Two stroke versus four stroke outboard motor we have been duped

[ccscott49]

There's nothing to stop a manufacturer making a two stroke with a pressure oil lubrication system and a sump.
Commer used to make supercharged 2 stroke diesels for their wagons.

The TS3

Entirely different kettle of fish I'm afraid, opposed piston two stroke diesels bear no resemblance to crankcase breathing petrol two strokes. The main difference being only air is blown into the cylinders by the supercharger, not the fuel mixture.

 

[Oldbiker]

Small direct injection 2T motors have been used successfully in small motorcycle/scooter applications for some while, and use injection systems based upon original design by the Orbital engine company of Australia, who have also tested larger 2T motors, which use less fuel, have lower emissions, are more powerful, and are cheaper to produce than equivalent 4T power units.

The nonsense about emissions from 2T motors has provided an ideal opportunity for manufacturers to introduce heavier, more expensive, and less reliable 4T power units, which ultimately mean their profits increase. But in the case of marine 2T outboards the designs seem so dated, that the cost implications of design and development of modern high efficiency 2T power units may be greater than that of 4T units which sell for more money, and need more spare parts.

 

[GSL]

In late 2007, I bought a brand new 9.9HP Mercury 4 stroke for my 3.2 meter Avon RIB and was very disappointed with the performance, low power and at 45 kilos, a very heavy engine if it ever needed removing from the tender.

I used it for a season, will admit that it used minimal fuel, it was very difficult if not impossible for my partner to start, the effort to pull the start cord was just too much for her, so with regret it was sold and I purchased a second hand 2003 Mariner 15HP two stroke........ chalk and cheese!

Easy to start, jumps up on to the plane and just so effortless to keep the RIB on the plane with about half throttle.

It does use more fuel, but for the number of hours the tender gets used each season, hardly a major consideration. In fact it gets used a lot more than previously because the engine is just so useable, and the RIB is now so much nicer to ride in.

We have just spent 10 days cruising around Ibiza, the boat used 1,000 litres of diesel and the RIB used 20 litres of petrol, so to answer the original query, I think we have been duped, the potential for polution from the 2 stroke is so small to be immeasurable in my opinion.

Just my experience.

Graham

 

[Will_M]

we have all been sold,or been forced to buy 4 stroke motors...

Hardly forced, there are options...

Nothing to prevent you buying Evinrude E-TEC Direct Injection 2-stroke outboards 25hp-300hp or Tohatsu TLDI 2-strokers 40hp-115hp. All sold and supported within the UK.

Sleva in other markets have a 2-stroke range of 50hp-80hp.

That said, other than the E-TEC, I'd keep with 4-strokers all day long and probably something from Yamaha around the HP size and usage I am interested with.

 

[TSB240]

small twin o/b suitable for well mounting

The import restrictions now mean that there is no new small hp lightweight twin cylinder OB that will fit most outboard wells on trailer sailers.

Most people who currently have the benefit of powerful and smooth running two stroke twins 9.8 ,8 or 6 hp Tohatsus , Mercs or Mariners will be forced into the running of lumpy, heavy, under powered teeth rattling single cylinder 6hp 4 stokers.

The legs of larger 4 stroke twins are too large to fit even if you can manhandle the extra weight of OHV gear.

Honda used to market a 6 and 8 hp twin four stroke that was just about suitable but withdrawn from market as it was too easily derestricted to give up to twice the horse power at a considerable cost saving.

The environmental issue is a big con. I wonder how much of the annualy serviced 4 stroke sump oil will be disposed of in an environmentally friendly way?(other than leaking out in the car boot or boat locker!)

 

[Oldbiker]

Indeed almost all measures taken to supposedly "protect" the environment, as in the case of issues to do with small 2T power units, are nothing of the sort and seem to merely fulfill the role of placating green lobbyists, most of whom are financed through champions of environmental matters such as FOMOCO and similar corporate interests.

If this nonsense can be used to force consumers into paying more for products that arent as good, then commercially it seems a very good idea for manufacturers to strongly support this type of legislation. In the end the consumer pays the cost big time though, as any effective measures to safeguard the environment are easily dismissed, with reference to things that make no difference whatsoever.

 

[lovezoo]

We have just spent 10 days cruising around Ibiza, the boat used 1,000 litres of diesel and the RIB used 20 litres of petrol, so to answer the original query, I think we have been duped, the potential for polution from the 2 stroke is so small to be immeasurable in my opinion.

I think that misses the point. Have you ever tried going for a swim off one of the beaches in Formentera, for example, where the crystal clear water has a film of 2-stroke oil on it from all the tenders zooming back and for down the boat lane to the 100 or so boats anchored off?

The pollution may be very small in comparison, but it is concentrated in the worst possible place to have it.

 

[GSL]

I think that misses the point. Have you ever tried going for a swim off one of the beaches in Formentera, for example, where the crystal clear water has a film of 2-stroke oil on it from all the tenders zooming back and for down the boat lane to the 100 or so boats anchored off?

The pollution may be very small in comparison, but it is concentrated in the worst possible place to have it.

I can honestly say that in the time there, mostly anchored off Espalmadoor I did not see any film of two stroke oil on the water. We swam ashore several times a day and did not encounter this at all. Were we lucky or have others encountered this problem?

I suspect that it is far more likely to encounter a film of sun tan oil from the bodies swimming in the sea in that area.

Graham

 

[lovezoo]

I can honestly say that in the time there, mostly anchored off Espalmadoor I did not see any film of two stroke oil on the water.

Shows the 2 stroke ban works.

Seriously though, swimming around the boat lanes near the beach there was always a stink of 2 stroke oil and a film on the water, especially on a flat calm day. This is also the case in the really small bays on Ibiza like Cala Salada.

 

[Davy_S]

The only film on the water in the Ionian harbours tend to be spilled Diesel fuel, I have a little Evinrude 3.3 2T, no gears, simple to get at impeller, behind the prop, Its 23 years old now, but still runs well. Seems to be quite smoke free. I could well understand a few trusty Seagull leaving an oil slick behind them though

 

[Lakesailor]

Entirely different kettle of fish I'm afraid, opposed piston two stroke diesels bear no resemblance to crankcase breathing petrol two strokes. The main difference being only air is blown into the cylinders by the supercharger, not the fuel mixture.

You've been misled by my example.
There is nothing to prevent a small 2T engine having a pressure lubrication system with a dry sump.A very little amount of oil mist may get inducted and burnt, but a bit of R&D would provide a solution. Perhaps now is the time to produce a small diesel supercharged engine. Economy and low emmissions, especially as small outboards tend to run at constant revs.
Cost and commitment are the lacking factors due to the already mentioned low returns.

 

[Kawasaki]

Shows the 2 stroke ban works

Earlier this Year, me an swmbo where boating in the Agean
As per 2009
In 2008 we spent a lot of time in the Med , boating wise

Most of My time is spent in the Irish Sea.

Which has a great 'life' underwater
The Med an the Ionian and the Agean are 'dead' in comparison.

It is nothing to do with the 2 stroke 4 stroke debate
'O

 

[Kawasaki]

Earlier this Year, me an swmbo where boating in the Agean
As per 2009
In 2008 we spent a lot of time in the Med , boating wise

Most of My time is spent in the Irish Sea.

Which has a great 'life' underwater
The Med an the Ionian and the Agean are 'dead' in comparison.

It is nothng to do with the 2 stroke 4 stroke debate
'O

Other 'issues' are more relevant.
Taint about outboards!

 

[AndieMac]

Other 'issues' are more relevant.
Taint about outboards!

Nothing to do with flushing all those sea toilets...;-)

 

[Assassin]

A very interesting question, and one with many facets and answers.

Two strokes biggest problems were the owners mixing fuel and oil inaccurately, many owners added more oil to be "on the safe side" which increased emissions, particularly the first tank full after standing them over winter.

This has been countered by the fact that modern injection systems are much cheaper to produce, and available cheaply on smaller market engines, they use oil injection to optimise the oil to exact amounts required. Modern synthetic additives make modern two stroke oils more durable, basically less is needed to effectively and efficiently lubricate the engine, add to this the various detergents which makes combustion much cleaner.

Modern two stroke design is much better, particularly the combustion cycle itself, with new computer software and techniques such as CFD (computational fluid dynamics) designers can optimise combustion chamber design. This leads to less fuel and oil being used for a given power output as fuel efficiency is optimised by these combustion chamber designs, and modern designs can be design tested rather than build it and see.

Modern materials and coatings contribute much to engine efficiency, these allow engines to run much hotter than older engines, this improves thermal efficiency without the significant engine deterioration of older engines. Coatings also allow less lubrication to be used, teflon and PTFE based coatinga have been around for decades, it is only the technology to coat surfaces which has improved. This allows very cost efficient thin coatings to be applied accurately, and reliably.

It is a combination of all these factors, amd many others which have reduced the oil requirement of two strokes, and the resulting emissions; and has led to so many manufacturers making and selling them legally and certified.

 

[1973keith]

Assassin, I agree with some of what you say particularly the tendency for people to massively over oil the fuel. But I believe you have missed the main reason directly fuel injected (not oil injection like the hateful Johnson VRO system) two strokes are more fuel efficient than their carbureted cousins...

The injection engines don't add the fuel to the cylinder until the exhaust port is closed.... so half your mixture isn't going straight out the exhaust unburnt.

The oil injection engines went some way to getting the oil/fuel mixture right until they went completely wrong and your engine seized anyway ;-) but they did nothing for economy, carbs were still in the circuit and a good proportion of the fuel used went out the exhaust unburnt.

The main problem facing the development of directly fuel injected small two strokes is the electrical requirements.... It's difficult to get all the computer driven trickery that measures everything and get the injector to deliver a well timed squirt of highly pressurised mixture to the cylinder in less than two turns of the engine by pulling a bit of string! I'm not saying it can't be done, but it's more expense and complexity that could effect overall reliability and will probably need a battery...

To my knowledge there are only 3 players in the direct injection two stroke market right now, Evinrude ETEC, Tohatsu TLDI, and the Mercury/Mariner Optimax engines (I'm not even sure if Optimax engines are still being developed?).

 

[Assassin]

I had assumed that from the technicalites of the replies that people would know the difference, and omitted this for this reason.

It is an interesting issue though as newer small petrols do not use battery power, and do not need it as they are using a combination of kinetic recovery from natural vibrations, and capacitor electrical storage. It is fairly new technology when applied to marine, but decades old technology when it comes to other fields, and the reason many engines take a couple of pulls to start.