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 (though not necessarily refinement). 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).
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 as 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).
In our 2009/10 refit we had the Aquadrive overhauled and the stern gland stripped, bead blaster and re-packed. At the same time we had the shaft bearings in the hull and P-bracket replaced.
Speedwell is fitted with a three bladed Maxprop feathering propeller. We did try Kiwiprops on Ocean Mist, but one fell off and the replacement seized (turning into a paddle wheel in reverse and probably causing the gearbox to fail – Kiwiprop’s distributor denied that the prop caused the gearbox failure but the two did go at exactly the same time), so we ended up back on a fixed prop on that boat. We hope the Maxprop will be more reliable. During the re-fit the propeller was fully serviced and cleaned up, we re-grease it during annual haul-outs.
In use the Maxprop is working well. It gives plenty of thrust in both ahead and astern while feathering easily when we’re sailing (Speedwell’s light wind performance has been very good, the feathering prop will be a significant contributor to that). The boat does have a moderate amount of prop walk in astern, but as I’ve never sailed an Oyster 435 with any other type of prop I can’t say whether the Maxprop is making that better or worse.
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.