2021 Mercury 115 Pro XS cavitating

[QBhoy]

All the Plugs have curvature, even the ones with vents. The one at the top is rotated enough to make a determination difficult, and is only about 69 pixels across in that image

Yeah. Hard to tell. But sure looks like one is and one isn’t.
Despite that..the vented one will be causing the affect described in the original post.

 

[jimmbo]

I have my Enertia vented, the effect is small

 

[QBhoy]

I have my Enertia vented, the effect is smallView attachment 360925

Yeah. I’ve had a few props vented previously. Didn’t like it much. But one of my boats has the same engine as this and an inch high on the set up. I tried the smallest vents on a prop with more pitch than I normally run. It doesn’t start to seal the vents until nearly 4000 rpm on it. Total pain and no good at all for slow planing on that set up. It’s constantly venting every now and then even at low 3000’s…right where I want to sit for cruising speeds. Just what I found on that particular engine and set up anyway.

 

[jerseydevil]

Hi...Just looked on the laptop there, at the pics...you have no vent plugs in that prop at all...That is 100% your issue. The 3 holes you have there (one between each blade at the forward end of prop) should have some form of PVS black circular plugs in there. from memory, there are 3 options. Some have a hole about half diameter, some a tiny hole and others are full closed plugs for no slip at all. The way yours are are full bore and must feel terrible until really high up the rpms. It will be useless for anything less than fast planing speeds and feel horrible at it too. Look up "mercury propeller pvs plugs" I can bet my life that this is your issue..no doubt about it.

Yep the 3 holes have a black bushing with the center totally open.

 

[jimmbo]

The Raker, which had larger vents sealed at 3200, then it was hang on. Wish I could kill the sound of the Porpoising
View attachment MVI_0364.mp4

 

[jerseydevil]

Hi...Just looked on the laptop there, at the pics...you have no vent plugs in that prop at all...That is 100% your issue. The 3 holes you have there (one between each blade at the forward end of prop) should have some form of PVS black circular plugs in there. from memory, there are 3 options. Some have a hole about half diameter, some a tiny hole and others are full closed plugs for no slip at all. The way yours are are full bore and must feel terrible until really high up the rpms. It will be useless for anything less than fast planing speeds and feel horrible at it too. Look up "mercury propeller pvs plugs" I can bet my life that this is your issue..no doubt about it.

The PVS plugs should be solid then?

 

[jimmbo]

Yep the 3 holes have a black bushing with the center totally open.

Those vents/plugs are one of the Medium choices.

 

[jerseydevil]

I can tell that's a Mercury Prop. What Model is it, Laser, Mirage, Tempest, or other?(I'm feeling lazy and don't want to look it up)

It looks like you boat places the Transom a few inches back from where the Bottom ends ahead of the engine(setback), that allows for a slightly higher engine height. Also you have the engine mounted on what looks like a Jack Plate, which provides a bit more Setback. With the correct Prop, the Engine will be fine at that height, and could be even a bit higher.

It's a Tempest 48-825864-23P

 

[QBhoy]

It's a Tempest 48-825864-23P

Have a look at the plugs. I think it looks like one is holed and one isn’t. Hard to tell.
But even at that. It would be worth trying the solid plugs. I know for sure that my 115 didn’t like them holed at all, with her sitting about one inch above the lower hull. Yours looks at least that. It didn’t stop venting until really high rpm on mine. Did exactly as you described

 

[jimmbo]

The PVS plugs should be solid then?

It is a matter of Preference, as there is no right or wrong. They do provide an easy way to fine tune how the engine responds to Throttle and were developed so people weren't taking drills to their Props

 

[jerseydevil]

Have a look at the plugs. I think it looks like one is holed and one isn’t. Hard to tell.
But even at that. It would be worth trying the solid plugs. I know for sure that my 115 didn’t like them holed at all, with her sitting about one inch above the lower hull. Yours looks at least that. It didn’t stop venting until really high rpm on mine. Did exactly as you described

Copy that. I'll try the solid plugs & see what it does. Appreciate the input.

 

[QBhoy]

Copy that. I'll try the solid plugs & see what it does. Appreciate the input.

No worries. Let me know how you get on. Keen to hear how that lovely set up performs too. Is it a CT gearbox? Presume it must be, if you are running a tempest. I run a tempest 19 and enertia 20” on mine.

 

[jerseydevil]

No worries. Let me know how you get on. Keen to hear how that lovely set up performs too. Is it a CT gearbox? Presume it must be, if you are running a tempest. I run a tempest 19 and enertia 20” on mine.

Got the solid plugs in Saturday afternoon & installed. Solid plugs were a bit tight to get in but they're installed. Now I gotta get a breank the work schedule to see how the change did. Not sure about the gear box, but I'll take your word for it.

 

[QBhoy]

Got the solid plugs in Saturday afternoon & installed. Solid plugs were a bit tight to get in but they're installed. Now I gotta get a breank the work schedule to see how the change did. Not sure about the gear box, but I'll take your word for it.

Good man. Let me know how you get on. Allan.