Minimum width of lofting surface (and other mylar ???s)

[dmede]

I have discovered a roll of 30" wide drafting mylar in my office (eureka!). But I had hoped to use 36" wide for my dory lofting. From checking my lines in illustrator it looks as though 30" will just work leaving 1/2" of space above the tallest part of the heights above base and 1" above the widest part of the half-breadths, if I use the bottom edge of the mylar as the base line.

So these are the questions:
1) Can I use the bottom edge of the mylar as the baseline or is that invinting disaster?

B) And is the 30" too tight a fit for a boat with a 29" width and stem hight of 29.5"?

Thirdly) Can the maylar be reused for several loftings? I'd like to keep it for the next two boats (a 12' canoe and a 14' dory).

Thanks all,
Dave

[ 01-16-2004, 01:32 PM: Message edited by: dmede ]

[JimD]

Not quite sure if I understand, but while mylar is great for drawing lines on, getting those lines properly lofted full size usually requires the use of battens and the battens have to be held in place somehow, usually with nails (that would have to be driven thru the mylar into the subsurface) or if you can manage it with weights. So you'll have to roll out the maylar onto some kind of surface that can take a nail, for a small boat often that means a few sheets of plywood or osb laid out on the garage or basement floor. No reason you couldn't roll out the maylar onto some plywood and use the bottom edge of the plywood as your baseline. Once the lines are on the maylar the only way I can think of to transfer them to the station molds without damaging the maylar would be with carbon tracing paper.

[dmede]

I'm hoping I will be able to use weights to hold my battens in place, but if I have to use nails thats ok. Nail holes wouldn't get in the way of re-using, just old lines that won't come all the way off the mylar. I'll probably be using the boat plywood as a base since I only need the base while I'm lofting, once the boat has been lofted and the frames taken from the lofting I will be able to roll up the mylar and then unroll it onto the cement floor or driveway as I need to refer to it. The real concern for me is if the close fit of the lines size to the mylar size is too close. The whole layout of the boat lines will fit on the 30" wide mylar but with little room left over. But I shouldn't need any extra room right?

[JimD]

Can't think of any reason you'd need extra room, just enough to hold the lines although you'd want the longest batten to be a few feet longer than the longest curve you need to draw. Suppose if you were careful you could draw the lines with erasable marker and then just wipe the mylar clean afterwards.

[Nicholas Carey]

Originally posted by JimD:
Can't think of any reason you'd need extra room, just enough to hold the lines although you'd want the longest batten to be a few feet longer than the longest curve you need to draw. Suppose if you were careful you could draw the lines with erasable marker and then just wipe the mylar clean afterwards.Drafting film has a matt finish on it to take pencil/ink. It doesn't erase quite that easily. If you use a pencil, you ought to be able to remove it quite well with a white vinyl eraser (preferable in an erasing machine).

[Bruce Hooke]

I definitely would not use the underlying plywood to provide the baseline because then once you take up the mylar you've lost your baseline. I think you could safely use the edge of the mylar as your baseline (after making sure it is lying straight), but I think I would probably draw a baseline 1/8" in from one edge. That way, if the edge gets bumped you won't have lost your baseline.

I think you can fit the drawings on the mylar BUT you will want to firmly anchor it down to the plywood while you are doing the drawings because there will probably be times when you will need to continue a batten beyond the mylar and quite possibly also times when you will need to make temporary layout lines outside the mylar.

Why not just use some lightweight plywood "door skins" for your lofting floor? Seems to me it would be easier to work with, cheaper, and just as effective...

[Paul Scheuer]

Nice find. You should be ok. This reminds me of the exercise in drafting class where I started a construction at the wrong spot on the paper and ended up drawing off the paper onto the board. I turned the whole thing, board paper and tape, for grading. I got full credit for the drawing, a slight deducton for the error, and extra points for imagination. I've never forgotten to plan ahead for such endeavors.

[Venchka]

Originally posted by Paul Scheuer:
Nice find. You should be ok. This reminds me of the exercise in drafting class where I started a construction at the wrong spot on the paper and ended up drawing off the paper onto the board. I turned the whole thing, board paper and tape, for grading. I got full credit for the drawing, a slight deducton for the error, and extra points for imagination. I've never forgotten to plan ahead for such endeavors.Interesting. We had a big bucks contract drafter do something like that. Ran him off the same day. His first day as I recall. I spent a Saturday doing it right.

As for lofting multiple boats on mylar, just buy the correct size mylar as you need it. It can't be that expensive.

If you can't find short lengths locally, these folks have 36"x20 yards for $108.91. Call that a lifetime supply. It won't go bad.

Drafting Film (http://www.reuels.com/reuels/product29788.html)

[JimD]

I definitely would not use the underlying plywood to provide the baseline because then once you take up the mylar you've lost your baseline I suppose, but if you line up the mylar so its an exact 6 inches from the plywood edge, for example, you'll shouldn't have any problem figuring out where the baseline goes for future reference.

[JimD]

Also, most table of offsets provide measurements either above or below the waterline, so if need be you may be able to use the waterline as a base as well, which will end up somewhere down the middle of the mylar

[dmede]

Thanks for the replies. I cut out a sheet 30" x 16' last week. I needed the mylar because I will be building in the same space I'm going to loft, my 1 car garage. Once it's lofted I'll be able to roll it up and out of the way and unroll it out on the drive way for refernce.

Venchka, I consider $108 expensive and a waste of money since I only need a fraction of that leangth, but it's ok since I got it for free. Cant beat that price.