Pontoon boat slipping/cavitation with quick throttle increase

[Deintinis]

Having an issue with my '15 115 CT Merc. I was having issues with engine RPMs bouncing around and felt like prop was not catching water. This started to happen when I accidentally left anchor in and went full speed near weeds and sandbar. I pulled anchor up and has not been same since.

I have:
1) changed plugs
2) changed prop hub (hub was cracked)
3) changed prop (old one chewed up)
4) sea foam in gas tank


if I gradually increase throttle it seems to be ok and eventually gets to 6200 RPMs. A little higher than 6k recommend but am getting 26mph at 6k rpm. Problem is that if I push throttle to quick, the prop is not getting a hold of water and revs up to 6k with barely any forward movement. I have to back it down to try to get it to catch. Or sometimes it will catch but when trying to get to WOT it revs so high the engine starts making a sound like it is limiting or not getting enough gas.

I am am not sure if I have an engine issue or prop issue. Before this incident I did notice it would slip every now and than, but I typically did not have issues getting it out of the hole. Now it just does not jump out if hole like it used to misses gear/bite on water.

I have a 24' cypress cay with the 115 with a 16" 13p prop.

Any ideas on next steps to troubleshoot?

 

[Sea Rider]

Is current prop a standard one, or one that has replaceable internal hub, if second probably hub is slipping, needs to be torqued more. Check. If ok and OB is 100% healthy could be OB sitting too high on transom.

Happy Boating

 

[Texasmark]

I'll go along with Sea Rider. To check prop slip, pull the prop nut and washer. Scribe or mark with an indelible magic marker, a line from the prop shaft spline across the brass part of the prop hub on out as far as you can go before getting to the open exhaust area. Put things back and go out and punch it a couple of times. Open it back up and have a look at your line/scribe mark. If not still a straight line, get your prop fixed, another hub, or another prop. Then worry about other issues but you probably won't have to. You will have found your "smoking gun".

 

[Silvertip]

Is the prop right for the motor? By that I mean very often folks find a prop that fits the engine but the hub is not designed for that gearcase. The other aspect is engine setup. If mounted too high you can experience "blow out" where the prop just blows all the water away (digs a hole so to speak) and therefore there is no forward thrust. This is not cavitation, but ventilation (the prop sucks air). Once hooked up things go normally. You may have the boat loaded to heavy at the front when that happens.

 

[harleyman1975]

common problem on pontoon boats. must trim load correctly and make sure prop is not damaged and hub is good and correct for your motor.