Cavitation getting out of the hole on bowrider with Merc 4-stroke 115 EFI

[dtos]

I just bought a new (2008) Glassmaster 18ft bowrider with a Mercury 4-stroke 115 HP EFI outboard. It runs well, except for one annoying issue: While trying to accelerate quickly (i.e. for waterskiing) the motor cavitates and loses power coming out of the hole. To remedy this, I was going to get a stainless steel prop, but was unsure of pitch. Any recommendations? Other solutions?

 

[Robbabob]

Re: Cavitation getting out of the hole on bowrider with Merc 4-stroke 115 EFI

Welcome aboard iBoats! Check out the stickies at the top of the page and give us more details about your current setup: rpm at wot, etc.

 

[SparkieBoat]

Re: Cavitation getting out of the hole on bowrider with Merc 4-stroke 115 EFI

not sure that going to a SS prop will stop cavitation. is your motor trimmed all the way down when you start out? you may need to lower your motor or install and anti cavitation plate, a 4 blade prop will usually not cavitate as bad as a 3 blade. they also make wedges for the bolt holes of your motor that points the prop slightly further down, this may help also and is cheap. they basically allow you to trim your motor down further.

 

[Texasmark]

Re: Cavitation getting out of the hole on bowrider with Merc 4-stroke 115 EFI

In addition to the above comments, lower pitch and blade cupping usually help. What's happening (as I see it from here) is that the load on the boat caused by the skier essentially holds your boat stationary in the water and with the engine turning the prop it creates a vacuum of sorts which amounts to a suction. Since air is just above the anti-vent plate (which the tips of the prop blades stick out beyond) and air is lighter and easier to suck through the prop wash, you get air across your blades which causes what you said. The vibration is present because the air entering the prop wash of each blade is probably not uniform so the blade loading is uneven and together all this causes:
Vibrations
Overreving
Slow forward movement

With what has been said in the post replies you have received, you should be to solve your problem quite nicely.

Good Luck,

Mark