So what we are saying is that it is simply a rough guess where we put the boards, is there anyway we could " float " the hulls and then by some method find the centre of Effort around which the hull turns, add in the sail CoE of then use that as the leading edge of the boards.

The reason I am asking this is because I always ( well almost ) sail single handed ie main & spin only. Now most production designs are built for 2 up so my guess is that the daggerboards are in the wrong place for a main only boat. Any clues anybody ?

I have never designed a boat, but I have fiddled with our boat, tought about it and tried some stuff. There are practices and a firm scientific basis for where to place underwater appendages. It is not really that difficult once you have decided on a rig and sailplan. You calculate the center of effort developed by the sails, and design the underwater appendages to suit this. Or start the other way around.

If you sail mostly with main and spi solo on a two person boat, you will probably need to change mast rake to balance the sailarea with the underwater area (CoE must balance CoLR) when you take off or put on the jib. So you will have less mast rake sailing one up and more mast rake when sailing with the jib. You can feel it quite easily when sailing if the sails CoE dont balance the CoLR, you will either have lee helm or windward helm. When the helm is neutral when sailing upwind, your boat is in balance.

Totally agree on the weather helm / windward helm but by just angling the rudders foward or back can also have the same effect or is this because the distance between board and rudder is now shorter so therefore the CoE is now foward or back.

I feel it is one area where one could get it so wrong I just need a method to get it roughly right before the boat has even sailed. Fine adjustment could then be made using the sail.

What boat are we talking about here? Have you designed and buildt your own boat, or heavily modified one?

Personally, I am pretty certain that rudder rake dont move CoLR much, but not everybody agree on that. I am of the opinion that raking the rudders more forward makes the part of the rudder forward of the pivot point act as a canard. I.e. the area in front of the pivot point works much like a servo in a car (lets not get into cars, after what happened in the other thread <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> ), aiding you when you change rudder angle while steering.