After all the systems are erected on the ship and when the ship is ready for delivery to owners, sea trials are to be carried out for the vessel. To test all systems at their full capacity and to confirm that the performance of the vessel meets the requirements specified in the technical specification signed with owners and also the rules and regulations of the classification society.
The important tests to be carried out during sea trials are as follows:
- Draft measurement
- Anchor test
- steering gear test
- Endurance test
- Speed trials
- Crash stop test
- Astern Running
- Turning circles
- Operation of navigational equipment
- Blackout test
- Running tests of other equipment
Draft & specific gravity of sea water are to be measured before going on trials and if necessary, the draft is corrected since speed trials are to be carried out at a particular draft to prove guaranteed speed.
Test procedure is as follows;
- The test is conducted at a depth of sea of 80m.
- The anchor is dropped (port & starboard one after the other) freely. While dropping brake is applied 2 to 3 times to test the capacity of the brake.
- The anchor is heaved and heaving speed is measured by noting down time on the stopwatch for heaving each chain length. Hoisting speed is not to be less than 9 m/min.
STEERING GEAR TEST:
The test procedure is as follows:-
- Vessel shall be moving ahead at full ahead speed.
- The rudder is moved from 35-degree port to 35-degree starboard (hard port to hard starboard) by using pressure from a) 1 hydraulic pump & b) 2 hydraulic pumps.
Measurement: time for moving rudder from 35-degree port to 35-degree starboard shall be less than 28 seconds, as per class requirement.
B) Emergency Steering Test:
The steering gear shall be operated using emergency power from emergency D.A. set when vessel is moving ahead at half ahead speed.
ENDURANCE TEST OF MAIN ENGINE:
The test procedure is as follows:-
- The main engine shall be run for 6 hours at full rated r.p.m to test the engine at full load. For the first hour or two, the engine is run on LDO.
- For the next 3 to 4 hours on HFO
- And the last 1 hour or 2, again on LDO.
- This is to check the changeover process from LDO to HFO and from HFO to LDO.
- All systems are checked for leakages.
- The temperature and pressure of all systems (Freshwater, lube oil, fuel oil, sea water exhaust gas) are measured and recorded.
- Fuel oil consumption in litre/hour is recorded and specific fuel oil consumption in gm/kw/hr is evaluated.
- Power is recorded from shaft horsepower meter.
- Exhaust gas boiler performance is observed.
- Fresh water generator capacity is recorded.
- Noise levels are recorded at various places on the ship.
- Vibration levels are recorded at different places on the ship.
- Load on diesel generated sets is recorded.
Speed trials are carried out to check the speed of the vessel at required draft as per contract.
The test procedures are as follows:
- The test is carried out at minimum three powers (example:- 75%, 85%, 100% or as per contract).
- At each power, speed is measured using GPS (Global positioning system) by running the ship in two opposite directions (which is called double run). Speed is calculated in each direction and average speed is calculated.
- Speed-Power curve is drawn for the three powers with corresponding speeds.
- From the curve, the speed corresponding to the required power (as per contract) is noted.
CRASH STOP TEST:
The test procedure is as follows;
When the vessel is moving ahead at full speed, the engine is reversed to full astern for stopping the vessel.
- Time for stopping the vessel is recorded.
- Distance travelled by the ship after putting the lever to full astern is recorded.
- The test is also carried from full astern to full ahead.
As per, rules all vessels shall have a facility to run in the astern direction. Accordingly, during sea trials, astern running is demonstrated at about 70% ahead revolutions by running the engine in reverse direction.
The test procedure is as follows:
- The rudder is put to hard port and the vessel is run to complete one circle.
- The diameter of the circle is measured using GPS.
- The test is carried out similarly by putting the rudder to hard starboard.
OPERATION OF NAVIGATIONAL EQUIPMENT:
Equipment like radar, communication systems etc., are checked during sea trials.
all the 3 main generators are shut down and automatic starting of emergency D.A. set is observed. The emergency D.A. set should come online within 4.5 seconds.
RUNNING TESTS OF OTHER EQUIPMENT:
All other equipment are kept running and their performance is observed for any defects.