Hydraulic cranking system is commonly used on life boat  and operate on the principle of pressure oil turning a fluid motor to produce mechanical energy. The oil is stored  in a pre-charged, bladder or piston type accumulator  and is admitted to the cranking motor through a starter control valve .
The oil enters the motor through an inlet port and is directed against a series of pistons located within a cylinderical rotor. When the pistons receive the pressurized oil, they move against an angularly mounted fixed thrust bearing. As they contact the bearing they slide downward around the race carrying the rotor with them, causing to turn. After discharging its work load the oil is returned through the motor outlet port to the oil reservoir. The engine pump system includes equipment for automatically recharging the accumulator supplied with unloading valve  and high pressure filter.
The use of a  hand pump ( muscle energy) is for emergency use if accumlator supply is exhausted and it is capable of regenerating system pressure for a starting attempt. There is also an option to in-corporate a pneumatic oil driven pump to externally recharge the accumulator to provide an almost instant start attempt.