Saildrive clutch slip?

[Pavalijo]

When we purchased Calypso the local Volvo dealer installed a new propeller as the existing folder's pins were worn. We were a bit disappointed with the performance but the Volvo dealer quickly closed and so we have lived with a top cruising speed of 4 kts at 2,400rpm (39hp VP 2040B engine, 120SD saildrive, 9.92m waterline length, 10 tons displacement fully laden). Other owners of the same model report 6kts plus, and when we have wind and waves against we can be down to 3 kts or worse!

I initially assumed that the wrong prop had been specified but we would have to live with it. We were tootling around the Clyde with short distances and little tide. However now that we are off cruising it has proven an issue that we are going to have to deal with.

When I started looking into this in earnest a year ago I discovered that the part number on the blades was different to the quote for the 17x12 blades - hopefully I had solved the problem. However Volvo (after a lot of head scratching) said that this was old stock and that the part number for the 17x12 LH blades had changed.

I have now spoken to the very helpful people at Darglow - they say that the prop spec sounds about right for the boat. I am taking my prop to them and they will measure it to make sure that Volvo are correct that the old part number is for the same blade as quoted. If it is then I am a bit lost where to go next.

My thought is whether the clutch may be slipping, however if it is then it is a very consistent slip, ie the performance is consistently poor and has not really deteriorated in the 400 hours or so that we have run under engine in the last 5 years.

The engine revs very freely under load, but acceleration/stopping is very slow, and speeds are very slow. On a trial we got to WOT very easily and my thoughts were that the prop must be underpitched. For the first time in a few years we had a trip on two other yachts this year and the acceleration was noticeable compared to ours.

At first service post purchase the saildrive oil was milky and the seal changed - it has been clear since (changed every year using engine oil as recommended).

Calypso is in a Spanish yard so we don't have easy access to her as we are home for the winter, but I wondered if anyone has experienced saildrive clutch slip and if so what were the symptoms and what was the remedy (I assume that a 22 year old saildrive clutch can be repaired/replaced)?

Many thanks in advance, Paul

 

[pvb]

The saildrive clutch can wear and slip. It's not a DIY repair, so you'll need a VP dealer ideally. Surprised you've lived with this for 5 years.

 

[duncan99210]

The engine is not revving anywhere near where it should do. At WOT you should be getting somewhere in the order of 3000 rpm or more. So, with the boat speed down and lack of speed, it doesn’t sound to me as if the clutch is slipping as you’d be getting higher engine speeds but a lack of boat speed.

To my mind, it could be down to two things. One is the prop is wrongly specified for the boat, you’re already checking that out. The other is that there is something wrong with engine, such as a partially blocked exhaust elbow. A lack of power is often associated that. Worth checking.

 

[Pavalijo]

I researched a replacement prop a couple of years ago - one year after we left the Clyde (where we mostly sailed so not a major problem) but held back when reading about corrosion issues on my preferred Flex-O-Fold option.
Then when looking into the mystery further came across the part number issue which has delayed matters further.
We are spending another year in the Rias next year but I will not be traveling down the Portuguese coast in 2020 if this is not resolved!
My query really is whether anyone has experienced a slipping clutch and (other than slow progress) are there other symptoms?
I never get zero drive or juddering or varying speed - just an easy revving engine and consistently slow progress!

 

[Pavalijo]

Sorry Duncan, I maybe didn’t make it clear - the engine revs very freely to WOT at around 3,600 rpm (the tachometer reads 4100rpm but I estimate - unscientifically - that it overheads by 10-15% or so after a Balmar alternator was fitted.)
So the engine seems to be working just fine.
The prop was correctly specified according to Darglow and we will know shortly if the old part number is indeed the same as that specified.
I can’t think what else the problem could be other than clutch slip, if the prop is as specified.

 

[Tranona]

Does it achieve 3600 rpm under load and if so what speed do you get?

 

[Pavalijo]

We undertook a trial to complete the Darglow data form on the Vilaine river, behind the barrage. This was fresh water, flat calm and no current.
We ran the engine in gear in 200rpm increments.
There was a wind of 8-10kts blowing straight down the river.
With wind at around 2400 rpm we achieved 5.2 kts and against wind 4.7kts. I believe we should have seen an average in excess of 6 kts at that rpm.
At WOT, about 3600 rpm (approx - actual tachometer reading 4100) on the downwind run we saw 7.1kts. The alternator belt was smoking so we didn’t repeat this upwind.
Calypso is a beamy boat and has a large sprayhood which gave considerable assistance downwind. This is perhaps best shown at around 1000 rpm when the figures were 1.1kts upwind and 2.6 downwind.
On the test we increased engine speed gradually, but from tickover in forward gear the engine does seem to rev freely with poor acceleration (compared to friends’ boats we went on this year).
The engineer I used in Hamble last year wondered if the excessive weight we have carried might be a factor. With full tanks and cruising gear on board the weight in the slings was 1.5 tonnes above stated displacement and she sits very slightly lower in the water than when we were driftng around the Clyde (3-4cm).
Darglow say that this will have a bit of an impact but not to this degree.

I am hoping that we find that Volvo sent out the wrong blades, but if not clutch slippage seems the most obvious answer. Before anyone asks - we clean and antifoul every year and that makes little difference.

 

[paddywackcocker]

I might stand to be corrected but the 120 sail drive doesn't have clutches, as in plate type.
The splined shaft on to the drop shaft is splined and they refer to that as a clutch but if it was slipping you would have lost all drive long ago
They might have supplied wrong prop for gear ratio, 130 different ratio but same lower shaft

 

[XDC]

I might stand to be corrected but the 120 sail drive doesn't have clutches, as in plate type.
The splined shaft on to the drop shaft is splined and they refer to that as a clutch but if it was slipping you would have lost all drive long ago

Have to say I was confused re clutch slip. I always thought that the gearbox was basically a load of cogs making a direct drive to the back of the box then “something” transferred the drive vertically to the saildrive leg.

See exploded diagram here:

https://www.marinepartseurope.com/en/volvo-penta-explodedview-7740690-44-4204.aspx

 

[pvb]

Have to say I was confused re clutch slip. I always thought that the gearbox was basically a load of cogs making a direct drive to the back of the box then “something” transferred the drive vertically to the saildrive leg.

See exploded diagram here:

https://www.marinepartseurope.com/en/volvo-penta-explodedview-7740690-44-4204.aspx

The sliding sleeve (part 22) has a conical top and bottom, which fits into a conical recess in the gear (part 8) and drives it through friction.

 

[Momac]

Have to say I was confused re clutch slip. I always thought that the gearbox was basically a load of cogs making a direct drive to the back of the box then “something” transferred the drive vertically to the saildrive leg.

In that case the prop would be turning all the time the engine is running and there would be no neutral or reverse gear .
I don't think that is the case is it?

If the OP's clutch was faulty a few years it would have failed by now.

 

[XDC]

@PVB Must admit that the fact neither you or Tranona had picked up on it did make me wonder :encouragement:

 

[XDC]

In that case the prop would be turning all the time the engine is running and there would be no neutral or reverse gear .
I don't think that is the case is it?

No I didn’t explain it well, I saw it more as a sort of non-synchro box, FNR, particularly as I often hear gears being selected on boats near me, let alone my boat. There’s a definite “clunk” that eminates particularly from charter boats where they don’t seem to have a neutral position when berthing

 

[Yngmar]

This is the correct drawing for the 120S-D saildrive upper unit: https://www.marinepartseurope.com/en/volvo-penta-explodedview-7746410-44-213.aspx

The MS2A linked previously is the shaft drive version, although the gear selector works the same.

Gear selector parts: https://www.youtube.com/watch?v=rWYZ8iPuHIQ
Gear selector in action: https://www.youtube.com/watch?v=D8nkoGnmLU8

The dog (34) slides the sliding sleeve (22) into either the forward or reverse gear (7), where the cone engages with the gear. This is where the friction happens and wear occurs.

As you can see in the videos, the sleeve can be extracted from the top of the gearbox, without hauling out, so it's feasible to inspect this, although apparently a special tool is needed to access the top gear. More at this CF thread, although the CF forums seem to be currently offline: http://www.cruisersforum.com/forums/f54/volvo-penta-120-se-saildrive-cone-replacement-113842-2.html

 

[VicS]

And the workshop manual is here

http://www.plaisance-pratique.com/IMG/pdf/VolvoMS2-SD120_manual.pdf

 

[Pavalijo]

Thanks all for the usual excellent response.
I am especially encouraged by Yngmar’s advice that the “clutch” can be inspected and presumably replaced without removing the saildrive.
The boat is on the hard for the winter. Is it possible that an engineer could test for slippage by selecting gear in the cockpit and trying to turn the propeller?
MartynG suggests that the clutch should have failed by now if it has been faulty over all this time (around 400 hours or so since we purchased the boat 6 seasons ago- not the 5 years as I correctly stated earlier). Do others agree? It is possible that there has been a half knot deterioration over this time, but certainly no more, and possibly none at all. I can’t say that I took much notice in the early years given that I was not aware of the speeds we should have been achieving and the fact that it was not much of an issue whilst weekend sailing in the Clyde.
The good news in all this - is that I would imagine that repairing the clutch would be much cheaper than the new feathering propeller that I was intending to purchase!

As a complete aside, maybe more relevant to a different thread, my 3 blade Volvo folder is in superb condition after 6 seasons. As routinely reported the anodes are not big enough, however Calypso is never in the water for more than 7 months, usually 6, and only one season did we see one of the anodes detached. For 4 of the 6 seasons we have relied on highly polishing the prop, antifoul has only been applied 2 seasons. So for me the Volvo prop has been good value for money, but I wouldn’t have been happy keeping it in the water for most of the season without changing anodes.

 

[Pavalijo]

In that case the prop would be turning all the time the engine is running and there would be no neutral or reverse gear .
I don't think that is the case is it?

If the OP's clutch was faulty a few years it would have failed by now.

There certainly is neutral. We always pause briefly in neutral between forward and astern, and there is no unpleasant clunk when engaging gear in tickover. See comment on failure over time on previous reply.

 

[Tranona]

We undertook a trial to complete the Darglow data form on the Vilaine river, behind the barrage. This was fresh water, flat calm and no current.
We ran the engine in gear in 200rpm increments.
There was a wind of 8-10kts blowing straight down the river.
With wind at around 2400 rpm we achieved 5.2 kts and against wind 4.7kts. I believe we should have seen an average in excess of 6 kts at that rpm.
At WOT, about 3600 rpm (approx - actual tachometer reading 4100) on the downwind run we saw 7.1kts. The alternator belt was smoking so we didn’t repeat this upwind.
Calypso is a beamy boat and has a large sprayhood which gave considerable assistance downwind. This is perhaps best shown at around 1000 rpm when the figures were 1.1kts upwind and 2.6 downwind.
On the test we increased engine speed gradually, but from tickover in forward gear the engine does seem to rev freely with poor acceleration (compared to friends’ boats we went on this year).
The engineer I used in Hamble last year wondered if the excessive weight we have carried might be a factor. With full tanks and cruising gear on board the weight in the slings was 1.5 tonnes above stated displacement and she sits very slightly lower in the water than when we were driftng around the Clyde (3-4cm).
Darglow say that this will have a bit of an impact but not to this degree.

I am hoping that we find that Volvo sent out the wrong blades, but if not clutch slippage seems the most obvious answer. Before anyone asks - we clean and antifoul every year and that makes little difference.

These figures are not too far out. Your problem is your heavy displacement - if your 10 tons is correct and you have a 17*11 2 blade prop. I ran the figures through Propcalc and using the design displacement (from your website) of 8650kgs the predicted speed with this prop is 7.6 knots but use a displacement of 10000kgs the speed drops to 7.3 knots. Speed predictions are the same with a 16*12 3 blade but this might give you better low speed stopping power and improve speed in adverse conditions.

So essentially your boat is underpowered for the weight (and your 10 tons is probably an understatement) and probably not helped by the extra windeage of all the bits you have added.

Similar size boats (such as the one Yngmar has) were usually fitted with the bigger MD22 50 hp engine which is obviously much more able to deal with the weight. With that engine (and the same propeller!) your maximum speed would be close to 8 knots with a corresponding improvement in cruising speeds.

Edit

Just re-read your post and see that you have a 3 blade prop but it does not materially change the predictions as the recommended prop size is 16.44*12.46 which is effectively the same as your 17*12.

So if the prop is confirmed as that size you already have the correct one.

I don't go with the "clutch slip" theory. It is not common and if it was slipping you would not be achieving the shaft speed to get the maximum speed you got on your test.

Just to add one thing. I think you should do a proper test on the revs your engine is achieving. It should be governed to 3600rpm but the drive belt should not be smoking at those revs. so first check the belt - both its condition and tension. Then buy one of those simple electronic rev counters that don't work off the alternator. I actually used to use a vibrating tacho when I did speed runs rather than rely on the electric tacho, and do the runs over measured distances at slack water.

 

[paddywackcocker]

Just stripped a, S120C. (In workshop due to input shaft spline ware)
Yep that is definitely a cone drive, akin to a synchro hub.
You could remove gear selector and rear mounting back plate and you have enough movement to see if the groves are worn.

 

[Yngmar]

Cruisersforum is back up, so you can read the thread I linked above yourself. Below image sticks out, showing an old sliding cone next to a new one. There's significant wear on the old, the grooves (which are presumably for lubrication) are entirely worn away.

Whether the clutch would still sort of work for 400 hours while severely slipping the entire time, I kind of doubt. I think it would wear the cone away to a nub until it no longer engages enough to spin the prop at all. It would also generate significant heat in doing so, so the gearbox would probably feel hot despite the oil being cooled in the submerged leg.

Only one way to find out though. Looks like the tool for removing the top gear is rather special though (also depicted in the CF thread).