Sheared Prop Key? Or Transmission Issue?

[dcondit]

I had a shaft key sheer once off shore. Prop didn’t work in forward or reverse. Of course, it was dead calm and I needed the engine. I managed to use the battery to weld some fork tines together to make a temporary key that at least got me to some wind.

[KelseyB]

Originally Posted by Bellinghamster

Get yourself a photo or laser tachometer ($20 on Amazon) and compare the engine RPM-to-shaft RPM ratio at idle and high-ish RPM in both forward and reverse. This'll tell you for sure whether the transmission is slipping.

If the engine to shaft ratio is constant, either you've got a sheared (or missing) prop key, plastic bag or other flotsam wrapped on your prop or it's REALLY fouled.

There's also likely a key at shaft coupling. Make sure you're not spinning your coupling on your shaft (although that would have almost surely backed the shaft out of the coupling when you were in reverse.)

That's a good suggestion—first thing we're gonna do is try and narrow it down to just the transmission, if that's what it is. We're gonna dive again and try to rotate the prop by hand with the transmission in gear (off, of course, but in gear), and if the prop can spin, then it's probably the key. But if it's not, then we might go this route.

[KelseyB]

Originally Posted by bil56

so, have you disconnected the cables and operated the control lever by hand?

and what color the oil?

We haven't done all that, but haven't felt it necessary because we can see the cables engaging and watch the shaft turning.

Oil and transmission fluid are brand new, only hours on them are the ones from trying to resolve this issue.

[Wotname]

Originally Posted by KelseyB

.......... But in forward, I'm getting plenty of prop wash, but not any substantial amount of forward thrust; not enough to put any strain on the docklines or even enough to counteract the current even at 1500-2000 rpms, and there is a lot of noise and vibration. ................

Where are you seeing this wash?

With the rudder centred, it should be seen well and directly behind your stern. If you see all around the stern area, the your prop is fouled and you are not creating any thrust with the prop. The prop is only throwing water around in every direction rather than creating thrust.

Go swiftly from idle to WOT (in forward) and you should see a large swirl of water some yards directly behind the stern. If you see the wash on either side of the hull, there is no thrust.

I bet your problem is the fouling on the prop, it doesn't take much.

[c.K.]

you may have hit something??!

[skipperpete]

Originally Posted by KelseyB

It's a Volvo MS-15L. We also suspected that the diaphragm could've blown from the excess fluid, but then dismissed it because if that wee the case we wouldn't have forward or reverse.

The gearbox is actually a ZF hurth rebranded to volvo and the method of checking the oil level is by unscrewing the dipstick, wiping it clean and then replacing it in the hole but not screwing it in, could your method differ from the mechanics dip? Overfilling a ZF Hurth would probably not cause the symptoms you describe. Is your mention of “the diaphragm”
a reference to the drive plate that connects the engine to the gearbox input shaft?
I’m going with the “shelled up propeller” suggestion of previous posters

[gonesail]

barnacles on a prop will stop you in your tracks.

[Audeamus]

Was the correct oil used in the service. Multigrade oils will cause some transmissions to slip....

[bil56]

I'd asked about oil ...

[Rumrace]

Sounds like clutch or coupling. Kick the mechanic who overfilled it. If the prop has a wooddrift key they rarely sheer unless the prop is hit.
You may consider a prop nut anode

[KelseyB]

Originally Posted by Wotname

Where are you seeing this wash?

With the rudder centred, it should be seen well and directly behind your stern. If you see all around the stern area, the your prop is fouled and you are not creating any thrust with the prop. The prop is only throwing water around in every direction rather than creating thrust.

Go swiftly from idle to WOT (in forward) and you should see a large swirl of water some yards directly behind the stern. If you see the wash on either side of the hull, there is no thrust.

I bet your problem is the fouling on the prop, it doesn't take much.

This is a good point—I do think the wash is more spread out than usual, although I didn't notice that at first because the prop is pretty close to the surface (reachable by hand without putting your head underwater), so the wash is usually a bit more spread out than most prop washes I've seen.

[KelseyB]

Originally Posted by c.K.

you may have hit something??!

Usually I'd say that's definitely possible, but 1) I've hit things before (a submerged traffic cone comes to mind) that didn't have any affect because the prop is pretty well-guarded and 2) this happened all of the sudden without the boat going anywhere. One day, everything was fine, then it wasn't, without ever leaving the slip in between.

[KelseyB]

Originally Posted by Audeamus

Was the correct oil used in the service. Multigrade oils will cause some transmissions to slip....

Yes—we provided our own oil and transmission fluid to the mechanic, straight from a Volvo dealer. Used the exact same stuff that's been in the engine and transmission their whole life. ATF for the transmission.

[KelseyB]

Originally Posted by gonesail

barnacles on a prop will stop you in your tracks.

This is what we're pretty confident it is at this point. Does anyone have any pro tips on scraping barnacles in the water when the river is full of sea nettles and so cloudy you can't see inches in front of your face? That's been our main issue with diving so far; long sleeves and long pants have helped with the nettles, but the lack of visibility has been a real issue.

[fstbttms]

Originally Posted by KelseyB

This is what we're pretty confident it is at this point. Does anyone have any pro tips on scraping barnacles in the water when the river is full of sea nettles and so cloudy you can't see inches in front of your face? That's been our main issue with diving so far; long sleeves and long pants have helped with the nettles, but the lack of visibility has been a real issue.

Jeezus, just hire a diver already.