The size of the rudder's central core is determined by the final shape of the foil, the thickness of the wrapped glass and the unidirectional (UD) placed between the two outer skins. I estimated the shape (erring on smaller than too large).
I rounded over the edges for the wrapping.
After the wrap had cured in the VB, I placed it with spacers in the blank. I went to great pains at each step to insure that the blank remained perfectly flat. Each step is making it stiffer. Also, holding the leading / trailing dimension exact is important at this stage, just filling any gap as necessary.
Again, I tried to be too economical. You can see I'm trying to conserve that expensive HD foam. After fooling around to keep all the little pieces oriented and wondering now how I was going to brace the router, I decided to own up to the fact that I was going to have to go out and buy some more. I wasn't going to go through this on the 'big brother' centerboard, whose blank is now sitting below.
Using the router table, I put a groove along the trailing edge and filled with strengthened epoxy. This will make sure the exact center is never lost, potentially add stiffness to this thin edge until it is glassed, and solve the problem of having foam near the edge, since the edge will have a slightly flat profile.
The larger centerboard requires lofting between the upper and lower profiles which are given. Because of its orientation, the shape is slightly more complicated, but the same techniques work well. The key is the centerline that is given for each shape.
Momentum is building as I work on multiple parts. I was able to get a great price on some Divinycell 3/4 inch pre-perforated when a local boat manufacturer went out of business. It's much different that my Corecell (I have to say I'm partial to the Corecell, but it may just be what I'm used too) but was an economical way to get extra material for the larger cockpit floor, seats, and centerboard.
Cutting out HD portions.
Inserts almost ready to epoxy in place. It makes the rudder look pretty small. The colors are: grey = Divinycell, cream = Corecell, yellow = Corecell 1200.
The central core gets it glass wrap and vacuum-bagging. The clamped hardwood strips help to insure it doesn't warp.
This picture is just to show that I do own a different set of clothes!
Getting all the bracing set before placing the central core back in the blank. Because of the centerboard's length I went out and bought a section of aluminum angle -- wish I'd done that earlier. It's a great straight edge for drafting and marking, and I think it will be useful when positioning large flat pieces in the main hull.
