Why ships must be inspected
A ship works for many years in rough sea, salt water and heavy loads. Steel slowly rusts and parts wear out. A hidden crack can become a disaster far from land. So there are rules that make owners show, again and again, that a ship is still safe.
These rules are made by countries (the ship's flag country) and by international agreements. Inspectors, called surveyors, check the ship. They may work for the government or for a classification society, an organisation that sets technical rules for hulls and machines.
The inspection system: surveys and certificates
A ship gets its first full check when it is built (an initial survey). After that it is checked on a schedule. The details differ between countries and ship types, but the common idea is:
- Periodic (regular) inspection: a big, full check, usually about every 5 years.
- Intermediate inspection: a smaller check between the big ones.
- Annual checks of safety equipment and certificates.
- Extra inspections after an accident or a big repair or change.
What does the inspector check? The hull (thickness of plates, cracks, rust), the engine and machines, lifesaving equipment (lifeboats, life jackets, fire fighting), radio and navigation equipment, and load line marks. When all is good, the ship gets or keeps its certificates. A ship without valid certificates may not sail and can be stopped in a port.
Port officers can also check foreign ships that arrive in a port. This is called port state control.
Repair works and dry docking
Repairs can be routine (planned, for example painting and servicing the engine) or emergency (after damage, such as hitting something or an engine failure). Small repairs are done afloat at a quay. Repairs to the underwater hull, the rudder and the propeller need the ship to be out of water.
For this, the ship goes into a dry dock. The dock is a big basin. The ship floats in, the gates are closed, the water is pumped out, and the ship rests on supports called keel blocks. Now workers can walk under the hull.
Typical steps: 1. clean the hull. 2. measure plate thickness and look for cracks. 3. cut out damaged steel and weld new plates. 4. repair or replace the propeller and rudder parts. 5. repaint with new paint, including anti-fouling. 6. fill the dock with water and float the ship out. 7. surveyor checks the work and the certificate is renewed.
A ship loses money when it is idle, so owners plan repairs carefully to keep the time in dock short.
Try it
At home: make a checklist for your bicycle: brakes, tyres, chain, bell, lights. Check each one. If one fails, fix it and check again before the ride. You did a small survey and repair.
In the 3D: press the four check buttons, then try pressing Repair while the water is high. What does the message say? Lower the water to 0 and try again.
Key formulas and definitions
- Sail only when: inspected + defects repaired + certificates valid
- Surveys: initial → annual → intermediate → periodic (about every 5 years)
- Dry dock work: float in → close gates → pump out → repair → refill → float out
Worked examples
1. A ship has a periodic inspection (full check) in year 0. When is the next full check due, usually?
About 5 years later, so in year 5. Between them there are intermediate and annual checks.
2. Why must the ship be put in a dry dock to replace a rusted plate on the bottom?
The bottom is under water when the ship floats. Workers cannot weld or paint under water in the same way. In a dry dock the water is pumped out and the bottom is open to air.
3. A ship's lifeboat is found with a broken engine during an inspection. What should happen before the ship sails?
The lifeboat engine must be repaired (or replaced) and checked again. Lifesaving equipment must work before the ship can keep its certificate.
4. Name one planned repair and one emergency repair.
Planned: repainting the hull or servicing the engine at a set time. Emergency: repairing a hole after hitting something, or fixing an engine that failed at sea.
Common mistakes
- Thinking inspections are done once, when the ship is built. They are repeated on a schedule for the ship's whole life.
- Thinking all repairs need a dry dock. Many repairs are done afloat; only underwater work needs a dock.
- Thinking a certificate is just a paper. It is the proof that a surveyor found the ship safe; without it the ship may not sail.
- Mixing up routine and emergency repairs. Routine is planned; emergency happens after damage or failure.