Saildrive clutch slip?

[pvb]

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).

I think the grooves, rather than being for lubrication, are to allow the oil to escape from the cone/gear interface. Once they've worn away, there's no easy escape for the oil, and the clutch can slip.

As I said in post 2, I don't think this is a DIY repair, some special tools are needed, together with the experience which a VP engineer should have.

 

[Pavalijo]

Thanks all for your interest and assistance.
Tranona - the prop specification was for a 17x12 3 blade.
Calypso has been weighed in the slings (not sure just how accurate that is) at 10.1 and 10.5 tonnes in the past couple of years. Darglow also said that the extra weight should have limited effect, maybe half a knot as you suggest. We have been shedding much of the extra tinned/dry provisions and other superfluous gubbins that we were warned would be unnecessary (and ignored the advice) but doubt we will get much below 10 tonnes! My test figures do show that we have a fair amount of windage, but even downwind in the test on flat water our speed was too low.

Thanks for the further detail Yngmar. I did look at the exploded diagram this morning but the photo is much clearer! The total engine hours is currently around 2,200. I had a good trawl through past threads and could find virtually no mention of clutch slip, and there will be many 120SD’s out there with much higher engine hours, maybe we got unlucky (assuming I don’t have an action against VP for sending out the wrong blades!)

The yard where we are now require first refusal on contracted works. I was happy with this given their excellent reputation for quality work at a reasonable price, but I think I may need to insist that a Volvo specialist is allowed in - or have the work done elsewhere whilst in the water. I am happy with oil/filter changes etc etc but this is beyond my capabilities! Here comes my first major challenge with the language barrier - my night school Spanish lessons have served me well when ordering a beer, or indeed arriving at a marina, but this will be an interesting challenge. Thank goodness for Google Translate!

I will confirm the result of the prop measurement tomorrow afternoon,
Regards, Paul

 

[Tranona]

I really think you are going up a blind ally pursuing the clutch slip idea. Weight is your problem and you simply don't have the hp to achieve the sort of speeds you are expecting.

Look at the other Moody 38 models of the era that were aimed at the cruising market rather than being a "cruiser racer" like yours. They all have both less displacement and bigger engines than yours.

Your 2040 is not capable of achieving hull speed even in minimum design displacement mode so when you add over 1500kgs payload and all that extra windage it is not a surprise that performance falls off.

I have some experience of what happens to 120 drives when they are abused. My last boat had a 2030 and a 120 drive. It did 7 seasons charter work in Greece where as you could imagine it had far more abuse than a lifetime of private use. It did 3500 hours before the drive failed. The cones seized and filled all the innards with metal particles wrecking the bearings and seals. Replaced with a new 130 drive as 120s were then long obsolete and out of production. If you have wear on the cones - as I suggested earlier you would see metal particles in the oil. If you have clean oil there is nothing wrong with the drive.

In the unlikely event the drive has failed it will not be worth rebuilding as the parts are hideously expensive and if the cones have failed replacement would be uneconomic for the reasons suggested above. Unfortunately new drives are also expensive and you may take the view that it is better long term to replace the whole engine and drive with a new 50hp D2. You will find a ready market for the engine itself. You will then have a much better engine for the boat and enjoy the sort of motoring performance that is appropriate to a long term cruising boat.

 

[Pavalijo]

Darglow confirmed that the propeller is as specified at 17x12.
They cannot say that there is no clutch slip (obviously) but Chris did say that an old Volvo handbook would suggest that 17x13 would have been the correct specification. Indeed he suggests trying a Featherstream set at 17x14, given our extra payload, which might see us “over-propped” and reduce rpm at WOT, but if that places too much load on the engine we can adjust it back to 17x13.
There are no 17” blades in the Volvo literature with a pitch greater than 12”, so a blade change is not an option.
I am going to discuss clutch slip symptoms with a Volvo trained engineer I have used recently, plus implications of wxcessive over-propping on saildrive wear before deciding how to proceed.
Darglow have been very helpful, as mentioned here in many threads.

 

[Martin_J]

Hi

Same boat, same engine and same 120sd on Jubilant.... I do get more speed at those revs but do notice a slow down when the boat is heavily loaded.

If the cones were worn I would expect to see the golden coloured residue settling in the gearbox oil.

Out of interest, what oil are you using in the saildrive leg? That can make a big difference..

If you're interested in what the cones actually look like when forward, neutral and revetse gears are selected then have a look at the short video I made last time I took the leg off to do the saildrive seal.

It's here on my one drive

Might be easier to download and then view it it doesn't play direct from one drive.

https://1drv.ms 120SD cones

 

[Pavalijo]

Thanks Martin.
Do you know what size/pitch your propeller is? What speed do you achieve at around 2200-2500 rpm and when loaded do you slow down to 4kts or less?
Even before we added bowthruster/arch/holding tank and all our cruising gear we struggled to achieve 4kts. Sometimes perhaps just over that in a flat sea.
I use the same Volvo (VDS3 from memory) engine oil for the saildrive, as printed on the saildrive itself. I have not heard that Volvo ever changed their advice for this saildrivee.
I said earlier that the oil has been clear - however in thinking about this, I can say that it is not milky, but have not left it overnight to see if anything settles out.
However if this was clutch slip I would have thought that performance would have deteriorated over the 400+ hours of our useage. There has been a very slight deterioration of quarter to half a knot perhaps, but that will be linked to the additional payload.
I will have a look at the video when back home, thanks, Paul

 

[Pavalijo]

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.

Many thanks for this further advice. The belt tension seems fine and we do not see any black dust on or beneath the alternator normally (after I cleaned the white Balmar following this test). I have a standard V pulley rather than the serpentine conversion.
I will look into the electronic rev counter as I would like to know what the actual rpm is rather than my crude 10-15% over-read guesstimate. I had never heard of such a thing.
The Balmar is switchable from 70 to 35 Amps and I don’t often need it for house battery bank charging, so maybe I will use the lower setting in future to send all available hp to the prop (not that I will notice the difference!)
I’m leaning towards just going with Darglow’s advice (which assumes no clutch slip) and see where we go.
Certainly other S38’s achieve much higher speeds than ours and something is amiss - Darglow agree that the weight will be a factor but not to the extent we are seeing.
We did remove a fair amount of “stuff” at the end of this season but we will still be around 10 tonnes I’m sure.
Even achieving 5 kts will be worth the expense (£1,900 less anything I can get for a very good condition 17x12 LH folder for saildrive and machined for Ambassador rope cutter).
As for new engine and saildrive - that is in my budget as a “might need but hopefully not”!

 

[Pavalijo]

UPDATE
After the posts on here I decided that clutch slip was highly unlikely and so went ahead and ordered a Featherstream from Darglow.
It is set with 14” of pitch (2” more than the previous folder) but I brought out (to Galicia) a replacement cassette to knock it back to 13” of pitch if the 39hp engine struggles - as suggested might be the case on here.
We launched yesterday and I’m delighted to report that at around 2200rpm in a fairly flat sea we saw 6.2kts - in conditions where we would have seen around 3.8kts with the old propeller.
In the middle of the Ria we turned into 12kt headwind and slight swell/chop and speed reduced to around 5.6kts - but we would have been struggling to get more then 3.5 at 2400rpm with the old prop in those conditions.
The alternator was running at its full 70 amps. I’m not sure that turning it down to 35 amps will make any discernible difference, but I’m not sending the spare pitch cassette back to Darglow until we see how the engine copes with a big headwind and sea state.
Many thanks to the contributors to this thread - it gave me the confidence to order the new propeller without paying someone to inspect the saildrive clutch - and saved another year’s delay on something we should have done a few years ago - Calypso is transformed (reversing out of the hoist bay and stopping in the marina berth confirmed that performance astern is also transformed).
Many thanks also for the recommendations on here for Darglow - well deserved.
Regards
Paul