I spose it's all to late as the OP hasn't been back and said he was buying this 100ft ferrocement "tall ship".
But I chuck my warning in that the rules change when the boat is over 24 Meters/80 feet internationally.
I don't know about the USA but I feel they would be in compliance with it.
A private person can't captain a boat 24 metres and over unless they have a pretty good license.
To employ a skipper to do it the boat would need to be seaworthy.
For it to be used as a commercial enterprise the USCG would want it inspected, even as a 'dockside attraction' or whatever BS word they used for the Bounty.
As most ferrocement boats are home built (probably in the 1970s) no naval architect will look at designing a new rudder, or if he wanted to, could.
One wonders how the old rudder disappeared, along with the prop and shaft, except for some weird misadventure.
The word 'misadventure' rings clear in my mind... of this boats past and its future.
Finally I think everyone here has written very politely in response to this guy's endeavour.
I hope he has reconsidered buying this huge boat and perhaps jump a bus to safety