may i suggest you contact a model boat club or model engineer club who has marine steam operateing
you are entering a minefield of red tape, dont let that stop you
but you must follow the code of your country ME authority, and any work you do now could be wasted, as most require inspection at every step
you also need some public liability insurence, be prepared to pull down and follow a inspection programe for every yr of operation
richard simpson who writes in Model Boats, is very good
our marine gas fired boi.ers are engineered to operate at 90 psi, but under load often only produce 15/25 psi, yet have being tested to destruction at 1200\1600 psi