Sheer Revelation

Gonzo,

We can take this to another thread if you'd like. The comparison of paper vs. computer is not the point here. In fact, I cannot figure out why you are trying to induce some sort of controversy. I don't believe I am making any sort of statement about what is better or worse. As has already been pointed out, this is just an approach. You are free to ignore it if you wish. There are many others who may find this useful.

 

Do you say that you can use this approach with any hull shape?

 

Sorry Rick. I am a bit at fault for hijacking this thread as well.

 

Sorry too.

 

Like many terms used around boat design, "fair" is totally subjective. It's difficult to describe what fair is, or what it might mean. But fair to you may be a mess to me.......For example a hull may have all sorts of nasty bulges in it's surface, cut a planar sheer in, you'll have a sheer that will not look fair in any view. That's an exaggeration.....but a nasty bulge to me may be "fair" to you.

I usually describe a fair curve as one where I cannot precisely pinpoint where the curvature begins or ends. But that's subjective too.....for instance in a Colin Archer type double-ender there may be considerable bunching of curvature in the ends.

 

The powder horn look is appealing in some designs and horrible in others. Fair is difficult to describe.

 

Tad. I ascribe to your definition of fair.

 

I really like this description Tad (especially the bolded part).

And no apologies necessary. Just see this thread for what it is. With that said, I think a CAD vs. Paper discussion would be a good one.

 

More Cones

In the case of your current Sheer curve, because it lies in a plane, then yes it would be the intersection of a cone with a plane. However, curves could be drawn on the surface of a cone that do not pass through a plane. Are the curves on the surface of a cone that are not contained in a plane good candidates for a sheer curve? ... That is still a quesiton of asthetics, not geometry. I tend to think a nice looking sheer curve could be drawn on the surface of a cone, yet not planar. And a sheer curve that can not be placed on a cone will not look good. ... not certain on this, but is an issue that i'm contemplating.

 

I don't think sheers need to be planar. Most of the sheers I draw are not planar, and yet are fair. I think pperhaps that restricting the sheer to lie on the surface of a cone would dictate the shape of the topsides too much.

 

I think it would be an interesting geometry experiment to try this on a cone.

And as Joe mentioned, no gospel here on whether a sheer should be planar. However, if one were inclined to use a planar sheer, it may go a long way to helping you with a pleasing shape. You can modify the sheer from there, but it could be a good starting point.

And honestly, I think Tad summed everything up nicely with his description of 'fair'.

 

Gonzo, my thoughts were the same as yours re. this:

I suspect that a reason you (and I) weren't familiar with the term "planar sheer" might have to do with the fact that it is, as stated here several times, just a tool (using a hull design program) to define a sheer. As it tuns out it's readily do-able using CAD, you just define a plane and slice your hull. If you like the looks of it then bingo! your design now has a planar sheer. If it doesn't fit well because (insert reason here) then "undo" is the next tool. There is nothing magical about a sheer which is planar, nor s-shaped, nor fair, fairer or the fairest of them all. Actually, some more experienced designers here are surely going to correct me and say "We've designed planar sheers for centuries!! We just didn't do it with the click of a mouse!"

p.s. TAD is right, "fair" is subjective, no matter what. It is relative, and definable mathematically, it is just not finite, ever.

 

Dreamer I use the curvature graph to show how much twist and where it is in the sheer in maxsurf and rhino. The first pic shows one sheer then the second shows the original (blue line) and a new sheer with more curvature while maintaining the shape in plan view. As you can see the angle of the graph changes as you add more curvature, you can add or remove twist along the sheer by adjusting control points.

 

those curvature graphs are essential. I use them on the sheer as well as the isolines. Along with the control point 'net', this is one of the strengths Rhino has over SolidWorks. I cannot understand why SolidWorks does not offer the ability to modify a surface by an 'inference' net like that in Rhino (and Maxsurf).

My typical workflow for sailboats is to do the hull in Rhino then open the file in SolidWorks. There is one-way associativity from Rhino to SolidWorks which is pretty slick.

 

I like to look at telephone lines .Depending on where you stand ,if you check them out with one eye closed , some very interesting lines can be seen .

Frank