Fells like prop slipping but it's not

I have a problem that only happens after 15 minutes or so in the water.

1st time I try to get on plane it works fine, then it doesn't it feels like a prop slipping but I replaced the prop with a new one and the same thing continues to happen.

I changed the lower unit oil it was sort of coffee milk color but no metal shavings on the mag-screw.

I give it full throttle and it starts to slip, i reduce rpm and it catches again. I took the lower unit out and check the impaler and snifter they all seemed fine, there is a lot of play in the rod but I check the forum and apparently that's normal.

Any ideas of what could be wrong? Its very frustrating to have a boat and not being able to use it.
Thanks for any help.


This is a Johnson 87 110hp by the way.

Re: Fells like prop slipping but it's not

I assume it doesn't feel like you're hitting a underwater object... engine's jerking, jarring the transom, that sort of thing.

And it's unlikely that the hub would be slipping in two different propellers. That leaves a scenario that either the propeller is too close to the surface of the water OR something on the hull is throwing a air pocket into the propeller area.

Re: Fells like prop slipping but it's not

Joe Reeves said:

I assume it doesn't feel like you're hitting a underwater object... engine's jerking, jarring the transom, that sort of thing.

And it's unlikely that the hub would be slipping in two different propellers. That leaves a scenario that either the propeller is too close to the surface of the water OR something on the hull is throwing a air pocket into the propeller area.

Click to expand...

Definitively not hitting objects.
I tried different trims, same result every time. When I installed the engine I put on the lowest possible setting so that it would hook into the transom. Should I lift the engine more maybe to see if changes?

Re: Fells like prop slipping but it's not

Hook into the transom? I don't know what that means.

Unless you're into racing or have that engine on a bass boat, looking for the highest rate of speed, the cavitation plate is usually about 3/4" below the keel of the boat (no lower). Raising the engine would just be bringing the prop closer yet to the surface.

What is puzzling is that you state that this happens only after 15 minutes in the water, insinuating that you can operate the boat under the same conditions with no problem... then after those 15 minutes, the problem appears.

What is taking place in those 15 minutes?

Re: Fells like prop slipping but it's not

Joe Reeves said:

Hook into the transom? I don't know what that means.

Unless you're into racing or have that engine on a bass boat, looking for the highest rate of speed, the cavitation plate is usually about 3/4" below the keel of the boat (no lower). Raising the engine would just be bringing the prop closer yet to the surface.

What is puzzling is that you state that this happens only after 15 minutes in the water, insinuating that you can operate the boat under the same conditions with no problem... then after those 15 minutes, the problem appears.

What is taking place in those 15 minutes?

Click to expand...

During those first 15 minutes the boat is cruising just fine. Then once I come out of plane (for example stop at the dock) I have a hard time getting it to plane again. This problem is very strange.
I'm lost, I really don't know what it could be.

Re: Fells like prop slipping but it's not

simplesolid said:

During those first 15 minutes the boat is cruising just fine. Then once I come out of plane (for example stop at the dock) I have a hard time getting it to plane again. This problem is very strange.
I'm lost, I really don't know what it could be.

Click to expand...

How does the Engine sound.. Compared to First Start-up & after 15 Min of run time? Does the Engine sound loaded or sound like its struggling? Is there a decrease in RPM's? ... How hot is the water exhaust compared to the first 5 min?

Re: Fells like prop slipping but it's not

Just to make sure you are not having a prop problem, scribe a line from the prop hub to the prop housing and run it until it happens again and check the mark, if it is still aligned the prop hub is not spun and you have eliminated one possiablity. If the mark is not aligned the prop hub is spun and you have found your problem. Stranger things have happened.