J-Prop - How much play is ok?

[Warby12]

Hi there We have vibration in our shaft that is causing our lip seal to leak water while under power. The faster we go the more water. We have just had the engine realigned but we do have a Vetus flexible coupling that I know can make alignment much harder.

There is a definite "thump, thump thump" back in the aft cabin. Boat was recently hauled and everything including the cutlass bearing looked fine. My thoughts are either:

• Bent shaft (ouch)
• Out of balance prop
• Loose prop

So that brings me to my question, we have a J-Prop feathering prop which to me had a lot of play when handled at the last haul. Maybe 2-3 mm up / down at the end where the anode goes. Is this bad? The propeller guy we had there said that was normal for them.


Does anyone have an idea regarding this? If the prop was shaking around on the end of the shaft that would explain the vibration and actually be easier to fix than a bent shaft which requires new shaft and lifting the engine out


Thanks for any advice, Steve

[Pete7]

Is this movement from the main body of the prop moving whilst the shaft remains still?

Pete

[Warby12]

Hi Pete, yes, the main body of the prop against the shaft.

[EWOL Props]

A play of 2-3 mm is a big one, not only you generate vibrations but also you might risk to lose that prop.

[Pete7]

Agreed not good. Has it ever worked okay without vibration?

I guess this isn't the original prop for this yacht. If so has someone put a metric prop on an imperial shaft so taper 1:10 on a 1:12 shaft?

Either way it need sorting. Just done mine but it was the cutlass bearing which failed due to sailing in muddy waters and parking the boat on mud banks when the tide goes goes out.

[Warby12]

Originally Posted by EWOL Props

A play of 2-3 mm is a big one, not only you generate vibrations but also you might risk to lose that prop.

Yeah that's what I thought! But the propeller guy said it was normal and we went back in the water on that basis. It may well be normal but I wish I could work our where our vibration issues are coming from so that if we have to haul out we can sort it out. It would actually be cheaper to fit a new fixed prop than have to pull the engine, replace the shaft etc etc

Thanks EWOL

[Warby12]

Originally Posted by Pete7

Agreed not good. Has it ever worked okay without vibration?

I guess this isn't the original prop for this yacht. If so has someone put a metric prop on an imperial shaft so taper 1:10 on a 1:12 shaft?

Either way it need sorting. Just done mine but it was the cutlass bearing which failed due to sailing in muddy waters and parking the boat on mud banks when the tide goes goes out.

Thanks Pete. No it's not the original prop but it has been on since we bought it and the noise as well. We changed the old traditional seal for a new lip seal type which has now started to leak from the vibration and movement (not the seal's fault). Maybe the previous owners bought a fancy folding prop that didn't fit?

[SV Bacchus]

Originally Posted by Warby12

Yeah that's what I thought! But the propeller guy said it was normal and we went back in the water on that basis. It may well be normal but I wish I could work our where our vibration issues are coming from so that if we have to haul out we can sort it out. It would actually be cheaper to fit a new fixed prop than have to pull the engine, replace the shaft etc etc

Thanks EWOL

Not to be a SA but several have said that amount of play isn't normal and probably IS the cause of the vibration and thumping. I think I would start there as it seems obvious.

Now my dumb question of the day: Since a lot of folks keep their fixed prop as a spare with putting on something fancy, can you find it stowed away somewhere and put it back on without pulling the vessel? If so you might have a quick, and free, answer to the issue of too much play..

[Warby12]

Originally Posted by SV Bacchus

Not to be a SA but several have said that amount of play isn't normal and probably IS the cause of the vibration and thumping. I think I would start there as it seems obvious.

Now my dumb question of the day: Since a lot of folks keep their fixed prop as a spare with putting on something fancy, can you find it stowed away somewhere and put it back on without pulling the vessel? If so you might have a quick, and free, answer to the issue of too much play..

Yes I do have an old prop in the bilge but is huge about 24inch diameter. Haulout booked for next Friday

[Warby12]

We think we have found the problem! The feathering propeller is loose!

Can we beg some advice? It looks like the thread length is too long. The manual states maximum thread length of 27mm to fit the propeller. I'm pretty sure ours is 27.5mm and the retaining nut is bottoming out on the end of the shaft, stopping it from being tight on the taper!

Do you think there is a problem in grinding or cutting 1 or 2mm's off the end of the shaft?

[Cruisingscotts]

Some shafting has to be modified going from a fixed prop to feathering depending on the brand, yours may have already been cut down but not enough. A fixed blade shaft would have taper with keyway threads and most likely a step down straight cut on the end with a hole thru for a cotter pin In the prop nut. With that said it is also common for the keyway to be milled from its set depth up to flush as it run out on the taper at the shaft side. This means the key for the prop is ground to match this run out, if the prop was installed at some point with the key not in the proper position it can move fwd on the shaft lifting up from its correct depth. The propeller would tighten on the shaft but not be making proper contact with the shaft and be loaded only in small places. Running this way will wallow out or deform the ID of the prop hub causing a poor fit. I would highly recommend removing the prop and key and cleaning then do a fit test for proper contact and depth. Use machinist bluing or have a prop shop check. Any repair done now is a lot cheep than a new prop or shaft or worse

[fstbttms]

Originally Posted by Warby12

Do you think there is a problem in grinding or cutting 1 or 2mm's off the end of the shaft?

No. This action is a necessity in many Max Prop installations.

[Warby12]

Ok, thanks guys. I might just ponder it today and do the deed tomorrow. Wish me luck haha

[Warby12]

Problem solved :bigg rin:

The prop was incorrectly fitted. There can only be a maximum of 27mm of thread on the end of the shaft. Trimmed carefully (and with a fair bit of terror) the prop now fits perfectly and the boat is transformed!

Very happy and thanks for everyone's help