5 Important Drains in the Ship’s Engine Room

In the ship’s engine room, there are several drains provided in order to prevent water clogging and damage to any machinery.

It is apparent that these drains must be closely considered by seafarers while taking watch-keeping rounds.

However, four of these drains are of utmost importance as their non-operation might lead to devastating consequences in the engine room.

Air Cooler Condensate Drain:

How Is Condensate Generated?

The air cooler condensate drain is one of the most important drains in the engine room. The charge is air-cooled in the air cooler and it then passes through its dew point temperature, generating a lot of condensates.

Related Read: How Marine Air Charging System For Engines Has Changed Over Time

The generation of the condensate depends not only on the humidity and temperature of the ambient air but also on the pressure and temperature of the charge air.

It also depends on the temperature of the cooling water by which the air is cooled.

It has been analysed that the ambient air has higher pressure and temperature when it passes through the compressor side of the turbocharger.

Moreover, the dew point temperature depends on the pressure which is apparently changed when condensate passes through the compressor side of the turbocharger, yet again.

How Does It Affects The Engine?

Proper condensate water drain is very important for the safe operation of the engine. Condensate water generally consists of small sediments such as dust and water, which are disastrous for the engines.

The drain lines will get clogged if not cleaned properly and hence the water and sediments might find their way to the combustion chamber of the engine.

Over a period of time, this mixture may peel off the paint and corrode the surface of the charge air chamber and the flange, if present in small quantities; else might also cause failure of the intake valve if it finds way to the combustion chamber of the engine.

Related Read: 8 Signs That Indicate Your Ship’s Auxiliary Engine Needs Overhauling

This peeled off paint is the main reason for the drain line to get choked.

Further, the water is incompressible and (over a period of time) may break the piston and even bend the connecting rod, causing a devastating breakdown of the engine.

Counter-Measures, If Any?

It is generally recommended by the engine manufacturers to remove the condensate regularly by installing a float chamber from the air cooler drain.

When the water level rises in the float chamber, the float rises and the valve tends to open which may drain the condensate.

An orifice of 3 mm is generally present on the drain line which tends to be clogged quite often by the sediments present in the condensate drain. Hence it must be replaced with a 5 mm orifice.

Several engine manufacturers have removed the ball float from the inside of the chamber or the condensate drain tank to get rid of the clogging problem. They have rather recommended to install a ball valve which may be opened partially to remove the condensate regularly. There is but a risk of it getting closed accidentally which is again a close concern.

There could also be a possibility of the air cooler drain line getting choked from inside because of remaining water and sediments for a prolonged period. Thus, the intake air chamber should also be inspected as well.

Hence, if the countermeasures mentioned above are followed, then the possibility of problems generated by the clogging of drains could be avoided but regular opening of the float chamber is recommended by most engine manufacturers as a precautionary measure.

The interval for opening of the drains and intake air chamber could be adjusted according to the engine running hours and a job should be created by the company in the Planned Maintenance System as well.

Thus, this drain is the first thing to be checked in the engine room while taking rounds on a running generator.

Auxiliary Engine Turbocharger Drain:

Is That A Misnomer? How To Check?

Auxiliary engine turbochargers are installed with a drain which must be regularly checked everyday during morning and evening rounds for the possibility of it being clogged. There is a faint probability that the drain might get clogged because of the particles of combustion from the exhaust gas being carried over.

Background. Does It Really Matter?

Supercharging is one method employed in auxiliary engines to increase the efficiency by a considerable amount by increasing the weight of the air supplied to the engine. This helps in burning more fuel per stroke of the engine which increases the output subsequently.

Turbochargers are hence used to increase the weight of the air. The turbochargers are driven by the exhaust gas from the engine which in turn drive a compressor wheel to compress the ambient air and hence supply as charge air to the engine.

Several types of fuel oils are available in the market mainly  – HSFO, VLSFO, LSMGO and ULSFO.  New fuels have been introduced in the market after the global sulphur cap of 2020 or IMO 2020.

Existing ships with scrubber systems are still using HSFO and the ones without are using VLSFO which apparently is something very similar to HSFO as it is blended with LSMGO.

Turbochargers operating on HFO and even VLSFO are subjected to fouling and deposits that originate from the burning of fuel.

  • The turbine side fouling depends on a lot of factors which may include the low load operation of the engine, which causes incomplete combustion and eventually the build up of coke in the exhaust gas
  • The fuel quality is another deterrent to the good combustion of the fuel
  • The fuel injectors leaking, dripping or set at incorrect pressures could be another major reason for the same
  • Similarly, the incorrect timings of the fuel pumps may be another cause of fouling of turbochargers
  • Not maintaining the correct viscosity of the fuel which directly depends on the temperature of the fuel at the engine inlet. It is generally recommended by the manufacturers that the fuel at engine inlet should be between 12 Cst and 18 Cst. The lab analysis reports must thus be paid a close consideration.

Fouling actually reduces the turbocharger’s efficiency which may increase the exhaust temperatures and the fuel consumption. Thus, the turbine side cleaning is necessary for the clean operation of the turbochargers. This will further help in increasing engine performance.

The water washing system installed on all the auxiliary engines will allow cleaning on the turbine side while the engine is operated on a certain load.

Two methods are generally used for washing:

  1. A short injection time mainly 3 X 30 seconds is permissible on any turbine casing.
  2. The long water injection time procedure which is 10 minutes has been introduced by makers recently.

The turbocharger is water washed every 100 hours and the drain is then opened for clear water to pass at a load of about 20 to 40% of the maximum rated.

The water washing drain is opened in this period to check the condition of water and is closed after its completion. The makers suggest to keep the load constant for approximately 10 minutes and then increase to maximum for the traces of water to be evaporated.

Is It Disastrous?

There have been several cases of water accumulation in the turbine casing after the water washing of the turbine side, leading to disastrous consequences. Some of them are enumerated below:

  1. Some vessels have experienced a hole in the T/C gas outlet casing and this has mainly happened because of the incomplete drain of the water during the periodical cleaning of the turbine of turbocharger and the entrance of water such as rain from the funnel. This water causes the corrosion of the turbocharger outlet casing and eventually a hole in the casing as well.
  2. In severe cases, the drain might be clogged and a lot water might collect inside the casing while water washing the turbine and mix with the exhaust gases from the combustion chamber to form dry coke and get stuck to the turbine wheel and the nozzle ring.
  3. There is grave possibility of the turbocharger losing its bearing and stop rotating completely to seize the generator operation. The vessel might lose the turbocharger and hence lose an important operation if there isn’t any spare cartridge present on-board. Thus, it is always advisable to keep one spare cartridge onboard.

Countermeasures, If Any?

The drain is to be checked everyday during rounds for the accumulation of water. Further, during and after washing the turbocharger the drain must be left open for a period of about 30 minutes so that all the water is drained from the casing.

Also, when it is raining, open the drain connected to the gas outlet casing.

If it is expected that the turbocharger is losing rpm, then it must be opened immediately and checked for the possible traces of soot and carbon inside the casing.

Fuel Oil Settling And Service Tank Drains:

These two drains are the most important drains in the engine room. The fuel oil settling and service drains are used to remove water from the tanks which is carried over when the fuel oil is transferred from the bunker tank to the settling tank.

Related Read: A Comprehensive List of Fuel, Diesel and Lube Oil Tanks on a Ship

The Loopholes?

Fuel oil is generally the product generated after blending the distillate and the residual fuel oil post-refining. In this process, water and several sediments are added to the blended product un-intentionally which arise due to the cleaning of tanks. This process of unwanted addition of sediments and water is unavoidable and hence is supposed to be removed.

Scaring The Obvious?

The water present in the fuel oil (in small quantities) is generally removed by a fuel oil centrifugal separator, most commonly known as a purifier. The purifier may fail to remove the water, if present in large quantities. Thus, letting it carry over to the fuel oil supply pumps.

One must understand that after the fuel oil purifiers, there is nothing that will aid in the removal of water from the fuel oil line of the auxiliary engines and the main engine. Hence the water might get carried over if present in large quantities.

If water finds its way to the auxiliary engines, then it’s certain that a blackout might occur and it would be very difficult to revive the engines. One must understand the gravity of the situation as it would be preposterous to start the engine till the time water is drained off completely from the engines. If auxiliary engines couldn’t be started, then the main engine can’t be started and hence there will be a chain of events leading to a complete fiasco of the entire control.

Similarly, if water finds its way to the boiler then the boiler will be very difficult to fire and there will be no steam generated to heat up the tanks and the fuel oil.

Once water gets into the system, draining is a heck of a task as it might take hours to get the system back to normal which might lead to probable off-hires and loss of reputation to the company. In this fast pacing competitive market, a large amount of money is involved and getting the cargo moved in a minimum possible time matters the most.

Countermeasures, If Any?

The fuel oil settling and service drains should be opened once in every watch and it should be made certain that the water is removed completely from the system. It’s a closed cycle and hence the water removed from the settling and service drains goes back to the fuel oil drain tank, which again is transferred to the settling tank. This is the biggest mistake that engineers do as they didn’t get rid of the water completely, rather circulated it back to the system which indeed is grave.

Thus, the water should be removed from the system.

Fuel oil settling and service tanks are often provided with two suction valves mainly low suction valve and high suction valve. The high suction valve is used to prevent the shut-down of main engine, auxiliary engine and the boilers in case of the tank contaminated by large quantities of water which generally stays at the bottom of the tank.

Air Receiver Drains:

The air receiver drains are used to drain the water that has been collected in the air bottle due to the condensation of mist passed over by the compressor. The temperature of the air compressed by the compressor is in the range of 90-100 degrees centigrade. It contains a considerable quantity of water and oil carried over in the form of mist, which generally condenses in the air bottle and hence is collected in the bottom of the air receiver.

Avoiding The Un-Avoidable?

Compressed air onboard is used for starting the main engine and auxiliary engines, it is also used for the instrumentation and controls which could be stored in a separate air bottle. The air is also used to drive the various pneumatic tools present onboard. Further, several ships are provided with air driven soot blowers for the economizers as well.

The compressed air onboard a ship can be categorized as starting air, service air and control air which are self explanatory.

The water and oil present in small quantities can be drained by the two drain valves installed in the bottom of the compressor. This water and oil, if not drained might find its way to the main engine (considering only starting air) while starting and hence enter the combustion chamber of the relevant cylinder. As it is understood that water is incompressible, it might be disastrous for the engine. Similarly, if oil along with water enters the starting air line of the engine, it could cause an explosion, provided the starting air valve sticks open as the line may be subjected to the combustion pressure which is relatively very high.

Related Read: How to Prevent Starting Air Line Explosion on Ships?

Thus, the main engine and auxiliary engines must be blown through every time before starting the engine to know the ingress of water, if any.

Further, water is also undesirable for the instrumentation and controls and hence must be removed immediately from the system.

Countermeasures, If Any?

Making it obviously obvious, the air receiver drains must be drained everyday in the morning and at least once in every watch, if the engine room is manned but there’s a specific method to do it. Every air bottle is provided with two valves in the drain line, one connected directly to the pressure vessel and the other just next to it.

The one connected directly to the pressure vessel must be opened in full and the one next to it must be throttled. This is done to prevent the leakage of the valve connected directly to the pressure vessel as it happens with all the throttled valves in the high pressure lines.

Further, an air bottle inspection just be carried out as per the job in the PMS to ascertain the condition of the internal wall and the mountings connected therein.

Starting Air Line Drain:

Starting air line drain is similar to the starting air receiver drain as it is used to drain the moisture and sediments collected in the starting air line after the engine is secured. This drain is supposed to be open every time after the engine is secured.

Similar Story, Dissimilar Explanation:

A lot of moisture and oil might condense in the starting air line as is the case with air receivers, which must be drained regularly. Unlike air receivers, these drains can’t be opened when the main engine is running and hence could only be opened when the main engine is stopped.

Again, if water gets into the starting air system, it might lead to uneventful consequences and hence that could be disastrous for the engine.

Countermeasures, If Any?

This drain should be opened after the main engine is secured and kept open to drain the residual oil or water present in the line. This should be a standard practice followed by all engineers every time the main engine is secured.

Incidents related to most important drains in engine room:

  1. The Air bottle moisture drains and
  2. Water Drains from fuel oil settling and service tanks

Most of you would know this for sure, but the fact remains that several mishaps happen due to improper handling and infrequent draining of these tanks. Mentioned below are two instances which explain the importance of these drains in ship’s operations.

Lesson 1

On one of our previous ships, we had an anchorage of 24 days and in this period everyone in the engine room forgot to drain the water from Fuel Oil settling and service tanks in the ship’s engine room.

We then suddenly received orders to move the ship. After a few hours, the engine slowed down and an overload alarm appeared on the engine control room panel.

We immediately tried to find out the reasons for the overload alarm and realised that the viscometer was showing “high viscosity” level. After some brain-storming, it was decided to check the service tank drains.

ship engine

The junior engineer, who was assigned the task of checking the drains, came back saying that oil and not water was coming from the drains. However, when asked to drain more, a large amount of water discharge was found.

Luckily the generators were on Diesel oil (D.O) which helped prevent the blackout on the ship. Moreover, we had two settling tanks, so removal of water was much faster, but we missed the convoy at Suez as the engine RPM did not increase until “good quality” oil came in the line and the viscosity reached near normal.

Lessons Learnt:

We should have drained the tanks every day until we saw (Collecting the drain in suitable container- half cut soft drink can) no water coming. In our case, the drain pipe end was ending too deep in the funnel so the contents could not actually be seen. It is thus extremely important that what is coming out of the drain is clearly seen.

In dry dock, while cleaning Fuel Oil service tanks, a senior engineer must carefully check the drain from both inside and outside. The steam heating coils must also be pressure tested at this occasion.

Lesson 2

Air bottles are important for supplying air to the marine engine air starting system and for other important purposes. On a new ship, it was found that we were draining water not from the Air bottle bottom drain but from a drain on the filling line.

ship engine

Below the filling line drain, a funnel was installed which was quite familiar to the air bottle drain funnel. The motorman was so sure about the drain that no senior officer bothered to cross check. Then, one day we got a doubt about the quantity of water draining from the funnel, which was of course not of the quality we expected.

Upon opening the air bottle manhole door it was found that the water was filled up to quite a high level and luckily it did not find its way into the main engine, else there could have been a massive damage to the engine or even injury due to water hammer. The Air bottle was then cleaned and the defect was rectified.

Lessons Learnt

Nowadays, it is often seen that the tracing of pipelines in ship engine room is not done properly, mainly because of shortage of crew members and fast turnarounds. Efforts should thus be made to trace the pipelines once in a while.

While opening air to main engine, moisture must be drained from the bottom most point of the line. Air driers and control air line filters must also be regularly checked.

ship engine

These days quarantine inspection has also become important. The cold room holding provisions thus must be kept clean. Meat room and fish room drains should be checked (put a handful of salt in them), along with the unit cooler pan heater and drain.

Related Reading

A Comprehensive list of lube oil and  fuel oil tanks on ships

A List of Important tanks on a ship

Understanding sounding, ullage, and frequency of sounding


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The information contained in this website is for general information purposes only. While we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.

About Author

Mahendra Singh is a marine engineer with more than 20 years of experience as chief engineer on a variety of vessels such as bulk, container and car carriers. He has also served as an engineer and ship surveyor with the Government of India. When not sailing, Mahendra Singh likes to teach at maritime academies.

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  1. Air Cooler drain is also very important especially in areas with high humidity as water carried along with the scavenge air could enter the engine cylinders leading to acid corrosion,washing away of the lube oil film and so poor liner lubrication etc

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