Just a bit more on the foam issues...

Back in the early days Hobie Alter was making balsa core surfboards. He created the foam core board process and his buddy Gordon Clark took on the business of making the (Polyurethane) foam. The foam Hobie used in the cats was the Clark Polyurethane foam for many years. Clark used to make the foam in large loafs, then the loafs were sliced like bread. Lower layers were more dense and throughout it varied. That seems to have made some of the difference over the years. We quit using Clark foam back in the early 80's. We have been using a PVC foam for many years without the original problems from the 70's.

Weights...

In the 1984 model year Hobie Cat took some steps to lower the weights of hulls. The change in process was marked by the addition of a red dye in the glue seam process. The new process involved a different glue seam technique, better control of excess resin and in some cases (Hobie 18) a change in the amount and location of the glass layup. The Class rules were fixed and needed to change, but Hobie Cat began using the new processes. To keep the hull weights at the minimum levels per the class rules, some boats had lead shot added in the rear pylon (for a short period). Why rear?... weight aft is a GOOD thing. Some people were able to chip out the weights after the rules were changed. Hobie 16 class weight went from 340 to 320 pounds.