ENGINEMAN  1  &  C The trials that are considered to be routine ship’s trials are numbers 3, 9, and 10 of the above list. Post repair, full power, and economy trials are the only ones discussed in this chapter, but information on the other types of trials can be found in Naval Ships’ Technical Manual, chapter 094. technicians carefully inspect it to determine the cause of unsatisfactory operation. Full Power and Economy Trials Post Repair Trial The post repair trial should be made whenever the machinery of a vessel has undergone exten- sive  overhaul,  repair,  or  alteration  which  may affect the power or capabilities of the ship or the machinery. A post repair trial is usually made when  the  ship  has  completed  a  routine  naval shipyard overhaul period; the trial is OPTIONAL whenever  machinery,  has  undergone  only  partial overhaul or repair. The object of this trial is to ascertain if the work has been satisfactorily com- pleted  and  efficiently  performed,  and  if  all  parts of the machinery. are ready, for service. 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. The post repair trial should be held as soon as practicable after the repair work has been com- pleted, the preliminary dock trial made, and the persons responsible for the work are satisfied that the machinery is in all respects ready for a full power   trial.   The   conditions   of   the   trial   are largely  determined  by  the  character  of  the  work that has been performed. The trial should be con- ducted in such manner as the commanding officer and   commander   of   the   shipyard   may   deem necessary. In cases where repairs have been slight and the commanding officer is satisfied that they are  satisfactorily  performed  and  can  be  tested without  a  full  power  trial,  such  trial  may  be dispensed  with. 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. Any unsatisfactory, conditions found to be beyond the capacity of the ship’s force should be corrected  by  the  naval  shipyard.  When  necessary, machinery should be opened up and carefully inspected to determine the extent of any injury, defect,   or   maladjustment   which   may   have appeared during the post trial. 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. A   certain   number   of   naval   shipyard personnel—technicians,   inspectors,   and repairmen—accompany the ship on a post repair trial. They check the operation of machinery that has  been  overhauled  by  the  yard.  If  a  unit  of machinery does not operate properly, the yard 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 2-50