Pontoon Boat & Deck Boat Forum

I have a 2016 23ft Avalon Catalina with a 115 Yamaha.. when I try to speed up it cavitates really bad.. could it be the prop? Should I upgrade?

Your boat could have a propeller problem. Or the engine may have been improperly setup by the dealer when it was new and the engine may be sitting too high. The dealer could have installed a 20 inch lower unit for a bassboat on a pontoon designed for a 25 inch long shaft.

It is up to the selling dealer to get any new boat operating at 100% of its capability, and that doesn't include a ventilating engine. Only when the motor is at the right transom height can you decide whether it is propped correctly.

You'll have to give these guys your max factory RPM's, what your max RPM's are currently, What size is your prop? like he said if it's mounted to high then none of this will make a difference.

Thanks for the help.. gonna contact the seller soon

Cavitation plate on motor should be even with bottom of mounting box. Should get a smooth flow from bottom of mounting box across cavitation plate-like air over an airplane wing. Motor too high-cavitation--motor too low-motor will throw up a spray around motor which affects performance and speed.

Are you venting or "cavitating"? I have been guilty of using the two terms improperly so here is the definition from Mercury's prop catalog:

"CAVITATION: Even slightly chipped or bent blade edges can cause surrounding water to BOIL ("cavitate"). Gas bubbles then condense elsewhere on the blade, releasing energy that causes metal erosion or "cavitation burn".

"VENTILATION: Air from the water surface or exhaust gases from exhaust outlet being drawn into the prop blades causes ventilation. This reduces normal water load, causing the prop to over-rev and lose a lot of thrust. Ventilation is most common with high transom mounting, extreme trim-out and sharp turns. Mercury props are designed to minimize ventilation."

So, summarizing, cavitation is from damaged blades, and ventilation is mostly from high mounting, without a prop that can handle it.

If you have a 2 toon boat, I have found trimming the engine up to be ineffective. I always ran my motor with the anticavitation plate parallel with the bottom.

I often had to ask people sitting in the front to sit in the rear. My motor was mounted a little high and weight in front raised the motor just enough to give me ventilation. Sometimes all it takes is an inch or two difference.

[quote="Bamaman"]If you have a 2 toon boat, I have found trimming the engine up to be ineffective. I always ran my motor with the anticavitation plate parallel with the bottom.

I often had to ask people sitting in the front to sit in the rear. My motor was mounted a little high and weight in front raised the motor just enough to give me ventilation. Sometimes all it takes is an inch or two difference.[/quote]


Yep---people in front---keep motor down---if you try to trim you will just blow out. I have a 20 ft fishing model with 2 fishing seats up front-no couches--I can trim out a lot before I cavitate. Still like pushing a big box thu the water tho'

I'm running 28 GPS here.....uhhh--little too much weight on rt side of boat

As opposed to my bassboat--circa 1979 Toledo Bend Tx Venture ---115 Merc. 55 mph. Notice motor trim....

ALSo--check prop slippage. Sometimes they need to be rehubbed--pontoon boats are rough on hubs due to being under major loads all the time. I've spun out two.

And--underskinning will provide a little lift to raise bow.

LOL>..Got ya beat.....5 hubs over the years! Yep, slipping hub is easy to think is cavitation or ventilation. I would check for spun hub first along with cavitation plate position i.e. motor height. Good Luck !!!!