Outboard decisions: 2 vs 4 strokes

[rslifkin]

Originally Posted by sailingharry

Not true. Our 2018 Tohatsu 9.8 2-stroke weighs 57.3 lbs. A Tohatsu 9.9 EFI 4-stroke weighs 94.7 lbs. Almost 40 lbs more! And already a bit of challenge lifting the dink by hand with the motor on (98% of the time, twice a day), and wrestling the motor on/off when needed. The Yamaha shaves 7 pounds off, for 87 pounds. The Honda is 103 lbs.

Our dink is rated for 10hp max, so getting 9.9 in a 20 hp frame is a bad combination.

Mixing oil adds 60 seconds to a fill-up, and we burn 10-20 gallons a year so it's hard to worry about environmental impact. And weird, but I don't see any oil on the water or smell a lot of exhaust.

The Tohatsu 9.9 EFI is heavy, but it's really a de-rated 20. The carbed 9.8 4 stroke is 81.5 lbs, so much lighter. The Tohatsu 9.8 2 stroke is particularly light for its output though, being the lightest 10hp outboard anyone made (ever, as far as I know). The 6hp 4 stroke weighs about the same as the 9.8 2 stroke.

When people talk about the 4 strokes not pulling as hard as an equal hp 2 stroke, props and a tach become important. I think many of the 4 strokes are more sensitive to being overpropped, so making sure it's actually winding up to an adequate RPM is critical to being able to actually use all of the rated hp. My 6hp Tohatsu doesn't hit rated power until 5500, for example (even though the min WOT rpm is listed as 5000). Running it with a prop that lets it wind out to near 6000 gives a very different result than a higher pitched prop that only turns 5200 with the same load (both in better acceleration and a higher top speed).

[s/v Jedi]

Originally Posted by sailingharry

Not true. Our 2018 Tohatsu 9.8 2-stroke weighs 57.3 lbs. A Tohatsu 9.9 EFI 4-stroke weighs 94.7 lbs. Almost 40 lbs more! And already a bit of challenge lifting the dink by hand with the motor on (98% of the time, twice a day), and wrestling the motor on/off when needed. The Yamaha shaves 7 pounds off, for 87 pounds. The Honda is 103 lbs.

Our dink is rated for 10hp max, so getting 9.9 in a 20 hp frame is a bad combination.

Mixing oil adds 60 seconds to a fill-up, and we burn 10-20 gallons a year so it's hard to worry about environmental impact. And weird, but I don't see any oil on the water or smell a lot of exhaust.

Misinformation! You are comparing different motors: a 9.8 vs a 9.9 which is a step up. You should have compared with the 9.8 efi but that wasn’t good enough?

Also, you fail to mention that the 9.9 is the same motor, with the same weight as the 15 and 20hp motors!

The 9.9 2-stroke is 90 lbs, as is the 15 and 18hp 2-strokes because they are the same motor.

So the difference is 94.7 - 90 = a meager 4.7 pounds. This means it was true after all.

[Tupaia]

You should be comparing apples with apples.

9.8 2 stroke = 26kg (57lbs)
9.8 4 stroke = 37kg (81.5lbs)

9.9 2 stroke = 41kg (90lbs)
(really can't understand Tohatsu's thinking behind this model 0.1hp extra)
9.9 4 stroke = 43kg (94.7lbs)

18 2 stroke = 41kg (90lbs)
18 4 stroke = 52kg (114lbs) old model
20 4 stroke = 43kg (94lbs)

If you only need a small motor the Tohatsu 9.8 2 stroke trumps everything for weight, once you get above that then the weight difference becomes less but engines in this range are heavy to start with and likely remain fixed on the tender.

There is the added maintenance costs of annual (100hour) oil and filter change on a 4 stroke when comparing to oil mixing on a 2 stroke. How many people keep a log of engine hours just another complication.

The Efi motors are smoother and arguably more reliable but only up to a point. If the Efi goes wrong, you are in for a replacement, expensive CDi unit. If it happens when anchored out, in a remote place, on a Sunday or Bank Holiday weekend your are stuffed. Cleaning out a carb can be done on a desert island.

In the end it will be down to where and how you cruise, how remote it is and how often you have to take off the motor.

[rslifkin]

For Tohatsu they've always offered a big and small 10hp range. The small one shares with the 8hp, the big one with the 15 and 18 or 20. Basically, the big 10hp is heavier, but has more torque from the bigger displacement engine and turns a bigger prop. So it'll push a heavy boat better if for some reason you can't go past 10hp. But a light boat that doesn't benefit much from the bigger prop will be fine with the small 10 (the 9.8).

In the current lineup, the Mercury 9.9 is actually the 9.8. The Merc lineup only sells the bigger engine as a 15 and 20, they don't sell the 10hp de-rate of it.

[Lake-Effect]

As a sidebar - are there cleaner options in 2-stroke oil for outboards, that minimize the pollution produced by their use? Eg - smokes less, or where the emitted residue evaporates or breaks down more quickly?

Google suggested some research (eg bio-oils) and some claims for better performance and less pollution from certain synthetics, but it doesn't seem conclusive yet.

[valhalla360]

Originally Posted by robert sailor

However if you ever dunk them in the outback they are really difficult to bring back to life for the average sailor where as the 2 strokes being so rudimentary can be cleaned up rinsed out and running again inside an hour or two.if you cruise off the beaten path in different parts of the world the Yamaha brand is the best to own as they are favoured by fishermen everywhere and parts are easy to get.

That's the kind of argument people made when EFI came out in cars.
- Old times lamented that they knew how to clean and adjust a carb and do basic engine work.
- Today, people don't even think about it. Engines just run and the old timers think it's evil magic.

[malbert73]

Yep, after 5 years and not a hiccup I’ll take my chances on the EFI every day over cleaning a carb. How many cars lose an EFI unit? I suppose going off grid you could just buy a spare. No idea how much but…

[malbert73]

Originally Posted by sailingharry

Not true. Our 2018 Tohatsu 9.8 2-stroke weighs 57.3 lbs. A Tohatsu 9.9 EFI 4-stroke weighs 94.7 lbs. Almost 40 lbs more! And already a bit of challenge lifting the dink by hand with the motor on (98% of the time, twice a day), and wrestling the motor on/off when needed. The Yamaha shaves 7 pounds off, for 87 pounds. The Honda is 103 lbs.

Our dink is rated for 10hp max, so getting 9.9 in a 20 hp frame is a bad combination.

Mixing oil adds 60 seconds to a fill-up, and we burn 10-20 gallons a year so it's hard to worry about environmental impact. And weird, but I don't see any oil on the water or smell a lot of exhaust.

As others said down thread- not apples to apples but if the 9.8 is enough for you to plane then you’ve found the unicorn. In the 15 range where we want to be, we did our research and weight was not a factor

[MicHughV]

Amongst the cruising fraternity, there is something for everybody.

If just one engine was the holy grail, we'd all be using it, but we don't.

Outboard selection runs from the one end to the other...brand names...horsepower....weight....etc and so on.

Somewhere in this mix is the right engine for YOU !!

[rslifkin]

Originally Posted by MicHughV

Amongst the cruising fraternity, there is something for everybody.

If just one engine was the holy grail, we'd all be using it, but we don't.

Outboard selection runs from the one end to the other...brand names...horsepower....weight....etc and so on.

Somewhere in this mix is the right engine for YOU !!

Agreed. And power requirements vary between dinghies. The 12 foot aluminum skiff we carry is fairly easily driven, for example. So even with only a 6hp on the back it just planes with about a 400 lb load at about 9.5 kts. Drop the load to 180 lbs or so and it'll do 13 kts. If I sacrificed some payload and more weight in the davits to put a 10hp on it the thing would fly right along. It's rated for a 15, but I can't imagine putting that much weight on the back. Plus it would just be stupidly fast when loaded lightly.

[sailingharry]

Originally Posted by s/v Jedi

Misinformation! You are comparing different motors: a 9.8 vs a 9.9 which is a step up. You should have compared with the 9.8 efi but that wasn’t good enough?

Also, you fail to mention that the 9.9 is the same motor, with the same weight as the 15 and 20hp motors!

The 9.9 2-stroke is 90 lbs, as is the 15 and 18hp 2-strokes because they are the same motor.

So the difference is 94.7 - 90 = a meager 4.7 pounds. This means it was true after all.

It wasn't intentional. I pulled up Defender and scrolled through outboards, and didn't notice the 9.8 (and frankly, it never occurred to me they would make a 9.9 and a 9.8, and thought I was comparing 10hp motors). So the 9.8 four is only 24 pounds more than the 9.8 two.

And I did mention that the 9.9 was paying the 20hp weight penalty on a boat only rated for 10hp.

[MicHughV]

Outboard manufacturers are slick...

Some time ago, there was a maximum 10 hp engine power required for lakes, etc.
Manufactures took a 15 hp engine, swapped out some jets...and voila....a 9.9 hp.

The difference between a 9.9 and a 15 is basically about 500 rpm...

Etc, etc, etc....who the hell knows what the manufacturers have been up to these days...they surely wouldn't tell us the truth....would they ??

[wsmurdoch]

For a 2-stroke, you need to bring 3-4 times as much gasoline and mix oil into it etc…. and deal with carburetors

I can only smile when I read that 8hp 2-strokes use very little gas you better bring 3-4 times as much gas as a 4-stroke efi motor needs.

If you are going where fuel supply may be limited, then the 4-stroke may be the better option, they get about 50% better fuel economy.

https://www.tohatsu.us/index.php?main_page=page&id=19 provides real data.

[Adelie]

Originally Posted by wsmurdoch

https://www.tohatsu.us/index.php?main_page=page&id=19 provides real data.

I stated my previous point confusingly, one of the interpretations is that 4-strikes use 1/2 the fuel of 2-strokes which is not what I interned.

What I should have written is 2-strokes use 50% more fuel and that over states the case slightly, it’s 30-40% more depending on the model.

[wsmurdoch]

I'm not being argumentative about fuel usage. I'm looking for measured data and wish more was available. It's something that is often stated but seldom is the statement based on careful measurement even though it would be simple to put a gallon in the tank, open the throttle, and run a timer until the dinghy stopped. My guess is that the EFI engines are better than the carbureted engines, and as EFI moves to smaller and smaller engines we will see more improvement in fuel economy whether the EFI is 2 or 4 stroke.