Posted by JimM on June 18, 2003 at 07:17:46:
In Reply to: 1/8 scale weigth posted by Brenner on June 17, 2003 at 07:54:43:
You're on the right track when you mention volume. 1/8th the length translates to 1/512th the volume, because 8 cubed is 512. Imagine a cube that measures 1 foot on a side - it occupies 1 cubic foot. Now take a cube that measures 1/8th of a foot on a side - its volume is (1/8)^3 = 1/512. Check it on your calculator to convince yourself.
I would be concerned with total model weight, rather than just your weight. Your model's weight might not be "scale", and you also need to consider equipment, fuel etc you'll want to carry. It might be easier to reverse-engineer it, and load the model until you think you've reached a practical limit. Then weigh the model and scale it up to full size by mutiplying by 512. If that weight seems appropriate, then you can proceed with your tests. What's "appropriate"? Look in Glen-L's catalog for a similar design and look at the hull weight, add fuel, equipment and crew, and that's an appropriate displacement. That assumes that you'll be using similar construction techniques to Glen-L's and not over-doing it on materials.
Notes on the testing:
Don't forget that hydrodynamics change when the scale changes! A perfected design in 1/8th scale will not behave exactly the same in full-scale.
I don't think you can get an accurate feel for handling characteristics without being IN the boat with a real engine and steering wheel.
Don't forget the balance, a vital part of boat design. That includes not only fore & aft distribution, but also "z-axis" (vertical). And you might even want to check its sensitivity to y-axis (left-right) off-center weight.
Don't forget that the aparatus you use to hold the boat in the sluice will impart loads which may not be the same as real-life.
See Boatbuilder Magazine, Nov/Dec 200, an article entitled "Designing Liz". The author went through a very detailed design study and scale testing program. You can now buy his plans for this excellent boat. See http://www.boatbuildermagazine.com or call 800-786-3459 to request a back issue or reprint.