Vovlo Penta D3 190 with Sterndrive F2 Duoprops

[Jackolas]

I am having a problem after snagging a mooring line in the props. The engine cut out when I snagged the line, so I cleared the rope and restarted the engine. Everything seemed fine when I left my mooring. When I increased the revs, the boat started to speed up, but there didn't seem as much power, only reaching 15knots at 4000 revs as opposed to normal which is about 25Knots.
It doesn't feel like a slipping clutch as the engine performs normally.......the revs don't race up while in gear. After advice, I've taken the props off to see if there was a problem with rubber bushing inside the props, but the guy who looked at them said everything seems really tight and nothing turns under force and he thought that the problem wasn't the props! I presume it's now time to get it lifted out for more investigation into the drive train!
Can anyone help with what's the next thing to look at?
Many thanks

 

[Portofino]

Maybe the smaller weaker drive shaft ( or componant of ? ) of one of the duo props has seperated .
So it's only really powering one prop now .
The bigger stronger one held on and stalled the engine .
Difficult to accurately Dx with out an examination .

 

[Jackolas]

Thanks for your reply.........That's what I was wondering. It would make sense that only one prop is providing thrust, but when I removed the props, the drive shaft and splines all looked good. So could I get the same symptoms with a problem further back along the drivetrain?

 

[julians]

Was it a proper propeller person who looked at the prop bushes? To the untrained eye you can have a spun bush that still feels tight when turned by hand.

Assuming there are no untoward noises coming from the drive, It most likely it just a spun bush in the prop imo.

 

[Portofino]

Try twisting them in N
If they don,t " duo " --ie are linked then somthings seperated inside the leg .
How ever the fractured edges may hand turn ,but not turn when Hp and water resistance is applied .

You have put them back on the right way round ,iam assuming its not possible to put the second one on wrong way round ?or have you mixed up the port n starboard of a twin set up ? you have not said if a single or twin ,ie took off 4 props and refitted in the water ?

 

[[2068]]

...the guy who looked at them said everything seems really tight and nothing turns under force ...

Under force?
Really?
How much force?

A D3-190 accelerating can generate maybe 390Nm.
If the outdrive ratio is 1.95:1 that's something like 760Nm acting on the prop.

I reckon I could maybe apply 300Nm with a torque wrench, although something in my back would probably go "sproing".
But 760Nm?
How would you test that?

Does your mechanic look anything like this?

As above, the most likely scenario is that one or both of the rubber hubs inside the props are slipping.

.

 

[Portofino]

Under force?
Really?
How much force?

A D3-190 accelerating can generate maybe 390Nm.
If the outdrive ratio is 1.95:1 that's something like 760Nm acting on the prop.

I reckon I could maybe apply 300Nm with a torque wrench, although something in my back would probably go "sproing".
But 760Nm?
How would you test that?

Does your mechanic look anything like this?

As above, the most likely scenario is that one or both of the rubber hubs inside the props are slipping.

.

Why would an engine stall if the bush,s are slipping ? Surley as they "bush " as designed they naturally disconnect to protect .
To stall the rope has overcome the torque that was available and the alledged " bushed " prop has not occurred

So big rope or tiny torque .

 

[[2068]]

Reading the original post again, the rope was large enough to stall a running diesel engine.
The forces needed to do that are large - by definition, larger than the torque being produced by the engine, otherwise it would not have stalled.
It's possible that this stall didn't cause any hub slippage.
But it's also possible that it did slip as the engine revs reduced to zero with the prop locked by the rope, so it's something I would check first before stripping down the drives.

As you say, it's also entirely possible that a shaft has sheared, but this can be checked in 5 minutes by lifting the drive in neutral (engine off ) and spinning one prop by hand. If the other prop doesn't rotate in the opposite direction, then a broken shaft or gear is likely. If was fractured but turned by hand, I'd guess you'd hear some very unhappy noises coming from the drive under load.

.

 

[Jackolas]

Thanks for your comments guys. The guy who looked at the props is a beta engine engineer, so not a 'prop guy'! and although he's is a big lad, he doesn't look like the picture!!;-)
it is a single engine drive and before I took the props off I did hand turn them and they both rotated together. There are no unnatural noises coming from anywhere and as I said, it does push the boat along at around 15knots.
So do you think the best bet is to get the props looked at again by an expert before lifting the boat out to investigate further?
Many thanks.

 

[julians]

Thanks for your comments guys. The guy who looked at the props is a beta engine engineer, so not a 'prop guy'! and although he's is a big lad, he doesn't look like the picture!!;-)
it is a single engine drive and before I took the props off I did hand turn them and they both rotated together. There are no unnatural noises coming from anywhere and as I said, it does push the boat along at around 15knots.
So do you think the best bet is to get the props looked at again by an expert before lifting the boat out to investigate further?
Many thanks.

Yep,sounds like a spun prop hub to me, easy to fix if thats what it is.

 

[No Regrets]

It doesn't take much to stall a Diesel engine at low revs. A small rope could easily do it! My Volvo 165's were both stopped quite horribly by an old tent, and took a bit of to-and-froing to get moving again, and a while with cutters to get the basted tent and pole off...

 

[Jackolas]

It doesn't take much to stall a Diesel engine at low revs. A small rope could easily do it! My Volvo 165's were both stopped quite horribly by an old tent, and took a bit of to-and-froing to get moving again, and a while with cutters to get the basted tent and pole off...

You shouldn't have been driving around a campsite!!! ;-)

 

[Jackolas]

Update to my issue!!!!
I marked both props and re-fitted them and took the boat for a blast. When I checked them both, neither had slipped! So now I am back to square one without a paddle!
Does anyone have any other ideas as to whats going on? As I said before, everything thing seems/sounds normal. There is no racing of the engine like a slipping clutch, the engine gets to its normal revs, about 3800, no weird noises coming from anywhere - just doesnt get up to its normal top speed of 25 knots, only gets to about 17.

 

[julians]

Presume the boat only has a single engine?

 

[Chris_d]

Just sounds like the usual dirty bottom and marginal power to get over the hump, how long has it been in the water?
Either that or the old D3 turbo / wastegate issue.

 

[Jackolas]

yes, single engine

 

[Jackolas]

Been in the water since middle feb this year, freshly anti-fouled. Someone did say that it could just be a dirty bottom!
Its moored on the Hamble in Hampshire and a lot of people have said that this year has been particularly bad.
Could that really cut 8 knots off the top speed and stop it getting on the plane??

 

[[2068]]

That's very strange.
Fouling could cause that sort of speed loss, but it would have to be bad: you would see it.
Are you measuring the speed from a GPS ?

The only other thing I can think of is that the rope incident damaged a prop blade, but I'm assuming you've checked to make sure they are prop shaped and not cauliflower shaped?

 

[Jackolas]

When I took the props off they and the leg were proper covered in weed. The onboard speed log has just stopped working.....more weed I presume. Just didn't realise that weed could cause that much of a speed loss.

 

[Jackolas]

The only other thing I can think of is that the rope incident damaged a prop blade, but I'm assuming you've checked to make sure they are prop shaped and not cauliflower shaped?[/QUOTE]

Yeah the props are in good condition