115hp Merc slips when trying to plane out

I'm new to the website, but it seems like a great place to seek some direction in trying to figure out what is wrong with my motor. I have a 1995 Merc 115hp. It has run like a top since we picked it up 2 years ago. Just had the motor gone over this spring before putting it in the water and the shop said everything looked great.

Here's the problem. I went out tonight and while at nearly full throttle the boat lost propulsion, not power. The motor sounded like it was still running wide open, but the prop quit pushing at full speed. Once we stopped I was able to go just fine, but I was unable to plane the boat out. As you approach planing speed the engine sounds like the prop disengaged and it just starts revving. I'm hoping that it's not the lower unit, but I have no idea what else it could be. Again, any input would be much appreciated...my 2 year old son just wants to 'Go Fast' again, hopefully before summer is gone here in Northern Michigan!

Thanks!

Re: 115hp Merc slips when trying to plane out

Could simply be as spun prop hub.If you have a spare,slap it on and see.If nott,make a line w/a paint pen or some kind if marking tool connecting the prop and hub.Run it and see if line is still connected.If not,then you need a new prop or have that one rehubbed.Sorta hard to explain where exactly to mark,but youre looking to see if the rubber insert in the prop,or hub, isnt holding under load and is allowing the shaft to spin,while the prop isnt or is slipping.sounds like and hope thats your issue.

Re: 115hp Merc slips when trying to plane out

Problem is "spun prop". There is a rubber shock bushing pressed into the prop hub. When this goes bad, the hub will just spin inside the prop under load.

Have a new bushing pressed in by any good prop repair shop.

Re: 115hp Merc slips when trying to plane out

Sounds like a spun hub on the prop. If you can find a prop shop close by it is a fairly cheap fix.

Re: 115hp Merc slips when trying to plane out

Thanks so much for the advice. From what it looks like, everyone that has responded has the same opinion...hopefully that's what it is. I'll pull the prop this week and get it to a shop. I'll post a follow-up once I get the final diagnosis on the prop/shaft. Thanks again!

Re: 115hp Merc slips when trying to plane out

Dude. mark /Index the prop. go for a ride. rubber to prop. don't spend money if you don't have to

Re: 115hp Merc slips when trying to plane out

Just curious...I think I may be having the same problem. If the "spun Prop" is the problem is there a chance that it will still function as normal part of the time or will it do it every time? Mine seems to be hit and miss, but mostly miss.

Re: 115hp Merc slips when trying to plane out

I had a spun hub and actually found out in the driveway. With the engine in reverse, try and turn the prop in reverse. mine was spun enough that the prop slipped before the engine's compression allowed it to turn the engine.

Just a thought

Re: 115hp Merc slips when trying to plane out

HeathB said:

Just curious...I think I may be having the same problem. If the "spun Prop" is the problem is there a chance that it will still function as normal part of the time or will it do it every time? Mine seems to be hit and miss, but mostly miss.

Click to expand...

Usually it'll take a little load, like maneuvering around the dock but when you stick it to it to get on plane, it just revs and you go no where.

Re: 115hp Merc slips when trying to plane out

Mark the prop and rubber hub. thats it. done deal.