Prop slipping?

[2ner]

I have a 18' Crestliner pontoon with a Johnson 40 hp 4 stroke engine and a 9 pitch prop. This weekend I took it out to lake Piru and it started of great I want to say 7 mph's with 7 people (4 adults 3 kids). After about 15 min of driving around the engine was at the same 5200 rpm's, but it seemed way slower. I beached it and checked the prop to see if it was loose or slipping and it looked fine. Any ideas?
I almost had a accident, I slowed down and gave it throttle and the front end started to submerge into the water, is that normal? It looked like we were going under, crazy!

 

[lowell7963]

Re: Prop slipping?

Not sure about the prop slipping, but you discovered one of the issues with pontoon boats. All boat types have their downside, for pontoons it's nose diving, something to be aware of and cautios.

Something interesting forward of the boat, the passengers rush forward to see, the captain stops the boat quickly. Almost guarantee a nose dive. The good news is the boat won't sink, but people can get thrown off so it is dangerous. In some rare instance the boat might flip over, but it would have to be extreme conditions.

In your case tas you slowed down the front of the tubes probably dipped into the water and when you accelerated you drove them deeper.

Scarey, but lesson learned.

 

[EGlideRider]

Re: Prop slipping?

I doubt if your prop was slipping. If it was slipping, your RPM's would have went much higher.

The most likely scenario was that the possible reduction in speed was a result of going into the wind, going upstream, or the shifting of weight toward the bow. A GPS speed check should be done the next time out.