Honda BF30A prop problems

"ok...need some help.

recen

"ok...need some help.

recently i bought a patio boat, a 16ft crestliner with a honda BF30A 4 stroke


the guy who bought it originally had some downriggers on it, so im assuming that he down propped the boat as it has a top speed at WOT of only 7 mph, and a top RPM of only 3000 ( if the tach is reading correctly)

even if the tach isnt correct though, im sure it should go faster than 7 MPH......my last patio/pontoon boat was a 20ft that was much heavier, it had a 25hp mariner (yamaha) on it, and it topped at around 15 i think, and it WAS propped for trolling.

does anyone happen to know what the "stock prop" pitch was?

id like to get myself another prop that will bring the engine RPM back up to specs and give the boat more speed.....any help would be appreciated"

"You are probably not going to

"You are probably not going to get the answer you want on this one...

1) If the tach is correct and you are only getting 3000 RPM, then the prop that you have on there is already too high in pitch (and/or diameter). If you change the prop to get correct RPMs, it is likely that the boat will go slower.

I see a lot of posts on various forums in this site that go like: " I just bought this used boat and it does not go fast enough and BTW, the engine does not get to maximum RPMs". By and large what they have is a boat that the previous owner sold because it was not fast enough for them and they changed to a bigger pitch prop and that did not solve the problem, leaving the new owner with an over propped boat.

2) Hull design... A displacement hull is limited to 1.34 * (Square root of the water line length in feet) speed in Knots. For a 16 ft LWL boat you are looking at 5.35 knots which is 6.12 MPH. Putting more power on a displacement hull will only result in pushing a bigger bow wake. If its a semi displacement hull, they can go a bit faster, but calculating their top speed is tricky. Besides they tend to get very unstable when you try to do this, i.e., put more power on them and try to go faster.

Your 20 ft boat, even though it was heavier had a higher top speed because it was longer."