Engine
I believe that the standard engine fit for the Oyster 435 was a 60hp Volvo unit. Speedwell is fitted with an 84hp Perkins 4.236. This is an engine that’s commonly found in agricultural equipment and has a reputation for reliability and longevity. Parts are widely available and if we do have a problem in some far away place the chances are that a local diesel mechanic will have seen one of these before.
It’s a 4 cylinder 236 cubic inch capacity engine (hence the name). That’s about 3.5 litres in metric so it’s developing 24hp per litre, a low figure indicating that it’s not a highly stressed engine. The engine is a direct injection diesel, so there’s no pre-heat (one less thing to go wrong).
Drive Train
The engine is coupled to a Hurth gearbox then through an Aquadrive to the prop shaft. The Aquadrive takes all of the thrust from the propeller and allows some flexibility in the engine mounting, so engine alignment isn’t a critical as it would be with a direct coupling between the prop shaft and gearbox.
Drive to the propeller is through a conventional prop shaft through an old fashioned stuffing-box stern gland and supported under the boat by a P-bracket. This is a good simple system (our previous boat had a sail drive, so there was a big hole in the bottom of the boat with a rubber diaphragm keeping the sea out).
Propeller
Speedwell is fitted with a three bladed Maxprop feathering propeller. We’ll see how this goes on the delivery trip, we’re expecting it to perform well. We did try Kiwiprops on Ocean Mist, but one fell off and the replacement seized (turning into a paddle wheel in reverse), so we ended up back on a fixed prop on that boat. We hope the Maxprop will be more reliable.
The prop is protected by an Ambassador Marine Stripper rope cutter. That’s the sort of equipment that, if it works well, you never notice.