Trials are necessary to test engineering readiness for war. Except while authorized to disable or partially disable, ships are expected to be able to conduct prescribed trials at any time. Ships normally should be allowed approximately a 2-week period after tender overhaul, and a 1-month period after shipyard overhaul, to per-mit final checks, tests, and adjustments of machinery before being called upon to conduct competitive trials.

Trials are also held from time to time to deter-mine machinery efficiency under service condi-tions, the extent, if any, of repairs necessary, the sufficiency of repairs, and the most economical rate of performance under various conditions of service.

INSPECTIONS AND TESTS PRIOR TO TRIALS.The full power and the economy trials, as discussed in this chapter, are considered in the nature of competitive trials. It is assumed that the ship has been in full operational status for sufficient time to be in a good material con-dition and to have a well-trained crew.

Prior to the full power trial, inspections and tests of machinery and equipment should be made to ensure that no material item will interfere with the successful operation of the ship at full power. The extent of the inspections and the tests will largely depend upon the recent performance of the ship at high speeds, the material condition of the ship, and the time limits imposed by opera-tional commitments.

Not later than one day before a trial, the engineer officer must report to the commanding officer the condition of the machinery, stating whether or not it is in proper condition and fit to proceed with the trial.

GENERAL RULES FOR TRIALS.During all full power trials, and during other machinery trials, the following general rules should be observed:

1. Prior to commencing a power trial, the machinery should be thoroughly warmed up; this can be accomplished by operating at a high frac-tional power.

2. The speed of the engines should be gradu-ally increased to the speed specified for the trial.

3. The machinery should be operated economically, and designed pressures, temperatures, and number of revolutions must not be exceeded.

4. The full power trial should not be con-ducted in SHALLOW WATER, which is con-ducive to excessive vibration, loss of speed, and overloading of the propulsion plant.

5. A full power trial should continue beyond the length originally specified, and all observa-tions should be continued until the trial is finished.

6. The trial should be continuous and without interruption. If a trial at constant rpm must be discontinued for any reason, that trial should be considered unsatisfactory and a new start made.

7. No major changes of the plant set-up or arrangement should be made during economy trials.

UNDERWAY REPORT DATA.Reports of trials include all the attending circumstances, especially draft forward, draft aft, mean draft, and corresponding displacement of the ship at the middle of the trial; the condition of the ships bot-tom; the last time drydocked; the consumption of fuel per hour; the average speed of the ship through the water; and the average revolutions of the propelling engines. The methods by which the speed was determined should also be described.

Reports should also include tabulations of gage and thermometer readings of the machinery in use, and the revolutions or strokes of pertinent auxiliaries. The auxiliaries in use during the trial should be stated. Each report should state whether the machinery is in a satisfactory condition. If the machinerys condition is found to be unsatisfac-tory, all defects and deficiencies should be fully described and recommendations made for correct-ing them.

TRIAL REQUIREMENTS.Trial requirements for each ship cover the rpm for full power at various displacements and injection temperatures. They are furnished to commanders and units concerned, by the Chief of Naval Operations (Operations Readiness Division).

As far as reports are concerned, full power trials are of 4 hours duration. The usual procedure is to operate the ship at full power for a suffi-cient length of time until all readings are constant, and then start the official 4-hour trial period. Economy trials are of 6 hours duration, a different speed being run at each time a trial is made.

Once scheduled, trials should be run unless prevented by such circumstances as:

1. Weather conditions which might cause damage to the ship.

2. Material troubles which force the ship to discontinue the trial.

3. Any situation where running or completing the trial would endanger human life.

If a trial performance is UNSATISFACTORY, the ship concerned will normally be required to hold a retrial of such character as the type commander may consider appropriate. The fact that a ship failed to make the required rpm for any hour during the trial, and the amount by which it failed, should be noted in the trial report.

OBSERVATION OF TRIALS.When full power trials are scheduled, observing parties are appointed from another ship whenever practicable. When a ship is scheduled to conduct a trial while proceeding independently between ports, or under the other conditions where it is considered impractical to provide observers from another ship, the ship under trial may be directed to appoint the observers.

The number of personnel assigned to an observing party vary according to size and type of ship. The duties of the observing party are usually as follows:

1. The chief observers organize, instruct, and station the observing party. They check the ships draft, either at the beginning of the trial or before leaving port; supervise the performance of the engineroom observers; check the taking of counter readings; render all decisions in accordance with current directives; and check and sign the trial reports.

2. The assistant chief observers assist the chief observers as directed; supervise the performance of the observers; check the taking of fuel oil soundings and meter readings; and make out the trial reports.

3. Assistant observers take fuel soundings, meter readings, counter readings, the ships draft, and collect all other data that may be required for the trial reports.

The following items should be accomplished or considered before starting the trial:

1. When requested by the observing party, the ship under trial should provide or designate a suitable signaling system so that fuel soundings and the readings of counters and meters may be taken simultaneously.

2. The ship under trial should furnish the chief observer with a written statement of the date of last undocking, and the authorized and actual settings of all main machinery safety devices and dates when last tested.

3. The ship should have its draft, trim, and loading conform to trial requirements. In case a least draft is not specified, the liquid loading should equal at least 75% of the full load capacity.

4. The chief observer should determine draft and trim before and after the trial, verify the amount of fuel on board and correct this amount of the time of beginning the trial. The draft observer should also determine the rpm required for the full power trial, at the displacement and injection temperature existing at the start of the trial.

5. The observing party should detect and promptly correct any errors in recording data, since it is important that the required data be cor-rect within the limits of accuracy of the shipboard instruments.

6. The chief observer should instruct members of the observing party to detect any violation of trial instructions, of instructions in the Naval Ships Technical Manual, or of good engineering practice, and then verify any such report and pro-vide the commanding officer or a detailed account of each violation.

MANNER OF CONDUCTING TRIALS. Some of the requirements in regards to the manner of conducting full power and economy trials are as follows:

1. Unless otherwise ordered, a full power trial may be started at any time on the date set.

2. The trial should be divided into hourly intervals, but readings should be taken and recorded every half hour. Data are submitted as hourly readings in the trial report.

3. Fuel expenditures for each hourly interval of the trial should be determined by the most ac-curate means practicable, normally by meter readings corrected for meter error and verified by soundings.

4. The appropriate material condition of the ship should be set during the different trials.

5. During all trials the usual housekeeping and auxiliary loads should be maintained and the minimum services provided should include nor-mal operation of the distilling plant, air com-pressor, laundry, galley, ventilation systems, elevators (if installed), and generators for light and power under load conditions similar to those re-quired for normal operations at similar speeds under the prescribed material condition.

6. All ships fitted with indicators, torsion-meters, and other devices for measuring shaft or indicated horsepower should make at least two observations during the full power trial to deter-mine the power being developed.

7. The chief observers report of the trial should state whether all rules for the trial have been complied with.

SOME HINTS IN REGARD TO FULL POWER TRIALS.There are special forms used for full power and economy trial reports. Illustrations of these forms are not given in this training manual, but you can obtain copies from your log room, and in this way get an idea of the data and readings that are required for full power and economy trials.

Trial forms, and such items as tachometers, stop watches, and flashlights, should be available to the observing party and to the personnel who take readings. Any gages or thermometers which are considered doubtful or defective should be replaced before trials are held. A quartermaster must check and adjust all clocks in the engineer-ing spaces and on the bridge before any trials are held.

It is important to make careful inspections and tests of equipment and items of machinery that may cause difficulties during full power opera-tion, since it is possible that unknown defects or conditions may go undetected during operation at fractional powersthe normal operating con-dition of the ship most of the time.

Before a trial run is made, the main engines should be inspected to make sure that the power output of the individual cylinders is equal; this ensures a balanced, smooth-operating engine, at maximum speed and power. Equal load distribu-tion between the individual cylinders depends on the following factors being as nearly equal as possible for all cylinders.

1. Compression pressures.

2. Fuel injection timing.

3. Quantity and quality of fuel injected.

4. Firing pressures.

5. Inlet valve timing and lift.

6. Exhaust valve timing and lift.

7. Exhaust gas temperatures.

A common practice among many com-manding officers, when making full power trials, is first to bring the ship up to a speed of one or more knots below the trial run speed of the ship and then turn the control of the speed (except in cases of emergency nature) over to the engineer officer. The control engineroom, under the super-vision of the engineer officer, brings the speed up slowly, depending upon the conditions of the plant, until the specified speed has been reached.