i tried to do that too but i only had a 3" diameter pvc pipe. it bends down pretty good
t learned to fill a 2 liter soda bottle...and a board. i'll try again
You can fill you PVC pipe with plaster or mortar
You can fill a soda bottle with mortar only has the skin IMHO is too thin for plaster.
Mortar has better mechanical properties that plaster (brittle)
let the thing dry for 5 days if mortar, 15 if plaster and it will do a perfect job
If you use a soda bottle, once dry, it is better put the cap back on.
Don't use too much water in the mix to lesser the retract.
I agree with PeterFrank, the best way is to try the hydrofoil in the water.
IMHO, after years of "twin tip corruption" I think that any device that forces you to deconnect and teach you how to apply equal pressure on both feet can only be beneficial and decrease the learning curve time on water.