Diesel Outboard 5hp 25kg

[Tranona]

My understanding is that the industry is working on an emission friendly 2 stroke and the market might not be so small.
I did not at this stage want to discuss who would buy this 25kg clean burning diesel outboard. I wanted to discuss if it is possible to make from an engineering perspective.

Forgive me - but I always thought that the purpose of designing and making things was to satisfy a need.

Yes, I have heard of work being done on 2 strokes. I was also surprised that manufacturers caved in and went down the 4 stroke route, but maybe it was easier and quicker to do it with existing technology.

 

[fuss]

Forgive me - but I always thought that the purpose of designing and making things was to satisfy a need.

Well, you are probably right. I should have established whether there was a need first before I asked if it is possible to engineer this.

I suppose I could have done a poll to ask how reliable everyone finds 2 stroke outboards.
and ask what sort of boat owner would benefit from a diesel outboard
and ask how they feel about keeping a volatile fuel onboard if they already have diesel.
and ask what weight for a small diesel outboard would be acceptable 15kg,25kg,35kg,45kg
what would convince them to buy it etc

but I thought that it might be a good idea to see if it was actually possible to make first.

 

[Tranona]

Well, you are probably right. I should have established whether there was a need first before I asked if it is possible to engineer this.

I suppose I could have done a poll to ask how reliable everyone finds 2 stroke outboards.
and ask what sort of boat owner would benefit from a diesel outboard
and ask how they feel about keeping a volatile fuel onboard if they already have diesel.
and ask what weight for a small diesel outboard would be acceptable 15kg,25kg,35kg,45kg
what would convince them to buy it etc

but I thought that it might be a good idea to see if it was actually possible to make first.

Well, I think if you know anything about this market then the answers to your questions are

1 Most people love 2 strokes and there is little complaint about reliability
2 Can't think of any for a tender or small dinghy application
3 No big problem. A 5 litre can of petrol in a well ventialted or sealed from the accommodation locker is no big deal. Can't recall a single reported incident of fire from this source.
4 Weight is important. 2 strokes could just about make the lowest level, over 20kg becomes hard work to carry and lift on and off a parent boat.
5 Lighter and cheaper than alternatives.

So, if your proposed product can meet those last two criteria, then it is worth expending some time and energy finding out whether you can actually make it. If not put said time and energy to some more useful purpose!

 

[Lakesailor]

Hang On.
When did anyone have to go before The Committee before they could develop an idea?

1984 came and went without anything untoward happening.

 

[2nd_apprentice]

Hang On.
When did anyone have to go before The Committee before they could develop an idea?

1984 came and went without anything untoward happening.

That's the Sinclair C5 school of thought.

 

[Lakesailor]

That's the Sinclair C5 school of thought.

Ah. Laughing on the other side of your face now.
Soon we'll all be electric cycling is wizzy-looking cars.
Years ahead of himself, Sir Clive.

 

[mattnj]

Well, you are probably right. I should have established whether there was a need first before I asked if it is possible to engineer this.

I suppose I could have done a poll to ask how reliable everyone finds 2 stroke outboards.
and ask what sort of boat owner would benefit from a diesel outboard
and ask how they feel about keeping a volatile fuel onboard if they already have diesel.
and ask what weight for a small diesel outboard would be acceptable 15kg,25kg,35kg,45kg
what would convince them to buy it etc

but I thought that it might be a good idea to see if it was actually possible to make first.

why bother? there just seems no point, "modern" diesels are mega complex compared to a 2 stroke, you are going to need a supercharger, a whole bunch of engine management electronic stuff, decompression system for starting, and for what? Slightly better fuel consumption? Very small diesels have a history of bad fuel consumption too (compared to petrol equivalent)
then you end up with a heavy (25kg for 4hp) super complex outboard that costs about £5000....you can buy one hell of a lot of petrol for that.

 

[lw395]

Probably not impossible to make one.
As someone once said, cc's are actually not very heavy.

Flywheels can trade off weight for diameter if necessary.
It might be better to have more than one cylinder.

You could lose a lot of mass from an outboard by making the leg out of carbon fibre, and lots of attention to detail. Not cheap though.
Also, clarify the question, are we seeking diesel as in compression ignition, or an engine that runs on gas oil?

Model aircraft diesels use very different fuel of course.

You might be able to make a spark or glow plug engine that did the trick, if running on gas oil is the aim.


But do you want the economy of a conventional diesel engine?


I think I'll stick with my yamaha. I do have a radical concept for powering tenders though, it's called 'sails'!

cheers.

 

[caiman]

You could put some of that 5000 quids worth of petrol into a generator,and charge batteries with it.
I dare say that if there was a light weight,quiet,competivly priced,diesel fuelled outboard available,then they may be popular.Just because something is not readily available does not mean there isn't a market for it,it just means it is not readily available.There is probably someone out there making one in their shed as we type.
Cheers

 

[westernman]

What are the priorities of people buying outboards in the < 10HP range?

For me (and I would guess most people) in order:-

1) Weight
2) Price

Then a fair way behind

3) Noise

Whether it uses petrol or diesel, I really don't care. Also as far as fuel consumption is concerned I really don't care either as in common with most people I probably won't use more than 10 litres of fuel per year in it.

So what does a diesel outboard get for me on my list of priorities????

IMHO the best way to meet those priorities is with a modern two stroke with a bit of intelligent electronics to meet all the environmental regulations.

 

[TQA]

I think we are at the stage where it is possible to make a lightweight diesel outboard that runs quietly, without smoke.

NOPE NO CHANCE.

Model aircraft diesel engines are "semi Diesels" and use a radically different fuel with a variable compression ratio to "tune" the ignition point. They are some around at 10 cc but work best under 5 cc per cylinder.

A conventional diesel stops working well below about 150cc per cylinder often getting very difficult to start when cold at this size unless some kind of pre heat is involved. A large storage battery will be required unless a flame breathing dragon is fitted to the inlet {AKA CAV thermostart}. Instant nostalgia trip for some who had Perkys in the past.

The cost of tooling up for a micro fuel injection system would not be prohibitive and I can see ways of building something down to a weight where it was around double the the weight of a Tohatsu 2.5 2 stroke at twice the cost.

A diesel 2 stroke is possible but you need a supercharger and they can be right b******s to start so it would be a 4 stroke I think.

However I for one would not touch it with a barge pole. The reliability of a modern 2 stroke outboard providing it has a CDI ignition system is fantastic.

This post will mean that my 22 year old Johnson 15 will fail the next time I need it to drive me through the rain back to my boat anchored well off from noisemaking civilisation and mosquito sources.

 

[2nd_apprentice]

Okay how about this: there are several companies producing outboards that run on paraffin. Bi-fuel really, as they have to be started on petrol but anyway. It has been said on the forum that paraffin and diesel are essentially the same. So that's probably as close as you'll get to a diesel outboard, eh?

 

[fuss]

NOPE NO CHANCE.

A conventional diesel stops working well below about 150cc per cylinder often getting very difficult to start when cold at this size unless some kind of pre heat is involved. A large storage battery will be required unless a flame breathing dragon is fitted to the inlet {AKA CAV thermostart}. Instant nostalgia trip for some who had Perkys in the past.

The cost of tooling up for a micro fuel injection system would not be prohibitive and I can see ways of building something down to a weight where it was around double the the weight of a Tohatsu 2.5 2 stroke at twice the cost.

A diesel 2 stroke is possible but you need a supercharger and they can be right b******s to start so it would be a 4 stroke I think.

However I for one would not touch it with a barge pole. The reliability of a modern 2 stroke outboard providing it has a CDI ignition system is fantastic.

This post will mean that my 22 year old Johnson 15 will fail the next time I need it to drive me through the rain back to my boat anchored well off from noisemaking civilisation and mosquito sources.

Thanks for the information...a reply I can relate to, even if I dont like the content. I had wondered why I had not seen a diesel at under 200cc.
200cc seems to be the limit and they remain conventional so in theory could have been made in the 60's. Surely these problems could be solved in 2010 or at least radically improved.
So lets give it some preheat then??
Can you tell me how you know that 150cc is the limit? This would be very interesting for me.

 

[reeac]

Forgive me - but I always thought that the purpose of designing and making things was to satisfy a need.

Yes, if you're taking a severe commercial [e.g accountant's] view but this is a forum where we throw ideas around between techies - more interesting than playing cards or watching most TV IMHO.

 

[Tranona]

Forgive me - but I always thought that the purpose of designing and making things was to satisfy a need.

Yes, if you're taking a severe commercial [e.g accountant's] view but this is a forum where we throw ideas around between techies - more interesting than playing cards or watching most TV IMHO.

Quite happy with that. However, if you read the thread, it is only the OP who shows any enthusiasm for the concept. In no way would such a device be superior to products already on the market. Not the accountant talking - just plain commonsense.

 

[westernman]

Quite happy with that. However, if you read the thread, it is only the OP who shows any enthusiasm for the concept. In no way would such a device be superior to products already on the market. Not the accountant talking - just plain commonsense.

Ok. A small diesel outboard may well be possible or not (I cannot tell you that, you know more than me on that subject). However, what is the point? There might be some niche market for the military (but I doubt that as well).

What our (pleasure boaters) priorities are for outboards less than 10HP is:

1) Weight
2) Price
3) Reliability (i.e. it starts)

Then a fair way behind

4) Noise

Whether it uses petrol or diesel - who cares? Also as far as fuel consumption is concerned I don't think anybody acres much either as they won't put more than 10 litres of fuel per year into the engine anyway.

So what on earth is the advantage of a diesel outboard?

 

[sarabande]

for use on a small fishing dinghy, with about 100 hours use a year ? It's the lower flashpoint of petrol than diesel that concerns me.

My priorities for an outboard are

1 starts every time if fuel is there and the o/b has been serviced properly


and way down the list,
2 exhaust noise
3 mass


A diesel o/b of about 4 - 6 hp would suit me fine.

There are lots of small diesel engines for scooters. All we need is for Mattnj to conceive an enthusiasm for a diesel outboard, and all our problems will be solved.

 

[westernman]

for use on a small fishing dinghy, with about 100 hours use a year ? It's the lower flashpoint of petrol than diesel that concerns me.

My priorities for an outboard are

1 starts every time if fuel is there and the o/b has been serviced properly


and way down the list,
2 exhaust noise
3 mass


A diesel o/b of about 4 - 6 hp would suit me fine.

There are lots of small diesel engines for scooters. All we need is for Mattnj to conceive an enthusiasm for a diesel outboard, and all our problems will be solved.

So one of these would be just the job:-

http://www.goodsdirect.net/fhdiesels.htm

 

[sarabande]

now you are talking ! That's good info, thanks, but no UK dealers as yet.

I do like their Power pole - an Outboard with a l o n g shaft poking out over the stern. Just the job for the visitors' pontoon at Salcombe on a Saturday evening ! Mince a few people, it would.

http://www.goodsdirect.net/powerpole.htm

 

[Tranona]

for use on a small fishing dinghy, with about 100 hours use a year ? It's the lower flashpoint of petrol than diesel that concerns me.

My priorities for an outboard are

1 starts every time if fuel is there and the o/b has been serviced properly


and way down the list,
2 exhaust noise
3 mass


A diesel o/b of about 4 - 6 hp would suit me fine.

There are lots of small diesel engines for scooters. All we need is for Mattnj to conceive an enthusiasm for a diesel outboard, and all our problems will be solved.

Why are you concerned about the flash point of petrol when used in a small fishing boat? Risk is negligble - unless of course you use a BBQ to cook your fish alongside your fuel tank.

The Star data gives an idea how impractical they are for low hp, low usage applications. Twice the weight of a petrol engine and even on 100 hours a year saving on fuel would be much less than 100 litres. Bet you would have to use ear defenders as well!