Shaft drives

Unless the vessel hits something, an inline (or V-drive) drive train should give years of trouble-free service with minimal, but necessary, maintenance. Keeping a maintenance log simplifies the job if checks and changes such as ATF (automatic transition fluid – gear oil) or propeller anode are noted. Early signs of trouble are easier to spot by comparing notes over time than trusting to memory.

PROPELLER SHAFT

Though shafts generally give years of trouble-free service they should not be overlooked in a seasonal inspection, and the condition noted in the maintenance log. Shafts do fail occasionally and with no apparent warning; caused by metal fatigue, concentration of stress points or corrosion. These are usually indications of other trouble, such as engine mis-alignment, excessive length between the strut (or stern tube) and propeller, a worn-out cutless bearing, or a bent strut that needs attention. Visible pitting near the coupling may be a sign of crevice corrosion happening inside the coupling. If there is heavy pitting, the coupling may need to be removed to allow inspection.

GEARBOX

Heat is the enemy of gears; best practice is to change the gearbox fluid every year and after any incident of likely overheating. Darkened ATF or a smell like burnt plastic are indications of overheating. Be careful not to overfill – some dipsticks only hang in their fitting to give the correct reading, while others need to be screwed shut.

COUPLING

The coupling connecting the gearbox to the propeller shaft transfers the full torque (rotational energy) of the engine and takes the full thrust of the propeller moving through the water. Only strengthened bolts should be used to connect the coupling, as ordinary bolts will shear. It’s prudent every season to inspect the bolts and the flexible coupling (if fitted) to ensure the nuts are tight, the flexible coupling is not cracked and that wires securing set screws are still secure.