Radius BOAT Question

Hello There. I have got a question that has customer technical support stumped! I am hoping this forum can help.

In short I am trying to achieve the same sort of result as creating a circle with “TANGENT TO CURVES,” but instead of using 3 curves, I am using two opposing surfaces and a yellow profile line (See attached screen shots). The last screenshot below is essentially the desired result. The surfaces have extended past the desire profile line and I intend on having the two surfaces trimmed off NOT BY THE PROFILE LINE, but rather a radius surface that intersects/ is tangent to the profile line.

Make sense? Is it possible to do this with RHINO?

My advise is you use 3 surfaces instead of trying to fillet the hull in the CL.
Depending on what operations and software are used to post-process that hull form, your approach may lead to connectivity errors.

Hello - this looks like a FilletSrf or a Sweep2 Can you post the surfaces and curves?


Uhm, I don’t know. Perhaps Patch would make a better surface, but I don’t like it so I do not recommend using patch.

@bstoddard, is the yellow curve the supposed connection point between the center and side surfaces?

In that case you can use that curve as edge by definition. So you don’t have to trim any of the surfaces.

Ok, so if I understand correctly, what you need is a rolling ball fillet that rolls over your yellow curve and touches both surfaces tangentially right?
Or in other words, if you would extrude the yellow line the fillet should be tangent to all three surfaces

Yes, the idea of a rolling ball would work, BUT the ball would have to constantly change diameter as the deadrise (angle of the surfaces) are constantly changing as is the relationship to the yellow line.

Yes I know.
If it doesn’t need to be an exact rolling ball, I would extrude the yellow curve and trim back one of the red surfaces and make a BlendSrf between the two, then mirror the trimmed surface and BlendSrf

Radius Issue.3dm (113.1 KB)

Here is the basic model.

Also, it is important that it is a radius so patch and a blend will likely not work so well. We currently use a Sweep 2 rails for keel radii, but there seems to be too much 2D work with sections. It also makes rebuilding surfaces laborious, especially when we are running hydros… a pain to get a quick “watertight” model. I would imagine there has to be a cleaner way?

Lastly, filleting the surface forces you to determine the radius. In this instance, I do not want to input the radius in that it is changing every inch along the keel.

I don’t follow. Yes, it is the centerline of the hull and the quadrant of the radius I wish to use. But how can I use the edge by definition? What commands uses that?

By that I mean you re-create your side surfaces, so that this curve is the edge and not the beam-curve. Then mirror and create the other surface between them. Blend may be useful, however I suggest you create new surface between them with the same amount of control points and degree.

Hello - if you Pull the green curve to the surfaces you’ll have the rails - you can use VariableFilletSrf and adjust handles to get close - you can be more careful than me, but:
Radius Issue_Maybe.3dm (234.4 KB)
Is that even on the right track?


In my opinion it all depends on what is going to happen with that surface afterwards. In naval architecture the quickest solution is not at all the correct one. Some software don’t like joining surfaces with different numbers of control points or not matching degrees of the surfaces.

I don’t think this is something you can do in Rhino. Basically what you need is something that is called "full round fillet’ in SolidWorks. See attached:

Radius Issue_full_round.3dm (927.2 KB)

I would not accept this on a ship.

me neither, but this is exactly what @bstoddard asked for: a fillet that runs through the surfaces and the green line

I think this is due to lack of experience. Either with Rhino, Nurbs surfaces, or hull design.

Thank you Gijs. For my purposes here, I will happily accept it. How did you do that?

Hello - sorry, I completely misconstrued your question before - here is another attempt, in case it helps, but made in the V7 WIP with the test command TestFilletSrfToRail
(half at a time)

Radius Issue_Maybe2.3dm (190.0 KB)

And one using some of the cleaner-surfacing options in that:
Radius Issue_Maybe2_Cleaner.3dm (145.4 KB)


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the example I posted was done in Solidworks. Result is I think Identical to the result posted by @pascal in Rhino 7 WIP, the only difference being that you end up with the Fillet split in two halves

Thanks for your help. I am always surprised by how active these forums. I really appreciate all of your input.