FreeShip Develop Plates - Errors

Hi,

I create a little rowing/sailing skiff ( 11' flat bottom, multi chine ) using the Carlson 'HULLS' program and imported the design into FreeShip version 3.47 (I am using a 32 bit Windows 7 as a VM on my Mac Air). The import and the adding of bulkheads (stations) went smoothly. I do get some errors on one of the panels during the development of the panels:

Part name : Bilge (P)
Minimum edge error : -0.00007
Maximum edge error : 0.00000
Maximum area error : 0.000001
Total area error : -0.000107

I made a 10:1 cardboard model of the little boat, which went together nicely. The question is, whether the plywood panel will work as well. There seems to be little explanation of what a 'Minimum edge error : -0.00007' actually means. What I would really like to know is, whether an error of that magnitude is of any consequence ( for 4/6 mm plywood S&G in particular ). Can anyone shed some light on this ?

Cheers,
Peter

 

Hi PeterRK, from 3 kilometres away from me
Depending whether your drawing is in MM, Metres or inches ( Looks like Metres to me), those figures look very, very inconsequential.
If you were ultra cautious, you could manually cut out the shapes in MDF, and fit them in a test mock-up, like I did. But on the face of it, it looks good.
PS. It costs nearly as much as the sheets of plywood to have them CNC'd. If you want to save money, just draw the offsets on the sheet, and hand cut it. For a small boat like this, its not going to be critical.

 

Thanks rwatson, this is what I wanted to hear. I have made a set of drawings for all the panels and I will cut them by hand, for sure.
I will stich and glue it together 'the right way up'. The bulkheads (seat supports / frames) will help to build it straight. Do you
know how to interpret the 'errors' ? Are they the amount (i.e. distance) of bend (torture) necessary to 'make' the joining edge ?

 

With a bit of luck, you wont even notice the "discrepancies". Just make every panel a mirror image of the other, and the structure should self assemble.

I think you will find that starting assembling it upside down will be easier to start. It means that you don't have to lean over a wobbly gunnel to stitch the keel line, for starters. Do the keel line, the first chine and stern, then I think I turned it right-side for the rest. I even had three internal formers ,made, to lay the first panels on. (assembling test mdf panels with zip ties below)



Use a flexible steel wire for stitching, like the stuff they sell for tying up plants on a trellis. Using steel mean you can also make each "stitch" push, as well as pull, and you can easily unwind it to adjust it, unlike cable ties.

 

Oohh, nice looking kayak. This will be my third S&G ... but my first own design.
The skiff has a flat bottom, so it invites itself for building the right way up (no keel line ).
But I will certainly use wire, stronger, as you said, and also smaller holes !

 

As rwatson says, just lay it out and cut it. He is correct that for something like this, those errors don't matter. FWIW, the errors show how much the developed panel line is off from the moulded lines. This error is given in the working units (i.e. in, ft, mm, etc. because the program doesn't care). So if you are using ft, an error of -0.000107 ft means that the correctly laid out and cut (and infinitely thin) panels will have a gap of 9/10,000 of an inch....1/10th the width of a human hair. So in reality, unless the error is very large, you could never even cut the full size panel with sufficient accuracy for the development error to matter.

And also notice that the panel development is to the moulded surface. Whether that is the inside and you have gaps between the panels on the surface due to panel thickness, or the outside and you have to cut rolling bevels to get the panels to fit; is a whole other layout issue.

 

Thanks, that is the info I was looking for: max error = max distance from edge to moulded line (i.e. calculated spline) in working units. So, the error is indeed inconsequential in this case.
The inside edges will have to meet exactly (within reason), because I want a bright finish, but the exterior will be have paint. Any gaps due to the panel thickness are not really an issue, i.e. thickened Epoxy 'Oakum' with tape over it. A bit of a bevel will reduce the amount Epoxy . . .

 

In this case, keep the port and stbd panels identified. The best way is to mark a big "I" and "Bow →" on the inside (i.e. the touching surfaces) of the two clamped together panels when cutting. This means that the inside panel edges will be identical port/stbd, because for various reasons, the outside edges may not be identical.