Propulsion options

Inboard diesel engines are common for sailing cruisers, but there are other ways to power a boat, as Stu Davies explains

- Stu Davies explains

Rarely do we get to choose how our boats are powered. The usual scheme of things is we choose a boat on a myriad of parameters, of which one is the propulsion system. But having talked about diesel inboard engines and their replacement last month, perhaps a few words on other types of installation wouldn't go amiss.

Conventional power units for cruising yachts, and I use the word 'power' to encompass electric power as well, usually drive through a propeller shaft or a sail drive. Of these two, a conventional prop shaft drive is the simpler and cheaper to maintain. Saildrives have bellows and seals that require regular checking and replacement and are principally made of aluminum that's permanently under the waterline - requiring a degree of monitoring that a stainless steel propeller shaft with a bronze propeller on the end of it does not.

However there are other ways of putting that thrust into the water, especially when we consider vessels beyond cruising yachts, and these installations can be electrically powered too. They are namely:

• Stern drive
• Outboard
• Jet drive

These forms of getting power into the water still use propellers but drive them through slightly different mechanisms. They're mainly fitted to power boats.

Stern drives

A stern drive is basically a sail drive but it is fitted to the transom of a boat with the engine hanging on the inside and the drive on the outside.