Lost Speed Somewhere

[Minnerman]

I hit a stump last week and now according to my GPS I have lost 4-5mph. The weird thing is I can't find anything bent. Prop looks fine and no dents on hull of boat. I have even put an indicator on the prop to check for bent shaft and only have .002"-.004" runout which could be the slack in the bearings. There are no vibrations but I have lost some RPM's as well. Went from 5400 to 5200. Again the prop has no visible damage. What could be the problem?

Thanks
Tracy H

[Barnacle Bill]

One of the blades could be bent ever so slightly that you can't see it. It wouldn't take much to loose just 200 RPM.

[Minnerman]

Could I check this with the indicator by checking the height of each blade as it rotates on the shaft? This demension would change the pitch wouldn't it? And if so, how close are props manufactored? .010"? .005"?

[Jim C.]

You might check the water intake on the front side of the lower unit it may have something in it. Jim C.

[Minnerman]

Its peeing fine and hasn't ran hot. Just got slower.

[Yodibuzz]

Hub could be slipping in prop. This would cause loss of RPM s and speed.

[Minnerman]

Hub could be slipping in prop. This would cause loss of RPM s and speed.

Haven't checked that yet

[grubby]

As Yodibuzz said the prop if it as the rubber insert in it it may be slipping and that is the reason it is in there to protect your lower unit if you hit some thing solid. If it is slipping it will get worse with use they dont charge to much at prop shops to replace it.

[speck chaser]

hub may be it but didn't he say he was loosing rpms i would think your rpms would rise with a hub slipping jmo

[deputyking]

hub may be it but didn't he say he was loosing rpms i would think your Roms would rise with a hub slipping HMO

Yes, any slippage whether it is in cavitation or in the rubber hub insert will increase the RPM of the motor. I think I would check the timing to see if anything has almost sheared or has slipped because of the sudden stop. Also the gears in the lower unit may be burred and binding somewhat because of hitting this stump .