Offsets

Hi,
I am using freeship as design software (www.freeship.org). I don't really understand how to use offsets to define a hull. Is there any beginners information on offsets?

Thanks

 

Offsets are halfwidths from the centerline, and heights on those hlafwidths from a baseline.

Chapelle's "Boatbuilding" has some good info on lofting (i.e. using offsets to define a hull, although not with a computer), there's a couple of other good books on the subject out there, "Lofting", but I can't remember the name of the author on that one (Valdez?).

Edit: It's sort of an X/Y diagramme, where the x (horisontal) is the baseline, and y (vertical) is the center line.


Andre

 

Ouch, I think I forgot to mention something rather important:

Each station (a station is just a defined distance from the stem or transom of the boat), has it's own offsets, naturally, unless it's a pipe, and by defining the distance from the end, and then the distance from respectively the base line and the centerline you get a series of points you can then connect.

I did it the analogue way, with bendable sticks, but it's the same idea.

You have to subtract the thickness (scantlings) of the planks/glassfibre and so forth, though.

 

Here's the book to which the Bagger referred:
http://tinyurl.com/rkwzr

It's called: Lofting by Allan H. Vaitses

Chris Ostlind
Lunada Design

 

Offsets define the hull thru an X,Y,Z coordinate system. X is defined as your station points from the bow or stern along the DWL. Y is the height coordinate when looking at the profile and Z is the beam coordinate. The beam is expressed as a half width...it assumes that the hull is symmetrical along the centerline. You can also use this system for plotting the lines of a developed panel...tho usually you only use X and Y as the panel is assumed to by 2 dimensional. Stitch and glue uses this method extensively, as the panels are pre-shaped to give the correct shape to the hull.

Steve
Chris, you must type faster than me

 

Yup, that's the one

 

thank you

thank you all for your help in such a short time frame!!!!

 

You're welcome.

As a p.s. I found it really funny lofting in real size. It's amazing. No "black art" to it as some will have you think, it's just a matter of being precise. To see the lines take shape from a few numbers is amazing. I think I could build another (simple) boat, just to have my fun with laying down the lines. I really enjoyed that part

Good luck.