Hull Design

I have a little problem. Maybe you guys have a better solution to this bulbous bow design. It’s just a quick sample. When I use 3 curves for bow shape ( loft – smooth ), I get little distortion at the start of Deadrise. If I could stack all three curves end point on top of each other transition would be smoother but rhino won’t let me. So what other options should I investigate. Any advice is highly appreciated.
Sample file attached.
Thank you

Hull_Sample.3dm (77.3 KB)

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For some reason, I can’t download your file. The link contains the characters </br> and even if I remove that, it still does not work. Could you try uploading the file again?

Hi Adam,

Stacking control points is a bad idea. Most hydrodynamic software tends to use sections to calculate volume and the maths goes a bit screwy when faced with zero separation of control points.

Do two of your lofting curves have the same end points? i.e. the bow profile and the next section back, if so then a small separation might fix this.

Have you read Rapid Ship Hull Modeling by Gerard Petersen?

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I think what you see is an artifact of the render mesh.

I see you are doing everything right with regard to my previous reply but the tangent of the lines at the keel is discontinuous.

If you want it to be fixed Set the Points of the first two control points in each curve to the same Z. (SetPts)

Curvature Analysis before:

And After:

Stacking control points will make a degenerate surface that will cause you many problems (for instance you won’t be able to get a good offset surface).

One way to avoid a degenerate surface is to make your loft go past the center line and trim it back to the center line. You can use history on the loft and edit the input curves to get the shape of the bow you want. See enclosed file:

Hullx.3dm (93.2 KB)

Thank you guys. Appreciate your advice. If I were free to change the bow shape any way I like that would be an easy fix, but I don’t. Please look at the profile image. There is a sharp transition between keel and Deadrise. It must be preserved. This is what makes it difficult for me.

Menno I’m not sure why you’re having problem downloading my file. Might be host issue. I’ve attached sample file again. Hope it works.


Hull_Sample.3dm (77.3 KB)

Hi Adam- Rhino will let you stack end control points of the inputs for Loft if all the ends are truly stacked up. If only some are, then it will force ‘straight sections’ lofting. In your file, the bow curves cross one another but do not atcually touch at the end points, by the way.


Appreciate clarification Pascal. That was my original point. I can’t use loose lofting when stacking end points of only 3 bow describing curves. I would have to stack all 7 curves… Obviously this won’t produce hull shape I’m after…

I think you have too many curves in close proximity influencing that area with Loose Loft.

If it’s so important to maintain shape why aren’t you using Normal Loft with better defined curves?

I’m trying to recreate historic ship hull based on a few hand drawn hull stations. Don’t have any offsets. Using loose loft in conjunction with history is the most effective, in my opinion, way of getting overall hull shape approximation. When I’m satisfy with this shape, I would use point editing to refine it.

Lei può fare automodelli personalizzati 3D?

Hi Andrea,

what kind of toy cars…? To be honest I don’t have too much experience working with automobiles.

Sorry for the delay but it took some time for the problem to perculate through my brain!
From my point of view it is a practical issue.
This is the connection (most likely rivetted) between the forefoot forging and the shell/keel plate. In lofting terms it is a knuckle and not fair.
It was a frequent conflict between a design office lines plan and the full size lofted lines.
To be fair all sections must be fair. You will also have the same problem with the skeg/stern forging.
Traditionally the problem was left to the platers to bodge on site.
Rhino is trying to produce a fair surface but cannot.

Hi again,
I looked at the curves and realised that you haven’t included the side of keel.

There is a flat of keel which, depending upon the size of ship, is 3 or 4 ft wide amidships tapering to nominally nothing where the forefoot forging starts. Note that the forging is used because the lack of space would preclude access for riveting.

This simplifies the lofting.

However, some waterlines are needed to define the bow below water. I have knowledge of bulbous bows but not ram bows but would guess that a curve of centres would have been used. this would mean a stem radius of 3 or 4ft at deck down to nominally zero at the waterline and up to a practical radius below water.

I tried developing the waterline endings by eye and it would appear that the stem profile is very dependent upon the ram shape and the first section.

I’ve attached my attempt to illustrate my thoughts. I guess that it depends how close you are going to look at the model.

I hope this helps

Hull_Sample 001.3dm (95.8 KB)

Thank you guys. I didn’t include keel edge because in my sheepish attempt at getting easy solution I was really hoping somebody already came across this type of problem and might offer something similar to Rapid Ship Hull Modeling by G. Petersen…

Strobe, how did you created your surface…? Loft and than rebuild…? I can’t recreate it using curves in your file. Anyway it has to wait till Monday when I have more time to experiment.

Since my project is not for working hull but display only I won’t be using welding, riveting or forging. More like cnc milling and 3D printing. Still very interesting comments. Appreciate it. Hopefully I can translate it into rhino methodology.

I didn’t realise that I had two logins!
The surface was made with surface network and then rebuilt. There isn’t sufficient data to warrent true lofting.
The rapid hull modelling is of more for concept work rather than the precision of lofting.
To get a decent model you should work full size and in the units originally used, I assume that these are feet.
The lines should be developed using both frame stations and waterlines. This would help identify whether my concerns about the hollow around the first frame are valid or not.
If you wish contact me privately and perhaps I can help more.

Shameless plug, but here goes. In my Modeling in Rhinoceros for Marine Designers tutorial series I discuss modeling just such a bow, beginning with a flat surface. The whole tutorial probably takes an hour to complete, but the hull can be modeled when you are not following directions in about 20 minutes and you have complete control over tangency at the point in question.

Worth a thought.

Strobe, thank you for your help. Private email sent.
Cestes, appreciate heads up. I just ordered your tutorial. Probably will follow with Rhino Offsets plug in later on if it works inside 5.0

well I tried a quick sample based on your one plane tutorial. My surface will require a lot of tweaking to make it fair but at this moment I was more interested in seeing how the transition from keel to stem Deadrise would look like. And what I’ve got is basically the same artifact as with lofting. Which is not that surprising since in both cases rhino returns pretty much the same type of surface… am I doing something wrong here…?

Hull_Sample 004.3dm (84.7 KB)