Prop slipping question

[spingley]

I have a 1986 Johnson 90HP Outboard on a 24' Pontoon, this is my first boat so I do not know a whole lot about them but am learning fast. The other day while on the water I decided to open it up to see how fast it would go and a few minutes later the tach started jumping up and down some, you could hear the motor revving also and boat actually started to go slower. I suspected prop slipping so I slowed down to about 6 mph and headed for dock. There was a guy on his boat that said I likely had a loose nut on the hub so I trimmed it up and he tightened it up and said that was the problem, so I thanked him and headed back out to try it out again. It seemed to help some but it still would do the same thing, so we just cruised around slow for the rest of the day and went home. So today I pulled the prop off and it looked to me like the hub is in the middle of the prop with black rubber in between but it appeared to be fine. Anyone have any ideas what is going on? Do I need to buy a new prop?

 

[Dhadley]

Re: Prop slipping question

Something to keep in mind, especially if you run into this "expert" again - you don't even need a prop nut as long as you are in forward gear. The nut has nothing to do with the prop slipping. In forward the prop is trying to move forward (therefore pushing on the thrust washer), that's what's pushing the whole rig. Now, if you shift into reverse (or slow down drastically) that's a different story.

There are pontoon specific props. What you're seeing is not unusual with a standard prop. You probably don't "need" to buy another prop but when you do just look for the pontoon specific props. If you need help feel free to send me a private message. Be glad to help if I can.

 

[spingley]

Re: Prop slipping question

Something to keep in mind, especially if you run into this "expert" again - you don't even need a prop nut as long as you are in forward gear. The nut has nothing to do with the prop slipping. In forward the prop is trying to move forward (therefore pushing on the thrust washer), that's what's pushing the whole rig. Now, if you shift into reverse (or slow down drastically) that's a different story.

There are pontoon specific props. What you're seeing is not unusual with a standard prop. You probably don't "need" to buy another prop but when you do just look for the pontoon specific props. If you need help feel free to send me a private message. Be glad to help if I can.

I tried to find Pontoon specific props on iboats website but could not find any, the link from the Pontoon section just came back to the regular prop web page. Can you give me any details as to what is different about pontoon props? Thanks for the help too!

 

[Dhadley]

Re: Prop slipping question

One major difference you'll see is the different rake angle. A more subtle difference will be in the cupping. Both placement and amount.

 

[spingley]

Re: Prop slipping question

When I last took it out and had it at WOT before the thing started slipping or venting or whatever, the tach was at 4200 RPM and GPS showed 23 MPH. The prop is 13.25 X 17P, does this sound about right?