noise from prop shaft

[Danned]

I've got this whooshing noise (sometimes it sounds like screeching/knocking) from the prop shaft, I don't think it's coming from the electric motor. I am feeling fairly confident that the BLDC 10KW motor is working as it's supposed to. I've been working a lot on the alignment (4 days) but I don't have enough experience to know how much of a large hole/gap the shaft can go, so I am now trying to use a laser crosshairs to redo the alignment. It takes an hour to get these bolts off it's so tight to get it aligned in that space.

When I had the old atomic 4, I am not certain I could hear it as it only makes the noise on higher RPM. The atomic 4 was fairly loud and it drowned out any prop noises. Right now with the electric motor when I get to about 2KW that is when the noise is most audible.

I used a stick against my ear to hear to try to pinpoint the noise and I hear it on the shaft, but not on the hull near the stuffing box. I don't hear it on the motor.

https://youtu.be/t5EepJA3fJw - video of under the boat prop in action
https://youtu.be/XtfSnm_n6-k - video of testing play in prop on shaft

I posted a couple of short youtube clips, the first one is video of the noise underwater which sounds weird, and the second is my testing the prop looseness and there is an extremely small amount of play, 1 or 2 mm amount of movement on the prop. Is that enough to wobble and cause that noise or is this still alignment?

[Rusina]

Hello Damned,
Is this NOT a problem with the curvature of the propeller shaft inside the boat at the pulley?
Or the alignment of the pulleys?
This is what comes to my mind, because outside the tube, I do not see ...
Have you installed an intermediate thrust bearing?
Good luck with this.

Bonjour Damned,
Ne serait-ce PAS un problème de courbure de l'arbre d'hélice à l'intérieur du bateau au niveau de la poulie ?
Ou d'alignement des poulies ?
Moi, c'est ce qui me vient à l'esprit, car à l'extérieur du tube, je ne vois pas...
As-tu installé un palier de poussée intermédiaire ?
Bonne chance pour remédier à cela.

EDIT: Google translation added

[Danned]

Thanks Rusina for the reply.

No thrust bearing as I'm using a 1 1/2" timing belt.

I am not certain I understand what you mean by curvature of the propeller shaft at the pulley. As far as I know the shaft is straight but I would have to pull it completely out to test that if you mean the whole shaft. There is only about 1 foot length within the hull, and the stuffing box covers about 3/4 of it, with the remaining space the helper bearing, and pulley.

Both the motor and the shaft pulley are fixed, and cannot move once bolted. I can adjust the alignment of the shaft pulley independent of the motor pulley. To confirm, the tension on the belt edges are equal on the front and back of the belt which is how I know it's aligned 100%.

[Rusina]

Hello,

Given the photos, there can indeed be no deformation of the shaft following the increase in engine speed, this was one of the assumptions.
In addition, if you have taken care of the alignment, which seems to be the case, it must NOT come from there either.
But on the other hand, if there is NO landing thrust inside, the thrust is exerted completely against the outer stern ring and this could explain the noise ...
Finally, this is my hypothesis, without wanting to be definitive.

Bonjour,

Compte-tenu des photos, il ne peut en effet y avoir de déformation de l'arbre suite à l'augmentation de vitesse du moteur, c'était une des hypothèses.
De plus, si vous avez soigné l'alignement, ce qui semble être le cas, cela ne do it PAS venir de là non plus.
Mais par contre, s'il n'y a PAS de pallier de poussée à l'intérieur, la poussée s'exerce complètement contre la bague externe d'étambot et cela pourrait expliquer le bruit...
Enfin, c'est mon hypothèse, sans vouloir être définitif.

EDIT: Google translation added

[BjornO]

No thrust bearing as I'm using a 1 1/2" timing belt.

You must have a thrust bearing as the propeller force is axial, i.e. in line with the shaft. The belt does not take up these forces. A normal ball bearing is OK, but it must be secured to the shaft as well as to the hull.

/Björn

[Danned]

Sorry I did not explain properly.

I attached a fixed bearing, or also called a support bearing between the stuffing box nuts and the shaft pulley. It cannot move 'axially', as it has collars keeping it fixed on the shaft. The support bearing also is fixed to the engine mount via the lower L shaped steel brackets bolted onto the box channel. You can't see it in the photo I attached as it's behind the pulley.

It is on there tight I can't pull or push it any direction. I do understand that the forces to move the boat push the shaft forwards or backwards axially. I am doing reading on this and with some diagrams I do believe this function would be the same as a thrust bearing. I will take a closeup photo and add to this post.

I also wanted to note that I have put a wooden stick on the bearing and I can't hear the noise from there. It is coming from under the boat.

When I totally dismantle and let the shaft free float I can tell by the resistance when I spin it in my hand where the shaft is touching the hull, but it doesn't seem to have much room for error. The middle seems to be a very small point. I am going to try taking it all apart again, and align it, put a laser crosshair on it where I think the least resistance is and then reattach all the bolt and frame hardware where the laser crosshair is. I'm still thinking it has to have some slight alignment issue.

I appreciate the feedback, it is keeping me thinking about the design of the whole thing....

[Rusina]

Hello,
After all these details that you give,
You seem to have done it right.
I therefore see nothing better to offer you but I am sure that you will find the origin of this noise eventually.
Good luck.

Bonjour,
Après toutes ces précisions que vous donnez,
Vous semblez avoir fait les choses comme il faut.
Je ne vois donc rien de mieux à vous proposer mais suis certain que vous finirez par trouver l'origine de ce bruit.
Bon courage.

EDIT: Google translation added

[Bikemad]

I attached a fixed bearing, or also called a support bearing between the stuffing box nuts and the shaft pulley. It cannot move 'axially', as it has collars keeping it fixed on the shaft. The support bearing also is fixed to the engine mount via the lower L shaped steel brackets bolted onto the box channel. You can't see it in the photo I attached as it's behind the pulley.
It is on there tight I can't pull or push it any direction. I do understand that the forces to move the boat push the shaft forwards or backwards axially.

There is an extremely small amount of play, 1 or 2 mm amount of movement on the prop. Is that enough to wobble and cause that noise or is this still alignment?

Hi Dan, here are some of my thoughts:

If there is no axial movement in the propeller shaft at the pulley end, but you have 1-2mm movement in the prop, either the prop is loose on the shaft or there is excessive radial movement in the rear strut bush/bearing (assuming it is a one piece propshaft).

If you do have 1-2mm movement between the outside of the shaft and the inside of the rear bearing, I would not consider that to be a "small amount".

Take a look at this article on boatingmag.com for more useful information. including the bit about the spacing between the propeller and the strut.

It is difficult to see clearly in your video, but it looks like your propellor is very close to the strut and might even be touching against it whereas there is a definite visible gap between the other end of the support and the sacrificial zinc anode.
I would say that the shaft needs to be moved back at least 10-15mm.

Try to ensure that the driven pulley is located as close as possible to the support bearing to minimise the bending force being exerted upon the shaft from the belt when under high tension.

30Nm of motor torque would produce ~600N of tensile force within the belt which causes an axial force to be applied to the end of the pulley end of the shaft. The distance from the fulcrum point (centre of the bearing) to the centreline of the pulley will greatly affect the amount of bending force being applied to the shaft.

Ideally there should be a support bearing on either side of the pulley to eliminate the bending forces completely. Let's not forget that the original engine (if properly aligned) would not have exerted any bending force on the shaft whatsoever. 

Alan
 

[Danned]

Updated photos of the support bearing and the laser to align the pulley. Appreciate the feedback, I read that article Alan I was looking for one like that, thanks for pointing it out.

Thanks also for the reference to the thrust bearing, and the distance between the propeller and the cutlass bearing. I am going to see if I can gain a little extra separation by working with the pulleys and see if I can push the shaft any further.

I stuck a laser crosshair on the front of the shaft pulley, after taking apart all the supporting brackets and bolts, and free spinning the shaft in my hand I was able to find that the center was 1 washer too much to port. I removed one washer separator on the starboard side and this largely got rid of the noise. It also turns easier in my hand. There seems to be some fixed guide on the starboard side that won't let the shaft move any more to starboard so it's about 1mm off of it.

As for the play in the prop, it is not the shaft that is moving around, just 1-2 mm movement on the prop. It must be moving and sometimes wobbling during use. I'm going to swim again under the boat and see if I can tighten it somehow. When I go from forward to reverse I hear a small knock which doesn't repeat so I am assuming that this is somehow related to the play in the prop. It's an old boat, it supposed to make noises right?

[Bikemad]

Hi Dan,

I have just been studying this photo:



It looks to me as if the retaining collar immediately behind the bearing has been rubbing against the brass/bronze nut assembly behind it at some point.

Is it possible that the knock you are hearing when you go from forwards to reverse is the entire propeller shaft and collet moving backwards, or does the inner race of the bearing have a grub screw to prevent the shaft from moving within it?

Alan
 

[BjornO]

Does the visible ring with screw on the photo take up the propeller force? In that case it uses the bearing when moving forwards and leans against the brass nut when moving backwards. If so, you need another ring atached to the shaft at the other side of the bearing to take up the force when moving backwards.

[Danned]

ok thanks for the help! I think I found the issue, my propellor castle nut is slightly loose. I swamn under the boat and was able to move it slightly with a wrench. The cotter pin is stopping it but I don't think it is supposed to move. I am guessing that the noise I am hearing is the prop slipping on the shaft. It doesn't have a key-slot.

I am going to pull the boat out and reseat the prop on the tapered shaft and tighten down the nut.

To answer your question on the support bearing photo the silver collar is on one side, with a threaded screw that stops the shaft from moving in one direction. The other side has a black collar which stops it from moving in the other direction. Hard to make out as you can't see the screw on the black one.

I also measured the space between the prop and the cutlass bearing and it is 1.5" so there is enough clearance.

Fingers crossed that this loose nut is my issue. With the old atomic 4 running it was so loud I couldn't hear the prop noise so it likely was doing it last season too.

[Raedy07]

hello,

there really shouldn't be any play of prop/shaft/cutlass bearing. bearing is old?  then, seing your pulleys, your prop must be super high-speed. amplifies any misalignment noises.  and, judging by that crosshair pic, alignment is not good.

something I noticed: why is your motor under d shaft, at bottom of potentially wet bilge? under a dripping stuffing box?? i'd put it as high-as-possible; with reasonable length of belt of course. would make alignment&maintenance easier too.

finally - how is motor-pulley fixed to shaft, set-screw only?

cheers,
Radek

[Raedy07]

PS   sorry, just noticed I confused your motor&shaft pulleys; your motor is of course on top, with d smaller pulley   

[Raedy07]

i have d same motor; make sure you can turn it over by hand. mine had a loose washer inside (brand new!)  which blocked it and 1 coil burned b4 I stopped it