Do CAD format Boat Plans still require Lofting?

Thank you All for the very useful feedback and Happy Easter!


I do posess some experience with building wood boats.

In the classic design to building process I the builder would scale up the design lines and plans

from their paper scale drawing to full size; and perform the lofting with wood battens on sheets of Mylar.

In the process I am the one who does the fairing eliminating small errors coming frm difference in scale.

Nowadays as the CAD design is performed on small computer screens; but as those CAD software do magnify each line up to a very minuscule detail;

depending on the designer skills and patience and the software he employs;

builder may be delivered CAD drawings wich when printed out directly to 1:1 scale may feature small irregularities.

This is why my question is mostly where does that lofting and fairing process; wich in the past was builders responsiility

where and by whom does the lofting and fairing out the small irregulaities is to be performed nowadays ????


by the builder like in the past?by the designer?


Thank you all and a Happy abd Spiritually Enlightening Easter !!!

 

There is no single, simple answer.

For stock plans it depends on what the designer claims, and how much confidence the builder has in the designer. I recently talked with a designer and builder who sells plans. His plans are intended to be built directly from without lofting, which is what he does when building his designs. But I would not assume all "CAD" plans are suitable for building directly.

For custom designs then whether the builder can build directly from the CAD files depends on what the designer and builder have agreed to.

 

Gonzo,
your post indicates that you are not familiar with computer modeling. I will be happy to answer any questions you(or anyone else) might have.
Lofting, as revolutionary as it was in the olden days of boat building with a rock and a sharp stick , is like sweeping the stairs upwards with a toothbrush, compared to computer modeling.
Screen resolution is inconsequential, in the design process. You are too literal in comparing one process to the other. Of course a larger screen is better than a small one - I use a 24"(main)display and do not feel the need to go bigger than that; using a larger one, sitting at a desk, you start moving your head to be able to see everything - tiring.
The huge advantage of fairing the lines in a 3D computer model is the ability to rotate and observe the 3D curve, or surface from all possible angles; it is possible that a curve looks good in profile and plan, but when you look at the boat sitting at the dock it looks weird as you move along - and that's too late. Being a 3D object, the boat is being looked at from all possible angles and should look good from all of them.
No room here to list, much less describe, other computer tools. Questions welcome.
I happen to work with aluminum, so in my case it is even easier. I only send the cut file to the material supplier and receive a palette of parts ready to assemble - cut to a 64th of an inch - however intricate they may be.
Computer programs also have their own mathematically defined "battens", and they do not break ;-)

 

I disagree in that computer modeling can compare to the eyeball method on a batten. I have a 37" monitor I use for sighting sheers and lapstrake line offs, but this isn't big enough. A sweet batten isn't going to fool you, though lines that seem fair on screen certainly can fool you, in full size. The human eye is quite discerning, being able to see a few thousands of an inch hole in a black card. With some skill, the eyeball method is faster and generally easier. I know several designers that employ these same tactics with certain curves, particularly sheers and lap line offs. Don't get me wrong, you can trust computer modeling, but it wouldn't be the first time I've adjusted a stringer, batten or whatever the designer insisted was perfectly computer fair.

 

We're losing in disquisitions that have nothing to do with the original question. I think it appropriate, at this time, remember what it was: "Do Boat Plans CAD format still requires Lofting". In reply to this with what is my opinion:
- CAD drawings not guarantee any accuracy. As always, the quality of work, manual or CAD, depends on the quality that "the artist" incorporate into their work.
- In general the design drawings are not accurate enough to be used as construction plans.
- Depends on what you ask your designer to get one thing or another. You have to know how to ask and, of course, be willing to pay.
So: if you have not ordered a plane planing forms, is not likely to get a smoothing fairing. In that case, you need to smooth the forms by the method that you like, with computer or visually. But use the procedure for you to have more quality assurance and forget what others, not knowing the means by which you have, we try hard to say which is best.

 

OK,
I agree, the initial question has been beaten to death.
Still, I think this tangent is very much worth of following.
Par,
your issue is similar to the one I pointed out for Gonzo. It is very difficult to judge the curve in profile or plan view, on the screen or even on a large sheet of paper. But going to full size for that is very time consuming(costly).
The old trick here, is to use the foreshortened view; the method developed by the old school generation. They would draw a "squeezed" sheer curve view, as if you are looking at it from the bow(or stern). This point of view easily shows any unfair regions. Years of experience help as well.
Having said that, the "paper" body plan view, which is also a kind of a foreshortened view, cannot be of much help here, because it is very difficult to draw it with enough accuracy on paper, especially if you use drafting curves(which makes it all but impossible).
In CAD however, if you rotate the sheer that looks perfect in profile(even on a gazillion $ huge screen), all unfair regions stand out like a sore thumb.
I have to run now, but can post a visual example later today.

 

Jarek: I am familiar with computer modelling and think that it lacks the experience of a shipwright. A computer programmer does not have the aesthetic capability or first hand understanding of a vessel's behavior I do. Also, people that learn design trusting a computer program never learn what the design should be,therefore can't tell the limitations and errors of a computer program. Lofting to a shortened lenght to exaggerate curves is a good method, but with a computer you are still limited to an algorithm. When I loft, I use a batten of the same thickness or close to the planking's. That shows if a curve will be possible with the planking or not. It works with metal too. Fiberglass has more freedom in shapes so it is not as relevant.

 

And..lofting is one of the pleasures of boat building.

As you layout the lines you can visualize the construction process. You will see the difficult pieces and will be able to mentally plan ahead for their construction or contact the designer for clarification.

You would be surprised how many times professional boatbuilders must contact the designer for clarification after they have lofted a shape.

 

I think Gonzo has nailed it down - it does depend on the experience level of the person behind the machine. Anyone that's lofted has foreshortened things, if only just to make it a more practical drawing. I've seen a lot of computer generated drawings, that were overly complex and didn't consider simple things, such as how a man is going to access a part, during maintenance or other only experience driven consideration. The multitude of modified scarf joints popping up in the last decade, are good examples of this. Keys, dog bones, sloped finger joints and all sorts of unnecessary complications, when all the joint needs is a "lock" to keep in in alignment until the glue cures. Had the designers actually tried some of these joints, they'd had cussed them, as their clients have. Simply put, I've found my structures have gotten much simpler over the years, regardless of the tools I use to create them. This is experience driven and the ultimate key to a good set of plans.

 

Gonzo,
hm, I am a bit confused as to why you use the term "programmer" in the context of boat design. Programmers do not design boats, they design software. I am not a programmer, I have no clue(very little) of how my software has been created, I only use it, and would like to think I do posses some "aesthetic capabilities".
I think you are making a pretty risky generalisation, saying that "people that learn design trusting a computer program never learn what the design should be".
The school I graduated - The Landing School of Boatbuilding and Design in Kenebunkport, Maine, first had us paper draft and learn "old school" design, before allowing us to touch the computers.
I guess what you are referring to might be the case with self taught amateurs.
I have a feeling, I might be wrong, that your computer experience might be from the late 80-ties, when the computers were teething.
Yes, each algorithm has its limitations, but a decent software has so many available that this is not an issue.

 

Thank you all for your answers to my question.

They do all bring considerable light into this issue of what is the next sytep to be expected after receival from builder of CAD format construction drawings.

So assuming in the CAD construction drawings three may still be some small in accuracies or irregularities of the order of say about 0.5mm to 1mm to ; 2mm maybe even 3mm;

And knowing that in the past the builder was responsible for scaling up the paper plan (lofting)
and in the process to be fairing out the small in accuracies

And assuming that the builder should as well take responsibility to perform the lofting&fairing nowadays



How should the builder of today go about this fairing & lofting process?

Because now the builder wont get that 1:20 paper plan;
but the CAD plan that he is
going to me more likely print 1:1

I thing this may be the essence of my question:


How do you suggest in a today Book of " Boatbuilding Based on CAD generated Plans"


the modern Chapter of "lofting and fairing" of those CAD generated construction plans

may be briefly summarized?


(versus the traditional boatbuilding manuals chapter on lofting and fairing : taking the scale paper drawing and loft/fair to 1:1 scale ???)


Thank you and a Happy Easter!

 

Some reading on the subject may be helpful, but if it was me, I'd build station molds, erect them on a strong back, then "line off" the sheer, any chines or laps, deck centerline and other important areas. You will find that even with the finest CAD drawings, you'll shim here and there or plane down portions of a mold, just to jet these "lines" to lie "sweet" under a batten. There is considerable argument that could be made to a full size lofting, which can iron out these small issues, before you make saw dust. At some point you will have to draw up the parts full size, either on paper as a lofting or on the actual stock you plan on cutting up. A lofting can save some stock, but most well developed designs will be easily adjusted in 3D on the actual molds with a few shims or mold trimming.

On a 10 meter yacht, you'd be well advised to make as many mistakes as you can of craft paper, instead of mold material. It's a small cost and has other added benefits, mentioned previously, that can help continuously throughout the project.

 

Yes; I would do precisely the same. But say you want to teach the boatbuilding to in-experienced young boatbuilders to be.

Or you are about to write a booklet : "The Boatbuilding of Wood Boats out of CAD Plans for Dummies "

Then you neeed to explain them(Dummies ) clearly what they are to do with that CAD plans once they print them out 1:1.

Best


Gerhart

 

Returning to the discussion of computer versus visual acuity of expert loftman, which I find fascinating though obsolete:
With modern techniques of CAM is possible to create a virtual model of the work to be performed, in which each and every one of the parts are defined. Can be studied with absolute precision the position of each part, interference between adjacent components, etc. etc. That is, you can do the same as the 1:1 scale model, but much faster and much cheaper, without the need for large spaces for mounting the 3D model. And what is best, in a short time can modify the model to correct errors or create alternative models to select the most suitable for the purpose intended.
The virtual model enables calculation of deformation and tensions in each of its parts, the total weight, and c. of g. the whole, the total amount of welding and some other things.The traditional 1:1 scale model is just that, one model. With the computer you can have many models and select the best one.
In large vessels, from many years ago, no one would think of doing natutral scale physical models of anything. No one can doubt the quality of the smoothed and the definition of parts in these constructions. I can not understand why good techniques for complicated vessels can not be used for boats.
Another aspect of the problem is how to get the pieces of the puzzle. Currently it is not necessary to draw anything at 1:1. CNC machines allow to obtain all the elements of the structure directly from a CAD file into the piece full size. Very few modern technical offices, not to say no one, use large format printers. This is simply because they are not necessary, not because these technical offices have moved out of the boats market.

 

paper and lofting... ????

still living in the dark ages???

If you live in a place with electricity and clean drinking water from the tap, then why even talk about lofting and paper plans and the like?

Get you designer to supply you a CAD drawing which also contains other files which have all your frames / sections and other parts nested together and can be sent directly to you local CNC router operator - any kitchen /cabinetry manufacturer will have one. Have all the frames for your build physically cut and ready to use in 24hours with 100% accuracy for around the same cost of printing a full size paper plan...

or, you could do it the hard way i suppose...