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Old 17-04-2010, 19:33   #1
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MPG with Johnson 4hp Sailmaster on an Islander 21 ?

Can anyone estimate what my fuel consumption would be. I have a Johnson 4HP Sailmaster on an Islander 21' sailboat. I think the hull speed is around high 5 knots.

Also, the fuel tank clip secure thing doesn't engage? Any help? The fuel tank rides on the outboard and locks in with a metal bar that gets inserted into a latch type thing. I can't get it to lock though.

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Old 17-04-2010, 19:47   #2
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That is a really great motor you have, the 2 cyl 2 stroke 4hp was light and strong... take care of it and it should last you some time.

How much fuel you burn will have to do with the throttle setting. Keep in mind that the fuel burn rate is not in linear proportion to speed, it will increase as a geometric function... in other words you might find that you can make a couple of knots at 1/4 gallon per hour, but if you go up to a few knots you will burn 4 times as much fuel.

When I had a 2 stroke (2cyl) 6hp Yamaha I could go 4 knots at less then 1/2 GPH (of course that was on a 25' boat loaded with gear and cruising).... bump that up to 5 knots and the extra knot cost me twice the fuel.

I have also got a 3 hp version of your motor, and while I have not motored long enough with it pushing the boat to come up with numbers I can say that they are tough little motors and I wish they were still being sold today.

Hope this helps.
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Old 17-04-2010, 20:26   #3
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On a posting the other day regarding 2 stoke engines someone said:
"A general rule of thumb for a two stroke is one gallon per hour for every 10hp run at full throttle."

This is about right from my experience.
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