2 vs. 4 stroke dinghy motor

[Victory Cat]

Getting ready to go cruising full time and trying to determine whether to buy a 15 HP 2-stroke or 4-stroke motor for a 10 ft dinghy. One concern is maintenance and upkeep. The other concern is whether I will have difficulty finding parts and knowledgeable repair technicians since I have been told that I will have difficulty getting repairs for 4-stroke motor in remote locations. Please share your experiance and knowledge to help me decide whether to get a new 2-stroke or 4-stroke 15 HP motor.

[Maine Sail]

Thought I would get better mileage out of the small 3 gallon gas tank but it did not really do much if any better than my 2 stroke of the same horsepower a Yamaha. I also lost the ability to get on plane quickly, it was very, very heavy and substantially more complicated than my simple two stroke. After owning my four stroke for about six weeks I sold it, took my loss and pulled my two stroke off the market and put it back into full time use. Even if they ban two strokes I will continue to seek out good used Yamahas.

[Intentional Drifter]

Welcome to the forum, Victory Cat, and good for you! We're planning to head out there, too, toward the end of the year and have been asking ourselves the same question.

There are advantages to the 4-stroke in terms of being quieter and emitting fewer pollutants. They are also heavier and more complicated. As Acoustic pointed out, they are touted to get better mileage, but actual field experience indicates this is equivocal, at best.

I'm pretty much decided to either try and locate a reasonably new Yamaha or Tohatsu 2-stroke, due to the lighter weight, simplicity and parts availability; or, I may just stick with my 1965 Johnson 18hp. It is butt-ugly, not as light as the newer ones (but nowhere near as heavy as the 4-strokes), andI can take it apart and re-assemble it with the lights off. I've had it a long, long time and it has never let me down. Of course, it is also much less likely to get stolen, too! (Eeww! Why did ya bring that thing home?!)

ID

[Rick]

For relatively small dinghys having a four-stroke is like having a two-stroke with a mother-in-law, like 'em or not.

[delmarrey]

I've gone into this heavily on other forums and it really has come down to two points.

1) If you’re going to be in the US, Canada or other British countries it's best to go to the 4 stoke due to environmental policies. Eventually, they may out law them entirely but that'll be a while. So far it's only on certain lakes, especially in California. Also a 4 stroke 15 hp is going to weight around 80-100 lb. depending on the brand, where a 2 stroke will be around 50-70 lb.

2) Pound for pound the 2 stroke is a better deal. The gas mileage, I haven't seen much difference either. Probably due to all the extra parts being thrown around in a 4 stroke. The 2 stroke is much simpler to figure out when a problem arises. It’s just that mixing of oil/gas that I don't like. They are starting to build injected 2 strokes that are environmentally as good as a 4 but the cost hasn't really justified me buying one yet.

If you’re going to under developed countries a 2 stroke would be better for finding parts.

My $P1............................................_/)

[cat man do]

We are being offered these nice 18hp 2 stroke outboard's in OZ at the moment for the same price of a 15hp.

I believe this is a Nissan in the US .

M18/TwoStroke/Products/Tohatsu Outboard Motors

Dave

[AnchorageGuy]

What the manufacturers don't want you to know is that although the two stroke puts more emissions into the air it is less damaging to the environment than the lower emissions of the four stroke. In many areas we have traveled outside the US it was next to impossible to get a four stroke repaired or get parts without a lot of shipping hassles. A little additional info, the oil for the two stroke is actually bio-degradable but not so for the four stroke. The additional weight and the fact that the four stroke really does not have the same punch as the two stroke makes for a good argument for the two stroke.

[GordMay]

During the combustion process, internal combustion engines generally produce, in varying quantities, the following substances:
- Oxides of Nitrogen (NOx) a potential contributor to photochemical smog and to ozone layer damage
- Carbon Monoxide (CO) a toxic gas
- Carbon Dioxide (CO2) a cumulative greenhouse gas
- Hydrocarbons (HC) a constituent of photochemical smog
- Sulphur Dioxide (SO2) an element in acid deposition
- Lead, a toxic heavy metal
- Particulate matter a potential carcinogen

4-Stroke engines generally produce higher CO, CO2, and NOx, but lower HC than 2-Stroke engines.
2-Stroke engines emit relatively high levels of HC in both burnt and unburned form, but low levels of NOx.
Diesel engines are more fuel efficient than 4 stroke or 2 stroke gasoline (petrol) engines and therefore emit lower overall CO and CO2, however, they produce greater quantities of SO2, Nitrogen Dioxide and particulates.

Outboard engines exhaust below the water surface and, as a result, all hydrocarbon emissions pass through the water. Most remain in the gas phase and are released directly to the atmosphere; the remainder condense and become suspended in the water column or form surface film until they degrade or are released into the atmosphere.

2-Stroke engines use a method of combustion which results in some unburned residual oil (and partially burnt oil) entering the marine environment through the exhaust. In fact, research carried out by the State of California Air Resources Board (1998) found that two-stroke engines can discharge as much as one-third of the oil/gas mixture, unburned into the water.

In response, the oil companies are putting increased emphasis on the use of biodegradable lubricants for 2-Stroke engines. Increased use of these biodegradable oils, in 2-Stroke outboard engines, could reduce the magnitude of any hydrocarbon impacts on the marine environment. However, the biodegradation process produces a number of toxic by-products which have an unknown impact on the environment. Furthermore, by-products of the 2-Stroke combustion process will continue to be emitted with the biodegradable lubricant.

[Lynx]

If you are buying a new motor in the USA it is almost a mute point as you cannot by a new 2 stroke per my understanding. Also, if you want to polute less, get a smaller engin or sail or don't go as far.

[tdw]

I had thought that 4 stroke would have definitely been the go but when talking with a dealer the other week , who sold both, he came up with a few advantages of two over four, some of these have already be covered but the ones that I most liked were

Two stroke engines can cope with not being stored vertically.
Weight, an obvious two stroke advantage.
Integral fuel tank, maybe this is not so with larger engines, I don't know.
Cost (of course).

I could ignor the cost difference as it was not great but I liked his other points.

The engine I was looking was nowhere near 25hp, more like ten from memory.

[Sunspot Baby]

Another point in favor of a 2 stroke. When you submerge it and eventually something will happen, it's a lot easier to get them going again than a 4. No crankcase to drain. I speak from experience.

George

[Vasco]

I'll add my two cents for a two stroke for all the reasons already stated. Get a Yamaha 15 hp 2 stroke and you'll never regret it. The only advantage of a four stroke is less noise or perhaps a less irritating noise.

[Maine Sail]

Originally Posted by Lynx

If you are buying a new motor in the USA it is almost a mute point as you cannot by a new 2 stroke per my understanding. Also, if you want to polute less, get a smaller engin or sail or don't go as far.

Yamaha is still selling 8, 10 & 15 hp two strokes in the US at least they are here in the North East..

[Sunspot Baby]

Someone on another thread in this forum said you can get Mercury 2 strokes for less money in the Bahamas than in the US. Seems funny with their duty structure, but could be.

George

[Vasco]

Most small outboards are cheaper in the Bahamas than in the States. It's part of the government plan to encourage small fisherman. But most anything else to do with fishing is more expensive. Go figure.