Losing drive at high revs.

[moresparks]

Hi I am looking at pointers at this early stage and would appreciate any suggestions.
I have a pair of AQ171’c on 290 SP-A drives. All season things have been fine so this is a sudden development on one drive.
At no wake zone things are fine and I can travel all day at 2000 revs, but the moment I push the throttle forwards to get on the plane one drive seems to lose drive around 3500 revs. Similar to suddenly going into neutral. Throttling back to displacement speeds and things are all fine again.
I have not had a chance to lift the boat out yet so cannot tell if there is water in the oil, not sure if this would cause this problem.
I replace the bellows every other year and undertake a pressure and vacuum test.
The propeller is only a season old.
The trim meter doesn’t seem to change as far as I can tell.
Is this a symptom of the cone clutch?
If it is; can these be repaired or do you have to buy the complete gear set?
Is there any checks I can do whilst it’s in the water or is this season end??

[RicardoMarine]

..................

Hi I am looking at pointers at this early stage and would appreciate any suggestions.
I have a pair of AQ171’c on 290 SP-A drives. All season things have been fine so this is a sudden development on one drive.
At no wake zone things are fine and I can travel all day at 2000 revs, but the moment I push the throttle forwards to get on the plane one drive seems to lose drive around 3500 revs. Similar to suddenly going into neutral. Throttling back to displacement speeds and things are all fine again.
It is possible that the prop hub has let loose. In other words, the inner hub is spinning within the outer hub.
Draw a line through both, and test it. If the line shifts, the hub is failing.
Or..... install that same size/same pitch spare prop that you have on board! (you do have a spare..... right?)

I have not had a chance to lift the boat out yet so cannot tell if there is water in the oil, not sure if this would cause this problem.
It's time to do so!

I replace the bellows every other year and undertake a pressure and vacuum test.
The vacuum test can be performed with gear oil installed. However, the pressure test requires that the gear oil be drained.

The propeller is only a season old.
The trim meter doesn’t seem to change as far as I can tell.

Is this a symptom of the cone clutch?
What gear oil are you using?

If it is; can these be repaired or do you have to buy the complete gear set?
While Volvo Penta makes no mention of this, an experienced tech can lap the components renewing the function.... if they are OK to begin with, but perhaps glazed a bit.

Is there any checks I can do whilst it’s in the water or is this season end??
I would certainly pull it so that several things can be looked at.

[kimcrwbr1]

Sounds like ether a prop hub or a clutch? You can check the oil with a skiff. I wonder if you can swap props around and just use the throttle controls backwards to see if the problem follows the prop?

[moresparks]

Many thanks for your very prompt responses certainly a couple of things to go on. I can quickly check the prop before hauling out.
In my mind I dismissed the prop as this is a brand new Volvo Penta prop only a year old.
The gearbox oil is the same as the engine oil as per handbook and has always been since I have owned the boat, i.e. SF 10/40 multigrade.

[RicardoMarine]

............

Sounds like ether a prop hub or a clutch? You can check the oil with a skiff.
Be very careful if you remove the dip stick while the boat is in the water. One small wave is all it takes.

I wonder if you can swap props around and just use the throttle controls backwards to see if the problem follows the prop?
Kim, all due respect, this could be a risky thing to be suggesting.
The OP can easily install his spare prop.

[moresparks]

May I ask out of interest – does the cone clutch become a problem over time or all of a sudden? Only the problem occurred half way through a day out whilst already on the plane cruising at 4500 revs.

[RicardoMarine]

As long is the gear oil is correct and his been kept clean, the cone clutch system typically works well for years.

[sandkicker]

Failure of a prop hub is not usually age related but rather "event driven", i.e. impact damage, sometimes not even noticed.
Try the simple to do and fix thing first, draw a line on the prop and then on to the cone. Run boat,see if line shifts. If prop is underwater when drive is up,then a light scratch in the paint with a screwdriver will do. Volvo props are good quality and tolerate several repair/rebuild cycles.

[moresparks]

Hi many thanks for your suggestions.
Now isn’t this just typical... I marked up the props and took the boat out for a short test run, and it duly went on the plane with no problems. Admittedly it wasn’t a long test but before I couldn’t get on the plane without “slippage”.
Now here’s the thing when I got back to its berth I went to raise the outdrive only to find that the drive had already lifted some way.
The marks on the prop are still in line so although not conclusive due to the short run, is leading me to something else amiss. On checking the hydraulic oil in the trim motor and it was a nice shade of pink – so water in the hydraulic oil! I am now wondering if the outdrive is lifting under full power and I am experiencing cavitation?