Re: Recommended vs. maximum hp.
Many boats handle better and operate more efficiently with less than the max HP.
My personal experiences are mostly Boston Whalers, but here are three examples.
BW 13 Sport: I tried three engines on this boat (max rated for 40hp). The 40 handled just okay, the 50 was damned scary and the 25 was better than either of the big ones. Handled better, rode better and used a lot less fuel. The 40 would do about 40mph and the 25 about 27mph. That was okay with me.
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I'm curious about how the MPG (as opposed to the GPH) played out with this boat. For instance, obviously the 40 gave more speed than you wanted or needed, but at a more moderate cruise, like 20 mph, do you know what the GPH was for the 25 vs. the 40? Obviously, for your use, the lower weight of the 25 was better, but I'm wondering if it really did use less fuel compared to the 40 if they were running about the same (lower) speed.
The reason I ask is that I tend to go right up to the HP limit of my boats because I tend to carry a lot of weight and therefore sometimes need all the power I can get. I've often thought that for a given reasonable cruising speed, a larger engine will get similar gas mileage to a smaller one because it's turning lower RPMs at that speed. The additional power (and the down side of higher fuel usage) is there if needed, but my theory is that it isn't a factor when not actually used. I've not actually tried various engines on the same hull like you have.
Of course, this doesn't address the handling difference you experienced with the smaller engine - interestingly, my boat handles better with more weight in the back. Thanks.
