Boat Building

[rick_d]

I am considering building a Whitehall 17 using a cold molding process. I would like to use the shopbot to cut out the stations for the mold. Have any of you experienced boat builders out there ever digitally lofted directly from the offset tables?

[hespj]

Rick, you mean you're looking at an existing design which has a table of offsets? Probably those offsets won't be spot on accurate and would have been lofted full size by the boatbuilder. You can do the same with 2D, or far better, 3D CAD. Is that what you mean by "digitally lofted"?

Mostly I've created new designs from scratch but twice I've been given a table of offsets or lines drawing of very old boats and been asked to redraw the hull. Both times I used 3D CAD.

Does it work? Yes, the 3D cad model is far more accurate than a hand drawn lines drawing, or even a lines drawing lofted full size.

I'm just building a 12' double paddle canoe, completely drawn in CAD and straight from CAD to ShopBot, no paper drawings. I love it.

........
6987

That jig just slotted together like a dream, and the ribbands went into those notches in perfectly fair curves.

[rick_d]

Thanks John, Yes I am looking at an existing design that has a table of offsets. It also has full sized templates for those who dont want to go through the whole lofting process. I just wanted to take advantage of the accuracy and control the shopbot would give me instead of hand cutting the sections and then trying to get everything nice and fair.

It would seem to be a simple process to transfer the offset point into a drawing program and then draw a smooth curve through them just like you would do on a lofting floor with a flexible batten, but I haven't done it yet.

What software are you using to redraw your plans? That sounds like a lot of work, but probably the best route. Can you stay true to a classic design redrawing like that?

Your canoe looks terrific. There is something about a boat at that stage of construction that is indescribably beautiful.

Thanks for your help, Rick.

If you are interested, here is the boat I want to build, http://boatdesigns.com/products.asp?dept=190

[magic]

I used the bot and partworks to build a wood frame for a Zeppelin. No paper just looked at the monitor and cut away. The frame was a bunch of concentric circles with notches for the stringers and the customer decided how far apart he wanted them.

[rick_d]

Magic, do you have a pic you could post?

[shuffler]

Rick, that is one beautiful boat. Good luck with that project.

[hespj]

Rick, you might ask Glen_L if they have a dxf file of the templates. Presumably the templates are accurate. Otherwise they might be able to assure you that the offsets are accurate - after all they're probably the same offsets as the templates are drawn too.

However, they might be a little suspicious at you wanting to use a cnc machine.

[hespj]

Rick, just to elaborate. Yes you can just enter the offset points into a CAD program and draw a curve between them, BUT, are those points really going to join up into a fair curve? They might have been drawn on a drawing board at scvale 1:10, so any error will be multiplied 10x when drawn full size.

Even if the offsets for each frame are drawn correctly, whne the frames are set up do they produce a fair surface (fore and aft)?

We have no way of knowing the answers to this. But Glen_L might.

I use Vacanti hull design software and Rhino. Rhino would do it on it's own, and no doubt many other 3D cad programs would too.

[rick_d]

Thanks again John, I have emailed Glen_L but haven't heard back from them. I also wondered if they would object to providing files to someone with a CNC. There are other sources for this boat's plans, like Mystic Seaport Museum, so we'll see.

[rick_d]

John, Do you have an email that I could contact you off forum?

[Mike Windsor]

to go from a table of offsets to the shopbot the lines should be faired in a cad program first . This is fairly easy in a program like Rhino, but involves a lot of tedious data entry . Use the offsets to create the stations and the profile curves , then loft these curves to create a surface .This surface will be pretty close , but may need a bit of tweaking to fair it . In Rhino there are qute a few surface analysis tools like zebra stripe to help visually fair the surface . After you have a fair surface , offset the surface the distance of your planking thickness , and you have a surface ready to slice sections through . I use these sections to create mold profiles. If you have a 3d cam program you can take sections at each side of what the thickness of your mold stock will be , and use the bot to create beveled molds using the surface between the two sides of the mold . http://www.windsorboatworks.com/new%20dispro/new%20dispro.htm shows a set of molds that I made for a lapstrake boat with bevels and notches for the laps . Another program that you could use to turn a table of offsets into a B spline ( or nurbs )surface is Prolines http://www.vacantisw.com/ I use this program for most of my preliminary design work . The basic version is $275 .----If you're only planning on doing one boat it might be cheaper to hire somebody to do a digital plan .

[mims]

When I've done this, I used Rhino and redrew sections, making sure that each section used the same amount of points. That can help things stay simple and accurate.. sometimes it's not possible if certain sections have concavity or something else. Rhino handles all the situations very well, regardless. I also did not trust the keel line location of each section, so I created a new keel curve and used the curvature analysis tool to get a perfectly fair keel, then snap the sections down to that new curve.. It can take many iterations to refine and get a fair hull. Typically, one would draw the sections, then use loft or 2 rail sweep to get a surface. From there, you can project lines onto the surface to cut new sections wherever you need.

Remember that aft of the widest point of the boat, the wood will be hitting the aft side of the section station. While in front of the widest point, the wood hits the front edge of the sections. This could make a difference if you are using thick sections.

If the offset numbers are in the correct formatting to begin with, you can just start the Points command in Rhino and paste the entire list in.. it will create all of the points instantly.

[magic]

Rick

I don't have a photo. All it was, was 9 2inch thick rings with dados on the perimeter. The customer spaced them out, directly using 1X3s. The rings were not sophisticated, they were just easier and more accurate to make then the customer using a jig saw.

The construction was similar to the picture above except the canoe however looks great and my "rings" were just that.... rings.

[gene]

How bout some finished boat pictures

[bleeth]

Many years ago before he passed away I had the pleasure of talking Whitehall with John Gardner. You have reminded me of that wonderful conversation. Personally if/when I build one I would go straight to the Howard Chappell or John Gardner lines and know that any adjustments for fairness would be minor and could be made on the cut parts once set up on the gaiter.