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Old 16-09-2015, 15:55   #1
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Catalina 18mkII 20' what size motor and MPG?

4 - 6' hp is the recommendation for a 20' Catalina 18mkII.

For cruising in Florida, the Bahamas, and Caribbean, I would assume bigger would be better?

And if the 6, would that be the right size for my intended cruising or should I go up a size or two?

I am talking lots of motoring, thousands of miles in light seas with no rush, what would be my average MPG?
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Old 16-09-2015, 18:51   #2
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Re: Catalina 18mkII 20' what size motor and MPG?

The specified 4-6 is plenty of hp. You're not going to plane in that boat, you're going to go at hull speed at most. Furthermore, it's a sailboat, so count on going in a relaxed manner.

If you want to go in the manner you're describing, get a hot skiff and fight with it.

I had a 19' O'Day Mariner with a 5 hp outboard. It got up to hull speed with power to spare. I don't remember the mpg. I have in mind 1 mpg, but that can't be right.

Now I must be the last person left on Earth who prefers a smaller motor. They're compact easy to handle, take off and install for maintenance. I am capable of putting a 3.5 hp motor on the Catalina.
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Old 16-09-2015, 18:59   #3
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Re: Catalina 18mkII 20' what size motor and MPG?

I would think a 6hp long shaft would provide all the power you need. My dad had a 5hp on his Grampian 23 and we covered some serious miles on her.

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Old 17-09-2015, 07:44   #4
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Catalina 18mkII 20' what size motor and MPG?

For cruising for many hours I'd only consider a 4 stroke and size it so I ran it at half throttle or less. Going for a long life and keeping noise down. I think. 9.9 but using only 3 or 4 or that 10 HP would yield a long life, low noise and low fuel consumption?
Fuel burn of a half a gl an hour sound reasonable?
If so maybe 10 MPG?
Now this is all just guessing so don't rely on any of it. More than anything I'm just tossing a different idea out there for discussion is all

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Old 20-09-2015, 21:24   #5
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Re: Catalina 18mkII 20' what size motor and MPG?

Do you think I would get better MPG with a 6, 8, or 9.9? Looking for most efficient as well as reliable for this type of trip.
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Old 03-01-2016, 15:00   #6
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Re: Catalina 18mkII 20' what size motor and MPG?

Anyone else have thoughts on this? Thanks!
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Old 04-01-2016, 07:53   #7
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Re: Catalina 18mkII 20' what size motor and MPG?

More horsepower means more fuel being used.

Horsepower ratings being equal, four stroke motors will deliver better fuel economy than two strokes.

Be aware that four strokes are heavier pound for horsepower than two strokes. That can affect the trim on a small boat, and is also more effort to carry the motor around, trim it up, etc.

If it was me I'd go with a 5-6 hp four stroke if I planned on motoring a lot.
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Old 12-01-2016, 20:05   #8
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Re: Catalina 18mkII 20' what size motor and MPG?

Do you think it would still be more efficient with a 5/6hp vs 9.9 even if the 9.9 is ran at less throttle?

What would be your thoughts on longevity and reliability between both options?

Thanks!
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Originally Posted by FSMike View Post
More horsepower means more fuel being used.

Horsepower ratings being equal, four stroke motors will deliver better fuel economy than two strokes.

Be aware that four strokes are heavier pound for horsepower than two strokes. That can affect the trim on a small boat, and is also more effort to carry the motor around, trim it up, etc.

If it was me I'd go with a 5-6 hp four stroke if I planned on motoring a lot.
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