Tricky hull modelling problem

[Andy]

I am wanting to design an International 6 metre (http://www.6metre.ch/) hull using Rhino (or MaxSurf academic) but am having problems with the discontinuity of the hull at the skeg (or bustle, as its also known on these boats). I need to be able to model a hull like the one below, in which the skeg is faired into the mainbody of the hull with the surface continuity being positional at the aft end of the skeg with a gradual transition to curvature continuity between the aft end of the skeg and amidships. As the design needs to meet strict measurement criteria it would be very useful if the model could be easily edited. Any suggestions, or am I asking too much of NURBS software?

Andy

[Tim B]

That hull is not actually too hard to model if you reduce it to the standard form... Canoe Body + Appendages.

You can't do the whole thing as a single surface, in fact I suspect it will take four surfaces per side. something like Hull, Keel, skeg, Rudder. It may take 5 or 6 depending on the exact geometry.

Once you have something that looks about right, then you start matching and blending surfaces to make the joints fair (if indeed they are).

Tim B.

[Andy]

hi Tim - I'm not too worried about the rudder and keel; what I'm finding difficult is managing the varying continuity between the two surfaces....I'll try what you've suggested so far tho and see what happens!

Andy

[Andrew Mason]

Andy

Actually, it's one of the toughest things to do with a quadrilateral NURBS surface. Designers such as Ian Howlett and Sebastian Schmidt have done 6 & 8 metres with Maxsurf, but getting the skeg right is a tricky business. I suggest using one surface for the hull and skeg, with three alternative modelling options.

Option 1 is to model the bottom corner of the skeg and the corner between the skeg and the counter with multiple control point columns. This is tricky and you really need to pay attention to the fairness of the area around the skeg.

Option 2 is to use a separate surface for the skeg, poke it through the hull and get it as close to tangency as you can, then use Rhino to do filleting between the skeg and hull.

Option 3 is to model the skeg all the way back to the end of the counter, then use a trimming surface to cut away the excess behind the rudder post. This is particulalrly effective on a metre boat if you want a defined flat on the underside of the counter.

Hope this helps