I would think a small bottle of air, similar to say a 15 pound or smaller fire extinguisher, with a regulator and a pressure relief valve (much like that on a typical SCUBA buoyancy compensator) would allow one to fairly rapidly inflate a small boat relatively quickly... and is a completely independent system from that which would require ships power.
I suppose a 12v inflater with a separate small battery (IE motorcycle) would work nearly as well... but might require more maintenance... to keep battery charged for instance.