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Old 16 March 2007, 19:19   #11
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Country: UK - England
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Boat name: April Lass
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Quote:
Originally Posted by ALANT View Post
So anyone going to give me a top speed and consumption for twin 90's?
At speed, about 8 gallons an hour, each.

Pete
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Old 18 March 2007, 14:34   #12
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Country: UK - England
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Boat name: Shearwater
Make: Halmatic
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I had a 7.5m humber which we used for Sea Safari trips. We had 2x 80hp Yamaha 4 strokes on the back. With 10 adults she would plane quickly and cruise at 19-20knots at 4200 revs burning about 20 litres an hour. Top speed with 10 was 28 knots. If you wanted to cruise at 24 knots the engines were running at about 4700 revs and the fuel consumption went up. The 90hp two strokes you are thinking of would probably give you higher speeds but I would imagine the fuel consumption would go up.
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Old 20 March 2007, 15:56   #13
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Country: USA
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I'm running twin 90's on a 6.5M Mako. With 4 divers, gear and 12 tanks with a 12x21" prop i'm burning aprox. 8 gallons an hour doing 25 MPH @ 3,000 RPM. I can open it up it will burn 18 gallons an hour and do about 42. Empty the motors wil turn 5,600 RPMs burn 18 gallons an hour and give me 53-56 MPH. On that big of a boat and with 8 divers 16 plus tanks i would think you would need about a 17" prop and with that my RPM's max me out at 35 MPH burning the 18-19 Gallons an hour.
I'm running the newer fuel/oil injected Tohatsu's i hope this helps a little bit. If you are looking at a carborated motor then i can't help you other then tell you to at least double the fuel consumption.
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Old 20 March 2007, 15:58   #14
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Quote:
Originally Posted by Donnie144 View Post
I'm running twin 90's on a 6.5M Mako. With 4 divers, gear and 12 tanks with a 12x21" prop i'm burning aprox. 8 gallons an hour doing 25 MPH @ 3,000 RPM. I can open it up it will burn 18 gallons an hour and do about 42. Empty the motors wil turn 5,600 RPMs burn 18 gallons an hour and give me 53-56 MPH. On that big of a boat and with 8 divers 16 plus tanks i would think you would need about a 17" prop and with that my RPM's max me out at 35 MPH burning the 18-19 Gallons an hour.
I'm running the newer fuel/oil injected Tohatsu's i hope this helps a little bit. If you are looking at a carborated motor then i can't help you other then tell you to at least double the fuel consumption.
one more thought. DO to the weight of the outboards the top of my transum is only about 3" out of the water. Given this i question the wisdome of going with the twins and wounder if i should have gone with a single 200 got more speed and shaved 180 pounds on the transome.
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