One more prop question

[Cranky18]

I have a 15hp mariner on a 14 ft V-hull with a 9 1/4 X 12 prop. I recently had the prop rebuilt and took it out for the first time this weekend. I have been out several times before with just me and my son and was able to get the boat on plane pretty easily. This time my wife went along and it wouldn't even come close to getting on plane and would only go about 10mph. It was a pretty sticky situation until I tried it without my wife onboard with the same results (whew). The mechanic at the marina said that that prop was what was recommended for the motor. Before being repaired, the prop blades were bent forward on the ends (dog eared) for lack of a better word. When you open it up full throttle, it seems to only turn about half the rpms as before. I do not have a tach on it so I cannot be positive. The engine seems to run o.k. although a bit rough at idle. Is it possible that the repaired prop is too big a pitch for this setup?

 

[pwiseman]

Re: One more prop question

I don't know about merc 15, but can tell you a johnson 15 on a 14 foot shallow v was scary fast with a 10 pitch with 2 people (400 lbs of beef). I would also say it took a bit of time to wind all the way up which indicate to me that 10 pitch is upper limit with two people in that boat with that motor.<br /><br />Also, hard to say what the deal is with that prop. Sounds questionable to me at best. You should be able to pick up a good used prop for $50. My guess is somebody bent the blades in to reduce diameter, which would make sense if it was not getting RPM.<br /><br />Last thing I will say about small boats. 50 lbs is a lot - enough to make noticable difference. With a small boat, every mistake is amplified.<br /><br />Recommneded pitch for a motor is just a guess and there are some assumptions made for the size and weight that the motor was designed for. Newer boats weigh more, and the Vs are deeper than the older ones. Not surprising that you would find the recommended prop to be on the steep side.<br /><br />The other possiblity you have is loss of compression. Rough idle and loss of power. I would check the compression before buying a new prop.

 

[Cranky18]

Re: One more prop question

Thanks Paul. Funny you should say that about the 10 pitch because I spoke with the guy that rebuilt my prop this afternoon (he has actually seen my boat) and he said that he would have put a 9 or 10 pitch on it. Regardless, I will check compression and find the cause of the rough idle.