Table of offsets advice

[Alex Low]

Ahoy,

Starting a lofting project and would like to know if anyone has created a table of offsets off lines drawings? I have plans, but they are from 1915 and don't have offsets. Anything and everything would be great!

http://www.dc004.com/cutter.jpg

Thanks

Alex

[paladin]

Trying to loft from paper that has been copied a few times could get interesting. If you are serious I might suggest that you find a nice place in a garage or a floor where you can lay out some masonite, paint it white, then make a table and loft it full size...there are going to be a lot of errors and lofting full size will allow you to locate the mistakes and fair the hull as you go.....how large is the boat in real life?

[Todd D]

What I do is to scan the body plan. on the drawing (the part on the lower right) and take it into my vector graphics program. I then trace it to convert it to a vector drawing and scale it to either full size or to 1"=1' and read offsetts from the drawing using the computer.

It is pretty easy to do. The conversion from a bitmap to a vector drawing is done to eliminate line width errors. I can generally produce offsets that are more than adequately accurate.

You can also simply measure the offsets directly from the body plan, but you need a good steel ruler to do it. You also have to be careful to always measure from the center of the centerline to the center of the line you are measureing to. If the drawing you have is at the 3/4"=1' scale, then you multiply your measurements by 16 to get full scale offsets. Of course, that multiplies any errors you make by a factor of 16 too. However, if you are careful, you should be able to generate offsets that are accurate to =/- 1/4" or so.

If you want to take a close-up picture of the body plan with a scale reference in the picture (quality steel rule for example), I can generate a table of offsets for you. It will be a couple of weeks though since I am pretty busy right now.

TD

[Alex Low]

Hey Paladin,

Thats the plan. We are going to loft it from a table of offsets I made from some Mystic plans... so they have been copied many times, and depending on which side of the line you measure, you can be out by 1/8"+. I have lofted full size before, but I would like to minimize blunders. The boat is 18'9" LOA.

Alex

[Paul Pless]

Alex, are those the lines for Cockle?

[Alex Low]

Paul,

Indeed they are.

[paladin]

Todd is your best bet because I would do it by hand and then refair it....and I go back to the vampires on Tuesday a.m. to be attacked again so I'll be drifting around the rafters for a couple of days afterwards.....are you planning on building it carvel or perhaps cold moulding or strip planking?...

[Clinton B Chase]

Alex, take note whether the lines were drawn to the inside or outside of the planking. If to the outside as many lines were drawn in those days, then you can easily correct for planking thickness when you draw the bosy plan on the loft floor.

Cheers,
Clint

[Alex Low]

It looks to be outside of planking. If we build it, she will be carvel for certain. A lot has to happen between now and the keel timber though... Just trying to get a nice, fair, pretty, lofting session in for starters.

[Don Z.]

Ahoy,

Starting a lofting project and would like to know if anyone has created a table of offsets off lines drawings?

Thanks

Alex

Isn't that how the designer would have created the table of offsets in the first place? He would have drawn the plans, then measured with his scale, and then created the table. The table would then be used to loft full size, and any errors would be corrected by the lofting.

See Chapelle, Yacht Designing and Planning, pp 184-186

[jackster]

What Don Z. said.

[Alex Low]

Thanks Don,

I am just fishing for advice from those with experience at this... as stated above the plans have been copied many times, unlike a designers drawing, and will therefore have some distortion. I am looking to avoid any classic mistakes that can be made during the process. So far so good!

Alex