[taxcontrol]

Concrete with fly ash and Grancrete supplements (5% ish) to reduce water permeability. Add fiberglass fibers to the mix to improve the strength of the concrete mix. Use fiberglass re-bar instead of Iron / steel re-bar. Paint the outer hull with epoxy.

Will last a lot longer than ferro-cement.

[Red Badger]

ferro-cement wasn’t expected to last long..................

[dirtymac]

I help build a cement fishing boat in Hawaii in 1967. what makes a boat float is not the material it is made of but how much water it displaces versus the weight of the boat. steel ships float same as concrete.

[BBQToadRibs]

I had a co-worker in Seattle with a 25’ ferro-cement sailboat. I had never heard of such a thing before, but was an interesting ship. He retired, sold it, upgraded, and sails from Anchorage to Cabo in a seasonal flotilla of like minded retirees.

[Wonder Warthog]

"Concrete with fly ash and Grancrete supplements (5% ish) to reduce water permeability. Add fiberglass fibers to the mix to improve the strength of the concrete mix. Use fiberglass re-bar instead of Iron / steel re-bar. Paint the outer hull with epoxy."

I'm not much into boats, but as a chemist, your proposed design changes should all "work".

[Boogieman]

I got another idea for you... mix some hollow rubber balls into the concrete mix. Yes, it will reduce the structural strength a little bit, but it should also reduce the weight of the ship without changing the displacement or the permeability.

I’m no engineer, but my intuition says reducing the diameter of the balls would also reduce how much they affect the structural integrity.