Why don't people use these engines in boats?

[ridgy]

Talking about the older small boats where the diesel has died and replacement far in excess of boats value. Hook up to existing prop shaft etc. Would be better than putting an outboard on the back.

13 HP 9.56 kW Petrol Engine (25 mm Shaft, Low Oil Protection, Air-cooled Singel Cylinder 4-stroke Engine, Recoil Start) - GG1-ER389-25

Obviously some engineering required e.g. for exhaust and gearbox but a base 4 stroke unit for that price? Commodity spare parts available...what's not too like?

 

[kof]

What's not to like? Maybe petrol (and it's fumes) down below in a confined space? You get a leak from a diesel tank and it's messy to clean up but not dangerous. You get a leak from your petrol tank and you've got problems.

There's a reason we don't store the outboards fuel tank in the main cabin.

 

[TernVI]

you can get Chinese 'equivalent' yanmar-esque diesel motors for not much more:
LA178F1 6Hp Diesel Engine Launtop Recoil Start Replaces Yanmar L70 AE 178F 6 HP | eBay

However, being in a small boat with an aircooled cement mixer engine for company is going to be horrible.

 

[ridgy]

Of course but petrol inboards were common in the past and lots of motor boats still do. No reason for fumes or spilt petrol.

 

[ridgy]

you can get Chinese 'equivalent' yanmar-esque diesel motors for not much more:
LA178F1 6Hp Diesel Engine Launtop Recoil Start Replaces Yanmar L70 AE 178F 6 HP | eBay

However, being in a small boat with an aircooled cement mixer engine for company is going to be horrible.

Even better with the diesel, though an old noisy smoky 2 stroke isn't much fun either.

 

[kof]

Right but these motor boats don't have the engine in the main cabin. They usually have a self contained and vented enclosure for the engine.

Of course but petrol inboards were common in the past and lots of motor boats still do. No reason for fumes or spilt petrol.

 

[mjcoon]

However, being in a small boat with an aircooled cement mixer engine for company is going to be horrible.

If the engine is air-cooled then arranging a wet exhaust is going to be more complicated than usual, and a dry one more like a stove chimney...

 

[Black Sheep]

Good question. Noise has been mentioned, as has potential hazard of petrol. They won't be marinised, so possible shorter life, and strong possibility it won't operate when heeled. And of course as you point out there might be issues with gearing.

But... depending on your type of sailing, and especially your type of motoring it might well work. Might not be ideal for motor sailing across Biscay. But if you're patient enough to sail everywhere, and only need an engine for harbour manoeuvring, it might just do the job. And be more appropriate than an expensive diesel that never gets enough use for its own health.

 

[MarkCX]

Nothing wrong with an old petrol inboard on a yacht ? (16hp Dolphin).
With the one above from OP, once it’s all fitted appropriately, you know the largest cost you’ll face if it goes wrong eventually would be to just slot in a new one.

 

[HissyFit]

... because petrol goes KaBOOM, where diesel does not? The limited quantities of petrol required for ICE outboards maybe manageable, but the fuel should be kept in an exterior locker. Inboard engines, being accessible from within the boat, mean petrol fumes would be getting into the living space, where there might be electrical switches that can spark, as well as gas hobs. I know that Bruce Robert would even like to see the back of gas for its explosive capabilities.

 

[michael_w]

I used to race on a Thomas quarter tonner that had an engine like that. It was probably the most dangerous thing I've ever sailed with.

As the fuel tank was hard against the deck head it required topping up with a milk bottle and a funnel on a hose. All the controls were on the engine itself so the change gear you had to reach round the back of a hot engine grab a lever with our fingers an inch or two from the v-belts that drove the shaft and wrench. Eventually the owner got rid of this monstrosity and replaced it with an outboard.

 

[anoccasionalyachtsman]

On the one hand I've spent days motoring with a Dolphin, and it's still the smoothest and among the quietest boat engines I've ever used. Plenty of ways to make a petrol installation very safe - after all, if the Septics can manage a pretty decent safety record I'm sure we can.

On the other hand, we used to have a user on here named 'Spark' after his beautiful built-from-scratch wooden, petrol-fuelled, sailing boat. He had to be rescued from it when it caught fire and was subsequently lost, a real shame.

 

[[178529]]

it's a great idea. I gave away (pretty much) my folkboat as the cost of a diesel replacement was way more than the boat was worth.

Looking at that it looks like it ould be easy to remove the attached fuel tank and have a feed from an existing fuel tank. It's very light so would be easy to engineer mountings to the boat. I think you would want a fume blower like in petrol cabin cruisers and also maybe to help the air cooling.

I wish i'd thought of it before.

 

[MarkCX]

When the big end went on my Dolphin, I toyed with the idea of putting the money towards something else, but I couldn’t bring myself to do it. Glad I kept it.

 

[mjcoon]

When the big end went on my Dolphin, I toyed with the idea of putting the money towards something else, but I couldn’t bring myself to do it. Glad I kept it.

Until I read that I was thinking that I thought diesels just kept on for ever and did not need replacing. Then I remembered being on flotilla when we were happily motoring when the engine just stopped and could not be restarted. Of course in our case it was "someone else's problem". We were given a replacement yacht at the next port, after being towed in. The last we saw of our original yacht the engine was being lifted out to have the broken crankshaft (IIRC) replaced. But I expect it got put back with a new, or at least refurbished, one...

 

[[178529]]

You could buy a couple of those to have in reserve and still be quids in.

My experience of old diesels is that they give loads of problems. Not because they wear out but because of lack of use, poor installation, damp, moisture, exhaust corrosion, fuel deterioration, etc etc.

I think if you serviced one regularly and used your boat everyday then they would be fantastically reliable. But they are left for weeks in a damp salty environment and used usually for a few minutes at a time. Then called on to run for a few hours when you really need it.

 

[AntarcticPilot]

Our Trotter (Grimsby Marine Plastics version of the Pandora built in the mid 60's) was powered by a Briggs and Stratton air-cooled engine that looked very similar to that. On checking Briggs and Stratton's website a few months ago, I found that they still make very similar horizontal shaft engines.
A JumbleDuck says, the reason they went out of fashion was that they run on petrol, which is a much bigger fire-hazard than diesel. Also, they are usually high revving, so need an entirely different propellor from one suitable for a low-revving diesel.

 

[[178529]]

Our Trotter (Grimsby Marine Plastics version of the Pandora built in the mid 60's) was powered by a Briggs and Stratton air-cooled engine that looked very similar to that. On checking Briggs and Stratton's website a few months ago, I found that they still make very similar horizontal shaft engines.
A JumbleDuck says, the reason they went out of fashion was that they run on petrol, which is a much bigger fire-hazard than diesel. Also, they are usually high revving, so need an entirely different propellor from one suitable for a low-revving diesel.

Indeed. But in an environment where lots of 70s and 80s yachts are effectively written off due to the cost of engine replacement maybe this could be an opportunity for an enterprising engineering company so sell a conversion kit for say prrevious yanmar installations. All it would need would be a mounting kit to convert from that wide parallel yanmar beds in the hull, and something to allow a yanmar gearbox to be connected to the air cooled engine.

I think the petrol fir risk would be manageable given the thousands of petrol powered inboard cruisers that the marinas are chock full of. They have engine fume blowers and automatic fire extinguishers.

I would think someone could make an installation kit including engine for around 1k.

 

[RAI]

The hot air made by the aircooled engine needs adequate ventilation and the noise comes out there too.
Aircooled engines are remarkably noisier than water cooler, even if a hospital silencer is used on the exhaust. Petrol engines are thirsty so bigger tanks needed for the same range compared to diesel .

 

[AntarcticPilot]

Indeed. But in an environment where lots of 70s and 80s yachts are effectively written off due to the cost of engine replacement maybe this could be an opportunity for an enterprising engineering company so sell a conversion kit for say prrevious yanmar installations. All it would need would be a mounting kist to convert from that wide parallel yanmar points in the hull, and something to allow a yanmar gearbox to be connected to the air cooled engine.

I think the petrol fir risk would be manageable given the thousands of petrol powered inboard cruisers that the marinas are chock full of. They have engine fume blowers and automatic fire extinguishers.

I would think someone could make an installation kit including engine for around 1k.

I think it would need an entirely different gearbox to make it work. I'm not saying it's impossible, I just think that it would end up being much harder than you suggest. Just for starters, to get that 13HP, you're probably emitting at least that much heat equivalent - in other words, around 10kw of heat. So, you're going to need an effective blower system to keep cool air round the engine and removing hot air from the enclosed space below decks. Without it, the engine will over-heat and the below decks will become unliveable. The exhaust is dry, so it's at a very high temperature - well over 100 degrees C, probably a lot over; certainly enough to melt solder. So, the exhaust will have to be rerouted and made safe, somehow. The existing exhaust won't do - the cooling water keeps its temperature down, so it can be routed safely through lockers etc. The existing gearbox is designed for the power curve of a particular engine; it almost certainly won't be suitable for an engine which, by its nature, will have a very different power curve.