"I have an 18 Beachcraft open-
"I have an 18 Beachcraft open-bow runabout with the 3.8 v6. My 3.8 is a 2bbl carb model which is rated at 175 HP.
I needs about 20 more horsepower - 30 would be better still. I have trouble getting my tall son up behind the boat on anything other than a kneeboard.
I have gone to a 15.25" x 15" prop (had a 15x17) and it pulls better. I wish I had gotten a v8 !!
Works fine - except that with this prop I can hit 4800 RPM, or 5000 if the water is just right and wind is at my back, and we don't have a lot of load in the boat.
But the owner's manual says I should stop at 4600 RPM. My mechanic says the engine should be fine up to 5500, but the outdrive manual doesn't, and I want to err on the side of caution. I don't know if the manual is right on, but I sure don't want to blow up the motor OR the drive.
4600 RPM clocks at around 38 MPH on my boat. I could do 45 with ease with the other prop, but it didn't have as good a hole shot. and the lakes I ski have speed limits - usually 35 MPH.
What am I saying? If you like the boat, buy it. But have some money set aside to repower with a V8 - that motor is a bit smallish for a 21 foot boat.}"