Full Version: Lofting a boat hull.

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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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Hi Tim,

It seemed to me the original poster was working from a line drawing of some type. Don't know if it is the same as what you are using though. One thing I did notice though is the issue of the curves not matching up. Moreover, they were off by quite a bit in some places. It looks like he digitally traced them and got some really funky results. In places where you would have a line, a radius, and another line, it was just one huge curve. You couldn't make it like that if you wanted to using normal tools. So I have to believe it was some sort of conversion. Other places where a fillet would be logical was not a fillet. But some sort of curve. That is why I was saying the profiles were not quite right and needed fixing. But other more advanced forum users where able to work with them.

I have to agree with you though, I can't imagine this is very accurate. I know with propellers I'm extremely accurate with the points and curves. To get the right aero performance. What you are saying makes me think you are doing the same to get the right marine performance. I'm not sure what the original poster's intent was. However, most of the people that post here aren't worried about engineering. There methods are advanced in terms of modeling technique but terrible from an engineering point of view. Burman brought this up years ago and got his head ripped off. He's since disappeared from here mostly, which is a shame.

I have found that most of the questions on the forum relate to a lack of understanding of the real world. If you use Rhino and MoI like you would build something in the real world, there isn't many questions you run into. Most of the people here are coming from Poly modeling though.

Anthony

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Hi Tim,
Your correct the method I mentioned is not accurate enough for an actual sea going vessel only a visual model.
The method you mentioned of producing curves in 2d and adjusting into a 3D curve using line drawings can be achieved in delftship, Freeship and Polycad softwares.
Cheers
Barry

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Thanks Tim. I am indeed very familiar with lines drawings. I'm a professional modelmaker and specialised in yacht models for various well known designers. I may be having to do a model of a tug and a barge for the owner who is having them restored to a luxury level. I was hoping to transfer those skills to MOI and set up the lines in exactly the same way as I would make a plank on frame model and then get it made on a CNC router. All is good until I discover you can't sand bits to shape very easily!

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HI, I'm developing often hulls and boats, and the lines plan are god for building and not for modelling, for a better result I use a few sections and a network surface, or a 2 rail sweep.

And other thing consider only an half boat when you make the model, is bit complex making the keel and hull both in one surfaces.






Here a simple Dinghy made with loft.. but in IGES, the Moi version has no more sections.

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