Why don't people use these engines in boats?

[[178529]]

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.

I suppose anything that sounds too good to be true is too good to be true.

 

[AntarcticPilot]

I suppose anything that sounds too good to be true is too good to be true.

I'm afraid that's the usual way it works. In fact, the laws of thermodynamics can be restated as
0. There is a game (consequence of zeroth law of thermodynamics)
1. You can't win. (consequence of first law of thermodynamics)
2. You can't break even. (consequence of second law of thermodynamics)
3. You can't even get out of the game. (consequence of third law of thermodynamics)

 

[JumbleDuck]

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.

That was HissyFit (similarly yellow avatar) not me.

I think it might be time to look again at petrol engines for yachts, for a variety of reasons ...

• Diesels were great for dank bilges where contact breaker ignitions were unhappy. Nowadays ignition systems are damp-proof (almost) and bilges are dusted once per year.
  
  
• Petrol is indeed kaboombish, but modern engines with fuel injection are nowhere near as prone to dripping the stuff as carburetted engines with float chambers and needle valves.
  
  
• Petrol engines are smaller, lighter and quieter than diesels. Under my workbench I have a couple of Reliant 848cc engines. I can easily lift them around myself, they are physically smaller than my 14hp Nanni and they're good for 40bhp max, untuned, so easily 20bhp continuous.
  
  
• Petrol may become easier to buy as red diesel is forbidden to us. LPG may be a viable option too.

I agree about rpm, but would it be that hard to have 4:1 reduction gearboxes instead of 2:1? And definitely not air-cooled!

 

[LittleSister]

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.

I viewed one of those Briggs and Stratton powered Trotters once, as a possible purchase. I'd assumed that the engine had come from a lawn mower and been installed by the owner.

 

[anoccasionalyachtsman]

That was HissyFit (similarly yellow avatar) not me.

I think it might be time to look again at petrol engines for yachts, for a variety of reasons ...

• Diesels were great for dank bilges where contact breaker ignitions were unhappy. Nowadays ignition systems are damp-proof (almost) and bilges are dusted once per year.
  
  
• Petrol is indeed kaboombish, but modern engines with fuel injection are nowhere near as prone to dripping the stuff as carburetted engines with float chambers and needle valves.
  
  
• Petrol engines are smaller, lighter and quieter than diesels. Under my workbench I have a couple of Reliant 848cc engines. I can easily lift them around myself, they are physically smaller than my 14hp Nanni and they're good for 40bhp max, untuned, so easily 20bhp continuous.
  
  
• Petrol may become easier to buy as red diesel is forbidden to us. LPG may be a viable option too.

I agree about rpm, but would it be that hard to have 4:1 reduction gearboxes instead of 2:1? And definitely not air-cooled!

I love engines with a multiple of three cylinders (you'll know why, but they sound gorgeous too) and had a long term plan to use a Suzuki GT750 engine in a boat. Of course, as soon as I got serious and decided to spend the money, the classic bike market went crazy, plan thwarted. I guess there must be some triple outboard 2 strokes around though....

 

[Laminar Flow]

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.

I had a hand-crank 2cylinder, aircooled Lister on my old Waterwitch. It sounded like an old tractor, you had to open the engine hatch to operate the controls and you had to leave one of the cockpit lockers open for the warm air to vent. On the upside, it was the perfect place to hang your feet on a cold day.

In an open boat, such as a launch, I would have no hesitation using either the petrol or the diesel variety on offer. Hell, for the price of servicing your standard marine engine, you could just drop in a new one.

I thought I should just add that my Dad had a C&C 25 with a Vire petrol engine; happy to say: no one ever died.

 

[rotrax]

I have seen on the TV programme 'Swamp People' those Chinese honda copies being used, some grafted on to an old outboard bottom, others in the vein of the thai 'longtail' types. The more powerful vee twin as used in farming and industry were used there.

 

[AntarcticPilot]

I viewed one of those Briggs and Stratton powered Trotters once, as a possible purchase. I'd assumed that the engine had come from a lawn mower and been installed by the owner.

No, they were a purpose-made installation from new.

 

[ridgy]

Exhibit B, 11hp diesel for 600...

PORTABLE DIESEL ENGINE 11 HP SINGLE CYLINDER MOTOR ~ YANMAR, LONCIN - BOHMER-AG 5060569760260 | eBay

Take fuel tank off and reuse existing fuel line. 11hp at 3600 rpm so reuse gearbox. Remote electric start with manual option. Just need an exhaust...?

 

[LittleSister]

Lots of ideas here:

long tail boat engine

 

[rogerthebodger]

Some chinese diesel engines here

China Water Cooled Single Cylinder Diesel Engine, China Water Cooled Single Cylinder Diesel Engine Manufacturers and Suppliers on Alibaba.com

 

[Habebty]

My first boat had a petroleum engine - no dramas. It was water cooled though so very quiet.
(Volvo MB2 50S 7.5 hp which was a Honda unit I think grafted to an outboard leg and fitted as a sail drive)
A blower was in place to get rid of any fuel fumes But crap charging and petrol consumption.

 

[AntarcticPilot]

Exhibit B, 11hp diesel for 600...

PORTABLE DIESEL ENGINE 11 HP SINGLE CYLINDER MOTOR ~ YANMAR, LONCIN - BOHMER-AG 5060569760260 | eBay

Take fuel tank off and reuse existing fuel line. 11hp at 3600 rpm so reuse gearbox. Remote electric start with manual option. Just need an exhaust...?

What are the chances of the existing gearbox mating to an engine it wasn't designed for? Usually marine engines have a range of matching gearboxes; the gearbox isn't an independent thing.

 

[Baggywrinkle]

My parents had an Albin Vega with an inbord petrol engine. Had a huge flywheel, was low revving and had no gearbox, just a variable pitch prop. Started using a crank handle. Fuel tank was in a stern locker, don't remember a smell of petrol or exhaust fumes, and it had a wet exhaust which exited low down the transom. Lovely boat, not let down at all by a petrol engine - just a bit quirky.

 

[ridgy]

What are the chances of the existing gearbox mating to an engine it wasn't designed for? Usually marine engines have a range of matching gearboxes; the gearbox isn't an independent thing.

I don't think you are entering into the spirit of the thread. Off the shelf probably no chance. Will a little help from a machine shop? Possibly.

 

[jbweston]

Maybe the problem with inboard petrol engines is that they're fine if well installed, well maintained and if the crew are really careful with the fuel. But in practice none of us are perfect, so poor installation or maintenace, or crew who are sloppy with refuelling, allow fuel to get in the bilges or an enclosed spaces.

My father told me he owned a small petrol powered ex-naval launch on the Trent in the 1950s. He got on well with her, but he knew that one of the deck fillers didn't go anywhere near the fuel tank, presumably because she had been re-engined or re-tanked without blocking off the filler. After he sold the boat she caught fire and was destroyed one day after taking on fuel and badly injured the owner, very likely because someone used the filler that went into the bilges rather than the tank.

There's a lovely old newsreel film that I can't find a link to now from the 1920s when in some endurance car races the rudimentary pit crew of those days wasn't allowed to refuel but threw cans of fuel to the driver or riding mechanic for them to pour in. One or the other is pouring petrol into an enormous funnel stuck in the fuel tank - and he has a cigarette hanging out of the corner of his mouth. Although this was probably safer than actually driving racing cars in those days.

 

[Mark-1]

I don't think you are entering into the spirit of the thread.

I will though:

 

[Black Sheep]

Maybe the problem with inboard petrol engines is that they're fine if well installed, well maintained and if the crew are really careful with the fuel. But in practice none of us are perfect, so poor installation or maintenace, or crew who are sloppy with refuelling, allow fuel to get in the bilges or an enclosed spaces.

Of course you could say exactly the same of gas installations for cooking...

 

[Laminar Flow]

For those freaking out about the petrol engines - they are offered in the same setup with a diesel for little more.

Many of us carry petrol onboard and have an outboard for the dinghy.

As I said: in an open launch/boat I would not think twice about it, air-cooled, petrol or otherwise. And, with a modicum of sanity, I might even consider it in a small decked vessel as well.
For someone on a budget, not mechanically left handed and able to hook it up to a gearbox, the little diesel might be just the ticket.

 

[black mercury]

Once had a boat with the 16hp Dolphin engine mated to a hurth gearbox. It had electronic ignition with an extra pick up sensor fitted so you could swap over if one failed. It never did. Started every time with a flick of the starter. Only once had a small petrol leak from the fuel pump and I noticed the smell as soon as I got into the boat and there was only an egg cup full under the engine. The fuel lines had hydraulic fittings from the fuel pump to the carburettor. I remember travelling around west coast of Scotland with 60 litres in the tank and four thirty litre containers full of petrol wedged inside the boat. It is easier to find diesel than petrol when away cruising. If you're sensible and careful it isn't an issue, after all we usually have pressurised gas on board.
I would be happy with a petrol engine again, but when it comes to selling the boat on it would be a disadvantage to most buyers.