Main role of the prime mover
to propel the ship by delivering mechanical energy to the propeller
The propulsion plant architecture, as well as the general engine room layout depends on what?
the type and operating profile of the ships, as well as on the type of the prime mover installed
The propulsion system architecture can be typically categorised as follows
1. Mechanical propulsion 2. Electric propulsion 3. Hybrid propulsion
Diesel-mechanic propulsion:
for what ships?
for ships that sail at a single cruise speed most of the time, because its fuel efficiency at full load is high. Examples of such ship types are cargo ships and fast crew suppliers
The propulsion power of cargo ships is delivered by…
a slow speed or medium-speed main diesel engine directly connected to the propeller shaft (direct drive) or indirectly via a gear reduction box (geared).
major machineries located at different levels/platforms
Bottom plates level – above the ship double bottom (at the tank top plating); 2. Middle plates level – at the fuel pumps level; 3. Upper/Top plates level – where the main engine exhaust valves are located.
Bottom Plates
Opens for acess to the crankshaft and sump to inspect the general condition and also to take deflections to judge bearing wear
Explosion relief doors
Spring loaded door shich is designed to relieve pressure in the event of a crankcase explosion
OMD
Oil mist detector in each cylinder
Middle plates
fuel pumps mechanical lubricators, electronic cabinets, rail units
Top plates
Exhaust valves: hydraulically actuated from pumps in middle plates
Electric propulsion: For what ship types?
Best for ships with different operating profiles
passenger ships
ferries
offshore vessels
research vessels
icebreakers
typical architecture of an electric propulsion system
Advantages of Electric propulsion over mechanical propulsion
(+) The electric propulsion is a fuel-efficient propulsion solution when the hotel load is a significant fraction of the propulsion power requirement and the operating profile is diverse, because the generator power can be used for both propulsion, through the electric motors, and auxiliary systems; (+) Reduced NOx emissions, because the propulsion power at full ship speed is split over more engines, which due to their lower individual power run at a higher speed; (+) Flexibility in positioning machinery spaces (due to the absence of the shaft-line); (+) Reduced maintenance load, as engines are shared between propulsion and auxiliary load and are switched off when they are not required.
Disadvantages Electriv Propulsion over mechanical Propulsion
(-) Electrical propulsion incurs increased electrical losses, that lead to an increase in SFC, particularly near top speed of the ship; (-) When running redundant engines to achieve high propulsion availability (for example in DP operations), the engines run at low part load. This leads to poor fuel consumption and a lot of emissions.
High voltage system on ships
A high-voltage installation means that the ship’s electric power system includes elements of generation, distribution and consumption of electric energy with a voltage of at least 1000 V
typically uses an electric propulsion system.
HV is used to power electric motors that drive the ships propellers
System generate slectricity using GenSets(DGs), gas turbines or even nuclear reactors
Hybrid propulsion for what ship types?
Best for shis with flexible power demand
naval frigates
destroyers
towing vessels
some ferries or yachts
A typical architecture of a hybrid propulsion CODLAD system
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