Autocad accuracy

[jerome]

Tim Watershed, this one is for you.

Now that you had this one builder rework all plans and measurements in Autocad, İ am really curious to learn if you indeed found out issues with the side panels and the hollows that everyone had to fight against. Was that corrected ? Are the side panels curved now or were the original plans correct ?

For instance, Aut1 is building his hull with a massive jig with straight sides. Will he succeed or will he be defeated by the curved side panels ?

[M&S]

Jerome,
First off, since we are new here, I had saved a draft of a post reply. Then when I returned I couldn't find it. Looked on FAQ's. Does someone know how to find saved drafts? Thanks.
OK. Will write again.
The original plan set as designed is correct. No boat in the world has been built exactly as designed. This is especially true when it comes to stitch & glue home builds by individuals in different parts of the world, with different levels of experience, materials, temperature and humidity.
Re: "For instance, Aut1 is building his hull with a massive jig with straight sides. Will he succeed or will he be defeated by the curved side panels ?"
I would not dissuade anyone from building a jig, but if it has straight sides, when released from the jig, no one can predict what the plywood will do. That's why there is a generous, one-inch convexity allowed for the hull side panels in all the rule sets.
The stitch & glue method success depends a lot on the type and quality of the marine ply. And each individual sheet is unique. Sam Devlin's book on Stitch & Glue boats is about the best resource out there. I found mine on Amazon.
The AutoCad expert volunteered to rework the CAD files as we told him that we had stopped selling the original CAD files when some users reported problems with them, some reported small problems, others reported big problems.
We didn't have the ability or the expertise to fix them ourselves. Plus we are all Apple products & the original files were done on a PC. So we had been looking for someone who could correct them & who we could be comfortable with their level of expertise. Lee, not only works for AutoCAD, but is a senior manager of 50+ software workers. He not only was able to rebuild the files from scratch, but he also generated a remarkable set of impressive plans. He did this on his own initiative & all the 70+ pages of different versions is amazing. So, everybody wants to know what the versions are. They are explained generally on a post on 1550.org if you care to go there. We will launch the new plan sets soon, but we are in the middle of packing up to go home to Colorado, as our time here helping my aging parents is over.
Tim

[jeff.dalsin]

Tim,

I would respectfully disagree that "the original plan set as designed is correct". There must be something wrong if the spec'ed materials are not capable of conforming to the shape(s) as drawn. I am unaware of anyone doesn't fall into one of two groups: 1) ended up with concavities in the topsides and filled and faired, or 2) relaxed the mid points for the topside panels. In both cases you end up with a convex curve from chine to sheer.

Jeff

[M&S]

First off, the autocad problems had nothing to do with the correctness of the plan. It was the skill of the original individual who drew the CNC plans. In his defense, any AutoCAD program requires a high degree of skill and understanding. But the pdf plan set was not drawn from the CAD files.
I lofted the i550 the old-fashioned way, to make the master templates and checked all the measurements on the printed plans for my plan set #42. I found a few, very minor errors & corrected them in the templates & the printed plans early on. I've been lofting boats for 33 years and worked many years in professional shops, before starting my own shop.
The i550 is meant to be simple enough for a home builder, with limited experience to build a simple cheaper hull, not a perfect, expensive hull. In an ideal universe, material always conforms to the way we want it to. Plywood doesn't weigh anything and always conforms to the computer generated shapes. No dimples, no hard spots, no bulges, no nothing. The allowed induced convexity of the hull sides within the rules is a recognition of the real world and our attempts to reconcile perfect with real. With all boat builds, there is always an immense effort to fill and fair, depending on the desire of perfection you wish to achieve. Even in an expensive, custom hull build, much less a plywood stitch & glue plywood boat.
A plan is nothing more than a described shape that can be approached, but never truly exactly acheived.
That is what I meant by the plan is correct. Results may vary depending upon conditions stated in my last post. Guess I'll have to include that as a disclaimer on our website.
Jeff, your boat, at least in your pictures, is very sharp & crisp & you seemed quite proud of it when it was launched. And you should be. It's a beauty.
Tim Reiter

[Chad]

This has absolutely nothing to do with jigs, right side up or upside down, gravity, or the nuances of plywood and a builder's skill in coaxing a fair shape.

My 25 year old copy of Skene's describes how to loft a developable surface "the old fashioned way", and I guaran-damn-tee that's not what you did to get these frame shapes! The shapes aren't "correct" if they're the wrong shape in between "the measurements"!

I recall Freeship (it's free!) has a module that will check a hull for developability- whether it can be wrapped in ply (or any flat panel material). It gives you a fancy FEA-style color coded distortion map.

Or you could ask one of the builders that have measured the frame gaps. The guy from Gougeon's wrote about it in his build essay, I think Lee mentioned it in his build blog, and I wrote about it in depth about two years ago. Before that was Kevin's and Ron's and even Chris's blogs, pointing to the same problem....

You can lead a Moose to water, but you can't make him drink?

[M&S]

any time a sheet of ply is twisted the forces will translate into an arced panel. the stress induced will be distributed unequally across the panel. It is indeed unfortunate that a disconnect exists between computer generated shapes and your build. Is the Design wrong or are your building skills not up to the task? Are you splattering everyones builds with the generalization that no one can make a TRUE i550 unless it comes off of a jello molded 5 axis CNC machine foam block product. But then you are facing a cored fiber/epoxy boat that is not plywood. are you mistaken about your own ability to follow the plans and accept a not so accurate facsimile of the true shape? a true dilemma.

what did you expect? At some point all the accumulated knowledge would be condensed and quantified.

Think about it

My copy of Skene's is more than fifty years old. The book has been around longer than either you or I. Sighting it as a source is pretense more than substance.

T

[Chad]

any time a sheet of ply is twisted the forces will translate into an arced panel. the stress induced will be distributed unequally across the panel. It is indeed unfortunate that a disconnect exists between computer generated shapes and your build.

This bit is correct, and I wrote of three ways for you to address it. I expected you to have addressed it a long time ago. Now that you're having your plans redrawn, are you missing yet another opportunity?

[slowpoke]

I think this needs to be addressed in another form of communication, i.e. email or pm. No one's insulting anyone else, but this is an issue that is obviously very sensitive, and this isn't where it needs to be argued out

[jray]

+1, thanks Rocky!

[Shazza 273]

Thanks to Tim & Susan for making it possible for us to enjoy winning races with Shazza

[jerome]

What a beautiful picture !