Making models of a project boat

[jedclampit]

Making models of a project boat to test prior to building the real thing.

I was wondering if this is practical.

I want to make two models of my project prior to building the real thing. First the project boat is a 10 meter (33 foot LOA, 10’ beam) cruising sailboat.

1) I want to build an exact 1/10 scale RC model for testing the hull (pulled along side my powerboat) hydrodynamics and the rig design for form and to keep the model in my den while I build the next model. Is this the correct procedure to make an exact scale model (including the weight)?
2) Next I want to make a 1/3 scale model to serve as dingy for the real boat. This will be to test the sailing qualities of the design. I will build the hull, rig and displacement to imitate the final design, but leave the deck and interior hollowed out for passengers and stores. I want to use this as the tender for the final project.

I read in Principles of Yacht Design that when you scale a boat that the proportions are not kept the same… they claim that when you increase the length by 50% or 1.5 times the original length then the width, height and displacement is only to be increased by 1.33 to simulate the same characteristics.

Do I follow this concept or are their other requirements or recommendations?

I’m only concerned with the tender, as this will be heavily used, and I want to test the sailing ability of the hull and rig. Will this work?

Thanks for your help…

If I were you I'd do everything with the big model because the data you'll get will be more reliable. The small model will not give you accurate data and because area varies as the square of length and displacement as the cube of length the small model will be likely to have too much SA and not enough RM to sail well in it's own right. That's why you see many models with short rigs or multiple rigs and a deep fin keel.
Your 1/3 model could be made to sail under radio control simply or more elaboarately and then if the displacement and stability were sufficient it could be converted to a dinghy.

[Guillermo]

If you don't have a computer program allowing you to visualize forms, you may go for a 1/10 model just to 'feel' the shape of the hull, as the wooden boatwrights did and still do.
And it's also nice to hang it over your firewall....

[jedclampit]

Here are the dimensions for the proposed models, what about the fin keels and the rudder? Should they be increased to be effective on the models?

SCALE MODEL DIMENSIONS FOR DAYLIGHT PROJECT

Original . 1/3 Scale Model . 1/10 Scale Model
DESCRIPTION . 100% . 33% . 10%
Length (LOA) . 32.00 . 10.56 . 3.20 feet
DESCRIPTION . 100% . * 38.61% . ** 11.7%
Width (Beam) . 10.00 . 3.86 . 1.17 feet
Depth (Draft) . 2.00 . 0.77 . 0.23 feet
Height (Hull) . 6.00 . 2.32 . 0.70 feet

* = 33% x 1.17
** = 10% x 1.17

What percentages should I use for the fin keel depths and the rudder size?

Thanks for your imput...