I built a 32' Hartley RORC in ferro too many years ago.
Many of the problems should be evident with a very careful inspection
As with any hull
material it may not be possible to be 100% certain that the hull is sound. Two particular traps that come to mind would be if the hull was cracked below the water
line and the steel reinforcing corroded due to electrolysis
and problems relating to integral internal tanks
A friend sailed his ferro from Oz to France
, no worries. Then he lightly touched a solid structure and a fair bit of his side (from his distantly remembered comment) caved in. He repaired and continued...
I still have Bruce Bingham's book, "Ferro Cement design, techniques and application". In his designs and designers section at the back he lists a lovely 42' Tops'l Schooner by Jay R. Benford and Associates and the 42' ketch
Doreana, designed by himself.
42' Stays'l Schooner