Main Engine Protections. Quick Check for Inspectors

Greetings! In this article, I recommend that you familiarize yourself with the main protections of the main engine on a vessel, which are most often checked by inspectors. The main engine and its auxiliary systems have a lot of protections, so only the main ones will be described, which are demonstrated when passing a particular check.

The main engine and auxiliary engines differ mainly in their purpose. But in terms of protection, they have much in common. In the article "Diesel Generator Protections. A Quick Check for the Inspector" oil mist detectors (OMD - Oil Mist Detector) were mentioned, which can be installed on diesel engines with a capacity of 500 - 1000 kW, so on the main engines, as a rule, they are.

And in this article, we will consider different models of such detectors and methods for checking them.

The main engine and auxiliary engines on a ship differ in their functional purpose, as well as in their design and operational characteristics. Here are the main differences:
1. Purpose
Main engine. Designed to ensure the movement of the vessel. It transmits power to the propeller shaft and propeller, which ensures the forward movement of the vessel.
Auxiliary engines. Used to power the ship's systems, such as generators, pumps, compressors, air conditioning systems and other mechanisms that are not directly related to the movement of the vessel.
2. Type and power
Main engine. This is usually a powerful, high-power engine running at low speeds (especially if it is a two-stroke engine) to efficiently rotate the propeller shaft. These are mainly large-sized engines running on diesel or heavy fuel oil.
Auxiliary engines. Less powerful, designed to work with the loads from the vessel's equipment. Typically, these are medium- or high-speed engines running on diesel or heavy fuel oil.
3. Operating mode
Main engine. Runs continuously during the vessel's passage from port to port, usually at a fixed or variable load mode depending on operating conditions.
Auxiliary engines. Run as needed, depending on the vessel's needs. At a minimum, under normal conditions, one diesel generator is always running.
4. Design
Main engine. Often has a complex design with an emphasis on reliability and durability, capable of operating in difficult conditions for a long time without stopping.
Auxiliary engines. Simpler in design, with lower durability requirements, since their operation is usually episodic.

The main engine, like the auxiliary one, has the same type of temperature and pressure sensors, in fact, it is the same diesel engine, only larger in size and with a different purpose. Accordingly, the protection and the procedure for checking them are practically the same. Therefore, I recommend reading the previous article on diesel generators for a complete picture.

The article mainly discusses MAN B&W series engines. The response readings of certain temperature or pressure sensors are considered on the MITSUI-MAN B & W 6S50ME-C9.5-EGRBP engine. Oil mist detectors are considered on SULZER RTA, YMD-MAN B&W 5S50ME-B 9.3 T II and HYUNDAI-MAN B&W 6S70MC-C MK7 engines.

OMD - Oil Mist Detector

As I wrote earlier, the main difference in the protection of the main engine and auxiliary ones is the presence of a device for detecting oil mist in the engine crankcase. Let's look at different models of oil mist detectors and how to test them according to the manufacturer's instructions.

Oil Mist Detectors

Oil Mist Detector (OMD) is a device designed for early detection of oil in the form of an aerosol (oil mist) in the crankcases of marine engines or other enclosed spaces. Its main task is to prevent emergency situations such as crankcase explosions or fires that may occur due to the ignition of oil mist.
Operating principle
Oil Mist Detector works based on the analysis of the concentration of oil mist in the air. The device includes sensors that measure the density of the aerosol in the engine crankcase. If the concentration exceeds a set threshold, the system issues a warning or alarm.
Main components:
Oil mist sensors. Detect the presence of microscopic oil droplets in the air.
Controller. Processes data from the sensors and makes decisions about triggering an alarm.
Alarm. Activation of an audible and / or visual signal when the permissible level of oil mist is exceeded.
Interlock system (optional). Can automatically stop the engine to prevent further damage to the engine.
Where is the OMD installed?
In the main engine crankcases.
On compressors.
In places where oil mist may form, such as in lubrication systems.
Causes of oil mist formation
Overheating of moving engine parts.
Faults in the lubrication system (e.g. oil leakage).
High friction speed between moving parts.
Why is an Oil Mist Detector needed?
Safety: Protection against crankcase explosions that can cause serious damage to the engine and endanger the lives of the crew.
Regulatory compliance: International maritime organizations such as IMO require the installation of such devices on ships.
Cost savings: Prevention of engine damage and subsequent repair costs.
Technical data:
Sensitivity: 0.1 to 10 mg/l.
Response to exceeding the level: Instantaneous (usually up to 1 second).
Connecting to the engine control system or alarm system.
Popular manufacturers:
Graviner
Daihatsu
Schaller Automation
Kidde
Heinrich Monitoring

As a rule, oil mist detectors are checked by inspectors at the first opportunity, so it is important to be prepared for this check. The task of the electrician here is to simulate a high concentration of oil mist on any sensor. Sometimes the inspector is satisfied with the check on the central unit using a special test procedure, but this is as agreed.

When checking oil mist detectors, a signal about a high concentration of oil mist (Oil Mist High Density) should come out, as well as a slowdown of the main engine (Oil Mist Slowdown).

Oil Mist Slowdown

DAIHATSU MD-SX

DAIHATSU MD-SX - the most reliable and trouble-free Japanese oil mist detectors in my practice. As a rule, they can be found on Japanese-built ships. Two options for checking, either on the sensor using a special smoke spray, or on the central unit. Often, inspectors find it convenient to check on the central unit.

Location of sensors

Central controller DAIHATSU MD-SX

Test procedure OMD DAIHATSU MD-SX on the controller:

Press "TEST";
Select ALARM OPERATION CHECK and press ENTER;
Use the arrows to select the sensor on which we will perform the test. Select the sensor and press ENTER;
Lower the alarm setting HIGH ALARM below the current value (using the arrows) and press CHECK;
As a result, an alarm occurs for high concentration of oil mist on the selected sensor;
Press ENTER to finish the test.

Instructions for testing OMD DAIHATSU MD-SX on the controller

Video of OMD DAIHATSU MD-SX testing

Procedure for testing OMD DAIHATSU MD-SX sensors

As for testing on the sensor, everything is simple. It is enough to remove the sensor from its seat and spray the spray on the sensitive element. In this case, it is advisable to close all other ventilation holes with your hand, leaving only the one where the spray is sprayed. Smoke sprays that are used to test fire systems are suitable.

OMD DAIHATSU MD-SX Sensor

Checking the smoke detector with spray

VISATRON VN (Schaller)

VISATRON VN (Schaller) - more "capricious" oil mist detectors than DAIHATSU, which require periodic attention. It is necessary to clean them regularly, change filters, calibrate the negative pressure, replenish oil in the siphons (if provided), and also clean special grooves. In this article, I do not consider maintenance and breakdowns, so I will not go into these procedures. If you are interested in information on the maintenance and repair of oil mist detectors, then write in the comments to the article.

You can check the VISATRON oil mist detector using a special test plate and glass.

VISATRON Central Unit

Test plate and glass

Oil mist test procedure on OMD VISATRON VN (Schaller)

Open the latches of the OMD control unit cover and fold the cover to the left side.
Press the test plate against the holes. Make sure that the holes are completely closed. Now the device starts to create negative suction pressure again.
Wait until the "Ready" LED lights up on the display.
Insert the test glass into the test plate slot. The glass simulates oil mist and generates an oil mist alarm.
Wait until the "Alarm" LED lights up. When it lights up, the engine should stop (shutdown) or go into slowdown mode.
Remove the test plate.
Carefully close the control cover.
Wait until the "Ready" LED lights up.
Press the RESET button of the oil mist alarm to acknowledge the alarm condition and enter the normal monitoring mode.

Instructions for testing the oil mist detector VISATRON VN (Schaller)

Instructions for testing the VISATRON VN oil mist detector (Schaller)

Test procedure for individual OMD VISATRON VN lines

There may also be an option to test individual lines by cylinders. To do this, simply give up a tube (they correspond to the cylinder numbers) and spray smoke spray into this tube. At the end of the test, press RESET.

Attention! As for testing with smoke sprays, be careful! Some sprays can heavily contaminate the sensitive element of the sensor or the entire unit (VISATRON). Then you will have to do a long separate cleaning, because the system will show a high concentration of oil mist. The best option for testing is cigarette smoke, more on that below.

Deficiency! On one vessel, the Italian PSC made a deficiency during the testing of the oil mist detector. The second engineer lit a cigarette in front of the inspector, while in the engine room (near the OMD unit) in order to test the detector.

If you want to test OMD sensors with cigarette smoke, then follow the safe procedure. Indeed, on some VISATRON models, after testing the units with smoke testers, which are used to test smoke sensors of fire systems, problems arose. Therefore, if you test with cigarette smoke, then collect smoke in a bottle in a place on the vessel permitted for smoking.

GRAVINER Mk 6 / Mk 7

GRAVINER - quite good oil mist detectors, but just like VISATRON, they can be capricious, and they need to be cleaned periodically. By the way, DAIHATSU sensors also need to be cleaned, especially on older vessels. I began my acquaintance with graviners with the Mk 4 version and eventually got to the Mk 7.

OMD GRAVINER Mk 6

OMD GRAVINER Mk 7

OMD GRAVINER Mk 7 test procedure on the controller

On the Graviner controller, you can test both the Slowdown system and each sensor separately. To perform tests, you will need to log in to the system under administrator (engineer) rights. To do this, enter the appropriate login and password.

Test procedure on the OMD GRAVINER Mk 7 control panel

Test procedure on the OMD GRAVINER Mk 7 control panel

Log in to the control panel as an administrator;
Select the engine for testing ME 1;
Press the "Test" button;
Press the "1" button opposite Slow Down Relay;
Press "OK";
You can test the Pre-Alarm Relay in the same way;
To test the Fault Relay, press the "0" button;
Backup Alarm, Optics Test, Front Panel Test - are tested using the "Test" buttons.

Procedure for testing sensors on the OMD GRAVINER Mk 7 control panel

OMD GRAVINER Mk 7 Control Panel Sensor Test Procedure

OMD GRAVINER Mk 7 Control Panel Sensor Test Procedure

Log in to the control panel as an administrator;
Select the engine for ME 1 testing;
Select the cylinder (sensor) for DET 1 testing;
Click "Alarm Test";
Click "Test";
Click "ME 1" - "Accept";
Click "OK";
Click "Reset";
Click "OK";
This way you can check each sensor.

OMD GRAVINER Mk 7 Sensor Test Procedure

Checking these sensors is quite simple, you need to use a special test device from the maker. This device is a bulb with a tube, you need to put a smoldering wick into the capsule, which is pre-soaked in oil and set on fire.

Bulb with a tube

And the test procedure consists of inserting a tube into a special hole in the sensor and letting smoke into the sensitive element. The sensor will work. Of course, as in the previous case, the wick must be lit in a specially designated place (without the attention of the inspector). By the way, in order for the wick to smolder for a long time and produce smoke, you need to press the bulb often.

Smoke test of the sensor

At the end of the test, pull the tube out of the hole, extinguish the wick, it can still be used for further tests.

Checking sensors on OMD GRAVINER Mk 6

As you can see, checking sensors on OMD GRAVINER Mk 6 is no different from the seventh version.

ME FO Leakage (Alarm)

The second most important alarm for inspectors is fuel leaks of the main engine. It is always checked. Usually it is implemented using a capacitive sensor that detects a high level in the leak tank of the fuel equipment of the main engine.

Main Engine Fuel Leak Sensor

To check, you need to take the sensor out of the tank and lower its electrodes, for example, into a container with diesel fuel. There is also an option that provides a "TEST" button. If the inspector is in the ECR during the check, then you can simulate the alarm by short-circuiting the electrodes with a screwdriver or wrench.

Video simulating a fuel leak sensor alarm

Main engine protection (additional)

Checks of oil mist detectors and fuel leak sensors are the main points for inspectors. And this is where they usually finish their checks on the main engine. With rare exceptions, there are other checks, which we will consider below.

Thrust Pad Bearing High Temperature (Slow Down)

Protection for high temperature of the main engine propeller shaft support bearing. It is triggered when the temperature reaches 70˚C. In my practice, such a check was often carried out on Panamaxes.

Thrust Pad Bearing Temperature

The Thrust Pad Bearing on a ship's main engine is a critical component of the ship's propulsion system that transmits axial thrust from the engine shaft to the ship's hull.

Main Functions:

1. Transmitting Propelling Force:

The main engine transmits torque to the propeller shaft, which creates the forward force of the propeller.
The axial forces generated by this (reaction from the propeller thrust) are transmitted through the thrust pad bearing to the ship's hull.

2. Shaft Support:

The bearing holds the propeller shaft in the correct position, preventing its longitudinal movement.

3. Reducing Friction:

Using lubrication (oil or other type of lubricant) reduces friction between the bearing and the shaft surface.

Simulation of high temperature of the Thrust Pad Bearing on the BMS-2000 III ME

Simulation of high temperature of the Thrust Pad Bearing on AMS JRCS

As a rule, this protection system has a regular thermal switch (thermostat). To check it, it is enough to simulate a high temperature on the sensor.

StandBy. By the way, usually all such checks are carried out in port or at anchor. And accordingly, the main engine is prepared and is in the F/E (Finish with Engine) mode. At the same time, many alarms and shutdowns for the main engine can be in the Repose status, i.e. disabled (this depends on the Remote control system). This means that when any sensor is triggered on the main engine, which is in repose, the alarm system will not work. Therefore, it is necessary to switch the main engine to the S/B (StandBy) mode to be able to check these sensors. This can be encountered, for example, on the Norcontrol (Kongsberg) system. Just keep in mind that the standby mode on the main engine starts the auxiliary blowers if they are in automatic mode.

Overspeed (Shut Down)

Simulation of overspeed on the main engine is usually done on the Remote Control System. Using a special menu, the speed is increased above the maximum.

Overspeed simulation on BMS-2000III

Overspeed simulation on BMS-2000III (instructions)

Overspeed simulation is also done on other systems (Kongsberg AutoChief, Nabtesco, etc.) in the same way. If you are interested in instructions on how to do overspeed on the above-mentioned control systems, then write in the comments, I will add them to the article.

In fact, I can’t remember when such checks were done with inspectors, it seems that overspeed on the main engines doesn’t interest them much. There is no dynamics in such simulations, the check is very simple.

Shut Down and Slow Down protection of the main engine

The main engine has many protections and it makes no sense to list them all, but it is worth paying attention to those that affect its dynamics, i.e. slow down its operation and shutdown.

Shut Down and Slow Down protection of the main engine (BMS-2000III)

Main engine pressure sensors

Manual Stop (Shut Down)

The main engine emergency stop buttons are usually located in three places (bridge, ECR and emergency control post of the main engine). When the button is activated, the main engine should stop.

Main engine emergency stop (Manual Stop button)

Main LO Low Pressure (Slow Down - Shut Down)

Low lubricating oil pressure is usually checked by stopping the main oil pump (the standby pump must be switched off). When the pressure in the system drops below 0.170 MPa (1.7 kg), slowdown is triggered, below 0.150 MPa (1.5 kg) - shutdown of the main engine. It is also possible to check the standby protection (start the reserve pump) simultaneously with stopping the main pump. When the main pump is disconnected from power or stops, the standby pump should start.

Checking the main engine protections for oil pressure (BMS-2000III)

Checking the main engine protections for oil pressure and cooling oil circulation in the pistons (BEMAC BE-D10)

On electronic main engines, there are also additional protections for the engine control system. A set of protections Slow down for EICU (Engine Interface Control Unit), as well as protections for hydraulic oil leaks, implemented using floats (like FO Leakage).

Man B&W electronic main engine control system

Floats for hydraulic system leaks

I will not consider these protections in this article (I posted them just for general information), usually inspectors do not check such protections for the main engine.

Slow down from EICU

Emergency control of the main engine

Emergency control is also a critical component of the main engine protection system. In case of problems with the Remote control system, the main engine can be controlled in an emergency manner at the local control station.

Emergency control station of the main engine MITSUI-MAN B & W 6S50ME-C9.5-EGRBP

Emergency control station of the main engine YICHANG (YMD)-MAN B&W 5S50ME-B 9.3 T II

The procedure for checking the emergency control is quite simple. Control of the main engine is transferred to the emergency station, where, using special devices, it is possible to start (stop) the main engine, as well as set the speed. In my practice, I do not remember any cases of checking the emergency control system of the main engine by inspectors.

Emergency operation of main engine (video)

Main engine protection on a ship (briefly)
Main engine protection on a ship is aimed at preventing emergency situations caused by malfunctions or deviations in engine operation. They include a monitoring system, signaling and emergency shutdown when critical parameters are detected. Let's consider the main types of protection:
1. Low oil pressure
Causes: oil leakage, filter clogging, oil pump failure.
Protection mechanism: oil pressure sensors monitor the pressure level in the system. When it falls below the permissible level, an audible and visual alarm is given. If the problem is not resolved, the engine stops automatically.
2. Overspeed (excessive shaft speed)
Causes: failure in the fuel supply control system, sudden load drop.
Protection mechanism: installation of a speed limiter (overspeed trip). When the maximum speed is exceeded, the fuel supply is blocked and the engine stops.
3. High coolant temperature
Causes: insufficient water flow (pump problems), clogged heat exchangers, faulty thermostats.
Protection mechanism: temperature sensors monitor the water temperature. If the set level is exceeded, an alarm warns the operator, and if the level is critical, the engine may stop.
4. Fuel leaks
Causes: damage to fuel lines, seals or injectors.
Protection mechanism: leak monitoring systems detect the presence of fuel in the sump or other parts of the engine. If leaks are detected, a signal is given, and the engine can be stopped manually or automatically.
5. High concentration of oil mist in the crankcase
Causes: oil overheating, fuel getting into the oil, excessive wear of parts.
Protection mechanism: oil mist sensors are installed that record the concentration of oil vapors. If the permissible level is exceeded, a signal is given, and the engine automatically stops.

Let's sum it up

In this article, we looked at the main protections of the main engine, which are most often checked by inspectors. These protections are critical and their operation can be used to judge the safety of the vessel's propulsion system.

What interesting cases have you had with checking the protections of the main engines on a vessel? Any questions or anything to add? Write in the comments to the article!

Manuals! By the way, if you are interested in the instructions for the main engines and the remote control systems, which were described in this article, I recommend our closed telegram channel Marine Engineering Manuals.

Thank you for your attention! I hope this article was useful for you.

Articles on problems with main engines:

Marine Electrical Engineer

13/05/2025

Main Engine Protections. Quick Check for Inspectors

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Main Engine Protections. Quick Check for Inspectors