replacing mast base
 

I have a 1978 Morgan out Island 41 ketch with a corroded aluminum mast base. It needs replacing, The aluminum is flakng away in the corners. I'd like to replace the base with something composite to prevent the corrosion the second time around.

I'm thinking that I can replace the aluminum mast step with GPO3 which has similar compressive strength as 6061 alu. The loads on the mast step are primarily compression not lateral so the side loads should be minimal at best. Are there any issues with buildng a mast step out of GPO3 composite sheet??

I don't know how it compares to the material you plan, but I have a friend who faced this problem and built a corian (Dupont) step. Similar boat. It works fine.

G'luck