Lifting Lines

[DavidG]

I would be interested if any of you have any experience of lifting lines of existing boats.

I am interested in finding a cost effective approach, so that I can input data into a NA package to calculate stability.

There are three approaches that I can think of;

1, Using chains and direct measurements, transfering these full size onto doors for various sections (we did this as a project at S'ton Institute) and measuring off. This is labour intensive and not very accurate.

2, Photographic methods (there was a paper in this in the Naval Architect some years ago). The essence of this was to photograph the boat at various predefined angles, with a calibrated stick at the station, and apply scaling and trig.

3, Laser/digital technology, I have seen info on measuring systems used in Formula 1 and quality inspection systems, these look very expensive and beyond the buget of this naval architect.

Any other ideas, refinments or references would be appreciated.

Many thanks,

David

I have been looking at digital laser measuring devices here in the UK and reckon I might buy one for taking lines. They're only £25.
Set up a vertical staff on the station line with a couple of nails as datum points - one high, one low on the staff. Pick off a point on the hull from the high datum with the laser, mark it with a pencil and record the distance. Pick off same mark from the lower datum and record distance. Drawing out the body plan in Autocad will be quite quick and then you can make a table of offsets (or whatever your stability programme needs).

[MDV]

You can do it cheaply by using string lines, plump bob, sprit level and a measure tape. Just set up the horizontal string lines along the CL and at the required sections, and with the plumb bob and measure tape you can get the X & Y offsets at those sections. For at least one section you should measure both port and starboard to be able to adjust for the heel. With some practise and patience this is a fast and accurate method.

As a source for other methods, I suggest to contact your local measurer for ISM etc. they must have a fast and reliable method.

Regards,

Michael

[kudu]

Greetings...You might want to check out the August 2002 #167 issue of WoodenBoat magazine. On pages 34-39 you will find an awesome explanation of the subject you are interested in. Enjoy!!!

I worked at a naval architecture firm last summer and we hired surveyors to lift lines using laser theadolites (?sp)... It cost about $500-1000 and we got a point cloud (~1000pts), then import them into rhino and fit a patch to them... It's involved however you do it, but I'm pretty keen on the theadolite method... I think there's a real art to the chains/measuring devices, they probably work well also... It just might take some time getting things laid out...

I think you can rent theadolites for $100-200/day... I guess I get excited about the technology of it... It depends on the application really... if you're doing something for a client who wants exact information on what they have I'd go with the theadolite, while if you're just trying to design something 'similar' manual methods might suffice... Of course it also depends on the size of the project... over 50', I'd imagine that the manual methods get quite difficult...

fireball682@hotmail.com

[Stephen Ditmore]

I think it can be done using www.photomodeler.com if you project a grid on the side of the hull and take photos from 2 known points. There might be more info on this at www.touchcad.com or www.eossystems.com

If you want to make a quick cast of a small boat or a portion of a hull check out www.runliteusa.com/products.htm

A warning: splashing the lines of a hull and building it without legal rights has become prosecutable, and the lawyers are waiting for a nice juicy test case! See the "Parting Shot" at the back of a recent Professional BoatBuilder magazine.

[yipster]

wow, all very interesting and gettin better all the time.
now how do i get 8 day's in a week?

yipster

[duluthboats]

Measuring a hull
Measuring odd shapes,

I think you have a grasp of what is out there. The threads above are what I know about the subject. I like the Faro stuff.

Gary

[yipster]

5 weeks back i asked for a demo CD, but like to learn more!
this photogrammetry system may be of great help and as long as its for measuring, background stuff etc i guess its as free as taking a normal photo?

i understood the simplest system uses ordinary digital camera input from varied angles without laser or target dot references, and then builds a wireframe? wow, this can be time saving! wondering what i get, if i can easely get it to work, what formats are supported and more i'm downloading a demo now...

[gonzo]

The first method is very accurate if done properly. A variation of it is shown in Dave Gerr's "The Propeller Handbook". He uses it for a quick displacement method, but can be use for stability as well. With the new laser levels the manual method can be used with advantage. The whole mess of leveling strings or boards is largely avoided. These levels sell for U$39.00 and are accurate to 1/8" in 30'.