Develop plates in Freeship

How about this output from the develop plate feature i Freeship? "Minimum edge error -0.00173. The hull is "green" in the developable check mode. Is this ok for aluminium plate?

 

I see no one has responded. Freeship plate development needs to b taken with a grain of salt (not trusted explicitly). I think that the blue lines in your developments indicate areas of stress and so there may be errors in those locations. I have taken Freeship output directly and built some kayaks from plywood, but there were areas where pieces did not lay or fit naturally.

The best bet in your case before spending big bucks on cutting expensive aluminum would be to do a scale model to check your developed plates.

 

A half block model and you cannot go wrong.

 

It worked!

This is the same hull developed in Delftship this time. The files was prepared in Draftsight, and sent to a watercutting facility. I was very worried about how the plates would fit. But everything went well

 

Hi
I am very new to this forum and am also trying to get my head around generating accurate development plates. I have just finished my first boat - started small with a Tango skiff 13'.

I now have the bug, and have started working on a new boat design. My real question is why you did not have confidence in the plate development from Freeship and felt more comfortable with the result from Delftship? The programs appear to be very similar to work with.

 

Hi.
Yes, they are similar. I searched this forum for help to interprit the Freeship stress values, but found nothing. Delftship has the colour indication, red, orange, green for the stress values. However i find it difficult to interprit these values. The hull i made was fitting together very well exept the sheerline didn't exactly match the digital model. this edge "wantet to be wider". You should aim for "green results" in the stress figures.

 

I think they are the same stuff. Delftship appears to just color the output in a different manner.
Plate development can be tricky, even for big bucks software. We have recently had problems with the output from a mainstream mechanical 3D CAD software and it has cost us some time, money and a couple of meetings to fix the resulting structure. Whatever software you use, the first build will very probably need some minor corrections to the theoretical output drawing.
Cheers

 

Thanks Guys
As this will be a one off for me, I guess the best bet is to make a scale model and check out how it pulls together.

The idea started with Wes Farmer's Sundance, but it has been stretched 29% and beam and height increased by approximately 15%. Above the chine the flare has also been increased and the shear line changed for a caddy cabin. So finally it does not look like Sundance at all!!!!

In Freeship there is a lot of green in the "developability" mode of the hull, with red at the chine and shear but my main concern is at the bow where as expected there is considerable stress. The total errors reported appear to be very small - but what is an unacceptable amount of error? The side panels look fine, my main concern is the bow of the bottom panels. The developed plates have a concave curvature in the bottom plates as the bow approaches the chine which just does not look correct to me. Delftship development plates are similar. I wanted to superimpose both Freeship plates over the Delftship plates and can export freeship to a dxf file but for some reason the Delftship icon is "greyed" out and not available. I have Autocad that will allow me to superimpose the files.

I intend to build out of marine ply and sheath with fibreglass, so I am sure the hull is buildable, but just trying to minimise time and waste. If you are interested please have a look at the attached and any comments or guidance would be greatly appreciated.

 

Nice boat.
I assume that the hydrostatics is correctly estimated, by calculating the effective CoG of the boat.

Regarding the red zone around the stem, it is due to the rather abrupt transition of the horizontal keel to the nearly-upright stem post. I guess it is present in 95% of the designs. It is possible that you will have to torture the ply a little bit in that zone, but nothing really to worry about.

The cabin top could surely be made better and fully developable. The red are over there is too big, imo. It shouldn't be very difficult to turn it all into green.

Cheers

 

It would be desirable to draw a cross section at 6250 mm from the stern, for example. In my opinion it is very likely that the surface of the hull has a double curve, easy to avoid opening the knuckle a little more.

 

Something else to look at is using some conic development techniques while creating your model in Freeship. This thread has an interesting development on the subject and it's use in Freeship.

http://www.boatdesign.net/forums/boat-design/small-quay-punt-lines-49650-4.html

It starts at post #38.

 

The red colouring at the forward end of the bottom plates is caused by a three-sided surface, i think. Freeship/delftship doesn't "like" such surfaces.
They should be foursided. This red triangel is not to worry about. You could try make it smaller.

 

Thank you

Ok

Lots of good advice.

LP, I had a look at the other post you suggested. Going to need some more time to fully understand how to complete the conical development. One point of guidance that was much easier and quicker to play with was,"to try and align the development edges with straight sections on the panels". When I created the initial model I just used the offsets for the frames to create the edges. As you will see in the images attached it meant that the bow half of the hull in the bottom panels had a concave curvature.

I have now moved the alignment of the edges in the bottom panels so that rather than the edges running directly perpendicular to the keel they are now running forward and better aligned with a straight section on the panel (this was a very crude judgement by me). The change to the hull form has been quite dramatic. The bow half of the bottom panels now have a convex curvature and the development plates look a lot closer to expectation. Interesting that the red bow is still there but a different shape, and the plate development errors are larger!

The first images are of the original model showing the concave curvature. The later images show the modified model and the effect to the bow form below the chine.

This weekend I will try to make up a small cardboard model using the development plates.

Thank you for all your inputs.

 

Cardboard model

Friday night in AU.

Given the medium used to make up a quick cardboard model I would have to say that the results are very encouraging. I constructed in typical S&G fashion, by laying the bottom panels together and stitching along the keel (using sticky tape). Unfolded the panels and then attached the side panels, starting at the bow. Finally I added the transom and only one bulkhead (middle bulkhead is a little short as I worked off my original offset spreadsheet that did not have the increase in shear height per the model).

Given the flimsy nature of the cardboard, the hull is quite fair. All the buttocks and waterlines have alignment, the bulkhead and transom fit was good given the limitations of scale and eagerness to get a result!!

Scale was 1:17

Photos attached.

 

Nice job ! Not sure I like the hull shape, but it gives you a bit of confidence with the development of the panels.