I will put this idea out for those that might want to use this proven and cheap technic for taking casts off of large models (boats maybe)that was used at Fisher Body many years ago. We would take casts off of wooden car model sections such as a station wagon car top. Lets think of this as taking a cast off a kayak boat haul. A flange would be built up around the shear seam sticking out a couple of inches or so usually held in place with clay. Then we sealed the model with green water soluble parting and put several coats of wax and a light coat of crisco on. With a large bucket of mixed USG Hydrocal (Green plaster, like cement and doesn't shrink of expand)a very liberal coat of this is put over the serface and an air vibrator is held against the model to vibrate out the bubbles. Then after this set just a little to stiffen some, another layer of hydrocal is put on and then bailed hemp,(like straw) is dipped in the Hydrocal and padded onto the model. This makes a very strong mold. If you can turn the boat and mold over you can make the matching deck half mold. Put alighment pins into the hull flange or drill large holes for alighments. You now have two mold halves to fiberglass a boat from. Of course there is a lot more to this and technique also but this is a starting point if you are ever serious.

John