Freeship: negative area error on developed plates?

Hi everyone. I'm trying to draw a simple stitch-and-glue plywood skiff of just under 6 metres (19ft) in Free!Ship. The bottom is flat side-to-side, with some lengthwise rocker. The sides should also curve in one direction only, at least that's my intent.
The developability check shows me red all the way along the chine, both on the side and the bottom. Is this something I should be concerned about? I don't understand what I would need to do to fix this, especially on the bottom which I know is curved in one direction only, with no twist or anything.

When I generate the developed plates, I get zero edge error for all the parts, but it shows what seem like large negative numbers for area error: -7.9 for the sides, -4.8 for the bottom and -0.7 for the transom (which I'm sure is completely flat!) What do those numbers mean, and are they a problem? The manual doesn't mention how to interpret the area error, or even what units it's in (I'm working in metres).

 

I had a half-hearted attempt with Freeship about a decade ago, but found more problems being created by the programming side, that i went back to pen and paper. The "manual" back then wasnt entirely clear either.

It is a useful tool if you can stick with it, it is a learning experience in itself. I have no idea what the red may represent in your example, i used to be a signal that bends were too severe, if i recall; which is not your situation......

 

Yes, I think that is what it's supposed to mean, that I'm trying to torture the material into a compound curve. I did wonder if it thinks I'm trying to fold the material to make the chine, which would clearly be a problem on a curved edge. But I did some further experimentation with taking out all the curvature and making all the edges straight and parallel, and it made no difference - it still shows the same red around the chine. So I'm inclined to think it's an artifact that I should ignore. But I'm still left with the question about what the "area error" on the developed plates means.

 

Just print out the plank expansions and glue the sheet onto some card and cut them out. I cant see what the issue is, it looks pretty normal for a flat bottom skiff with rocker, there shouldnt be any forcing of the side planking where it meets the bottom.

The only software i used had a mix of "splines" for curvature to ensure bends were within wood limitations, I do not recall Freeship having that, but the red area is still bizarre.

 

Good idea, a model will prove it. I'll try that.

 

This might be of help or something to consider as you move forward. Twisted panel development.

Small Boat Design for Beginners: 2017

 

Per the manual, the red is a non-developable area.

http://www.marin.ntnu.no/havromstek...s_Designeren/Freeship/Freeship_Manual_2.6.pdf

 

I think the chine ("knuckle") is not defined as a "crease edge" in your model. That makes the program believe that the bottom and sides are one surface, which is not developable along the chine.
This will cause a hickup in the unrolling math; you are using the dimension in meter; the area error comes out in absolute value, ie m (but negative).

 

I double-checked that, and the chine is definitely set as a crease. When it's not a crease, I get a completely curved hull, which is entirely undevelopable. (But is not unattractive, and makes me start thinking about planked construction...)

I think you're right it is interpreting it as a fold though. I tried this really simple example with completely plumb sides, so everything on this is clearly developable:

Any join between panels that's not a straight line shows as non-developable. I'm not sure if there is a way to make it realise the edge is a joint and not a bend. I have the edge set as a crease, the panels on separate layers, and the development does show them as separate panels.
This really simple design shows similar area error numbers as well.

 

The software I used was only for chined boats. Is there not a box to tick for "chine"? Recognizing that as a "crease" and not a chine joint, is obviously the issue.

 

The card model seems to confirm the panels are developable It even ended up with rocker that matches what I drew to a fairly surprising degree of precision.

 

According to the manual, the "crease" option is how you create a hard chine, there doesn't appear to be any other option. When creating the actual plate development, it does recognise the panels as separate parts, but not in the "developability check" view it seems.