Need a Formula to figure out the "Blow" on Aluminum Hull Plates and Side Plates

[jdnelson97]

Hello,

I am looking for an accurate CAD process or mathmatical way to figure out the "blow" when creating an Aluminum Hull and Sides (or any devolpable surfaces) . I am currently using Rhino. I have created a few new hull shapes and have flatened them out and had them CNC cut. But they tend to be off when the boat goes from straight to curved. The software does not compensate on how much the Aluminum bows out for example: From the shear line to the chine edge. The software projects a straight line between the 2 planes. This works on straight sections of the boat, but when it starts to curve, I need to figure out an accurate way to come up with what builders call " The Blow" in the sides and bottom plate. Any help would be appreciated.

Regards

[philSweet]

See attached

[micspoko]

in rhino use a plugin squish for developable surface of course you need properly divide plates to do this

[DCockey]

See my responses in your other thread about this: Need Help With Aluminum Lofting

If you create a developable surface in Rhino using DevSrf it will properly model the curvature of the surface. Loft can also create proper surfaces but it can also cause problems as I discussed in the other thread.

It is very easy to create a surface between two curves which looks okay but is not actually developable. Check the Gaussian Curvature with CurvatureAnalysis. It should be a very small number everywhere on the surface. If it isn't modify the surface so it is.

Using Squish to get around problems when trying to flatten surfaces which are not actually developable is likely to cause problems later. Use UnRollSrf instead.

[jdnelson97]

Thanks Phil. That answered my question.

[Kiwifinn]

DCockey is right on, Loft can be a bit of a handfull and often takes a few goes to get good robust results. Interstingly I've found that sometimes the resulting surface differs when clicking the stern end of the chine and keel lines compared with the bow end. Go figure.

A robust developable surface has a Gaussian curvature of Zero.

Squish only works on small animals as the tool button clearly points out =)

[micspoko]

I have been involved in to conversion where curved plate were developed usuing commend squish in rhino and all the plates have been well developed

[Kiwifinn]

Interesting, I will have to try out squish on plates I know unroll well and compare results.

[DCockey]

If the surface is developable, then Squish should give the same results as UnRollSrf.

The problem with using Squish instead of UnRollSrf is Squish will flatten almost any surface, but if the surface isn't developable or sufficiently close to be developable the result probably won't be close enough.