# Best Free or Low Cost Marine Design Software? (2011)

Discussion in 'Software' started by Admin, Jan 9, 2011.

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## Which free or low cost hull modeling program(s) do you use?

2 vote(s)
3.3%

3 vote(s)
5.0%

4 vote(s)
6.7%

2 vote(s)
3.3%

19 vote(s)
31.7%

19 vote(s)
31.7%

22 vote(s)
36.7%

1 vote(s)
1.7%

2 vote(s)
3.3%

2 vote(s)
3.3%

2 vote(s)
3.3%
12. ### Other (please post below)

5 vote(s)
8.3%
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### alanrockwoodSenior Member

There are some interesting approaches presented above.

My strategy is somewhat complicated. I won't give a full and detailed description, but I will outline my approach. I define the intersections (particularly "stations" for transverse frames and "diagonals" for longitudinal frames) and then I export the offsets.

At this point I have the outer border of the frames, the parts that will touch the hull. However, they are just lines, having no width. I then import the data into PsiPlot, which is a plotting program that also has a lot of mathematical capabilities. It this point I generate the inner borders of the frame members.

This step is not easy to do, partly because it involves lots of operations. Typically, the first thing I do is use PsiPlot to calculate the distance between successive points on a given station or diagonal. Then I perform a running sum, which basically gives the arc length of the station or diagonal, divided into a series of segments, each segment corresponding to successive points. This parameter (the arc length information) can be used as a parameter to parameterize the curves in the offsets files.

At this point I can use PsiPlot to calculate certain derivatives with respect the the arc length parameter. This information can then be used to build the widths of the various members using certain vector operations. Along the way it is sometimes necessary to interpolate the curves onto a new set of points, partly so certain points on certain frame members can be aligned with certain points on other frame members. This is necessary for several reasons, one relates to building the widths of the longitudinal frame members, and another relates to building the notches into the transverse frame members that mate with the longitudinal stringers.

All this is very cumbersome and time consuming, and there are a lot of subtle traps that one can fall into.

One thing I haven't figured out is how to take a twisty-curvy stringer and flatten it (develop it) so it can be cut out of sheet or plate metal.

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### Perm StressSenior Member

All this description sound rather complicated to do (and with traps ... ).
In my practice, it is much easier and straightforward to make Delftship model to inner surface of hull.
Stringers no coinciding with orthogonal planes or 45 degree diagonals, could be modelled in Delftship as surface, protruding the hull with attribute "developable", paying attention they are indeed developable; Delftship has a function to find intersection of two surfaces. The downpoint is you need much more (I mean at least 4-5 times more) control points for "stringer" as for hull itself, over given area, to keep discrepancies within millimeter or so. Than (not possible with free version) develop it and export as .dxf and use for further design process.

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### daiquiriEngineering and Design

That's what I intended when I said that it can't be done in a simple way. Both methods described imply an export of either frame offsets or lines in another software and then finishing the job there.

This sounds very interesting. :idea: How do you find an intersection of two surfaces? I have tried to create transverse planar surfaces but I'm just unable to obtain the intersection lines of these planes with the hull surface.

Right now I use to export everything as IGES file and then complete the job with Rhinoceros. That's pretty time-consuming and gives me an unsatisfying feeling of having two half-jobs on the hard disk, instead of a one file with a complete framework and hull plating. If, later on, I have to modify the hull for some reason, it means redrawing the framing from scratch. I'd be much happier if I could finish everything that can be finished in Freeship before exporting to Rhino for detail work.

In this example below I have a hypothetical canoe hull in the layer called "Hull", and the 3 planes in layers named "Fr 1", "Fr 2" and "Fr 3" respectively. How would you perform their intersection?

#### Attached Files:

• ###### Planes.jpg
File size:
45.7 KB
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2,021
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### frank smithSenior Member

daiquiri ,
The intersection tool worked for me. I labeled hull 1 layer and the bulkhead another , then added the intersection. Of course this requires fairing of the hull again and cleaning up.

The bulkhead section is a new trick to me , thanks . I made it and stored it as a part. How did you do it ?

I can see how frustrating trying to do the things in freeships can be , but I use it as a sketch tool , to kick ideas around .

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### frank smithSenior Member

Another problem I found is that if the hull is not closed off , removal of bulkhead out side the hull cant be done easily .

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### frank smithSenior Member

Now I moved the transverse section out of the hull and the intersection that i made previously remained in place. So I guess using this section as a tool you can just move it to where you want a frame intersection . Ok but you still have to fair the hull again .

Now I a limited to intersecting 2 layers unless i relabel the hull again .

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### DCockeySenior Member

I'm interested in why you use FreeShip when you also have Rhino? Is it for the analysis functions in FreeShip?

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### daiquiriEngineering and Design

Yes, I find that Freeship is a very fast and productive tool when design spiral iterations have to be checked against hydrostatics and powering requirements. The results of shape modifications can be checked in a blink of an eye.

But I guess it could be also a matter of my personal mental inertia. In the past I've been working in an engineering firm which uses UGS NX (which is the most complete and well-done software for 3D mechanical design I've put my hands on), and have switched to Rhino not very long ago. So I'm still not sufficiently productive with Rhino, contrary to Freeship which I've been using for various tasks for several years by now.

Apart the said problems related to the design of structural details, Freeship gives me a very intuitive and fast control of the hull shape parameters. And the plate development tool was precious even for some non-boat-design jobs.

Cheers!

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### daiquiriEngineering and Design

That's the problem. After the creation of an intersection the hull shape changes... Slightly, but enough to piss you off after all the efforts put into fairing.

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### frank smithSenior Member

I guess you have to export it into a different cad program , and back to square one.
That being said i agree that Freeships is very quick way to play around with ideas.
I am trying to export to schetchup as it is evolving rapidly , and I want to learn it.

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### Perm StressSenior Member

You, like many other ship designers (including me) dream about totally parametric design tool.

I am told that some systems do parts of this. Like Nauticus, Ship Constructor (latest versions), Tribon. I have no personal experience with them, only repeat waht I am told about by colleges.

I use Poseidon from Germanisher Lloyd for structural design and modeling of structures (for me, it is often faster as to draw in AutoCAD, even with cross-section-limited geometry description capabilities of Poseidon). With what I have worked with, it is as close to parametric as I did encounter . With proper description technique, using as little as possible geometry definition in mm, and tying everything to X, Y, Z, frametables and other elemnts, as possible, you can sometimes do wonders, like moving upper deck and superstructures up 0.5m of fully modeled passenger ship in one hour. Unfortunately, design vise, Poseidon export capabilities are limited to pictures to pre-determined scale, so all drawing work is still left to the designer.

"In this example below I have a hypothetical canoe hull in the layer called "Hull", and the 3 planes in layers named "Fr 1", "Fr 2" and "Fr 3" respectively. How would you perform their intersection?"

This is very easy. To make it easy, control net on planes Fr 1 ... have to be much more dense than on the hull you want to intersect. If control net is not dense, you can make it denser in various ways, as described in manual. Than go "edit/point/intersect layers" and specify intersection you want.
However, it is a one-way ticket. As you modify the hull, intersection will not follow.

To say my opinion, Delftship is not intended for any structural design work, and there is no wonder it is not capable to do it. It is easy to work ship surface modelling tool, various hydrostatics, including probabilistic damage stability according to SOLAS calculation tool. It is possible to do some 3D "sketching" in it. But not much more.

Last edited: May 16, 2011
12. Joined: Sep 2009
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### Perm StressSenior Member

To not change the hull, intersection has to be done the following way:

edit/point/intersect layers:

intersect Fr1
with
Hull

now, new point(s) will only appear in layer Fr1, and Hull will remain untouched. And new points will only appear where control edge of Fr1 intersect Hull. If there are no such edges, program will say "no intersection found", even if surfaces actually DO intersect.
Of course, as you modify the hull, new control points thus created will remain in place, not follow the hull.

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### daiquiriEngineering and Design

That's what's happening, and I don't get why. I'm used to how software like solidworks, UGS, Rhino et al. perform the intersections, this looks so odd to me.

This is a simple example I've created to try this function:
View attachment Canoe-like boat.fbm
It is a Freeship .fbm file. I'd be very gratefull if someone checked it out and told me what did I do wrong... Why cannot it find an intersection of vertical planes and a hull wall?

Cheers!

P.S.
I believe this has got well beyond the off-topic... So I'll create a new thread about this issue. The moderator will decide if the previous posts should be moved there.

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### Perm StressSenior Member

To daiquiri:

in this file I did modify Fr3 to have control edges intersecting hull and made an intersection. To point out, intersection line is made a knuckle, and a curve added. In order to have proper ends of this intersection line, certain Fr3 control edges would have to coincide with keel and deck lines.
Now you can delete parts of fr3 you do not need.
However, all this trickery will not go far beyond creating nice looking views in Freeship.
I for one, would not use this for anything requiring iterative process.
And would not use this kind of lines for design, except when say, bulkhead is not parallel to one of the four planes freeship can make intersection lines -frame, waterline, buttock, 45degree diagonal.
If I need to use this intersection for further work, I would make the control net on fr3 incredibly dense -due to the nature of surface description in freeship , any two lines will only be the same, when all their control points are the same, if this is a knuckle; if this is not a knuckle, surfaces containing said lines will have to be the same to the nearest knuckles. Otherwise we are in brute force situation -very dense control net on intersecting surface, loosing core benefit of delftship/freeship -few controls for any size of surface.

For possible results example, you can check "loyalist" -gaff schooner in Delftship site downloads section.

#### Attached Files:

• ###### Canoe-like boat mod.fbm
File size:
20.4 KB
Views:
368

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### alanrockwoodSenior Member

openboat?

Anyone ever heard of the openboat software project. From what i can gather it is a fork of the FreeShip (Free!Ship) project.

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