7-22. What must you do if the bull gear churns and  aerates  the  oil? 1. Slow  or  stop  the  engine  until  normal conditions  are  restored 2. Remove  some  of  the  oil  without changing  the  engine  speed 3. Stop  the  engine,  and  drain  and replace  the  oil 4. Stop  the  engine  and  add  some  fresh oil 7-23. Gears  should  be  slowed  down  or  stopped altogether when which of the following conditions   occur? 7-24. 1. Oil  is  emulsified  in  the  gear  case 2. Unusual  noises  are  heard 3. Both 1 and 2 above 4. Bearing  temperature  are  below  normal When  should  the  main  shafts  be  locked? 1. When the divers are inspecting damaged   propellers 2. When strong currents are present at anchorage 3. When  the  ship  is  underway 4. At all of the above times 7-25. Which of the following conditions should be in effect when the main shaft of a ship  is  allowed  to  trail? 1. The windage temperature in the low- pressure casing is kept at a maximum 2. The  lubricating  system  must  be operating 3. The  shaft  brake  must  be  engaged 4. The  turning  gear  must  be  engaged 7-27. 7-28. 7-29. 7-30. 7-31. 7-26. Which  of  the  following  gears  must  be disengaged  before  the  main  engines  are started? 1. Reduction 2. Turning 3. Pinion 4. Bull 7-32. Learning Objective: Point out factors that  affect  the  power  output  of  an engine  and  recognize  the  terms  and formulas  used  in  computing  engine performance  and  efficiency. Which  of  the  following  characteristics will affect the efficiency and perform- ance of internal combustion engines? 1. Engine  design 2. Compression   ratio 3. Operating   temperatures 4. Each of the above To  calculate  the  indicated  horsepower  of an  engine,  you  need  to  know  the  indicated mean effective pressure and what other factor? 1. The  engine  speed 2. The  brake  horsepower 3. The  fuel  consumption  rate 4. The  brake  mean  pressure What is the speed of a piston if the rotation  speed  of  the  crankshaft  is 1,000  rpm  and  the  piston  stroke  is 12 inches? 1. 1,260 fpm 2. 2,000 fpm 3. 12,000  fpm 4. 24,000 fpm When the engine rpm drops below rated speed,  what  usually  happens  to  the brake mean effective pressure? 1. It remains the same 2. It decreases 3. It increases 4. It  increases  and  then  decreases If  an  engine  is  operated  for  long  periods at  idling  speed,  how  frequently  will overhaul  be  necessary? 1.    More  frequently  than  if  operated  at 50% of load 2.  Less  frequently  than  if  operated  at 100% of load 3. As frequently as if operated at 75% of load 4.  Less  frequently  than  if  operated  at 90% of load An  unbalanced  cylinder  load  is  indicated by  which  of  the  following  conditions? 1. Black  exhaust  smoke 2. High  exhaust  temperatures 3. Low  cooling  water  temperature 4. Low  lubricating  oil  temperature 44