What do we do about an engine?

 

Cygnet will be a traditional wooden motor launch, whose main job will be ferrying passengers and crew out to the Frederick Henry Swan once she is finished and on a fore-and-aft mooring on the Tyne.

And because she’s a proper boat, there won’t be an outboard engine, but an inboard one. This means that we need to think carefully about how we build this into our construction plans. Unlike an outboard, which you can sling on the transom at the end, an inboard engine is an integral part of the design.

This is a possible engine that we already have. Actually we have two of them, both in a condition that you can see Phil is delighted with!

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Phil worrying about the state of the engine

It’s a Stuart Turner P55M, which is a two-stroke twin cylinder petrol engine of 1930s design. It’s about 8HP, running at 1650rpm. But as you can see, it’s in really poor condition, is seized solid and would take a lot of work to restore. Plus, at 8HP it’s more powerful than we need for Cygnet.

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Restoration project?

An engine of that power needs a large propeller of around 12″ diameter, and there isn’t enough space in the existing design for one that big. So should we look for an alternative engine, and if so, what? Whatever we do, we need to move fast, because we can’t proceed very far with the build without knowing what engine will be installed.

Whatever engine we choose will drive a propellor via a prop shaft – and we will need some other bits and pieces to support the prop shaft and keep water out of the boat.

We will probably get these bits – stern gear, it’s called, from a firm called T. Norris who specialise in this sort of kit. They want to know what fitting the gearbox has – that’s something to check out when we decide on which engine to use.

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Stern gland from the coble Irene Patricia

Working backwards from the engine, the prop shaft will pass through something called a stern gland – it’s a bronze casing that contains grease-covered bits of rope that act as a bearing and seal the water out. That’s the theory. The prop shaft disappears into the wedge – see the previous post for details about that – and emerges via another bearing. The propeller fits on the end.

Another question – do we mount the engine directly onto the inside of the hull, probably resting of a couple of chunky bits of oak? Or do we fit some flexible engine mounts?

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Solid engine mounts on Irene Patricia

And how do we drill a hole, big enough for a 3/4″ prop shaft, into the wedge? That’s a seriously long hole, and it needs to be very accurately drilled. Our boatbuilding guru Nigel Gray already has some tips on drilling long accurate holes – more of that later.

 

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