How to transfer to the real world

danray35 · 29 Jan 2011, 21:31

I have designed a boat, I am going to build from plywood. I have drawn all the framework and outer skins out. I painstakingly unfolded them and laid them all flat onto cgi 4x8 sheets.
Most of these shapes have multiple curves in them. There are very few straight lines. So I needed a way to transfer the shapes into the real world onto plywood. The best way i can think of is to create a graph over my cgi plywood shapes so that I can figure out where to draw my lines on the real plywood.

The only graph I could come up with was grid you can create with work plane except it doesn't actually get very accurate below one foot squares apparently, and I need something on the order of 1/2 inch.

does anyone have any ideas in this area on how to get a graph or grid that will work accurately?

Dave R · 29 Jan 2011, 23:20

How about creating a table of offsets for the panels? That would be typical, proper boat building technique.

Draw a line down the length of your panels in SketchUp and then draw perpendicular lines at some interval like 12". The perpendicular lines are "stations". At each station measure out from the line to the edge of the panel. Make a note of the distances. These are the "offsets". Then lay out the same line on the plywood and measure out the offsets. Stick a small nail in at each offset. Wrap a long, flexible batten around the points and trace it with a pencil. Before tracing the batten check to see that it hits all the nails and sight down the batten to make sure the curve is fair. When you're satisfied with the curve, trace the line for cutting.

Since your boat should be symmetrical about the keel line, stack the planks for both sides and cut them at the same time so they are the same shape.

d12dozr · 29 Jan 2011, 23:24

Have you tried the grid plugin on this page? http://sketchup.google.com/intl/en/download/rubyscripts.html

More printing info here (by Dave R http://www.finewoodworking.com/item/15159/another-look-at-creating-plans-from-a-sketchup-model

Dave R · 29 Jan 2011, 23:41

Thanks for the plug, Marcus.

In the case of building a boat, it would be better to work with points every foot or so. Otherwise you'll be chasing your tail trying to get a fair curve.

I pulled out an ancient model I started of the sailboat I built.

And here is the bottom flattened out with offsets added.

You could dimension the drawing and print it out or create a proper table of offsets like this:

Sta.......Offset
0.........1-1
1.........6-6
2.........11-7
3.........16-3
4.........20-1
5.........23-0
6.........25-2
7.........26-5
8.........27-0
9.........26-1
10.......24-4
11.......22-1
12.......19-1
13.......16-0

The offsets are given in proper boat builder's format of inches and eighths.

Lofting the panels for a boat doesn't require a small grid and I think if you tried to use one off a SketchUp drawing, you'll have problems.

Here's an illustration from a plan from Dudley Dix showing what I was trying to show. The process has been widely used for many years and works perfectly for building boats.

tpstigers · 30 Jan 2011, 06:11

@danray35 said:

The only graph I could come up with was grid you can create with work plane except it doesn't actually get very accurate below one foot squares apparently, and I need something on the order of 1/2 inch.

does anyone have any ideas in this area on how to get a graph or grid that will work accurately?

Umm.....

You realize that this is all virtual, right? Therefore, you can scale your ship to anything you want. Just do the math.

Terry

chrisjk · 30 Jan 2011, 08:14

Perhaps TIG's slicer plugin would be useful? Can get it here http://rhin.crai.archi.fr/rld/plugin_details.php?id=396

Box · 30 Jan 2011, 13:35

Another option would be to get your plans printed full size.
You should have a local print/copy shop that can do it for not too much money.
The cost would probably outweigh the time and headaches involved in trying to draw it full size yourself.
I have a vinyl cutter/plotter that I use for such things, I simply export my plans as DWG, open them in Corel Draw and print away. If you were going to do it all the time it makes a great addition to your arsenal, but if it's a one off, the copy shop should sort you out.

Dave R · 30 Jan 2011, 13:41

Ben,

Could you print out panels for a full-sized boat? Would your cutter handle 4 foot by 8 foot panels?

It would be great to have a CNC machine cut out the panels for a boat but I've looked into the cost of having it done. It's much less expensive to loft the panels by hand and that is accessible to anyone. Having built several boats, I find the process enjoyable.

Box · 30 Jan 2011, 13:50

Dave The length is not a problem, it's a continuous feed roller so will draw any length.
The width on my machine is 700mm/28" but it's no problem to print two halves and just join them together, It's not perfect but for around 200 bucks it's a godsend for my work.

If it's a hobby and something you do for the pleasure of it, then obviously doing it by hand is best.

Dave R · 30 Jan 2011, 13:59

I wish I had one. I've been looking at CNC routers for cutting large sheets of plywood but they are quite expensive and if I put one of those in my shop, I wouldn't have room to build another boat.