suit a common output on a 36" roll of paper, or whatever is most common where you live.

7.) You can also nest the individual .dxf files for each panel and make them ready to be cut on a CNC router on a standard sheet, or sheets, of plywood.

Really simple stuff, once you get it to a .dxf file environment and will yield quite accurate cut paths, or templates, whichever you choose to use to build the hull.

If this doesn't work for you, get back to us and someone will be able to help you.

 

Hi Chris,

Thanks for the info.I had just downloaded and installed Freeship, and saw what you were referring to, just using one of the included sample designs.
I suppose the easy bit is to go through the steps, monkey see monkey do.
The hard part will be to gain the qualitative experience of when a panel stops being developable, using a given material. I think it is also no use torturing a plywood panels into shape, and stressing it so much that it fails at the first thump during use.
By the way, I have a 4x8' cnc router, own design and build. It cuts consistently to about 0.5mm accuracy, and I can easily get 1200mm/min cutting MDF or particleboard (known as chipboard here in SA.) So this should help somewhat to gain said experience.
The idea is to cut scale models of the intended panels (to fit into a standard sheet size so I don't have to scarf panels together, it takes too much time for a verification exercise) and see how the material behaves. Luckily we get quite decent Okoume marine ply locally( from Malaysia I think) and most of the known brand epoxies are also freely available (SP Ssystems, WEST etc)
Thanks again for the reply. I now have to knuckle down and do the bascs of the boat, which will probably be a seaworthy little(16') double ender for picnic and camping trips.

 

Depending on beam, your boat will be more like 15.5 - 15.8' in length, so size it accordingly. Otherwise, the little dude will not fit on two sheets when scarfed.

The scaled model boats for proof of concept will need to be done in much thinner material, or they will likely not take the bending. Door skins will work for this process, if you can get them, as will the spendy aircraft guage plywood that can be had at 1mm in thickness.

Another source of really bendy stuff is (really) called Bender Board, or Wigglewood. It bends easily along one axis and is used by the guys who build signs, or trade show exhibits. Ask around.

 

Thanks Chris,
We know the wood as Taalflex or bendyply. Mostly grain directions of plies are aligned, so easy bend in one direction only
I'd be a little worried as this does not emulate the final material with more homogenous properties, very well. But worth a shot. Luckily I can get doorskin.
I am having real trouble trying to interpret the developability indication from Freeship. I see some green with some red splotches, so what.
If I look at a section of the lower panel near the bows, it is a straight line. I'm pretty sure that this panel should have some camber in order to be developable. Is there a way of defining camber on a panel, and keeping the hard chine constraint on the edge. Any help much appreciated.

 

This is what I'm referring to....

 

I think I have sorted out the problem in ProChine. Their rulings seem to make sense to my muddled brain, the developments look right for the first time. I took the surfaces into Wildfire and had a look at the Gaussian curvature, and it ties up with what I expected (zero or extremely close thereto everywhere.)
The resulting hull also look extremely fair, with nothing funny in the surfaces. So far so good, I feel confident enough to risk cutting material for a model now. BTW it is a nice looking little 15 foot double ender, I suspect it may grow a bit depending on the sailplan. The constraints are a nice mast extrusion which I already have, plus a new addition to the family which makes the existing dinghy a bit small. Oh to have a valid excuse to build a new boat.......

 

The easy way, is to lay the plywood over the molds or frames and trace the edges with a pencil. Thousands of boats have been built with that method.

 

I've done some work since last braging about it. Drew and cut the panels for a sea-kayak and the double-ender, from doorskin. The kayak went together alright, but the doorskin is still way too stiff to emulate the final material accurately. The double-ender is still in pieces, haven't had the time yet to assemble it. But clarity is slowly coming. Thinking of buying pro-chine from New Wave systems?

 

Chris, I tried to do what you said, to look at developed panels in Freeship, but when I click on TOOLS, the Develop Plates function is grayed out. I have opened some of the examples and it is turned on. So how do I turn it on for my design?