It's best to have several outboards on a boat

Without a good definition, few people can answer this question. There are many sports enthusiasts abroad or at home. Their motives for buying a boat have their own expectations. Many people are looking for a boat that is fast and can move (sound) and quiet (sound). For some, that means having a pair of fridge-sized engines, for others, it could be a row of engines linked together. We can't say which looks better aesthetically, but we can make a logical observation - assuming that in a ship with a 2,000 horsepower engine, logic might play a role.

The reason is simple, whether it is a long cruise or a daily fishing operation, there is a balance between efficiency and reliability, and if you look carefully at commercial vessels (mainly small and medium-sized vessels), you will notice that almost all of them have only one engine. This is done for two reasons, one is to reduce the original cost, and the other is to reduce the space occupied by the power unit, leaving more space for loading cargo or expanding storage space.

However, there is a more important reason, and that is efficiency/speed. Single engines are more efficient than multiple engines, mainly because of water resistance. Anything protruding from the hull will slow it down, including the cross struts, shafts, and even the underwater parts of the stern drive and outboard engine shafts. As you can imagine, the more stuff there is, the greater the friction loss. Of course, those in the know will also think that when we consider adding an outboard, the underwater wet surface will also increase, and the resistance will also increase, but this efficiency loss is almost negligible.

With more wet surface underwater, resistance will increase, fuel consumption will increase, and engine efficiency may decrease by 10%, which may not mean much for recreational boats, but for people who are trying to make a living with boats every day, it means something. Logically, then, the next question is how much drag is added to each underwater section, which is not easy to answer. But it should be possible to find studies that quantify the loss of efficiency caused by additional underwater components.

According to the principle of constant power, it is easy to understand, for example, the comparison of two 500 HP outboards with five 200 HP outboards. This needs to take into account the parameters of the underwater part of the engine, 500 HP underwater wet surface is larger than 200 HP. For the average shipowner, the difference in efficiency may not be a major consideration, especially where fuel prices are low.