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Thru hulls are not all that easy to add. I do not know the current thinking on installing thru-hull fittings but when I was more involved with ferrocement boats, the recommendation was to build up extra thickness in the area where the thru-hull was to be installed and to add extra reinforcing around that area of the hull. A wooden plug made from a closet pole or dowel was inserted on the jig at thru hull locations, and the reinforcing was stopped short of the dowel. There are issues with adding thru hulls after the fact because you are cutting through the steel reinforcing providing potential access to the reinforcing for water to start corrosion and also the potential for electrolysis between the steel reinforcing and typically bronze thru-hull fitting. The use of bronze thru hulls and electrolysis on FC boats was a heavily debated topic in the 1970's and early 80s and I don't know how that issue resolved. The last FC boat that I was on used Forespars' marelon plastic fittings which is actually a pretty good solution.
Most Ferrocement boats that I have been on have had fiberglass over plywood decks and cabin structures, essentially built as you would a wooden boat. This makes adding deck fittings much easier and actually helps keep the weight out of a weight sensitve area of the boat. Having the weight of a Ferrocement deck that high above the VCB and roll axis would raise the VCG pretty dramatically and result in a boat that had less stability and a pretty uncomfortable motion.
Of course using fiberglass over plywood decks and cabin structures is a pretty high maintenance solution over the long haul and cited as one of the reasons that ferrocement boats were seen as being one of the highest maintainance materials in the study of long term maintainance costs that I believe was performed by 'Boat Builder' magazine some years back.
Respectfully,
Jeff
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