Boat lost power to prop and revved while under way

[GoneBoatN]

I had my boat out today. Boat information in signature below. I enter an area that I thought was starting to get too shallow so I slowed down and began to turn around. Then all of a sudden the engine revved and the boat lost power. I immediately shifted to neutral. At first I thought maybe the prop got caught in some plant life in the water. I put it back in gear and at idle the boat started moving forward again. I got out of the area I was in at idle but when I went to accelerate it lost power and revved again. Again I shifted to neutral immediately. I repeated this a couple more time while idling back to the boat ramp, where it would lose power and the rpms would increase - this seemed to happen at about 3000 RPMs consistently. I decided not to push my luck and I stayed just above idle all the way back towards the launch ramp.

Before I entered the launch ramp I tried to repeat the problem. Now, I could accelerate with no problems. I tested several times slowing down and then acelerating again without problem. Decided I would look into it more at home and it was time to call it a day. I did not smell rubber burning nor did I see any smoke from the engine compartment.

At home I removed the prop and examined. All looked fine. I stuck my fingers by the area where I thought was the coupler and came back with only the expected dirt, nothing really black to indicate burn rubber.

Any thoughts as to what the problem is or what is the list of possibilities?

Thanks in advance to this forum as always!

 

[elkhunter338]

Re: Boat lost power to prop and revved while under way

The only item that would act like that is the prop hub. You spun a prop hub and it would hold at lower rpms, then for some reason it held for you later in the day. There is nothing in the drivetrain that would spin at high rpms and hold at low rpms other than the prop.
Maybe engine coupler, but I do not think so.
I assume you have an alum. prop, these typically have a rubber hub incase you hit something.

 

[GoneBoatN]

Re: Boat lost power to prop and revved while under way

Yes, Alum prop with the Flo-Torq II hub. I examined the hub and it does not appear to have any damage. With this setup, I would think I would see damage if it spun; but that is just my impression.

When I check the prop, instead of just unbolting I first tighten to see if it was not torked correctly. It turned about 1/8-1/4 turn before the tork wrench clicked. So I'm not sure how much it was off but I would think that small amount would not be much.

 

[nofuss]

Re: Boat lost power to prop and revved while under way

easy check for prop hub. mark two points one on the prop and an adjacent point on the prop. run the boat if it slips again check the marks, if they are out of line that is an indication that there is movement. im not familiar with your type of hub, but the first time i had that problem even the prop shop did not see a problem, but they marked it and had me try it and yes it was moving.

 

[GoneBoatN]

Re: Boat lost power to prop and revved while under way

I will check marking the hub and prop. I don't like the idea of taking it out again without finding the problem first but I'm not sure I will have an alternative.

I did move the prop by hand while in gear. Lots of resistance due to the engine. I marked one of the fly wheels turning a belt and the prop hub and prop shaft. Turning by hand there was no slip. Not conclusive because not the same conditions but it was a thought.

Anyone know/think what other possibilites to check as well. Not sure how to check the coupler beyond what I did unless I pull the engine.

 

[bruceb58]

Re: Boat lost power to prop and revved while under way

If you lost your coupler, you probably would have eventually overheated since your impeller in your drive also would have stopped turning.

Have a spare prop to try?

 

[GoneBoatN]

Re: Boat lost power to prop and revved while under way

If you lost your coupler, you probably would have eventually overheated since your impeller in your drive also would have stopped turning.

Have a spare prop to try?

It only "slipped" for a very short period of time. While at idle or low RPM it seemed to not have any problem, at least any that was noticable. Normal water Temp, normal oil pressure, etc.

I have a spare prop/hub setup (Flo Torq II) and will be sure to have it with me on my next trip.

 

[Alpheus]

Re: Boat lost power to prop and revved while under way

I did the exact same thing you are describing. Got shallow,lifted drive all the way up ,gave gas revved but boat went nowhere. Ran back to the dock (in reverse) gave it gas and worked perfect. Read lots of threads on here and immediately started tearing my boat apart. Started with prop,then outdrive,then engine to check coupler. Found nothing. Turns out that when I was in shallow water and had the drive lifted that when I was giving it gas it was pushing the back of the boat deeper into the mud. It acted exactly as the symptoms of a spun prop hub or a coupler, but it was just mud...

http://forums.iboats.com/showthread.php?t=415879&highlight=hit+sandbar

 

[security6]

Re: Boat lost power to prop and revved while under way

Same thing happened to me last weekend. My boat would run fine up until around 15 or 20 mph, then the prop would lose "traction" and the engine would rev higher. I too thought it was a spun hub. We stopped for a bit and I put the prop up and I found a large mass of weeds stuck to the front of the outdrive. I pulled them off and then the boat ran perfect.

Near as I can figure, the weeds were somehow blocking the water to the prop, creating turbulence, or bringing air down towards the prop, so the prop couldn't get a good "bite" in the water. The boat ran perfectly the rest of the weekend. I bet the same thing happened to you.

 

[Brentathon]

Re: Boat lost power to prop and revved while under way

I had a diffuser ring fall off of the hub of an aluminum prop one time.......and as soon as I trimmed the drive up a little, the exhaust gasses entered into the blade area, and felt just like I was spinning a hub or going into neutral. So, the diffuser ring prevents ventilation, and keeps the exhaust gasses away from the blads.

 

[GoneBoatN]

Re: Boat lost power to prop and revved while under way

As with the last few posts, I'm starting to think it was a severe case of cavitation caused by weeds/mud/muck stuck to the lower portion of the outdrive. I stopped by the local repair shop that I take I like to use and it was their first thought as well. They said that if I spun the prop, the flo-tork II hub would have been destroyed. They also said, if a coupler, it really has limited times it would spin and recover (really limited, like once or twice and then it would be toast).

That level of cavitation was new for me. Hopefully that is all it was and now I know what it feels like.

End result - not a mechanical problem most likely.