Slipping, but not the prop. 25 HP Mercury

[Fishstew]

Slipping, but not the prop. 25 HP Mercury

I just brought my boat about 3 months ago. It's a 14ft aluminum with a 25 hp Mercury tiller. The rig is a 2001. It had a 4 blade 13 pitch composite prop on it when I bought it. The motor ran very strong in the 7 or 8 times I took it out. Well, I hit the bottom ( not very hard ) and it chipped a couple of the blades. That was at the beginning of my day of fish. I ran the motor taking it easy for the rest of the day. I ran strong for a while but the performance went down hill form there. As the day went on the prop just kind a tore a part. When I felt the performance goes down ( like the prop slipping ) I was careful not to over revved the motor. I bought a new aluminum prop. The next time out I could feel slippage when trying to get on plane. It slips so bad that I couldn't get on plane. I try another prop with of course a new hub but had the same problem. It's no jumping out of gear and runs fine at low speed. I tried holding the fly wheel a turning the prop when in gear. It did not slip. I adjusted the trim and tried it in every setting. There is not and information out there that I can find describing the same problem .

Please write with any suggestions.

Thanks,

Patrick

 

[CharlieB]

Re: Slipping, but not the prop. 25 HP Mercury

Pull the spark plug wires, put it in gear again, hold the flywheel and STEP on the prop to see if you can make the hub slip.

It HAS TO BE the hub, you don't have 20 HP with your hands but your body weight may be enough.

Otherwise, mark a line across the prop and hub, run the boat and re-check your line.

Everything from the engine to the prop hub is steel, it cannot fail without makeing noise.

 

[Fishstew]

Re: Slipping, but not the prop. 25 HP Mercury

Thanks for the suggestions.....I just tried what you said. Held the fly wheel a stood on the prop. I weight 185 lbs. There was no slippage. It's a after market prop and hub. The hub comes off the prop. On this hub if it were slipping there would be signs of damage. The original prop that came with the boat was a composite 4 blade 13" pitch. I tried a 11" and a 13" pitch. Same thing. At slow speed it's fine. As soon as I try to get up on plane the RMP's go up and it sounds like cavitation or slippage. If the lower unit gears or clutch dog is slipping, I can't hear them over the motor noise. Nothing has change as far a the motor position. I did adjust the trip in every available setting. Can you think of anything else to try ?

Patrick

 

[JB]

Re: Slipping, but not the prop. 25 HP Mercury

Where is the AV plate relative to the bottom of the boat, Patrick? Sounds to me like you are ventilating the prop.

 

[Fishstew]

Re: Slipping, but not the prop. 25 HP Mercury

JB,

The AV plate is 2" bellow the bottom of the transom and even with the keel. Nothing has changed there. It ran great in that position "I think it's a little to low " but until I resolve this problem, I don't think I should move it. I agree that it does sound like it cavitation or the prop slipping. The prop hub slipping has been pretty much eliminated. The prop I put on is a aftermarket Turning Point Rascal aluminum
10 x 3/8 x13 ( Part # R2-1013 ) with a # 28 removable hub. I guess at this point if I had a OEM prop that would eliminate another factor. I did try 2 of these aftermarket prop an 11" and a 13".

JB, thanks for your reply. Any help or suggestions or help is appreciated.

Patrick

 

[Martian]

Re: Slipping, but not the prop. 25 HP Mercury

I had a similar experience my first time out. I was in a very weedy lake (thick,expansive weeds from top to bottom) and was experiencing a loss of power and corresponding high-rev. I interpreted it as a slipping clutch.

I was later told if that clutch was slipping the boat would be making a very loud noise and that it was just the weeds clogging things up. I still dont;t fully understand but in weedless areas I was fine.

Martian

 

[Fishstew]

Re: Slipping, but not the prop. 25 HP Mercury

The problem is fixed !

Ok, if you have follow the tread the last messages told you how the problem started. I needed a prop because I damaged the first one. I went to my local boat deal Philadelphia Boat Works. I asked the guy behind the parts counter for a new prop supplying him with the correct model and serial number. I told him that I wanted a quicker hole shot so I wanted to go down in pitch. I got a 10" pitch prop. I installed it but didn't test it for a week until the next fishing trip. As soon I tried to get on a plane I couldn't. It sounded it like the prop was slipping. I pull the boat out and everything looked fine. I drove back to the boat dealer with the prop in my hand and told him of the problem. He examined the prop and hub. Said all looks well. I insisted that there was a slippage problem. He agreed to give me another prop and hub the same type but a 13" pitch. A Rascal Prop with a slip out easy replaceable hub. I drove back to the fishing spot and put the boat in the water. I still can't get up on plane. The next day I drained the lower unit. No medal in the oil. I went back in to the same parts guy and told him of the problem. He said it must be a motor problem. I turned to the I-boats forum for help. At this point I had the boat in and out of the water testing about 5 times. Then I went back to the same parts guy and ordered a lower unit carrier bearing removing tool so I could see if I have any damaged gears etc. Waited a few days then picked it up. The next day I go to use the tool, it's to big. Being a bit ticked off I start researching more online. I found the prop hub for the Rascal prop was the wrong part number. So, I went back and there is a different guy behind the parts counter. I told him of the problem. He gave me the correct hub and said that the other looked up the wrong parts and that I could return the tool because it was clearly the wrong one. Now thinking I finally have the correct prop and hub I install it , but it not looking correct. There was a gap between the lower unit and the prop were the exhaust could come around the prop. ( at this point I would try anything ) The next day and put the boat in the water and figured I would just try it.... The same thing. I went back again, the parts guy said that the prop is the correct on and that gap was normal. He recommend that I let them work on it and said they would get to it in a few weeks. I said, I need time to think about it and left. The next day I fabricated my own tool using a 1.5 pipe nipple. It worked great. I disassembled the lower unit and found everything was looking good. The gears and clutch dog were ok. The next day I went to different marina and talked to the parts guy. I told him of my problem. He said there is never supposed to be a gap between the lower unit and the prop and that the exhaust must go thru the hub not around it. ( That's what I was thinking as well ) I asked him for a OEM prop and $ 106 later I went home but it on the motor then drove to the nearest access and put the boat in the water. As soon as I throttled up the boat jumped up on plane.

My night mare has ended!

I still have to go back to return the wrong prop and hub. What should I say to these guys ?? Nothing they can stay or do at this point can make up for this prophetical blunder.

Moral of the story. Go OEM. And if seems like the prop is ventilating it is.

Thank you all for you help !

Patrick