A vessel’s engine and propeller are optimized and designed for a given operational and max. speed.

If the operational speed of the vessel is generally lower than the one originally optimized for, it may be beneficial to consider derating of the main engine and propeller.

Derating as a retrofit product offers reduction of the total fuel consumption by improving the match between the operational speed and optimization speed.

Derating is usually an attractive option for fuel oil savings if a reduction of 10-15% of the max. speed at SMCR can be accepted.

A standard derating calculation made by MAN Diesel & Turbo takes into account the benefit gained from exchanging the original propeller with a new propeller having an optimized diameter designed for the required optimizing speed and reduced max. speed.

The above saving is based on a reduction of 10-15% of the max. speed at SMCR.
Fuel saving originates from
– Optimization of the engine and propeller layout to the actual operational speed
-Utilization of the latest engine tuning methods
– Utilization of state-of-the-art high efficiency propeller design.

De-rating benefits
– Reduced SFOC at optimization load
– New refurbished turbocharger(s)
– Increased overall propulsion efficiency with new propeller
– Less power demand for same vessel speed.

Derating includes
In order to change the engine SMCR, a number of engine and turbocharger components must be exchanged along with retrofit of a new optimized propeller matching the chosen SMCR.

A derating project includes:
– Specification of new operating/optimization speed and max. speed of the vessel
– Engineering
– Design of new propeller
– Derating of the engine
– Re matching of turbocharger(s)
– On board NOx measurements (parent engine)
– New technical file
– Torsional vibration calculation report
– Shaft alignment calculation report.

Price indication
A rough budget price estimate for derating of an engine and a new optimized propeller is approx. EUR 0.9-3.0 million (5S50MC 12K98MC) depending on bore size and number of cylinders and turbochargers.

Vessel and Engine Specific Study
In order to clarify the full optimization potential of an actual vessel (series), it is necessary to carry out a ‘Vessel and Engine Specific Study’, which establishes the optimization potential and possible tuning methods in
detail. The study will cover the actual vessel and possible sister vessels and result in one or more solutions for fuel reduction. As the study is vessel specific, MAN Diesel & Turbo will have to charge an engineering fee to cover the comprehensive calculation and design work involved. If the derating project is ordered based on the ‘Vessel and Engine Specific Study’, the engineering fee will be considered as a down payment and as such
be deducted from the project price.

The Vessel and Engine Specific Study includes
– Specification of a new operational and max. speed of the vessel
– Full engine derating potential is investigated
– one or more solutions are described
– Turbocharger re-matching is included
– Propeller performance for new propeller at new rating
– Torsional vibration calculation analysis
– Torsional vibration countermeasures are decided upon, designed and included in the project
– Quotation for engine derating
– Quotation for new propeller.