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Replace motor

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jwwjr

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I have a 1998 20 foot Duracraft Explorer boat with a 1998 Johnson 115 hp Fast Track motor on it. I also have a 2005 Yamaha 90 hp 4 stroke motor that I want to put on this boat. This is kind of a heavy boat. I was looking for advice on difference this motor will make.
 
If I'm not mistaken that's a flat bottom aluminum hull, yes? If so, unless you're loading it with a heck of a lot of gear it's a light hull, compared to a fiber hull of same length. Obviously decreasing HP you'll decrease speed. But unlike V-hulls, a flat bottom doesn't need to "get on plane", which would be a concern with decreasing HP with a loaded down 20' ft fiber hull. So if you're ok with less speed, I don't forsee a drop in 25hp being a cause for performance issues. Also, I reckon the johnson 115 is a 2 stroke. If so you'll notice a difference in low end power with the 4 stroke, which notoriously have less than low end than 2 strokes.
 
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Yes I would say it is a flat bottom boat with a semi-v front. At 5000 rpms with 3 adults and 1-8 year old it was going 40 mph according to gps. That is faster than I want to go. Just double guessing myself about 90 hp.
 
Well suffice it to say, changing engines for the only purpose of not having the ability to go as fast seems a bit peculiar. Unless there are other reasons to decrease hp that you haven't stated.
 
I already have the 90 hp Yamaha on a 16 foot homemade alum. boat, and is too much weight. The 115 hp Johnson 2 stroke is kind of loud and uses a good bit of gas. Usually like to just ride around quite a bit at lower speeds and just thinking about 90 hp 4 stroke being under a load of 20 foot boat and people in boat. I am thinking about power of 2 stroke compared to 4 stroke with less hp. I think I am over thinking this.
 
Ah, now I gotcha. No worries, we all have a tendency to over-analyze at times. No doubt the 2 stroke is louder, I have a 2 stroke 115hp myself. I think changing to the 4 stroke will accomplish all that you have outlined as the reasons for changing. Good luck.
 
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