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post #1 of 24 Old 01-21-2017 Thread Starter
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Who'da thunk?

About 8 months ago I picked a lil 3hp Yamaha Malta as a spare dinghy motor as our 4 stroke Johnson 15 was getting long in the tooth. We've been using it while the Johnson is in the shop awaiting parts, and the thing runs like a champion, but boy does it burn the gas!
For years on this forum Iíve been reading of folks who cruise with these little outboards on their inflatables, raving about the benefits of the smaller motor. One of the points raised was how fuel efficient they are?
Well, after a month or so of learning extreme patience, I can unequivocally say that the 3 hp Yamaha Malta we have uses at least 10 times more fuel (and oil) than our 15 hp Johnson 4 stroke, to go 1/5th as fast or less.
Donít get me wrong, this little motor starts and runs like a charm and has definitely saved our bacon, but there is no way that these little motors can be considered fuel efficient, especially considering they move the boat at about the same speed as one could row a proper dinghy. I think Iíll stick with the Johnson (as long as she lasts) as it gets such good mileage out of the 2.5 gallon tank that we invariably forget we need gas until we are desperately low. And thatís tootling around at only 15 to 20 knots.

"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.

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post #2 of 24 Old 01-21-2017
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Re: Who'da thunk?

Is that 3hp a 2-stroke Capta?

Iím not much of an outboard motor guy, but Iíve been using our 3.5hp 4-stroke (Tohatsu) for few seasons now. I find she gets great economy if I keep the throttle to 1/2 or less. My little onboard tank will last a long time. But if I try and push it beyond for a bit more speed my little tank drains like thereís a hole in it. Seems thereís a sharp cliff between good mileage and absolutely terrible.

Perhaps this is a characteristic of these small engines??

Why go fast, when you can go slow.
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post #3 of 24 Old 01-21-2017
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Re: Who'da thunk?

I suspect it is a 2-stroke. No doubt the 4-strokes are at least 50% more fuel efficient, and the 2-stroke inefficiency is made worse when pushing a too-small engine to full load or overload.

That is the one thing the small engine brigade overlooks - the engine/prop is often times not matched for the boat, so it is working in an overloaded situation almost constantly. This burns a lot of fuel.

Our 20hp Suzuki on a 300lb 11.5' RIB with two people in it burns 0.6gph at 15kts, so a gallon takes us 25nm. Capta's 3hp at an assumed 3kts would need to burn less than 0.12gph pushing the same dinghy to achieve better range.

I don't know how much a 3hp 2-stroke burns, but I seem to remember my old 2hp Evinrude used more than that pushing around a small hard dink better matched to it.

There is a reason the 2-strokes come with a 6gal tank and the 4-strokes with a 3gal tank.

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post #4 of 24 Old 01-21-2017
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Re: Who'da thunk?

It's trying to push above hull speed instead of getting on the plane.

On the plane you use very little fuel and you get there faster.

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post #5 of 24 Old 01-21-2017
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Re: Who'da thunk?

In the end what is the real dollar cost of an inefficient outboard?

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post #6 of 24 Old 01-21-2017
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Re: Who'da thunk?

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Originally Posted by MarkofSeaLife View Post
It's trying to push above hull speed instead of getting on the plane.......
Yep.
Something small and lite like a 8' portabote would prob get on plane with that 3 2-smoker...w/1 person anyway...
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post #7 of 24 Old 01-21-2017
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Re: Who'da thunk?

Not relevant to the thread really, but FYI; My 10í portabote easily planes using my 3.5hp 4-stroke with one overweight person on board . Even with a normal load it gets up pretty easy. It will plane with two on board, but only in ideal conditions.

Why go fast, when you can go slow.
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post #8 of 24 Old 01-21-2017 Thread Starter
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Re: Who'da thunk?

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Originally Posted by MarkofSeaLife View Post
It's trying to push above hull speed instead of getting on the plane.

On the plane you use very little fuel and you get there faster.
We don't push it that hard, Mark. There's a sweet spot between going nowhere and pushing too much water and that's where I try to run. The dink and motor weigh about 160#. About 100# more with the 15, so it's a pretty light rig for an 11.5 foot inflatable.
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"Any idiot can make a boat go; it takes a sailor to stop one." Spike Africa aboard the schooner Wanderer in Sausalito, Ca. 1964.

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post #9 of 24 Old 01-21-2017
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Re: Who'da thunk?

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Originally Posted by Don0190 View Post
In the end what is the real dollar cost of an inefficient outboard?
It's your backup, that lite too-small motor...the what-if motor you dragged onboard, just in case...and lo and behold, you're glad you did..

I have a small 2 or 2.5hp 2-smoke Nissan that's been hibernating in storage for too many years, and it's going onboard.
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post #10 of 24 Old 01-21-2017
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Re: Who'da thunk?

If it's not on plane, no prob, just needs more quarters dropped in the slot per mile.
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