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Comment by jimmaswell | Hacker News Reader

Is 2 stroke really that common for personal-use boats? I've only heard of them running on 93 gas, which is all I see sold at marinas, no oil to mix in.

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With 2 stroke you need to mix the oil with the fuel before injecting it into the engine in order to lubricate all the moving parts. With 4 stroke the oil and gas are kept separate and you just feed the fuel in.

4 stroke is more commonly sold today but with boating, the lifespan of the equipment is so long that there are a non-trivial amount of 2 stroke engines still in use today.

True, and they're so bad that CARB published a report saying one long day in a 2-stroke jetski pollutes as much as 10 years in a typical car.

It depends. My family bought a boat, and it came with a 90HP outboard engine that was 4 stroke. For they same price, they offered a 2 stroke engine that was 120HP. Everyone agreed adding a single bottle of oil when you fill up the tank with gas was a simple enough thing to do to get the extra 30HP. My family also never filled up at the marina because of the extreme mark up. The boat was always on a trailer, so it just got filled up on the way at any normal gas station.

I’d damn near take that 90 over the 2 stroke. The father in law just got one on his McLay boat and it’s quiet with none of that 2 stroke smell. I’ve lost count of the number of times we’ve been idling out at sea idling and asked each other “is that thing still running?”

Wow. That makes me consider upgrading. I feel guilty just staring at or hearing my (2 stroke) motor idling!

Many small boats have an oil injection system that injects 2 stroke oil from a tank into the fuel as it's consumed (so that you can fill the fuel tank with pure gas and the boat manages the injection/mixing).

I grew up in the 80s & 90s running a 150HP 2-stroke Mercury outboard. Fed it oil on each fill-up. Amazing sounding engine, but in hindsight, horribly polluting.

With that outboard at wide-open-throttle, you were emitting ~ 4 gallons of unburned gasoline per hour out the exhaust, not to mention the oil you cited.

I've seen tiny outriggers used for fishing,etc that are two-stroke. Maybe some jet skis too? I'm not sure.

Certainly anything substantial won't be two-stroke.

As I understand it, there are increasing restrictions and calls to ban 2-stroke marine engines for smaller lakes, because the exhaust contains a fair amount of oil mist that settles on the water.

If nothing else, the noise is a nuisance on small lakes. I grew up next to a small community-governed lake on which all gas was banned. People have been using electric on that lake for ages, which is particularly feasible since it's a small lake (300 acres or so iirc). Electric for small stuff makes a ton of sense and has for a long time.

My parents-in-law also live by a lake where all ICE's are banned. Mostly people row, and a few have electric outboards.

It's really wonderfully quiet, even though it's close to a city.

Besides the oil, the carbureted 2-strokes emit 25%+ of their fuel unburned.

A long time I read about some "next generation" 2-stroke thing, where they had fuel injected directly into the cylinders, after the piston had already blocked the exhaust port. The intake port was only used for air. A bit like those behemoth 2-stroke marine diesel engines.

Evidently it didn't really work out well enough, considering most outboards they sell these days are 4-stroke. I've always had a soft spot for 2-stroke engines, seems so wasteful to "waste" half of the strokes on a 4-stroke. Oh well.

Evinrude's E-Tec line is two-stroke and goes up to 150 horsepower in the G1 series, and to 300 horsepower in the recent G2. That's pretty substantial.

OTOH, they have done a lot of engineering to meet emissions requirements, so they are a far cry from grandpa's old outboard that left trails of blue smoke.

The E-Tecs have done exactly what you said - a lot of engineering to meet emissions requirements. Unfortunately, the requirements for outboards include CO, NOx, and HC, but not P2.5 or P10 (particulate) emissions, because they are much simpler and less scrutinized than the regulations on cars (which DO have particulate limits). The E-Tecs put out 30X as much particulate emissions as the 4-strokes.

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