2021 Mercury Pro XS Cavitating

[Gfd63]

Got the break in period in. Around 3000 rpm or so the motor feels like it's cavitating. Trimming the motor up seems to help a bit & steadies out around 4500 rpm. Called the dealer & they suggested moving the motor down one mounting hole. It only has one hole left to move the bolts to. Plus I would think if that's the case, it would shutter at the lower rpm's as well. Anyone have similar experiences or suggestions?

[A-Jay]

Are we talking about the Pro Team 190TX with 115 4 stroke Mercury ?

 Also does your rig run on plane at 3000 ?

If it doesn't, why would you run it at that rpm ?

A-Jay

 

[J Francho]

First, let's diagnose what exactly is going on, and what your doing.  As A-Jay says, why run at that RPM if the boat settles down at a different RPM?  Anyway, here's what cavitation and ventilation are:

 

[Gfd63]

56 minutes ago, A-Jay said:

Are we talking about the Pro Team 190TX with 115 4 stroke Mercury ?

 Also does your rig run on plane at 3000 ?

If it doesn't, why would you run it at that rpm ?

A-Jay

 

Boat is a 2021 Ranger RB190. Yes it's a 115 Pro XS 4 stroke. Starting out from a dead stop it'll get up on plane around 2800-3000 rpm.

35 minutes ago, J Francho said:

First, let's diagnose what exactly is going on, and what your doing.  As A-Jay says, why run at that RPM if the boat settles down at a different RPM?  Anyway, here's what cavitation and ventilation are:

 

Thanks for the clarification & great explanation. Still trying to figure out exactly where it does break over on pad & planes out honestly. But somewhere around 2800-3000 rpm seems like right when it does the vibrating.

[WRB]

You have the engine tucked all the way down starting off then as you reach plane speed trim the up until the bow lifts then accelerate the throttle. If your engine is set too deep the bow tends to plow and needs more throttle to lift it. 

Proper engine depth is 3 1/2” to 4”  prop shaft center line to bottom plane surface measured level or parallel to the plane surface.

Aluminum or SST prop?

Tom

[Gfd63]

On 5/18/2022 at 4:53 PM, WRB said:

You have the engine tucked all the way down starting off then as you reach plane speed trim the up until the bow lifts then accelerate the throttle. If your engine is set too deep the bow tends to plow and needs more throttle to lift it. 

Proper engine depth is 3 1/2” to 4”  prop shaft center line to bottom plane surface measured level or parallel to the plane surface.

Aluminum or SST prop?

Tom

It's a Mercury Tempest Plus stainless steel vented prop. It was suggested that I try solid plugs in the vent vs the large holes.

[WRB]

You have a jack plate, is it hydronic adjustable? 

I don’t believe the prop vents are your problem, easy enough try.

I am still on the prop height vs plane surface as the key issue.

Tom

[Siebert Outdoors]

Call your dealer or boat manufacturer and get the recommended Prop to Pad.   Since you have a hydrolic jack plate you can go from there in messing with the trim of the motor up and down for optimum performance.  NOTE:  You must watch your water pressure and make sure you have plenty of water pressure for the motor.  Do not lift the motor to high.

[Way2slow]

Two things about this setup that concerns me.  If you are getting a vibration, you have a serious problem and I would not be running it until the problem is fixed, like maybe the hub adapter is not properly installed in the prop or the porp shaft got bent in shipping.  Even if it cavitates, there should be absolutely no vibration. 

The other concern is the prop pitch.  A 23" pitch prop on a 115 is a whole lot of prop, unless that's a 60+ mph boat.  With you and a light load, you would want the motor to be turning right at manufacture's  max recommended rpm.  If it's not, it's going to be a dog coming out of the hole with two people, tank of gas, gear and full livewell.  

Looking at your picture, the motor might actually already be a little too high.  It looks like the anti-cavitation plate is up from the bottom of the transom a couple of inches already.  So precede with caution and monitor the water pressure gauge if you try raising it more.

 

[WRB]

20 pitch is appropriate for 115 hp, over looked that somehow.

Prop wobble is a serious issue!

Tom

[Gfd63]

On 5/26/2022 at 3:28 PM, WRB said:

You have a jack plate, is it hydronic adjustable? 

I don’t believe the prop vents are your problem, easy enough try.

I am still on the prop height vs plane surface as the key issue.

Tom

Jack plate is hydraulic & adjustable.