Offsets

[wrabbit]

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

[DanishBagger]

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

[DanishBagger]

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.

[Chris Ostlind]

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

[lewisboats]

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

[DanishBagger]

Originally Posted by Chris Ostlind

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

Yup, that's the one

[wrabbit]

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

[DanishBagger]

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.