Redneck diesel outboard?

S

sam_uk

Well-Known Member
Joined
26 Mar 2009
Messages
292
Location
On the boat. Europe somewhere.
Visit site
Hi all

I am new to sailing, last year I got myself a kingfisher 20 JR. I am very happy with the boat in general, But now I wish I had got a boat with a inboard diesel engine.

I have a 2stroke 7.5hp in the outboard well which pushes me along nicely, But it is noisy, smoky and I worry about economy, reliability and fire.

I happened across a youtube video
http://www.youtube.com/results?search_query=lawnmower+outboard+&aq=f

Which shows it is a popular redneck hobby to convert lawnmower engines to outboards..

So I am thinking of having a go!

I am hoping to be able to pick up a 8hp Vertical shaft Chinese diesel for about £350- £450 (ebay prices for horizontal shaft) http://johnnysale.en.ecplaza.net/8.asp

I would hope to get a old 10hp longshaft outboard leg, for about £100 and mate them together, run the exhaust down into the water

Adavantages;

* Improved reliability
* Diesel for £700-£800
* Improved fuel economy

Questions;
What would need to be 'marinised' on such an engine?
Would running the exhaust into the water cause problems with pressure?
Are there any other 10hp diesel outboards in this kind of price range?
Am I mad?


Thanks

Sam
 
You are mad BUT there were some Italian diesel outboards some years ago - Carnita?. I think you biggest problem would be weight - it will probably end up twice as heavy as a your petrol outboard and being a single cylinder engine would possibly shake you and your boat to bits - particularly when idling. It would also be much (possibly) harder to start by hand. Being aircooled will mean it will be noisier than a watercooled outboard.
Interesting project though and if you succeed then please let us know - and you'll get lots of advice on here when you hit problems.
 
I recently overheard half a conversation about the same thing. You are not the first to think of it. I wouldn't see vibration as a big problem - most 20'ers with an inboard would have a single cylinder 1GM10 or similar which runs reasonably smoothly. A Chinese aircooled diesel could be a right noisy batard though!
 
Lots of small diesel engines, from scooters and generators, are available.


Why not go for an electric outboard with a 240v motor (direct replacement for a o/b with a battered head), and run a small suitcase genny so that you can have 240v on board power as well ?

Sounds as if you are a practical person with the right skills....
 
New boat

It seems to me that you are looking at the green grass on the other side of the fence. (Always looks better)
The set up you have with 7.5 HP OB is perhaps the best arrangement you could ask for.
Indeed I have a friend with a Spirit 28ft which had a small diesel. He has abandoned the diesel and fitted an outboard on the transom bracket. The diesel did have problems but he seems to prefer the O/B. of course most people believe diesel I/B is better but certainly not worth the cost of installation as an inboard.
Diesel outboards have been around for many years but are just no match for petrol to do the job. Vibration can be aweful on a proper inboard installation so would be terrible on an o/b. Of course the weight would be a killer too.
Fire is not a real concern provided fuel fumes don't get into cabin. Economy is really not bad for a petrol O/B.
Just get on with enjoying your sailing it is a much more reliable/pleasurable way to go. Or be like me and leave O/B home. good luck with the new boat olewill
 
Man after my own heart. I have one made from a 10hp o/b leg and a vertical shaft l/mower 4T petrol engine.
Couple of probs: The leg expects rpm of around 5/6000 Your small diesel will be somewhat lower. I put the engine along side the leg with a layshaft and toothed belts to speed up the drive 2:1. This is not really an o/b, more a sail drive, but uses the well.
Also, as said, vibes and noise. Mine is a bit thumpy, a diesel will need an enclosure or serious ear muffs.
Practicallity? Not a lot, but bits were free (and I like fiddling!). It is heavier than an o/b. The leg was surprisingly so. It is not finalised yet, as the boat is not finished, and the eng. mountings will be to the boat, not the leg. Exaust will be SS watercooled from the o/b cooling pump. Big plus is the 40amp alternator.

I await comments (small genny thread!!!)


William H is right
 
Last edited:
I don;t know anything about your boat, but have you looked at the possibility of fitting a stern-tube and a conventional inboard.

If it could be done, it probably wouldn't involve much more time/money and the result would be much more satisfactory.

Your plan souds thoroughly "Heath Robinson" and the result might be the same as his!
 
sam_uk said:
I have a 2stroke 7.5hp in the outboard well which pushes me along nicely, But it is noisy, smoky and I worry about economy, reliability and fire.
Click to expand...
You want a four stroke. That's the ticket. For a 20ft boat a 5 or 6hp is plenty.
Fire? Very, very unlikely. There are thousands and thousands of small boats with petrol outboards and not very many fiery accidents.
 
sarabande said:
Lots of small diesel engines, from scooters and generators, are available.


Why not go for an electric outboard with a 240v motor (direct replacement for a o/b with a battered head), and run a small suitcase genny so that you can have 240v on board power as well ?
Click to expand...

I have considered this. Slightly unhappy with having such high voltages near so much water. I also dont think there are any 240v electric outboards
 
Lakesailor said:
You want a four stroke. That's the ticket. For a 20ft boat a 5 or 6hp is plenty.
Fire? Very, very unlikely. There are thousands and thousands of small boats with petrol outboards and not very many fiery accidents.
Click to expand...

I have considered a 4 stroke, it seems like they would be about the same price as my heath robinson diesel though.

Where I sail in the Severn we get tidal streams of 7+knots, so the extra couple of HP does make a difference to at least get up to hull speed
 
For what it's worth, for many years I've had a plan to graft a B&S lawn-mower engine onto a Seagull leg, in order to retain the Seagull's low gearing and BIG prop, along with the economy of a 4-stroke.

I have already converted all-but-one of my BIG Seagulls to so-called water-injected exhaust, which makes them so much quieter (it's actually the closing-off the exhaust-tube holes which mutes the noise, not the water injection itself), and having been so impressed by these conversions, I decided to put the B&S's exhaust underwater in order that I could judge the noise-reduction improvement - before firing-up the welder.

Much to my surprise and disappointment, it made precious little difference: sure the exhaust was quieter, but now I was being deafened by the engine noise itself, which is normally masked by the exhaust noise.

So reluctantly I abandoned the idea. The noise is just tolerable from a distance of around 6 feet (pretty-much the same distance as from engine to ears when mowing), but I'd hate to be sitting in a boat with peace and tranquility all around me, except for that bl##dy engine.

Inside a noise-reduction cover it might work better, but my advice is to stay away from air-cooled engines on boats, unless you intend wearing ear-plugs.

BTW - with a tidal stream of 7 knots on the river, you're going to be travelling backwards in a K20, no matter how many horses are on the transom.
 
You must log in or register to reply here.

Share this page

Top