Very simply the commonest type of engine fitted to a canal boat is the diesel fuelled engine. Diesels are used regardless of whether the engine is used directly via a gearbox to drive a propeller or indirectly to provide charge to a large battery bank for electric propulsion.
Diesel vs Electric
There are licensing concessions available to those who choose electric propulsion but in reality the battery bank required for power still needs to be recharged. There is not the infrastructure on the main waterways in place yet to provide regular and cost effective recharging points so the trusty diesel still has a very important place in our market.
Diesels are simple, easy to maintain and safe. Fuel is readily available and at the time of writing relatively inexpensive. Carbon monoxide content of the exhaust is minimal so they are safer in this respect than petrol engines. They do not rely on highly energised, high voltage ignition circuits so are far more adaptable to an environment that is cold and damp.
Diesel fuel will burn in air but it will not explode, far safer in an enclosed marine environment where accumulations of vapours can form in poorly ventilated engine bays.
The nature of how the engines are built to allow diesel to be used mean they are much more heavily built than petrol engines. As a result of this heavier construction and the fact that diesel is a better lubricant than petrol means diesel engines have a greater lifespan than petrol engines.
Early diesel engines fitted to working canal boats around the turn of the 20th century were made by companies such as Bolinder and National.
Vintage engines fitted to canal boat include marques such as Gardner, Lister and Russell Newbury.
Classic engines were supplied by manufacturers such as BMC, Perkins, VW and Lombardini and marinised by companies such as Tempest and Thornycroft.
Modern engine manufacturers and suppliers/marinisers include Vetus, Beta Marine, Isuzu, Barrus Yanmar/Shire, Nanni, Kubota and Engines Plus/Canaline.
How A Diesel Engine Works…
So how do they work? Unlike a petrol engine where fuel is ignited by a spark, diesel engines use very high cylinder compression to start the ignition process.
There are various styles of diesel engine available, from early vintage engines to the most modern electronically controlled units.
They all use same fuel however so a basic understanding of the way diesels work may help.
Fuel is delivered from a main integral, usually stern mounted, tank or a smaller unit that is known as a day tank. Day tanks are often installed in boats with a separate engine room where a vintage engine does not have a lift pump to bring fuel from the main stern tank. Day tanks are topped up when necessary, usually using a hand operated pump in line with the vintage outfit. With a more common set-up an engine mounted mechanical lift pump draws fuel from the tank, the fuel is filtered sometimes both before and after the lift pump.
There are no spark plugs on a diesel engine; the fuel ignites with a little bit of pre-heat and compression. Near to the injectors in the tops of the cylinders are what are known as glow plugs. Glow plugs are used for a few seconds before starting the engine and are effectively little heaters that pre-heat the combustion chambers. Some canal boats will have a position on the ignition key that allows current to flow to the glow plugs, others will use a separate button which requires the skipper to press in before turning the engine over. The engine is turned over, either by the battery operated starter motor of by hand crank, and this motion starts the fuel pumping.
The lift pump delivers the fuel into the injection pump which pressurises it.
This complicated unit is synchronised with the up and down motion of the pistons in the cylinders and pumps fuel to a row of fuel injectors in the top of the cylinders.
…Compression & Ignition…
As the piston rises in the cylinder air is compressed and heated, diesel fuel is injected & the mixture ignites.
The resulting explosion fires the piston back down the cylinder. As one piston is on its way down, so another is rising to continue the cycle.
The pistons are connected to a crankshaft which converts the vertical motion of the pistons in the cylinders into rotary motion which is then used to drive a gearbox which in turn is attached to a propeller. Simple.
The very simplistic description above hints at some of the features of a diesel engine.
Because fuel is mixed with highly compressed air and the revolutions of the engine rely on this mixture igniting, the quality of construction and components used is important. High compression in the cylinders is vital to aid easy starting and a regular service plan is recommended to keep everything tip-top.