Full Version: Lofting a boat hull.

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I see no other way of getting the frame data in other than tracing it with the freeform curve tool?

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Hi Gord,

re:
> I see no other way of getting the frame data in other than tracing it with the freeform curve tool?

Yes, that's correct you would need to trace that, there isn't anything like a bitmap image to structured curve automatic tracer if that's what you mean.

Do you happen to also have any 3D exterior photos? The part that is not so clear to me is the stern. It's going to be difficult to make the stern station to be such a shorter curve than the rest. That will add stress to a loft surface when one section is suddenly significantly different in size from all the others. So one thing to do in that type of situation is to make the initial surface to be extended so that it is more regular and then you cut pieces of that extended surface away using Edit > Trim or booleans. You usually want to do that kind of extended and regularized surface with cuts later on rather than trying to build the initial surface directly to an irregular boundary.

- Michael

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I get the same issues on a real model having to get the material to suddenly sharpen up at the stern!

G

Image Attachments:
Screenshot 2019-12-09 at 09.50.51.png 

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from what i can tell your method is right. it's just the loft takes the structure of your curves pretty much literally. you can use some loft settings to basically curve fit them, but then you loose your design intent. what i saw with your curves is the one near the middle had a much different structure than the others. so this throws the loft way off. the reason i brought up the sharp (90 deg bends) is that really makes the curve fit have problems. it makes waves in them. so it's best to not have a 90 bend in any of the profile curves. one thing as a newbie you might want to get familiar with is the rebuild command. that functions a lot like the loft options. so once you get one profile curve in, try the rebuild command to see what it does to your curves. but, if you don't want to loose any design intent, you won't want to use rebuild or the loft simplification options. in that case you need the profiles to all be structured fairly similarly. which means the profile curves all have points and breaks in roughly the same positions.

i attached a pic, showing what i mean, about the curve structures affect on the loft command. when the curves have more closely related structure you don't have a loft that looks like that.

i attached a second pic where i took out all the sharp 90 bends and did a rebuild on all curves with 20 points and a 3rd order curve fit. you can see the loft is nice and goes end to end like you want.

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Hi,
did some work on the curves removed the right angles and added some extra curves at the rear.
I extended the loft curves and then used the loose loft trimmed top to shape required.
Having then created a solid Boolean diff the rear and filleted.
Not sure its accurate enough for your model ?
Cheers
Barry

Image Attachments:
Screenshot (354).png  Screenshot (355).png 

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Thanks! Looks good.

First, where is the rebuild command, how to I get that? What does it do?

Also where are the 90 deg bends? I wasn't aware I had any.

So, I need to trace the frames using a similar number of points on each one. I need to extend the frames up more, then chop it off at the end to get the bulwark rail shape.?

G

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WOW! Thanks Barry!

That's what I was trying to get.

Where did you get the extra curves from? How did you do the curve work, and why?

I wish someone would do a stage by stage tutorial of this sort of thing. I find it much easier to follow if I can follow along each part as it's being done.

Thanks!

G

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someone else will have to say where the rebuild command is for MoI v3 and v4. i'm not sure. i know it has one though.

the 90 bends are at the bottom on various profiles. not all of them have them. i would probably add in a radius to them if it where me. unless they are really there. so if you have two different pieces of wood for instance. but in that case i would create the flat sections separately from the curved ones.

you don't have to keep an even number of points. that might be impossible in some cases. but if you can do it, it's worthwhile. with the propellers and fan blades i make, i can keep an even number of points. so the lofts work out good. your ship hull is a lot more complicated. you might have to rely on the rebuild command. the only thing is, it's a curve fit. so you loose a little bit of accuracy. however, the loft is also a curve fit. so you can loose accuracy there too. it really depends on what profiles you are working with. for me, i can get the loft to exactly match the profiles. when i was working with your curves, that didn't seem possible.

you had some tricky areas and it looks like Barry got much better results than i did. i got stuck near the rear. his tips seem like good ones to try.

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Hi Gord,

re:
> First, where is the rebuild command, how to I get that? What does it do?

The rebuild command doesn't have a button in the UI, you can launch it by either setting up a keyboard shortcut or by typing the Tab key to put focus in the XYZ input box and then type rebuild and push enter. Some info on it here:
http://moi3d.com/3.0/docs/moi_command_reference10.htm#rebuild

It probably isn't needed for your case here, Loft will usually already incorporate a rebuild of the profile in it anyway.


> So, I need to trace the frames using a similar number of points on each one. I need to extend
> the frames up more, then chop it off at the end to get the bulwark rail shape.?

I wouldn't worry about the similar number of points so much but some of the key things are try to keep things as uniform as possible so extending things to have similar lengths is better than having them suddenly become shorter and irregular areas are better to cut out afterwards instead of attempting to build a surface directly to a detailed boundary rather than a simple boundary.

Barry's example above of making a simpler extended surface and then trimming away some areas is good, and also I recommend using Loft style = "loose" like he mentions as well.

The "loose" loft style will only force the surface to go directly through the start and end profile. The ones in the middle will generally guide the shape but not be forced to go directly through them. This makes a very much more relaxed and smoother surface at the expense of accuracy. You can increase the accuracy by having more profiles. With normal non-loose loft it is easy to make a very stressed and lumpy result, with regular loft you need to use fewer profiles to reduce over constraining the surface.

If you need more accuracy than you can get with a loose loft then you're probably looking at needing to divide things up into many surfaces instead of trying to use just one single surface. This increases accuracy but now you will have a different problem that it's hard to make each surface fragment to look like it's all one smooth surface. It will generally take a lot more time and effort to try that approach.

- Michael

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Thanks, good info here.

I think I'll try again from the lined drawing and retrace from square one. As I said, this was a test piece anyway. I was told by an America's Cup yacht designer '..never be tempted to keep a mistake just because you took a lot of time making it'...

G

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Hi,
ths method developed by Zarkow may be a better option.
You will need 3 scripts to do it.

1) Michael's ReconstrucCurve to convert curve profiles to polylines.
I used 12 points in my convertion.
Straight loft the polylines to get a faceted surface.
You will need to trim this surface with the polylines to be sure the
facets are not longer than distance between the polylines then re-join.

2) Run Max Smirnov's SubD Classic this will allow point manipulation if required.

3) Finally run SubD beta 9 again this from Max Smirnov.

A free Hull software mentioned on this forum is Freeship but I haven't used it.
Finally Zarkow as posted some video's on the forum showing his method.
Cheers
Barry

Image Attachments:
Screenshot (369).png 

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Cool method that can be works also for cars! ;)

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Looks good, thanks!

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As you are talking to a Computer User Non Technical here, how do I get scrips and what do I do with them please?

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Max Smirnov Scripts:Plugins are here
http://moi.maxsm.net/media/files/

Generally you put them in the commands Moi's folder
and call them by a Shortcut or Pressing Tab then write the name of the plugin (without space)

Reconstructuct curve is here --- manual inside ;)
http://kyticka.webzdarma.cz/3d/moi/#ReconstructCurve

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Barry. I got those scripts and put them into the commands folder. When I type ReconstructCurve into the size box, it all works! However, nothiong seems to happen with the SubD things though. Where did I go wrong please?

Tx G

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Hi,
select surface before activating the Subdiv_beta9 script.
Cheers
Barry

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I design sailing yachts (among other things) and this was the first model that I tried with MOI. There is a traditional way of designing a hull, which is called a "Lines drawing". It is, in fact, a bunch of lines (curves). The problem is that the drawings have to be in two dimensions, but the object being designed is three-dimensional. For various reasons, CAD programs have been very poor at making lines-drawings. It is quite easy, in 3D, to make Something that looks like a hull. But if you really design these things, that's no good. You need to really control the shape in every detail, and this is where things get difficult. If you know what a lines-drawing is, you know that all the curves that define the shape have to intersect. But using polygons, you do not have control over the actual surface and lines on that surface. I though that NURBS would be the solution, but the trouble is that the control points are not on the curves. So if you have two curves at more-or-less right angles, and you adjust one of those curves, how do you get the other curve to shift, locally, and intersect the line that you moved? When you have 50 lines to contend with, and a multitude of intersections, this is a Big Problem. I did find a solution and I can make a fine lines-drawing in MOI, but the method is too complicated to explain here. What's important is that I do not do what others say to do to make a hull. I do the design the traditional way; which for me is the only acceptable approach. Here is an example of my method.

Image Attachments:
Sailer btm fwd.jpg  Sailer btm rear.jpg  Sailer top aft.jpg  Sailer top fwd.jpg 

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Seems a cool result!
Of course will be fine if you can explain your method used with moi in a decicated thread!

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The trouble -- or part of it -- is that I'm doing this by the traditional method, i.e. a "lines-drawing". I think one needs a few years of work on this method, with paper and pencil, before adapting the process to MOI. If you don't know how to make a lines-drawing, you have nothing to go from, or to. If you do a google: "yacht lines drawing", you will find some examples of these. I looked and couldn't find what I though was a good example, so I'm not offering anything here. But basically, you design the hull entirely in two dimensions, with sections corresponding to 'x', 'y', and 'z' planes. As I said, the trick is that all the points which correspond to intersections -- in three dimensions -- must be coincident. Once you have all the sections in 2D, you can select, move, and assemble them into the 3D form. Then, 'Network' will add surfaces. BTW, you need those 2D sections in order to figure the displacement (which we usually do using 'Simpson's Rule'). And if anyone is really interested in this subject they should get a copy of 'Skene's Elements of Yacht Design'.

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