Bays / equipment

Start air compressors are locat­ed in each engine room and start automatically. Electric power for the compressors comes from different LV switch­boards through different HV/LV transformers from two HV switch­boards all located in the same en­gine room 

Working air compressor 

Two pumps for seawater cooling system 

Two freshwater cooling coolers. Each cooler has the ca­pacity of cooling three main engines

The seawater system consists of two pumps provided with an automatic standby starting system. Failure of a running pump will cause automatic starting of the standby pump. Each seawater system supplies cooling water to the individual heat exchangers of the main generator sets in that engine room as well as cooling water to the two heat exchangers serving the freshwater system.

The freshwater service system is executed per engine room each with 3 50% pumps supplied from switch­boards. The pumps are provided with an automatic standby starting system that starts the third pump when one of the two running pumps fails

The fresh­water service system is also used for the thruster cooling systems. The thruster cooling circuits are arranged in the same way as the electric power circuits for the thruster mo­tors. Thus, thruster 4 which is powered by the SB switchboard has freshwater cooling from the SB en­gine room. Thruster 5 also from SB and thruster 6 from PS. 

Consequently, a failure in an engine room freshwater cooling system can cause failure only of the cooling of the thrusters supplied from that engine room.

The main engine freshwa­ter systems have engine- driven pumps. The system is duplicated per engine room. 
One engine room is shown, the other engine room is identical 

However, when the ship is operating on DP, the diesels are running on gasoil, and not on heavy fuel. The FMEA is drawn op for the DP mode. The fuel oil service units, with the heating sys­tem, are therefore not part of the FMEA. Fuel oil is supplied to the diesel engines out of tanks in the engine room, via fuel oil ser­vice units (heating, viscosity control) which have their electric supply from the low voltage switchboards 

The one-line diagram above shows the main electrical power arrange­ment of the subject vessel.

The bus tie breakers in the main switchboards (8) and (9) can be open/closed to connect the genera­tors two by two to different switch­boards in three engine rooms. A single failure would then result in a 33 per cent loss of capacity and the vessel would be able to con­tinue to operate 

        Frequency converter                     L-Drive aft thruster (motor with a vertical shaft located inside the vesse)                               

All supporting systems for the die­sel engines and thrusters should be carefully assessed to ensure these are available with the primary sup­plies. The two 24 DC supplies have to be from different sources and a com­mon failure must not cause failure of more than one engine.

Most HV switchgear requires an ex­ternal power supply to close and open the circuit breakers. This is essentially different from LV switchgear where no-volt coils in the circuit breakers arrange for time delayed tripping at under-voltage. These circuits have to be included in the FMEA.

It is helpful to predetermine the lo­cation of the auxiliaries, the power for lubrication, pitch and direction hydraulics and all the control volt­ages. It is useless to design a completely redundant power supply system for thrusters operated by a single pow­ered control circuit.

It is not allowed to get the main power from one engine room and the control power from the other, as failure of either engine room would stop operation. In this layout there are two engine rooms, with individual air, fuel, freshwater and seawater systems with fewer LV switchgear sections than in the HV systems.

The most disastrous result of a sin­gle failure is the failure of a com­plete HV switchboard and the as­sociated LV switchboards resulting in a 50% reduction of propulsion capacity. When keeping the position of the vessel is essential, such as during operations in the vicinity of offshore platforms, the operator may not use more than 50% of the available power. If environmental conditions require more, the work must be stopped and the position abandoned.

Abandon and recovery wire of the pipe laying installation