Page 5A Suitable Niche Application?


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If you live near near a lake, river or canal,
boating is a very pleasant activity.
Inland, in the UK, there are some 40,000 boats. Many are canal boats or cabin cruisers.
But there are many open day boats. rowing boats, skiffs, dorys, even canoes.

Unfortunately, many of the inland boats are over engined. Yes, a coastal boat does need
tens of horsepower to be able to counter tide, wind and swell.
Inland there are no such challenges.
A rowing boat needs something of the order of 50 watts to propel it for leisure purposes.
There are 746 watts to a horsepower.
One tenth of a horse power – 74.6 watts - is enough to push a small rowing boat.

Frequently, a 12 ft cabinless, or open day boat, has a 5 hp outboard motor slung at the back.

All boats have a maximum hull speed. As the power at the back of the boat is increased,
so does the wave at the front of the boat - the bow wave gets bigger. All the extra power does, is to tilt the boat up at the front. It is climbing its own bow wave.

This is a “hard” limit. It is called the maximum hull speed. For a 12ft boat it is 4.6 mph.

But then, just as our roads have speed limits, so do our waterways. In the UK, it is 5 mph.

So 10 hp, 20 hp, even 40 hp outboards for small inland waterway boats, are just ludicrous.

40 hp is needed for waterskiing, but, inland, that is only sensible in special water skiing lakes.
Tidal waters need low tens of horsepower. A slim hull in still waters? How about 2 hp or less?

Then there is the noise. At tickover, the average outboard is tolerable.
As soon as the engine is revved up – put under load – the noise soars.
I have measured a 2.3 horsepower (new) at 90+ decibels. You can’t even shout against that. This is the level where hearing damage starts. And this is for a leisure boat?

So, let’s go electric. They’re silent you know – and none of those poisonous exhaust fumes.
Let’s cut CO2 emissions!



Lady Astor’s 1920’s electric canoe has been recently restored at Cliveden in the UK.
They were (and still are?) all the fashion.

The snag about lead acid batteries powering electrical devices is that they decline.
This year you are doing 5 mph – say for 6 hours – then the batteries need recharging.
Next year, the control unit will keep you going at 5 mph – but for less than 6 hours.

Each year you loose range, then you loose top speed.

You can’t replace a single battery – they all need replacing. Say six batteries, certainly at £100 each. My friend has some “hi spec” batteries – just four of them - £400 each.
And that’s
cheaper than Lithium ion batteries. They are 5+ times more expensive.

She is advised by the installer to cruise at 10 amps. It’s a 24 volt system.
Watts = Volts x Amps
When cruising, she is powered by 24 x 10 = 240 watts = 0.32
of a horsepower.

She converted to electric because her old 1.5 hp petrol Stuart Turner was too noisy
and was a real “pig” vs reliability.

The boat is now quiet and reliable, but is just far, far slower. Not enough horsepower.

Can the Stirling provide a better solution?

A Stirling engine is very quiet – I have measured 40 decibels when cruising.
The engine runs at the same noise level as the breeze and the birds.

It is reliable. My Stirling boat engine was built 21 years ago.
I have had one mechanical failure. There was a poor weld in one of the components.

It only does 3.2 mph. I would like more – but that raises the crucial point.

WHERE DO YOU BUY A STIRLING BOAT ENGINE!!!