How to create section frames for a hull in Grasshopper?

Hi Everyone,
Im quite new to Grasshopper, but use Rhino 3D in my daily work. Up until this point Im using Rhino when creating hulls, but I would like to see if I can do this more efficiently in Grasshopper. I’ve watched beginner tutorials and have played around a little bit with different types of arcs, bezier curves and tangents and so forth, but find it quite hard to get a nice smooth curve. Does anyone here share my interest for hulls and have some suggestions? Each section curve along the lenght of the hull the curves has a different tangent in the end and this is quite time consuming in Rhino and my hope is to find a quicker way to get nice smooth section curves. I attach a image showing section curves on the port side (left) of the hull. My hope is as I said to quickly create these section curves and loft it and be able to quickly change the shape of the hull surface. This is relatively time consuming in Rhino. Thank you very much in advance!

Best regards,

Can you post either a Rhino file example or GH file example?

There are so many things you can do to create good curves in GH but it can be tricky to get a nice interface that gives you the control you need.

I’ve tried GH for making surfboard shapes which can be similar to hulls.

I can take a look later but I’m sure someone on here can help.

In Rhino I create a fair surface with the desired shape using the minimum number or curves required, and then create section curves where needed using Contour and/or Section. The surface is primary and the curves are secondary.

Thank you for the reply! Very interesting, it is the opposite approach that I have used so far. I’ve put quite much time in creating nice smooth curves where upon I create surface(s) with curve network command. Do you use subD for your approach when shaping the surface?

Thank you for your reply!
Sure, surfboard or sailboat hull, more or less the same. Yes, it is the interphase in GH that Im unfamiliar with and would like to get recommendations for. I can definitely post a simle file with basic curves for GH. Will do it later.

There are many ways. It’s usually best to use as few curves as possible, as explained in this verbose bit I created six years ago:

More here:

And you might find this utility useful for obtaining hydrostatics for hulls. I use a more current version and need to update that web page.

I posted this image a few days ago in another thread - all done with Grasshopper. 21 meters, 10 tons.

One more:

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This one creates curves for the sheer and chine, then creates straight lines at six stations, fillets the joined lines to get radius chine and sheer.

P.S. This hull is rotated slightly (for a reason) so doesn’t exactly match the white station curves.

P.P.S. Proas go both directions so the main hull was rotated 1.5 degrees to windward. Here is the end view again with rotation removed:

Yeah listen to David. No matter how long you spend fairing your curves, the resulting surface will have weird waves between the sections, which will lead to adding more unnecessary sections. NURBS are too precise for that, if you will. If I had to make anything like a boat hull, I would just point-edit a plane (or planes.) That’s how you do almost everything once you get the hang of this stuff. That’s how they model cars, that’s how they make iPhones, anything where surface quality matters, not drawng a bunch of cross-sections and then trying to find a way to fill in between them.

Hi Joseph,
Thanks a lot for the several replies with pictures and the added video! Yes, as few curves as possible is also my experience that results in a smooth fair hull. I will have a look at your video and the GH setup.

Hi Jim,
I agree that you can spend to much time on fairing curves and I try to use as few as possible and generate as large surfaces possible. In my work I frequently patch and fix not so nice hulls, made in rhino and then solidify them. Many professional designers still create hulls in the old fashioned way of stitching many, many small surfaces in areas of large curvature, for instance in the area of the bulbous bow and in the stern region around the skeg(s). With R7 and subD I however see larger surfaces now.

I’m a little skeptical about the precision of this approach, though I found this 12 year old video demonstrating how it’s done: Not much point in using Grasshopper for it, eh?

SubD certainly changes everything, as did T-Splines so long ago, but I have little experience so far with either one. This two+ hour video shows R7 SubD being used on a couple of boat hulls:

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I actually attended this webinar, although I didn’t had a webcamera. The subD is truly amazing new feature, but the setup that you @Joseph_Oster showed in your video makes it possible to quickly design new hull shapes and I really like that about GH.

Posting your email address on a public forum is an invitation to spam. I would remove that and use PM instead, if necessary, though I prefer to keep my forum contributions public.

That code was written six to seven years ago in R5, when I was just getting started in GH. It still works (I just looked at it) but is terrible in some ways, like renaming standard components instead of their outputs and inputs, for example. Even a screen image of that code is nearly useless because so many components were renamed. :man_facepalming: So I’d be embarrassed to share it, explain it, defend it, etc.

How about if you start your own version and post it in this thread, then we’ll make suggestions? Start by creating the sheer curve (there are many ways), then add a section curve (or two), then add the Sweep1, split, etc. You’ll learn much more that way instead of copying my old mistakes.

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Hi Joseph,
Posting my email was maybe not that smart … thank you!
Ok, :slight_smile: I see, no problem at all. I got the idea of a possible setup, when looking at your video and I totally agree, that you learn more from doing it yourself from scratch, so that is what Im gonna do. I had a look at the list of parameters that the hull assistance in Orca 3D provides and I will simply create something similar to the hull assistance in GH and also include the hydrostatics so I can follow it in real time when modelling. Good idea, I will definitely post my progress here.

All my hulls are double-ended which probably isn’t what you want anyway. The many subtle details are where learning really happens and you don’t want to miss that. Like the way Perp Frames twist along a sheer curve, which can be very annoying and can be “corrected”, unless you like it. I’m still learning how to make fair surfaces, which can be insanely difficult, even when lofting just two curves together…