2013 255 freedom cavitation issues

[dmc84dds]

Hello
I purchased a 2013 255 freedom with 2013 f300 Yamaha engine. As i pick up speed suddenly or even gradually in certain rolling conditions my engine revs up quickly and the boat slows down. I'll quickly reduce throttle then very slowly bring it
back up to speed and its running OK but sometimes it cavitates again. Also, a separate issue is port list which i was told was prop torque weight distribution is even, it is level when still, but it seems excessive and requires more than 50% trim tab adjustment to level off. Are these two conditions related? Is the prop an issue? (it came with the boat and is in good repair) My feeling after doing some reading is that the engine may be mounted too high. Can anyone make sense of this?
Thank you
dmc

 

[seasick]

Sounds like a spun prop symptom to me.
The prop could be wrong also. That can cause excessive prop slip.

The sound you hear when the motor revs up and speed drops off can be ventilation not cavitation. What hole of the engine mounted in? Can you tell if the ventilation place remains below the water when on plane.Do the checks with no motor trim and no trim tabs.

 

[DennisG01]

As Seasick menitoned - and just for "correctness" so we're all on the same page, it's most likely ventilation, not cavitation. They're really two different things.

Put a match mark on your prop hub (rubber vs metal) and then see if the marks are no longer matched.Another cause of ventilation is running with too much up trim.

The listing may be due to you running with the engine trimmed down too far. That will cause the listing effect you're seeing.

I realize those statement are somewhat contradictory regarding the trim... but you didn't mention how you're trimming the engine - adding that info will help.

Where is the anti-ventilation plate in relation to the bottom of the hull (how far above/below it is in inches) with it trimmed neutral... and what is the setback of the engine vs the transom/hull bottom?

 

[Sardinia306Canyon]

As above, can be either, ventilation or a prop hub going bad and will spin free soon and you need to be towed home.

Dennis already mentioned how to check for slipping prop hub, do this test and check it to exclude this possibility.
I had spun hubs twice on my heavy dive boats and a completely free spinning hub came usually after a few days when i noticed slipping.

Honestly i believe that your problem is ventilation, the prop sucks air when

1. accelerating to go over the hump (transition between hull/displacement and planing speed)
2. because engine is trimmed too much up
3. wave action lift the stern and lower unit more near to the water surface
4. boat is stern heavy what create turbulence on the transom (ventilation when going over the hump)
5. engine/s are mounted one hole too high (also ventilation in hard turns at planing speeds)

The check for correct maximum trim up angle is to hear when sound changes when engines start to suck a bit of air what changes the noise they make. Maximum trim angle is not always good as it can make the boat squirrelly and dangerous to operate.

For further diagnosis we really need to know:

1. is this a new problem (probably not as you just bought the boat)
2. your boating experience
3. your trim angle as shown on the gauge
4. your weight and it's distribution (all passengers on the stern is bad)

Chris