Saildrive slow to "pick-up" on forward throttle

[PaintedKite]

Originally Posted by DougR

To answer your question regarding the clutch components, the clutch plates in the parts book exploded drawing are numbers 20 & 21. The forward clutch pack on the engine end of the shaft toward the left and the reverse clutch plates on the other end of the shaft toward the right side of the picture.

This is important (to know that there's both a FWD & REV clutch). So now I've REALLY got to ascertain whether the behavior's the same in both directions.

Yes, the lubricating fluid works the same on both, but it seems unlikely that both sets of plates would wear/degrade at EXACTLY the same rate.

I'll run more tests today to see if it's likely that I've got a "hardware" problem or a "lubeware" problem.

[PaintedKite]

I can't thank you all enough for this excellent input!

You know ... it's odd: I CERTAINLY cannot be the first person to get water into a saildrive that then affects the performance of the clutch friction surfaces. Yet, there's NOTHING online about it (at least nothing that I can find).

I'm so glad that this conversation is being recorded here for the subsequent use by others.

More testing today ... with stopwatches! (Interestingly, the delay seems to have nearly the EXACT same duration each time. But that's just my anecdotal impression. Today we'll collect data in both FWD & REV.

P.S. -- I can't seem to find anything anywhere which indicates that I actually HAVE a hub cushion on this 2-bladed prop.

[DougR]

Can’t tell what brand your propeller is, but probably 99% of the fixed blade two and three blade saildrive props are VP props, and 100% of the VP saildrive props have a rubber cushion hub in them.

The prop is built with an aluminum splined inner hub which has a donut shaped rubber cylinder bonded to it. This assembly is then pressed into the aluminum prop hub under a few tons of pressure. From wear and tear, fatigue, high speed shifts, etc. these rubber donuts can tear or start to slip within the aluminum casting, and the more they slip the worse they get. For some expensive stainless steel sterndrive props and three bladed bronze folding props it’s worth re- hubbing, but two bladed fixed aluminum props are usually just replaced.

As mentioned earlier, the failure mode of a spun hub is usually that the prop holds at low RPM but then slips when more torque is applied......as opposed to slipping to begin with, then hooking up under more torque.

Slipping early under light throttle, then hooking up under more throttle pressure is more indicative of a cone clutch or plate clutch displacing the oil from the friction surface and then grabbing.... ie. a clutch issue.

Suggest you do your testing and check the prop hub for slippage. That’s easy and relatively quick and will point you in the right direction.

[PaintedKite]

UPDATE 2: Tested in FWD & REV this morning. Results:

FWD: 7 tries, 5 successes, 2 failures. Delay on failures = 28s, 29s
REV: 4 tries, 4 successes, 0 failures.

So the delay -- when it occurs -- is (a) consistent in duration and (b) about twice as long my anecdotal estimates.

And the failure happens more frequently in FWD than REV. This, to me, points to worn FWD clutch plates.

Also...
1. We changed the oil a few days ago and have run the engine a bunch of times but have not gotten underway. The oil still looks amber/gold, clear, and brand new. This means (a) no immediate, catastrophic-level water ingress, and (b) there would be no additional benefit of changing the oil again. [According to the manual 0.5 qts remain (of 2.9 total qts) when you change the oil from the top.)

2. I disconnected the throttle cable to see if perhaps it could be that the cable just wasn't pushing the arm (the arm on the saildrive) far enough. Doesn't seem to be an issue. Once the arm "clicks" out of neutral (at about 2/3 the cable travel), the arm has free play. Pushing it further doesn't do anything.

OK ... gotta pause for brunch (crab & red potato salad!). Back later...

[PaintedKite]

Originally Posted by DougR

...the failure mode of a spun hub is usually that the prop holds at low RPM but then slips when more torque is applied......as opposed to slipping to begin with, then hooking up under more torque.

Slipping early under light throttle, then hooking up under more throttle pressure is more indicative of a cone clutch or plate clutch displacing the oil from the friction surface and then grabbing.... ie. a clutch issue.

Yep, that's what I'm thinking now, too (clutch plate wear due to water in the oil for, probably, a long time).

Diver guy is not available for a few days, so we might still haul the boat, just to pull/check the prop and replace the shaft seal at the prop end.

[psahd]

Don't you just love it when someone wants help, they jump onto this forum as though it is a bible, but very seldom do they complete the thread by reporting back on the conclusion to their problem...

In this case, what was PaintedKites's solution?

Sad...

[PaintedKite]

Originally Posted by psahd

Don't you just love it when someone wants help, they jump onto this forum as though it is a bible, but very seldom do they complete the thread by reporting back on the conclusion to their problem...

In this case, what was PaintedKites's solution?

Sad...

That's a bit much drama, don't you think? Geez ... chill. Just ask the question. All the window dressing is rather pathetic.

[PaintedKite]

End result: I had to replace the entire saildrive. The local Volvo shop (great folks, really) pulled the unit, took it to their shop, found lots of scoring and excess wear, and explained that it would cost more to rebuild than to replace. So we replaced.

I believe, actually, that an out-of-round prop was the original problem. (it wasn't until a new prop was installed -- 3-blade, folding -- that we realized how much vibration we had been getting from the old one.) It put too much stress on the prop shaft seal, causing it to fail and allowing seawater to enter the unit.

The out-of-round prop could have been caused by one of 2 things. First and most likely, somebody could have hit something with it, causing an ever-so-slight deformation. Second, it was just an awfully cheap and light-duty OEM prop (fixed 2-blade ... I've kept i as an emergency spare); I half-way suspect that it was just manufactured slightly out-of-spec.

Anyway ... the replacement 'part' was ~$10K, the new prop was something like $3K, then labor for the whole job took the entire bill up to around $20K. But please note that we also had some HX, alternator, and mixing elbow work done (seawater leakage).

Call to action: know your propulsion systems, inspect them frequently, and correct any issues immediately! This was an expensive lesson.

[belizesailor]

Well, if its any consolation, a friend of mine is a factory trained Volvo mechanic. He has been to training specifically to work on and rebuild sail drives. During class they rebuilt a bunch of drives a bunch of times. At the end of the class all these pro mechanics and the instructor were having a beer and reached the conclusion that it is better and ultimately less expensive just to replace the drive in situations like yours. So I think they steered you in the right direction.

[psahd]

Originally Posted by PaintedKite

That's a bit much drama, don't you think? Geez ... chill. Just ask the question. All the window dressing is rather pathetic.

Sorry PaintedKite! Was meant in a very lighthearted manner! Really did not mean to offend. Thanks for the update and not nice reading that you had to replace the entire drives for what is essentially a wearing part?? That scares me..