WWW.RLYACHTS.NET
RL24, RL28, and RL34 Trailable Yachts
from Rob Legg Yachts

RL Yacht Owner's Discussion Forum

Return to the Forum List

2 stroke vs 4 stroke motors
The survey is showing that most new motors on RLs are 4 stroke.

In the search for a replacement for my old motor, most dealers say that there is now little difference between the 2 and 4 stroke motors in noise and fuel consumption compared to those of 10 years ago, and the 2 strokes are half the price of the 4 strokes.

And the 2 strokes are much lighter which is very important when the weight is located right at the aft end of the boat.

Unfortunately, the Honda 15 hp, the lightest and quietest of the 4 strokes, no longer fits an RL28 well because of the redesigned cowling, and Ken Fraser's experiences with Tohatsu suggests other models will have the same issue.

Has anyone done a side-by-side comparison of equivalent 2 and 4 strokes for an RL28 or seen a recent review that could help me with my decision?
Keith Merkley9-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
Keith

It appears that small, cheap to make, ‘low tech’ 2 strokes engines/outboards are being banned all over the world at the moment as they are classed as being environmentally unclean ( see the following attachments). It should be noted that the specific fuel consumption of the small 2 stroke is also substantially higher than that of the same powered four strokes.

I have been really impressed with the 5 hp 4 stroke Honda outboard that came with the IF Folkboat I bought a few years ago. The quiet, low revving, high torque engine, pushes the relatively heavy 2 tonne boat along at close to its displacement speed. I think you should checking out if the 8 HP Honda 4 stroke outboard model fits into your RL 28 engine area?

Alastair


1: HONDA SUPPORTS MINISTER'S MOVE TOWARD TWO-STROKE BAN

Honda has thrown its weight behind Federal Minister for the Environment and Water Resources, Malcolm Turnbull, in his plea to fight urban air pollution caused by marine outboards and garden engines.

It is widely agreed that traditional carburetted two-stroke engines are a major cause of high emissions and contribute significantly to urban smog.

The proposed state/territory government initiative includes funding for a study to look at the viability of introducing regulations to control these emissions. Traditional two-stroke engines represent approximately 60 per cent of small engine sales in Australia and are responsible for an alarming rate of emissions.

On average, each two-stroke outboard or lawn mower engine is responsible for 20 to 30 times the emissions of a modern day motor vehicle.

Honda’s managing director Stuart Strickland said it was “about time” federal legislation was introduced.

“One of the government’s own environmental reports conclusively identified several years ago just how bad two-stoke engines were for the environment,” Mr Strickland said.

“Other countries around the world have had legislation regarding the use of polluting two-stroke engines in place for many years, so it’s certainly time Australia followed suit.”

The government report to which Mr Strickland referred, the ‘Comparative Assessment of the Environmental Performance of Small Engines – Outdoor Garden Equipment’, states:

‘It is therefore clear that the most expedient path to reduce emissions from these small engines is through national regulation.’

An earlier Department of Environment report regarding two-stroke engines also said about two-stroke mowers:
‘Assuming six people in a block of 10 homes decided to mow their lawn during the same period, the emissions would equate to about 240 cars driving around in their yards for almost an hour…’

Mr Strickland said the Federal Government’s call to consider regulating out-dated two-stroke engine technology was inline with Honda’s own environmental mission, which dated back nearly 50 years.

“As one example, Honda adopted the policy of manufacturing only four-stroke outboard engines back in 1964,” he said. “Today, Honda is the only outboard company in Australia to have every model in its range achieve the Outboard Engine Distributors Association (OEDA) three-star ultra-low emission rating for superior environmental performance.”

In fact, Honda’s commitment to first-class four-stroke outboard technology can be found in the words of the late Mr Soichiro Honda himself, when he gave the following directive to Honda staff in the 1960s:

“What will happen to our oceans, lakes and rivers if all that exhaust gas mixed with oil gets pumped into the water? I don’t care if everyone else is making two-strokes – Honda has to make four strokes.”



2: From the East Down Yacht Club in UK

The new EU 2006 emission regulations.
The new European emissions regulations are due to come into force on 1st January 2007 and will have a major impact on the sale of new 2-stroke outboards.

All 2-strokes that do not meet the new regulations are banned from being placed on the market in the EU after 31st December 2006. All outstanding stock can be legally sold, and all 2-strokes that are in the EU on the cut-off date can still be used and freely bought and sold second hand.

There is the technology to make 2-strokes clean enough to pass the new regulations, but it's expensive and will be confined to the larger 2-stroke (40hp plus) engines.

The only option for tenders and smaller boats appears to be a 4-stroke engine.
If you are thinking of buying a new small 2-stroke then hurry, as once dealer's stocks have run out there will be no way that you can legally get a new small 2-stroke for leisure use.


Alastair Russell10-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
Alistair,
Thanks for that information.

I find that the RL28 performs best with at least 15hp. In normal conditions a much smaller motor is adequate but against wind and tide and particularly big waves, the bigger motor comes into its own.

I have heard we will be introducing in Australia the ban of 2 strokes in 2010, I guess unless they can reduce emissions. Not surprising the Honda are behind it seeing they only produce 4 strokes. Hopefully the ban will encourage smaller, lighter, and cheaper 4 strokes than we have now.

The weight difference is what is driving me to still consider the 2 strokes - 35 kg compared to 50 kg. Lifting 35 kg out of the well to take the motor for service is bad enough to disregard anything heavier. And that is a lot extra weight to have at the ends of the boat.

Besides I work for a mining company so the extra emissions from a 2 stroke the small amount of time I use a motor is insignificant!
Keith Merkley10-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
Guys
I live in a high theft area so I have to remove my motor after use and take it home. My 6hp 4-stroke Merc weighs 23 kilos and is easy to shift. The biggest reason for me to go 4-stroke was that 2-stroke motors produce black sludge that pours out of the prop(exhaust) when you put the motor in the boot but not before! 4-strokes don't!
Matthew FRANCIS10-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
Keith

There has been 3500 heavy 2 tonne Marieholm 26 Folkboats built in the world (100 in Australia) and it should be noted that the recommended engine for the Marieholm 26 is a Volvo Penta 7.5Hp inboard diesel. You have got to remember that after a displacement boat hit its speed wall, for that boat to crack on say an another extra knot of boat speed over the boats declared figure you have to double the boats horse power which of course doubles the boats fuel consumption (7.5 HP x 2 = 15HP). I rest my case!

From the Marieholm 26 website:

Security of a 7.5 hp Volvo Diesel Engine.
When the wind fails and you wish to come to harbour as quickly as possible it is reassuring to have a substantial inboard engine. The engine in Marieholm 26 is a Volvo Penta diesel MD-5, 7.5 hp. It is placed under the cockpit in a sound insulated compartment with good accessibility for servicing.


Alastair10-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
I have been steering clear of these RL28 threads because I do not have any first hand experience with the RL28. BUT I wonder whether the boats are getting heavier, the weather worse or whether I missed something.

Somewhere on this site is one of Rob Legg's stories where he clearly states his own RL used a 6hp Evinrude.

I had a Southcoast Magnum that was pretty close to the RL28 and it was probably overpowered with the Yamaha 10hp with saildrive propellor. Many other Magnums used the 8hp 2 stroke Yamaha outboard that was more than enough to do the task.

What brains trust is pushing the RL28 owners to 15 or even 20 horsepower. Get real a modern 8 or 10 hp outboard with high thrust prop should be fine.

I saw a very nice Yamaha 8hp with high thrust prop and power tilt and start was on the back of a trimaran where I tied up a few days ago.

I don't have the solution to the RL28 engine fitment but I can't believe anyone needs such a big outboard.

I use a 5hp Mariner 2 stroke with high thrust propeller in my RL24, apart from the smoke it works fine even though I have lost count of the number of people that have told me that 8hp is the new minimum requirement for good performance on an RL24. As Alistair points out hull speed is all you get (although I have power sailed at 12 knots unintentionally).

For the record I note there is a huge difference in the performance of the 5hp Mariner 2 stroke and 4 stroke models with the 2 stroke pushing significantly better. I suspect the new cleaner 5hp 4 stroke is just 5 hp whereas the old 5hp is well above the 5hp. The Mariner/Mercury/Tohatsu 5hp 2 stroke is recognised in many magazine articles as the best performer in its capacity. There is bound to be an excellent 6-10hp outboard that will suit the RL28 without breaking the bank or overloading the stern.

I don't like the 2 stroke smoke so I use brands of oils that smoke less and for long trips I set the tiller pilot and move forward away from the noise and smoke. Surely someone can find a good new outboard to fit in the RL28 without masses of modifications.
Greg10-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
Greg,
There is no problem fitting any of the 2 strokes in the RL28 well. The problem comes with the 4 strokes that have a wider cowling and considerably more weight. This will become more important if 2 strokes are banned. My question is whether the 4 stroke is worth the extra weight, cost, and fitting hassles.

While I agree that most of the time 10 hp is quite sufficient, I have tried motoring an RL28 with a 10 hp into a nasty Moreton Bay chop and progress was so slow as to be dangerous - and extremely uncomfortable - and certainly nowhere near hull speed. For those times when you are caught out with strong headwinds and time constraints, 15hp offers a safe refuge, faster. Also the more powerful motor can be run at lower revs for less noise at the same boat speed.

I think more than 15 hp is a waste. I have 20hp at the moment because it was actually cheaper than 15hp at the time, after the cost of adding charging components was added, and the weight is the same. But I never need to run it anywhere near full throttle.

It is interesting you found the 2 stroke to be more powerful than the 4 stroke, but as you pointed out, the rated and actual may differ by quite a bit.

And then there are the propeller options - I am almost afraid to ask...
Keith Merkley10-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
During the early days of building the RL28 we experimented with various outboard and sail drive motors, and the one thing that sticks in my mind was the big difference that propellor pitch and blade area made, you must keep in mind that most outboards these days are designed for light planing type boats, and hence use two blade big pitch props designed for speeds maybe up to 20 knots, and on a displacement hull they do push you along at a reasonable pace untill the going gets tough.
We learnt a lesson after being caught in very bad conditions with a 6HP motor on a 28 and couldnt make headway, so had to hoist and double reef the mainsail to help get us home. I kept the motor, but bought the small pitch three blade prop, it was a very big improvement and was happy with that in any conditions, it is just like dropping back a gear in a car, suddenly you find a lot more power.
I would just like to add that if you are considering mounting an outboard on the transon instead of in the well and are used to motor sailing , you will find it difficult to prevent the motor from cavitating when the boat is heeled, this can also be the case in choppy water under power alone.
Re 2 stroke vs 4 stroke I opt for light weight down that end of the boat every time.

Read Pauline Fowlers story, and judge for yourself how powerful a motor needs to be on a 28.
Rob11-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
I have an 8hp honda four stroke on my RL28,the reverseing exhust is a bonus when try to stop, the low noise is great ,the economy is fantastic and the power sufficant "what more do you want"
gary trost 11-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
PS the attributes of these motors are a real consideration when purchasing ;slow speed manouvering is a big plus
When we bought our boat, Polaris, it had a 15hp yamaha on it -- would not slow idle hence when berthing etc the speed was to great {quite scary} when reverse was engaged would not stop [too much air around prop] this dose not happen with the Honda.
My point here is that speed across the bay should not be the only consideration these boats are cruisers after all.
My 8hp pushes us at comfortable 5 knots - 6 flat out and with the high thrust prop against head winds and swells satisfactly
The weight of this 40kg dose not pose a problem ; 7hp Volvos weigh considerably more - they were fitted to these boats successfully
There was very little modification needed to fit this motor; 5mins with a jigsaw and some epoxy to fill the voids between the double skins 1hr job done.
Of course we all have our needs ;this motor suits mine beautifully.

gary trost 11-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
And now, lets hear it for the 2-stroke.
Evinrude's E-tec and Tohatsu's TLDI motors have recently been approved by Wide Bay Water for use on Lenthall's Dam, Hervey Bay's water supply. Mr Honda might not like it but their emission levels are equivalent to a 4-stroke. These developments will continue.
The quality of the 2-stroke oil is another consideration. If it's cheap, (I can name a couple of brands but won't) it is probably smoky. Look for something low ash. We used the American Torco oil for a while before changing to the locally produced Synforce. There may be others. Smelly outboards that fill the cockpit with fumes are no longer a problem.
I have opted to hang the motor on the transom because of the improved performance with the well closed up. Light weight is therefore a key criterion.
Mike11-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
After reading all the 4 stroke/2 stroke info in this thread and going through the engine survey , I think that quite a few RL owners may have bought outboards kitted out with the wrong propeller option. In the old days the small portable outboard range engines were sold giving one the option of fitting one of two types of propellers. One was for pushing heavy displacement boats and the other for use in light planning hulls. Nowadays they use the term ‘high thrust propeller’ for the displacement boat propeller.

In many cases then the 5 or 6 hp outboard model had the same external size and weight as the 8 or 9 hp versions with the only major difference in the models being an increase in cylinder bore.

Mike, I agree with you, the technology is there now to clean up the 2- stroke engine (see below). If you check out the Evinrude and Tohatsu range on offer at the moment you will notice that they do not fit the high cost E-Tec and TLDI engine combustion technology to their smaller portable outboard range that we need for our type of boat. They say that they that they cannot make the smaller 2- stroke comply with the new pollution laws and also compete price wise with the cleaner running 4-stroke if they fit their new combustion technology.

In the early eighties I remember having no trouble towing an RL 28 with a crook engine, down the Avon River and out to the start of the Marley Point Race with my RL24. Parahandy is fitted out with a Suzuki 8 HP 2- stroke engine with the high thrust prop.



ATTACHMENT Orbital Engine Technology 1995

Technology for efficient clean-burning engines

Ralph Sarich of Perth first won fame when he was named Inventor of the Year on ABC TV's “The Inventors” program in 1972. His invention was an orbital engine that used only one triangular shaped piston to create five combustion chambers as it orbited inside a single cylinder.

Huge support from the media, and investments by the public, governments and BHP enabled Sarich to take the engine further. In 1983 it was as good as it was going to get, but still not good enough to replace normal car engines.

A spin-off from the years of research rescued Sarich's company.

Two-stroke engines are lightweight, 'dirty' engines that run mowers, generators and some small cars, motorbikes and boats. The Orbital Engine Co discovered that the sophisticated fuel-injection and combustion system developed for the orbital engine could be used on two-stroke engines, making them much more powerful, fuel-efficient and clean.

The Orbital Combustion Process engine has been refined into a two-stroke engine that is 50% lighter, 30% more fuel efficient, 20% cheaper to make, 70% smaller, and produces 30% less pollution than traditional engines. A plant was established in the USA to build these engines for sale to car, motorcycle and boat manufacturers to test and develop as licensees to the Australian company.

In 1995, Mercury Marine used direct fuel injection to make its high performance outboard motors cleaner and more fuel-efficient. This was the first commercial application of Orbital’s technology.

The Orbital Engine Corp earns its money from the sale of its intellectual property through licence fees and royalties as well as fees for the provision of engineering services. Orbital has earned in excess of $150 million in licence and related fees. Its technology package includes over 1000 patents or patent applications lodged in more than 20 countries worldwide, covering innovation in all aspects of engine and control system technology.

Licensees include General Motors Corporation, Ford Motor Company and Fiat Auto as well as non-automotive companies including Brunswick Corporation (the parent of Mercury Marine), Outboard Marine Corporation, Bajaj Auto Limited and Piaggio V.E.s.P.A. In 1996 Orbital fitted its two-stroke engine to a prototype sports car and a government fleet of Ford Festivas in Australia.

In 2000, Aprilia of Italy released the first two-stroke motorcycle with Orbital’s direct fuel injection technology, and Orbital signed an agreement with Sundiro, one of China's largest scooter manufacturers, to use Orbital’s engine in its popular Chinese scooters.
Who Did It?
Key Organisations
Orbital Engine Corporation Limited : R&D, design
Key People
Ralph Sarich : inventor and developer
Kim Schlunke : engineer, director

Alastair14-Jan-2008    Edit    Delete 
Re: 2 stroke vs 4 stroke motors
I have to state my concerns at the bias against small 2 stroke outboards that seems to be based on "environmental" aspects. I agree the smoke in the RL cockpit is an issue.

Most of the statistics used for determining the effect of outboards is based on large outboards and high usage applications. Trailer yachts use there outboards infrequently meaning the pollution caused by a small outboard is insignificant. A similar conclusion could be made for small outboards used on tenders.

My point is that I can see the value of 4 stroke engines in outboards above 20hp but the limited use of smaller outboards reduces their impact on the environment to an insignificant percentage of the rest of the power boat fleet. Of course commercial users of outboards are an exception and most of them use 4 strokes anyway.

That said I still use Castrol Biolube oil (or an equivalent) to mimimise the impact I have on the environment when I use my outboard.

It will be a very sad day for common sense when they ban small 2 stroke outboards.
Greg14-Jan-2008    Edit    Delete 

Return to the Forum List       Add a message to this discussion