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Old 29-10-2018, 23:12   #1
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Two stroke or four stroke

Hi,

First ever post so be kind.

Looking to buy a new motor for my 2.6m inflatable tender and trying to decide between a four stroke and a two stroke (while they're still available)

Two stroke appear to be lighter, perform better and are more affordable so should be a no brainer right?

Anyone out there made the change to four stroke? Was it a good move? Are they worth the extra investment?
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Old 29-10-2018, 23:24   #2
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Re: Two stroke or four stroke

I've had a four stroke pushing a small yacht and this is a no-brainer. 4 stroke all the way. Ditto with outboards over 20 or so hp. I also had a centre console plate boat fitted with a gas guzzling V4 two stroke and I hated it. For a dink though, IMHO, you'd have to have some compelling reason to favour a four stroke over a two stroke for this application.
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Old 29-10-2018, 23:28   #3
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Re: Two stroke or four stroke

I have had two four strokes and four two strokes in the past twenty or so years and for practicality on a smallish dingy where one needs haul the dingy up beaches and boat ramps the two strokes are by far the most practical alternative. If I had a big boat and a large dingy with a large outboard on a power davit and only cruised between marinas I would have a four stroke, they consume considerably less fuel.
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Old 29-10-2018, 23:30   #4
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Re: Two stroke or four stroke

Quote:
Originally Posted by Reefmagnet View Post
I've had a four stroke pushing a small yacht and this is a no-brainer. 4 stroke all the way. Ditto with outboards over 20 or so hp. I also had a centre console plate boat fitted with a gas guzzling V4 two stroke and I hated it. For a dink though, IMHO, you'd have to have some compelling reason to favour a four stroke over a two stroke for this application.
Have to agree, two stroke lighter and more powerful for it's size, able to store in any orientation but does use more fuel. Four stroke needs to be stored in a specific orientation however is less polluting and usually quieter.
You pays your money and takes your pick.
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Old 29-10-2018, 23:32   #5
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Re: Two stroke or four stroke

Thanks Guys, great feedback. This is an awesome site.
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Old 30-10-2018, 03:41   #6
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Re: Two stroke or four stroke

Greetings and welcome aboard the CF, champo.
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Old 30-10-2018, 04:15   #7
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Re: Two stroke or four stroke

If it's just for a 2.6m tender, two stroke is ideal. Though it all depends what you want. 2T is easier to work on and repair, but you need to remember to mix the oil (no biggie. 4T pollutes a bit less, can only be laid down on certain sides, and has slightly more maintenance (need to change the oil).

A 6-8hp two stroke is about the same weight as a 6-8hp four stroke, but with the two stroke it'll likely be twin cylinder, so actually much smoother and with a bit more thrust. Once you get to 10hp, a two stroke weights a good 12-15kg less than a four stroke.

The four stroke uses a little less fuel overall, not much though unless it uses fuel injection, which it won't at the powers you'll be looking at.
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Old 30-10-2018, 05:20   #8
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Re: Two stroke or four stroke

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perform better...?

Anyone out there made the change to four stroke? Was it a good move? Are they worth the extra investment?

I think the "perform better" part is debatable. Depends on what your test criteria for "better" might be.

I did change from a 5-hp 2-stroke to 15-hp 4-stroke, so that move also incorporated more horsepower (up to what our new -- at the time -- dinghy actually needed all along), another cylinder, and fuel injection. The fuel injection and extra cylinder seem to play better with the ethanol-gas (petrol) mixture we have to use where we are. The 4-stroke does run both quieter and smoother. Mostly all good, for us... but the additional weight is significant... so we also went to a trailer for off-season storage.

None of that sounds like it would suit your situation. Can't say I've shopped for smaller 4-strokes to compare to the 5-hp 2-stroke we had before.

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Old 30-10-2018, 06:37   #9
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Re: Two stroke or four stroke

When we started cruising about eight years ago, we had a New Zealand-made AquaPro with a 15hp Honda. It was a great combination as my wife and I could fairly easily drag it up on a beach, it was very economical and performed decently. However, by the time we got to Thailand, both the dinghy and outboard were in need of replacing.

We selected a 3.1 fiberglass RIB but struggled choosing an engine. The new dinghy weighed 60 kilos which was 20% more than our old AquaPro. The outboard we wanted was the Yamaha 20hp 4-stroke (the 15hp weighs the exact same) but it weighs 51 kilos - a combination that would have been too heavy for us. Ultimately, we chose Yamaha 15hp 2-stroke ‘Leisure’ model as it only weighs 36 kilos but it’s still heavier than the AquaPro/Honda combination that we used to have. Even with dinghy wheels on packed sand, it’s a workout getting it up a beach. Plus, it seems to use almost twice the fuel that the Honda used.

Fair winds and calm seas.
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Old 30-10-2018, 06:53   #10
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Re: Two stroke or four stroke

Most of the comparisons between the 2 and 4 stroke have been well covered in the discussions above. In summary, for the lower weight and ease of maintenance, a ~8 or 9.8 hp 2 stroke motor would be a good choice for a 2.7m inflatable.

Look around for the weights on various manufacturers as some are lighter than others (ex both Nissan/Tohatsu 8/9.8 are 59lbs/27kg).

We had a 2.7m inflatable and used a 5 hp 2 stroke (44lbs). It needed more power to get it up on plane w/2 people and this is the reason I suggested to go for a ~8 or 9.8 sized motor.


Also you'll want some sort of motor lift/davit as even a 44lb motor is cumbersome to get on/off the dink.


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Old 30-10-2018, 09:09   #11
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Re: Two stroke or four stroke

Be careful, two stroke engines are becoming illegal in some areas due to emissions.
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Old 30-10-2018, 09:21   #12
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Re: Two stroke or four stroke

Depending on how far you hope to travel in each dinghy trip you may want to look into electric.
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Old 30-10-2018, 09:57   #13
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Re: Two stroke or four stroke

Unless you're planning on something less than 30 pounds (13.5 kg), you're probably not going to be hoisting the engine off and on the dinghy by hand. To get the horsepower to plane, probably looking at 9.9 hp. Already too heavy to handle without a davit. So I would choose a 4 stroke. No fuel mixing. Can idle all day without fouling the plugs. Much better fuel efficiency. And doesn't spew raw gas and oil into the environment. And in many areas no 2 strokes allowed, especially rivers and lakes. Tohatsu, Suzuki, and Yamaha make two cylinder, fuel injected 9.9s, no carb to foul from gummy oil gas mixes. Good sailing.
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Old 30-10-2018, 09:59   #14
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Re: Two stroke or four stroke

I used to own 2 strokes which where lighter but way too polluting. Then a 4 stroke 9.9 on a 2.6m RIB. Worked fine but way too heavy to get off the rail. My SO has weak arms and it’s nearly impossible to get the boat up the beach. Now we have an electric 3hp motor and love it! Super light, breaks down into 2 pieces which means it can be easily carried onto dinghy by hand. No stinking exhaust or noise and no fuel to spill. It can sit on the rail or be stashed inside the boat. Charges when I charge the house batteries with genset or with shore power. Solar to come. Slower, yes, but we usually just need to go a short distance to shore or crab pots. We looke at Torqueedo but the EPropulsion Spirit 1.0 won out. Most quiet and less money. Very happy with this setup.
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Old 30-10-2018, 10:59   #15
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Re: Two stroke or four stroke

Quote:
Originally Posted by champo View Post
Hi,

First ever post so be kind.

Looking to buy a new motor for my 2.6m inflatable tender and trying to decide between a four stroke and a two stroke (while they're still available)

Two stroke appear to be lighter, perform better and are more affordable so should be a no brainer right?

Anyone out there made the change to four stroke? Was it a good move? Are they worth the extra investment?
For a tender go 2 stroke. Right!
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