The propeller drive shaft is one of the most important parts of the ship. During construction, the shaft is inserted with millimetric precision into the ship and interlocked with the engines. However, the rigours of maritime travel exert all manner of force into the shaft and the slightest damage will wreck the entire assembly, even trigger an unfortunate accident. As such, aligning the shaft is a tedious but important procedure.
A realignment process begins at the engine mounts. A dead giveaway of a misaligned shaft is that the mount’s studs are leaning in any direction, indicating a degree of stress. It is possible to uncover a misalignment by running the engine up from idle to at least one-third throttle speed. Your team should note the proper alignment relative to the bearings. This way, you will see if something is wrong with the shaft, even it is just 1/8th of an inch off center.
A wobbly shaft can be noticeable if the power setting is at cruise speed. Check if the engine tachometer is above 1,200rpms at the time the wobbles are felt. The shaft-to-bearing alignments will warrant a check as well; the opening and exit holes at the bearings must be lined up perfectly. A properly-synced up screw will preserve the transmission of thrust from the engine to the propellers.