A sea trial is a valuable way to establish the true condition of a yacht in exactly the way in which it is to be used and enjoyed. This is particularly important in respect of a motor yacht. A pair of large marine diesels can represent a significant percentage of the value. The cost of a complete rebuild can be damaging to the realisable value and can only be carried out by removal of the engines. On some vessels where the engines were installed before the deck was assembled, removal requires major surgery to the superstructure.
Diesel engines of all kinds only run at full efficiency when they are at their designed working temperature and delivering close to, or at their maximum load. Internal glazing and carbon build-up is caused by prolonged periods running at low loads. Such conditions cause low cylinder pressures and consequently poor piston ring sealing. Low cylinder pressures cause poor combustion. This poor combustion leads to soot formation and unburnt fuel residues, clogs and gums piston rings and burns valves.
Diesel engines should run at full working temperature and at least around 75% of their maximum rated load. Short periods of low load running are allowable providing the engine is brought up to full load, or close to full load on a regular basis. This is often impossible when vessels with fast planing hulls are kept in speed restricted waters.
Click below for a sample survey which includes a full sea trial