Saildrive with a brake.

[Sneaky Pete]

I have a Yanmar 3YM30 connected to a SD20 saildrive. The problem is that if boat has been motoring for a period of about an hour or so I am approaching a pontoon or other mooring and have to engage reverse to manoeuvre when revving the engine to apply power to the prop there is no revs but there is a bit of blueish exhaust smoke. It appears that the gearbox in reverse has applied some kind of brake and is straining the engine. Just engaging the engine in reverse at idle will move the boat backwards prop seems to be in reverse but applying engine revs engine does not rev.
Has anyone came across this problem and been able to diagnose the fault?

 

[JumbleDuck]

Have you checked the gearbox oil level?

 

[Lucky Duck]

Or possibly something hanging off the prop, this summer some we had a load orange fishing 'twine' round the prop which occasionally would stop the blades unfolding properly leading to the odd interesting moment until the other half swam down and cut it off.

 

[Sneaky Pete]

Oil level is good that was my first thought. Saildrive does work perfectly forward and back when boat has not been motored for a longer period of time an hour or more, but struggles to rev in reverse after this time it is like something in the gearbox is preventing the shaft from turning faster than idle. Disengaging the gear selector and revving engine in reverse works fine.

 

[JumbleDuck]

Oil level is good that was my first thought. Saildrive does work perfectly forward and back when boat has not been motored for a longer period of time an hour or more, but struggles to rev in reverse after this time it is like something in the gearbox is preventing the shaft from turning faster than idle. Disengaging the gear selector and revving engine in reverse works fine.

Without a drawing of the workings I am guessing wildly, but I wonder if it's a problem with forward gear staying partially engaged, so its cone clutch is dragging. How long does it take matters to resolve - is it ok after 30 seconds or do you have to wait until everything has cooled down?

 

[Neeves]

I don't know the sail drive unit, but have you checked that the morse cable is actually activating reverse at the SD itself.

 

[sailaboutvic]

Do you have a folding propeller? Mine take a little while before it bits

 

[johndove]

Is it a kiwi Prop?

 

[Sneaky Pete]

Without a drawing of the workings I am guessing wildly, but I wonder if it's a problem with forward gear staying partially engaged, so its cone clutch is dragging. How long does it take matters to resolve - is it ok after 30 seconds or do you have to wait until everything has cooled down?

This may be the answer as once the engine has cooled everything works well. I am considering removing the cable and manually engaging the gears but don't know what it will prove.

It is a Kiwi prop but like all props like this engage gear wait momentarily and apply revs. What is worrying is the engine does not rev and the blueish smoke (unburnt fuel) that comes from the exhaust.

 

[VicS]

This may be the answer as once the engine has cooled everything works well. I am considering removing the cable and manually engaging the gears but don't know what it will prove.

It is a Kiwi prop but like all props like this engage gear wait momentarily and apply revs. What is worrying is the engine does not rev and the blueish smoke (unburnt fuel) that comes from the exhaust.

I agree. Disconnect the remotes.
Engage forward locally, check that you can rev the engine locally, check that the prop spins normally.

Then engage astern and try to rev the engine. If it wont rev it suggests that there is gear box fault or something obscure wrong with the prop

 

[Slipperman]

Since it is a Kiwi prop it is most likely just the reversing rollers which have got gummed up and need freeing. This happens to mine occasionally towards the end of the season, when they get covered with a sort of calcareous deposit. If you can get to them (e.g. with a snorkel or dried out), all you need to do is twiddle them a bit to free them up and remove any fouling.

 

[Neeves]

First up I'd have someone apply forward, with revs, then reverse with revs and I would watch how the morse cable is acting. Our Volvos have the lever for the gear change linkage 'secured' by simply tightening a bolt if this slips, even slightly, then the morse cable will engage one gear but not the other. The alignment is fairly critical (as I found when I had to replace a morse cable).

Once you have confirmed the cable and linkage is correct then I'd try manually altering gear and raving the engine, though I suspect you will need to remove the gear change morse cable first as (from distant memory) it might be difficult to change gear with it attached (but maybe a big adjustable will overcome the resistance).

If the prop was not opening surely a closed prop would simply spin (at whatever revs were imposed) but unopened. You seem to suggest, or its my understanding that when you engage gear and throttle then reverse is not engaged and revs do not increase (which again surely) has nothing to do with the prop.

If the morse cables are not correctly adjusted the symptoms you describe might eventuate.

 

[Slipperman]

The Kiwi is a feathering prop, not a folding prop, so the blades are always 'open'. The reversing rollers allow the blades to set themselves to astern pitch once astern gear is selected and the shaft rotates the other way. If the rollers get stuck, this doesn't happen, so although you get some astern power (because the shaft is going astern), the blades don't go to their optimum setting so you don't rev properly in astern. I find that if I have a mid season scrub off and clean up the prop/rollers then I don't usually have a problem but if the hull/prop gets badly fouled that is when these symptoms appear.

 

[Neeves]

I understand.

its easier to check that reverse is engaged than to swim and check the prop (or worse) lift and check the prop.

The OP has not confirmed that he has even engaged reverse, he might have put the engine control into reverse - but that's not quite the same as the sail drive being IN reverse.

I'm into checking the simple (or cheap) things first - I'm not disagreeing with either Slipperman nor JD

 

[prv]

The OP has not confirmed that he has even engaged reverse, he might have put the engine control into reverse - but that's not quite the same as the sail drive being IN reverse.

Well, it's not in forward or he'd have known by the boat shooting forwards, and it's not in neutral because something is resisting the engine turning (lower revs, and blue smoke from the load). I don't know anything about Kiwi props, but if they can get stuck in a kind of paddle-wheel configuration with the blade faces parallel to the shaft axis then that seems like it could create excessive resistance and produce the stated symptoms.

Pete

 

[Tranona]

Well, it's not in forward or he'd have known by the boat shooting forwards, and it's not in neutral because something is resisting the engine turning (lower revs, and blue smoke from the load). I don't know anything about Kiwi props, but if they can get stuck in a kind of paddle-wheel configuration with the blade faces parallel to the shaft axis then that seems like it could create excessive resistance and produce the stated symptoms.

Pete

That is one of the weaknesses of the Kiwi as it relies on centrifugal force when reversing direction rather than the normal positive gear activation. So when the rollers foul the direction of rotation changes, but the blades stay in the forward position and give the symptoms described. Can also happen that the blades do go into reverse and then stick when you want to go forward.

The instructions are clear from what I remember when I read them about the importance of keeping the swivel pins and rollers free of fouling.

 

[VicS]

That is one of the weaknesses of the Kiwi as it relies on centrifugal force when reversing direction rather than the normal positive gear activation. So when the rollers foul the direction of rotation changes, but the blades stay in the forward position and give the symptoms described. Can also happen that the blades do go into reverse and then stick when you want to go forward.

The instructions are clear from what I remember when I read them about the importance of keeping the swivel pins and rollers free of fouling.

Would a prop stuck in the feathered position give the symptoms, viz failing to rev plus blue smoke, that the OP describes.

Curious that it seems to work OK when the engine is cold.

 

[Tranona]

Yes. The blades would be parallel to the waterflow and therefore at roughly 90 degrees to the direction of rotation. The issue with the sticking rollers is because they are not used so much.

The only way to find out is to either dive, lift the boat or dry out to clean the prop.

 

[johndove]

That's why I asked if it was a kiwi Prop. The blades stick in featherd position and cause a paddle wheel effect and stop revs building. Happen to me and Wear on blades. The boat next to me had a broken or jamed saildrive caused by the same.

Never used the kiwi Prop again. Not worth the Risk! Just in case the same happened going into a berth or another time I needed to Brake!

 

[Lucky Duck]

A friend's Kiwi prop shed at least two of its blades while entering the lock at Shoreham last summer!

I notice the OP seemed to ignore any suggestions regarding issue with the prop but as an aside my understanding is the SD20 has a dog clutch rather than the cone arrangement.