The disclosure relates to marine craft which are capable of operating in the hydrofoil mode, many with extensible and retractable hydrofoil posts. Specific embodiments of large commercial hydrofoil craft are described, including those with structure which is the water during hydrofoil travel mode and which can be retracted to partly fit within recesses in the hull during other operating modes. Other craft, including those with hybrid electric drive, are disclosed having un-cooled reciprocating internal combustion engines. A number of arrangements for pistons and cylinders of unconventional configuration are described. These included are toroidal combustion or working chambers, some with fluid flow through the core of the toroid, pistons reciprocating between pairs of working chambers, tensile links between piston and crankshaft, energy absorbing piston-crank links, crankshafts supported on gas bearings. In some embodiments pistons mare rotate while reciprocating. High temperature exhaust emissions systems are described, including those containing filamentary material, as are procedures for reducing emissions during cold start by means of valves at reaction volume exit. Compound engines having the new engines as a reciprocating stage are described.