Marine Engineering ©
The Secrets of the Profession

Solutions you will not find written in any book, because they come from my personal experience on ships

SECRET 1

How to open a sea strainer that does not isolate.


How to open a sea water strainer (Sea Chest / Strainer) that does not isolate, using the vacuum method

On ships, sea water strainers (sea water strainers / sea chests) are critical for the proper operation of cooling systems. In many cases, it is observed that the strainer does not fully isolate, even when both valves (external and internal) are closed.
This creates a serious flooding risk when opening the cover.

A safe and proven solution is the so-called vacuum method.

When this method is applied

The vacuum method is applied when:

  • The strainer leaks or fills up even though the valves are closed
  • There are worn seats, sand, shells, or corrosion
  • The strainer is double (double strainer) and the other one is in operation

⚠️ Condition: The other strainer must operate normally and feed the system.

Basic principle of the vacuum method

The idea is simple but clever:

We create negative pressure (vacuum) inside the strainer we want to open, so that the sea water cannot rise.

Step-by-step procedure

1️⃣ Make sure the other strainer is in use

  • Strainer A (in operation) feeds the system normally
  • Strainer B is the one we want to open

2️⃣ Close the external valve of strainer B

  • That means the valve communicating with the sea (even though we know it does not isolate 100%)
  • Close it as well as possible

3️⃣ Close the internal valve of strainer B

  • The one leading to the pump / system

4️⃣ Create the vacuum (the critical point)

  • Close about 90% of the internal valve of strainer A (the one operating)
  • Then slightly open the internal valve of strainer B

What happens here:

  • The pump “pulls” water from strainer B
  • A VACUUM is created in strainer B
  • The water does not rise, even if strainer B does not isolate properly

5️⃣ Check before opening

  • Unscrew the cover very slowly
  • If no water rises ✅
  • If you hear a slight air “suction” sound ✅
  • Then the vacuum is working correctly

6️⃣ Open and clean the strainer

  • Open the cover fully
  • Clean thoroughly:
    • Basket
    • Seat
    • Sealing rubber gaskets
  • Check for:
    • Shells
    • Sand
    • Corrosion

SECRET 2

HOW TO COOL THE MAIN ENGINE WHEN BOTH SEA WATER PUMPS HAVE FAILED


How to cool the Main Engine when both Main Sea Water Pumps have failed, using the Emergency Fire Pump

On a cargo ship, the loss of both sea water pumps of the main engine is a serious emergency condition. Without sea water, the cooling system cannot reject heat, and the main engine is immediately at risk of overheating.

In such cases, an emergency but proven practical solution can be applied, using the Emergency Fire Pump as a temporary sea water source.

Basic principle of the method

  • It has an independent sea suction (usually at the bow)
  • It is outside the main engine room
  • It can provide a continuous flow of sea water
The idea is to feed the Central Cooler of the LT (Low Temperature Water) system directly, completely bypassing the Main Sea Water Pumps.

Arrangement description

  • ❌ Both Main Sea Water Pumps out of service
  • ✅ Emergency Fire Pump available
  • ✅ Fire line in good condition
  • ✅ LT system Central Cooler available
  • ✅ The Central Cooler strainer has been removed
  • ✅ Special hose connections are welded onto the strainer cover

Connection steps:

1️⃣ Remove the Central Cooler strainer

  • The internal strainer is removed completely
  • Goal: free water passage

2️⃣ Connect the Fire Line

  • Use 2 fire line hoses
  • The hoses start from the fire main and connect to the Central Cooler strainer cover
  • The hose connections are specially welded and fitted with the correct thread / flange

3️⃣ Start the Emergency Fire Pump

  • The pump draws water from a separate sea suction at the bow
  • It provides a stable sea water flow to the system

How the main engine cooling works

  • Sea water from the Emergency Fire Pump enters directly into the Central Cooler
  • The Central Cooler cools the LT fresh water
  • The LT water cools:
    • Charge air
    • Lubricating oil
    • HT water (through heat exchangers)
  • Thus, the main engine can continue operating at reduced load

Important limitations ⚠️

  • 🔻 Reduced engine load — not full ahead, continuous temperature monitoring required
  • 🔻 No firefighting reserve — while this setup is used, firefighting capability is lost
  • 🔻 Temporary solution — only until the Main Sea Water Pumps are repaired

What must be continuously monitored

  • Temperature: LT water, HT water, lube oil
  • Fire line pressure
  • Leaks in the hoses
  • Flow stability to the Central Cooler

Personnel safety

  • One person on permanent watch
  • No hot work
  • Keep ready: wooden plugs, wedges, flashlight
  • Immediate shutdown if flow is lost or temperatures rise

Conclusion

Using the Emergency Fire Pump to cool the main engine is:

  • smart
  • practical
  • marine-engineering acceptable in an emergency

It does not replace proper repair, but:

it gives you time,
saves the engine,
and gets you out of a dead end.

SECRET 3

How to install new piston rings in bad weather in the middle of the ocean.


How to change Main Engine piston rings in bad weather, in the middle of the ocean

A piston ring failure (blow-by) in the main engine, while the ship is in the middle of the ocean and in bad weather, leaves you with no choice.

The job must be done on site, without dock, without workshop, without ideal conditions.

When the rings are damaged:

  • temperatures rise
  • compression drops
  • the liner and piston are at risk

If you continue, you will cause even greater damage.

The main problem in bad weather

  • The ship rolls heavily
  • The crane cannot safely keep a load suspended high
You adapt the job to the conditions, not the other way around.

Critical decision: Do not lift the piston high

  • As soon as the piston crown comes just out of the liner
  • DO NOT continue lifting

Reason:

  • With ship movement, the piston becomes a pendulum
  • Danger: impact and personnel injury

How it is done:

  • Place 2 strong wooden blocks on top of the liner, parallel and stable
  • Lower the crane slightly
  • Rest the piston crown on the wooden blocks

This way:

  • The piston is stabilized
  • It is not suspended
  • We can work with relative safety

Cleaning the piston crown in place

Without moving the piston:

  • Clean: ring grooves, piston crown
  • Remove: burnt oil, carbon deposits, remains of damaged rings
  • Inspect: grooves (no step wear), signs of overheating

⚠️ If the grooves are broken, the job stops.

Piston ring replacement

  • Install the rings one by one
  • Pay attention to correct direction (TOP / marking)
  • Pay attention to correct gap
  • Rotate the gaps according to instructions, not all in the same line

Reinserting into the liner – slowly and by hand

Because there is no ring guide:

  • Lower the piston very slowly
  • Use your hands to press the rings one by one so they enter the liner smoothly
  • Continuous check: no ring must catch, and no edge must pinch

If it jams:

  • STOP
  • Lift it slightly again
  • Realign it

Why this method works in bad weather

  • The piston is not suspended
  • Control is slow, stable, and human-guided
  • You do not depend on tools that cannot be used effectively in those conditions

Safety rules (non-negotiable) ⚠️

  • ONLY experienced personnel
  • No hands under a suspended load
  • Clear coordination between crane operator, engineer, and assistant
  • If weather worsens: stop, secure everything, wait

Conclusion

  • It is not textbook work
  • It is experience-based work
  • It is done only when there is no other option

But if done correctly:

you save the engine,
keep the ship moving,
and return to port standing strong.

📌 This ARTICLE is intended for:

  • Merchant Marine Academy students
  • Merchant Navy engineers
  • Friends of shipping and marine engineering

⚓ Marine engineering is not just power — it is control, knowledge, and proper synchronization.