Prop slipping?

[Rayzor]

I have a 71 electric shift 50hp. I have been having a issue with what I thought was the prop slipping. When taking off at about quarter throttle the motor shutters and free revs very similar to slipping a clutch in a car. I seem to notice it lower on the rpm scale when starting to plane. I pulled the prop and made punch marks on the inner and outter hub rings and went and ran it. When I pulled the prop I noticed it had moved ever so slight, maybe a 1/8 inch. But it was doing the slipping thing like crazy. Am I on the right track and need a new prop or could there be something inside going tilt. If it matters the current prop is a 18 pitch on a 19ft fiberform boat. I dont have a tach so I cant help there.

 

[steelespike]

Re: Prop slipping?

Is this a new developement? New to you?
It doesn't seem like a prop from your description.
I don't know the gear ratio on that gearcase but an 18 sounds like a lot of prop for a 19ft boat.It appears it uses a hydralic shift but a dog drive like a manual shift.
Its possible the dog doesn't engage as it should until the pressure builds.It does require a special
gear oil If someone put in regular lube it won't work right.
Does the shudder seem like it hits something or maybe feel like the dog not quite grabbing?
Once finally on plane does it stay engaged? Is the prop in excellent condition?

 

[Rayzor]

Re: Prop slipping?

The boat is new to me and has been doing it since I bought it. I am not real clear on how the electric shift works other then it defaults to forward and uses the selinoids to shift to neutral and reverse. I changed the lower unit oil with outboard high viscosity that the marina told me to use. It did the same problem before I changed the oil. I am not hearing any grinding noises and it shifts in and out of gear good and positive. The slipping is mostly on quarter throttle but you can here it at top speed as well. sometimes you will be cruising along and it will sound like a overdrive kicked in the rpms drop guessing 2 or 3 hundred. I am sure its the wrong motor size and prop and I will be putting my 80hp on and parting ways with this 50. I just dont want to sell off a pile of junk or something broken to the next guy.

 

[steelespike]

Re: Prop slipping?

This seems more like a motor problem.I don't think a hub would slip and then catch usually if a hub fails it is 100% with speeds reduced to idle or slightly above or it slips comepletely.
Post this in the E/J section With an explanation we don't think it is prop related.