Virtually all modern yacht engines are diesel engines however there are some other engines which are found on smaller yachts and high speed yachts (see gas engines, turbines at the bottom of the post).
All yacht engines have common requirements which will allow them to operate reliably for long periods:
1. Enough Air – Yacht engines require lots of fresh air for combustion. Engine compartments must be able to provide this even if it is forced in via fans. The ideal situation is to pull air into the engine room via the top deck, where the air is not as salty in ocean conditions, through fans that are variably controlled to provide positive pressure on demand, and with flaps that can shut off the supply of air in the event of fire.
2. Clean Fuel – With water and particulate matter filtered out. Most used yacht engines are equipped with pre filters such as Racor, to filter water and particles down to 10 microns before the engine filters which take it down to 2 microns. Another nifty product is the RCI purifier, which can take large amounts of contamination out of the fuel even before it hits the filters with cartridge elements. Fuel quality for yacht engines is more questionable the further yachts travel from populated areas, therefore it is imperative to have good fuel cleaning equipment on board.
3. Proper Loading – Yacht engines perform and operate best with correctly sized propellers which are kept clean. Engines must turn up to rated WOT (wide open throttle) and propellers should match this engine parameter closely. If not, there is a chance that the yacht engines will not load properly and have a life reduction.
4. Clean Oil – Yacht engines require oil and lubricants to be changed at regular intervals. Most modern yachts have built-in pumps with hoses and valves making this an easy task.
5. Efficient Cooling Systems – The cooling system and raw water pump must be serviced on a periodic basis. Note that new methods allow for descaling procedures without taking apart the units.
It is often argued that modern large diesel engines, especially with high horsepower ratings, are not designed to operate at slow speeds.
There is lots of debate among professionals in this regard. The common agreement is that engines of any type must be broken-in correctly when new or overhauled and that they should be run up to high speeds at least periodically every day of operation (to blow out soot).
It is a very good idea to have oil analyzed (even transmissions) every oil change, similar to a blood work-up – as one can often catch problems early before they get detrimental.
Yachts for sale which were built before 2000 would most likely find either Detroit Diesels (GM) or Caterpillar.
Detroit Diesel Yacht Engines
Detroit Diesel (GM’s) is a two-stroke diesel engine, which means that it completes its combustion and exhaust cycle in two strokes. The advent of clean emission mandates forced these engines into obsolescence.
Mechanically controlled and governed up until the mid-1990′s with the DDEC series, these yacht engines pioneered the electronic controls which are now commonly found on most modern diesel engines.
Most commonly found in yachts prior to 1998, the 6V71 (rated between 210 and 480 hp) and the 12V71 (various ratings between 550-900 hp) (the 1271 is two 671′s put together – 71 referring to the cubic inches per cylinder – either 6 or 12 cylinders) engines are the most common engines found in older US yachts today, along with their sister engines – 6V92,(550 hp) 8V92 (710 hp), 12V92 (1050 hp), and 16V92′s(1350 hp) (these engines eventually obtain the higher DDEC ratings via electronic controls).
These yacht engines were notorious for lots of low end torque and simple mechanics. Noted for shortened intervals between overhauls when operated (or loaded too hard) and run in hot conditions with not enough air. If an owner takes care to maintain and operate these popular yacht engines at slower speeds, they last quite a while.
Caterpillar Yacht Engines
Caterpillar – Noted prior to 2000 for the 3412 (a V12 engine commonly rated between 1000-1450 hp on used yachts) and the 3208 (rated between 375 -425 hp). The inline-6 series engines started coming out in the late 90′s with the 3116 (350 hp), 3126, (450 hp), the 3176-3196 (660 hp) and the 3406 (800 hp).
All of these early CAT 6 cylinder engines suffered from some issue or another. The point is that all yacht engine manufacturers have issues with engineering flaws. The important thing is how they take care of it – and CAT developed a good program to deal with this.
The newer models of these same engines – the C7, C9, C12, C18, C30, and C32 – all have been pretty reliable and are one of the two predominant engine manufacturers in today’s yachts. The CAT 3512 is the powerhouse for the larger yachts.
Modern emission requirements have brought the advent of the modern electronically controlled diesel and the high-pressure injection service used to more efficiently controlled fuel injection. Most engine manufacturers refer to this technology as ‘common rail’ while CAT refers to it as ‘acert’.
MTU Yacht Engines
MTU of Germany merged with Detroit Diesel in the late 90′s and developed a series of popular 4 stroke engines – the 8V2000, 12V2000, 16V2000, 12V4000 and the 16V4000 engines.
The Series 60 engine has also been a very popular model, long upheld in the trucking industry. Many of these yacht engines are found on today’s yachts and have held up quite well. Some of us wonder if their parts are made of precious metals due to the cost.
MAN Yacht Engines
MAN has been a popular German engine in used yachts – especially sport fishers, because of its superior horsepower to weight ratio and relatively compact size.
Yanmar Yacht Engines
Yanmar has been a very reliable Japanese engine, popular with sailing yachts, trawlers, sport fishers and some motor yachts. Their mechanical 500 hp engine has been superb. They have recently merged with a little known (but excellent) Scandinavian manufacturer Scania to build a larger series of electronically controlled engines.
Volvo Yacht Engines
Volvo engines have been a long-time supplier of used yacht engines. Most recognizable are the 480 hp engine (noted for smokiness) and the 700 hp D12. Volvo is pioneering the ‘pod’ technology for yachts, eliminating typical shaft driven/rudder systems.
These engines are designed with the whole engine, transmission, exhaust and propeller as one unit, thus saving lots of space (not to mention problems associated with traditional shaft systems).
These 660 hp units can be installed as 2 or more units next to each other that electronically turn as a synchronized system – or ‘fly by wire.’ The drives are designed to tear away without causing a hole in the hull in the event of grounding or hitting something hard.
Yacht Engines by Cummins
Cummins is also a big player in the yacht industry. Especially noted for high quality, reliable service, the Cummins 300-400 hp Diamond series and the QSM11 (660 hp) have been terrific engines.
Mercruiser and Cummins have partnered up to produce a pod diesel engine as well – known as the Zeus for multiple unit installations and rated at 715hp.
Diesel engines of lesser notoriety, but still found on yachts, are:
- Deutz (German)
- Sabre
- Perkins (British)
- Hino (Chinese)
- Ford Lehman (US)
- Lugger
- John Deere (US)