Catalina 18mkII 20' what size motor and MPG? - SailNet Community
 
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post #1 of 9 Old 09-16-2015 Thread Starter
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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 6hp 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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post #2 of 9 Old 09-17-2015
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Re: Catalina 18mkII 20' what size motor and MPG?

Personally, I think the goal with sailboats is to use the smallest engine that you can get away with. Weight is not great for sailing performance, and weight on the transom is particularly bad. Most sailboats have displacement hulls and can't routinely get over their hull speed anyway, so there's little advantage to upsizing. You just burn more gas for no speed increase, and drag your stern needlessly.

On that boat, I'd probably want a 2 or 3 hp. If you planned to cruise with it, needed an external tank, or something else that required a more substantial engine, 4 to 6 would be the absolute max for me.

Whatever line of engines you're in to, check the specs. For example, in the Tohatsu/Mercury/Nissan line, the 4, 5 and, 6 hp models are all the same block, just with different carbs and rev limiters, so you might as well go with a 6 since it weighs the same as the 4. I guess there's a slight difference in efficiency, but we're talking about such inherently efficient engines, it may be irrelevant.

I sailed a heavier Catalina 22 pretty hard for 5 years with a 5hp engine, and never wished for more power. I don't know the specific mileage (it's usually measured in volume per hour, not mpg) but they're ridiculously efficient. I used to pull the fuel line on my engine to run it dry and it would run for 10 or 15 minutes on the ounce or two of fuel left in the system.

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post #3 of 9 Old 09-18-2015
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Re: Catalina 18mkII 20' what size motor and MPG?

With a 5Hp 2-stroke you should get about two hours per gallon at 4.0 knots.

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post #4 of 9 Old 09-18-2015
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Re: Catalina 18mkII 20' what size motor and MPG?

External tank connection is likely a bare minimum requirement for you, the smallest ones to offer that today, are 4hp. There IS a weight difference between 4hp and 6hp... 4hp likely will be big enough for you for most weather, 6hp will help punch through some chop and higher winds, but I doubt will be MUCH better when it gets REAL choppy.

That's a tough little boat, but larger cruising using it will be, how can I put this, a bit of an adventure, for sure.

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post #5 of 9 Old 09-18-2015
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Re: Catalina 18mkII 20' what size motor and MPG?

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Originally Posted by SHNOOL View Post
There IS a weight difference between 4hp and 6hp...
I don't think that's the case for Tohatsus. I cobbled this together from the brochure here:



Technically the 4hp is one pound heaver than the 5 or 6 (I'm guessing due to the integral fuel tank), and the SailPro is a couple pounds heaver than the non-SailPro 6 due to the extra shaft extension, but there's essentially no difference in weight between a 4, 5 or 6 hp Tohatsu (or Mercury/Nissan, since those are basically re-badged Tohatsus). They're all the same engine...at least the heavy parts.

The same is true for the 2.5/3.5 as well as the 8/9.8.

Agreed regarding the "adventure" though...

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post #6 of 9 Old 09-18-2015
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My 23 ft Santana says not to exceed 9hp, and that a 5 is sufficient. We have a 9, but the transom is one of the weakest parts on my boat so that's their limiting factor. We could get a way with less but Ive had a few times where I've been caught in pop up weather where I was fighting heavy wind and current to get into shelter and was able to do it comfortably. It's rare that I've used full throtle, but it's nice knowing I have it as a "reserve" when I need it.
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post #7 of 9 Old 09-18-2015
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My fuel tank is a 5 gallon. I filled it once at the beginning of summer and still have over half a tank. It's only about 50 yards to the breakwall so we don't use it all that much.
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That's the engine that came with the boat. Maybe it's 8hp now that I think of it.
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post #9 of 9 Old 09-19-2015
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Re: Catalina 18mkII 20' what size motor and MPG?

I used a 2.2hp integral tank on my Capri 25, on my inland lake... worked great until the winds got to about 20 knots (no motoring into the winds at that speed), but then I usually sailed in those conditions

Yeah, I couldnt' remember the break points for weight (which sounds like its less important)... but the integral tank, and external connections, are a big deal. Note the 5 and 6 have external connections, the 4 does not. So to the OP, sounds like you need a 5hp or bigger. I wouldn't go bigger than a 6 myself... and the Sailpro is a smart choice (for the longer shaft) and I'd get the alternator option, cause running lights aren't optional.

I looked at a Capri 18, and I wouldn't even call it much more than "tent accomodations." While the 18 is really a 20 footer, it's still not a heavy, or large cruising 20... such as a nimble or the like. It's going to bob like a cork in any kind of chop. Large amounts of Bonine will be necessary.

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