Boat Building

[tws1]

I'm currently building a Chamberlain Dory from offsets I've found in The Dory Book. I want to be able to sail her but I need to know how far aft I need to put the mast and how far aft of that I need to put the centreboard. Is there some sort of fomula I need to work to? How big should the centreboard be? This particular boat is 13' long by 4' beam and I would like a rig similar to a Mirror. Can anyone help?

 

[Peterduck]

Find the longitudinal centre of the lateral area of the immersed part of the hull by cutting out of cardboard a scale model of the immersed section of the hull, looking side-on. Balance this on a ruler's edge. The centre is where the ruler is. This is where your centreboard should go. Work out the centre of the exposed area of centreboard below the hull, and place it coincident with the centre of area of the hull. Now find the centre of the area of the sail, and place that about 10% of the waterline length ahead of the the centre of the combined lateral area of the hull and centreboard. While not fool-proof, this will give you as serviceable setup from which you may need to make small adjustments to achieve perfection.
Peter.

 

[tws1]

Peter Duck

Thankyou for your explanation of finding out where I should put my centreboard and mast. I will certainly give your method a try. Wish me luck!

Tony

 

[Nathaniel]

If in doubt, shift the CBoard forward a bit, or the rig aft, so as to give you weather helm (the boat turns up into wind when you let go the tiller). This is safer and much more desirable than lee helm. Too much of either though and you will be sailing with loads of rudder (brake) and will have dificulty going about.
Also, for fine tuning it try and figure out a way of either moving or raking the mast. Some designers deliberately incorporate a number of mast positions in a prototype in order to establish good balance as it's a pretty in-exact science and can often come down to experiment.