Do CAD format Boat Plans still require Lofting?

An interesting debate. It also clearly shows where posters with boat/shipyard experience shines through compared to those with just an “office” based or “amateur” environment for experience.

Both PAR & Gonzo have nailed it, several times.

One needs to understand what is lofting and why, and does a computer program replicate this and then how is the boat being fabricated.

In my world, i.e. larger boats, 15-70m size, all of the above arguments/debates have been doing the rounds for years. With ever increasing sophistication of 3D geometry for starters, but this still only tells part of the story.

What is it one wishes to do?....simple…build a boat.

The 3D hull, that has been faired in the 3D world by a programmer/user, will not have the same eye nor experience of an experienced mould loft person. At my previous company we had endless software companies visit us to show us their latest fancy tools for hull modelling. All looking great and fancy on a PC screen, even when projected onto our very large board room monitor.

Yet every single time we asked to see examples….as a "typical" hull was shown and rotated and twirled about…wow, came the cries of the young graduates and lesser experience DO. And every single time, from the back a small voice was heard. “er..sorry but those lines are not fair”….out would come our ex-mould loft now CAD draughtsman. He would immediately point out where the 3D hull was not fair. It took some explanation before the software salesman had to admit, yup…there is a minor error because the software was not able to fair it correctly, yet no one had ever noticed it before.

That’s one side of the coin.

The other, is that once the parts have been plasma/CNC cut, what do you do with them? In my world, we generally (as 90% of my work is metal 10% composite) weld the boats together. And in general, most of my work is with aluminium. What occurs after welding…shrinkage/distortion.

So these nicely cut 3D parts, are they still fair?

This goes back to PAR’s point about, what the purchaser of the plans does ..well, it’s up to them.

We would place the welded frames over a scrieve board. This is a 1:1 body plan of the hull burnt onto a 25mm thick steel plate. The frames are then offered up back onto this scrieve board to perform a final check, i.e. is the now fabricated frame still correct and fair. If not, it was corrected. Below are 2 typ examples:



So, the fairness of the parts you receive is all about how accurate the hull lines are, i.e. its method of generation and the experience of the user and the method of manufacturing. Everything in-between is your choice and has no bearing on whether the lofted part is hand or computer generated, since the final accuracy is still dictated by your method of manufacturing. No matter how accurate a lofted part may be, if your methods of manufacturing/skills/experience/tools are inferior, you will still end up with a poor hull shape.

 

Any experience with a hull faired on a computer by "experienced mould loft person" who has taken time to learn to use the software?

 

Is that a question or a statement?

 

That is absolutely true but the fact that the next step in the production process, do not work well, does not justify the lost of rigor in your work. Each phase of work should be done as accurately as possible, regardless of the other. If welders weld not correctly, the solution is not to diminish the accuracy of the smoothing, but to teach them welding and / or to buy them suitable welding equipment.
It scares me to think that in a large shipyard had to check each cross section using templates drawn on the ground. ! It's crazy to think! (Have I he understood it wrong?)

DCockey : "Any experience with a faired hull on a computer by "mold loft experienced person" who has taken time to learn to use the software? "
When implanted a CAD-CAM system in one of the yards in which I worked, of course, was elected the best manuals lofters to teach them the new procedures. Was a success. From a group of 15 people only one had to leave not to be able to adapt.

 

Yes...

 

I'm very sorry, my friend.
Recall what is wrong in my words.

 

I think you misunderstand my comments.

If you take 2 parts of a web, butt them together to make one complete transverse frame, and then weld a rider bar all around the periphery to make the frame into a Tee....will the finished frame be the exact and correct shape as on the lines plan?

 

An experienced "eye" with the requisite 10,000 hours under one's belt, can do great and efficient work with modern tools but the most sophisticated tools can not make up for the wisdom needed to inform critical decision-making. This can not be automated by using clever algorithms alone.

 

Yes, if not exact, at least within acceptable tolerances. (Incidentally, I´d weld first individual tires to each of the three parts of the ring, before welding together to form the ring). The structure of a ship is built, as you know very well, based on a large number of sub-assemblies, each made ​​from a different site and different personnel that are then assembled to obtain the big assembly. And it depends on doing things right, step by step, from lofting the hull surfaces, the way up to the final check of the hull. The computer has the great advantage that we can provide a lot of information to check all intermediate processes. Manual work would need months to get the same information that a computer gives us in just days.
I do not want to teach you anything, Ad Hoc, for all this you already know. I try to show the advantages of the computer in case anyone still doubt.

 

Hello TANSL

I'm new to marine tech but I've designed many one-off assemblies that required either TIG or Electron-beam welding and I learned the hard way that proper setup/preparation is the single most important aspect of welding metals, because they always move. I try to minimize the number of welds required where possible, and/or anticipate the error and design for a correction procedure post-weldment. In most assemblies, I usually can not count on welding being the final procedure before something can be considered finished.

 

Not with aluminium.

Precisely. Thus, the finished part, is no longer the "exact" shape, and need to be checked to see how far out of tolerance the final fabricated part has become, owing to welding. This is basic QA/QC.

I would never weld up a frame and then erect it without checking it first. Aluminium moves..and a lot. No matter how accurate (or otherwise) you template or frame has been cut.

 

Totally agree.
One of the problems we have in our times is that people think that anyone with a good computer program, no experience, can build ships. This may seem excessive, but, how many people show us a thing that looks like a boat, with great detail, colors, shadows, railings, ... without checking the capacity of that "thing" to navigate, stability, .... But seeking to demonstrate their mastery only with a very nice drawing of something that looks like a boat.
Keep in mind that the computer is a stupid machine that only does what we ask of quickly and accurately. But if we ask for a stupidity, will quickly and accurately. No decisions or fix the errors of "designer", gives only elements of analysis, the user can use correctly or incorrectly.
Another problem is that we tend to believe everything that comes out of the computer, because we have no ability to analyze it.

 

Question, not a statement.

 

I constantly experience this expectation-mindset with undergraduate and graduate engineering students. I also had a utopian view of technology when I was younger

 

tomas, clearly, metals, and especially aluminum, are deformed by heat. So, for example, some cutting machines CNC perform underwater cutting of aluminum parts. Others prefer cold cut with shears or saws. That is, each material has its working procedures. And, of course, upon completion of welding a piece, you have to think about the possibility of crop, modify it, to give it the proper shape thet, in the work process, has been lost.