Principles of naval engineering - Historic Naval Ships Association

Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERINGset of readings is taken with the ship in drydockand another set of readings is taken with theship waterborne— under normal loading conditions.The main shaft is disconnected, marked,and turned so that a set of readings can be takenin four different positions. Four readings aretaken (top, bottom, and both sides). The alignmentof the shaft can be determined by studyingthe different readings taken. The naval shipyardwill decide whether or not corrections in alignmentare necessary.NOTE: During shipyard overhauls, the followinginspections should be made:a. Inspect condition and clearance of thrustshoes to ensure proper position of gears. Blowout thrusts with dry air after the inspection.Record the readings. Inspect the thrust collar,nut, and locking device.b. If turbine coupling inspection has indicatedundue wear, check alignment between pinions andturbines.c. Clean oil sump.When conditions warrant or if trouble is suspected,a work request may be submitted to anaval shipyard to perform a "seven year" inspectionof the main reduction gears. Thisinspection includes clearances and condition ofbearings and journals; alignment checks andreadings; and any other tests, inspections, ormaintenance work that may be considered necessary.Naval Ship Systems Command authorizationis not necessary for lifting reduction gearcovers. Covers should be lifted when trouble issuspected. An open gear case is a serious hazardto the main plant, therefore, careful considerationof the dangers of uncovering a gear casemust be balanced against the reasons for suspectinginternal trouble, before deciding to liftthe gear case. The seven-year interval may beextended by the type commander if conditionsindicate that a longer period between inspectionsis desirable.The correction of any defects disclosed byregular tests and inspections, and the observanceof the manufacturers' instructions, shouldensure that the gears are ready for full powerat all times.In addition to inspections which may bedirected by proper authority, open the inspectionplates, examine the tooth contact, the conditionof teeth, and the operation of the spraynozzles. It is not advisable to open gear cases,bearings, and thrusts immediately BEFORE fullpower trials.In addition to the inspections which may bedirected by proper authority, open the inspectionplates, and examine the tooth contact and the conditionof the teeth to note changes that may haveoccurred during the full power trials. Runningfor a few hours at high power will show any possiblecondition of improper contact or abnormalwear that would not have shown up in months ofoperation at lower power. Check the clearanceof the main thrust bearing.SAFETY PRECAUTIONSThe following precautions must be observedby personnel operating or working with propulsionequipment.1. If there is churning or emulsification ofoil and water in the gear case, the gear must beslowed down or stopped until the defect is remedied.2. If the supply of oil to the gear fails, thegears should be stopped until the cause can belocated and remedied.3. When bearings have been overheated,gears should not be operated, except in extremeemergencies, until bearings have been examinedand defects remedied.4. If excessive flaking of metal from thegear teeth occurs, the gears should not be adjusted,except in an emergency, until the causehas been determined.5. Unusual noises should be investigated atonce, and the gears should be operated cautiouslyuntil the cause for the noise has been discoveredand remedied.6. No inspection plate, connection, fitting, orcover which permits access to the gear casingshould be removed without specific authorizationby the engineer officer.7. The immediate vicinity of an inspectionplate should be kept free from paint and dirt.8. When gear cases are open, precautionsshould be taken to prevent the entry of foreignmatter. The openings should never be left unattendedunless satisfactory temporary closureshave been installed.9. Lifting devices should be inspected carefullybefore being used and should not be overloaded.10. When ships are anchored in localitieswhere there are strong currents or tides,109