Regarding your comment, sure, if you want to plane below 4000 RPM's, it aint gonna happen on a 50HP Mac. I haven't been out a whole lot in the last few months, so I don't remember exactly, but it does come up on a plane somewhere around 4200-4500 I believe. I think this is really more of a function of what prop you select. If you select a much higher pitch, you may not get all your power out of the motor (ie. top speed), but you will likely be able to cruise on a plane at lower RPM's.
Other things that help of course are a 4-stroke motor (sorry if the modern 2-strokes are quiet...but all the ones I've owned are louder than a 4-stroke...and afterall, it does fire twice as many times for a given RPM so it does make sense). Another thing that helps a bit is putting the hatch cover under the captain's seat. Overall, its a fairly quiet ride when you compare it to other boats of similar size. My former sailboat with its inboard diesel could still make some noise unless you wanted to cruise at 2 knots. And my former jetboat with its inboard 175HP with its six pack of carbs would also let know know when it came alive...even with the extra sound deadoning that an inboard has over an outboard. Also, my overpowered jetboat which would hit 55mph top speed still needed close to 4000 RPM to get on a plane...albeit, that boat wouldn't plane until 18-20 mph which may have been around 3900 or so. Of course, a few hundred more...at 4500, you were probably humming along around 35 mph.
I think my point would be...if you want to have a nice conversation aboard....then slow way down and enjoy the scenery
