prop pitting, repair or not ?

[BartW]

after cleaning the props on Blue Angel,
the yard discovered a few points of prop pitting (is that how you call the small holes ? )
caused by cavitation,

this is the worsed spot:

there are a few more spots on the other blades of this prop, but a lot less than on this blade.
the other prop has almost none.
I'm not sure if this is recent, or if this is there since many years,

coincidently the surveyor (for the coding) was there the day before (props not yet cleaned)
he hammered on all blades, and all sounded the same.
he commented: if they sound different, you would be in for some serious spendings


well the yard proposed to take off the prop and have it repaired,
but the quoted price was staggering. (2500 euro/prop)

should I worry / have this repaired,
or just wait another season and see if it gets worse,
is there a possibility for DIY repair, filling the holes with... ?

thanks for advice

 

[omega2]

Are you sure it is cavitation? what are you anodes looking like.

 

[BartW]

Are you sure it is cavitation? what are you anodes looking like.

I'm not sure, that's what the yard manager told me,
and all pitting appeared in that area of each prop

the anodes looked all well eaten up (20...40% gone)
similar last year and the year before

all underwatergear looks in very good condition, (even after 21yo)
the fouling was really not that severe, compared to some pictures I ve seen on here, and confirmed by the yard.

 

[jfm]

Bart that is cavitation. Quite normal, being close to the hub as shown in your pictures. IMO you must get that repaired, by weld not by filler. If you don't the blade will snap off. A friend with manhattan 70 had exactly the same last summer and lost a blade in Ibiza. It ruined a cruise and cost loads more to get a new prop flown out and fitted, etc. €2500 is cheap compared to that. But surely if the boat is already OOW you can get this done for less cost?

 

[Fantasie 19]

Interesting, as a raggie, I had no idea cavitation could do that.... amazing what abrasive quality a bit of salt water and air (under pressure) can cause..

Is that little silver patch to the right a previous fill/repair do you think???

 

[DAKA]

after cleaning the props on Blue Angel,
the yard discovered a few points of prop pitting (is that how you call the small holes ? )
caused by cavitation,

this is the worsed spot:

there are a few more spots on the other blades of this prop, but a lot less than on this blade.
the other prop has almost none.
I'm not sure if this is recent, or if this is there since many years,

coincidently the surveyor (for the coding) was there the day before (props not yet cleaned)
he hammered on all blades, and all sounded the same.
he commented: if they sound different, you would be in for some serious spendings


well the yard proposed to take off the prop and have it repaired,
but the quoted price was staggering. (2500 euro/prop)

should I worry / have this repaired,
or just wait another season and see if it gets worse,
is there a possibility for DIY repair, filling the holes with... ?

thanks for advice

I used to get damage that looked identical to that on my last boat (aluminium props).
Cavitation.
tried filler but it only lasted a few miles.

a blade would shed every 1000 -2000 nm but not from the pitting point.

In my case it was caused by the front counter rotating prop.

Yours problem could be

poorly finished leading edge on the prop (note mark on the leading edge , is that smooth from turbulence where a stream of bubbles has been sent towards your pitting or where a barnacle did the same ??)

P bracket damage poor design sending bubbles towards pitting .

or assuming all the above were manufactured by experienced engineers my best guess is

Shaft anode

You dont need shaft anodes, they are a throw back from steel ( stainless) shafts and brass props.

Modern types of stainless steel and Bronze props are made from metals with very similar electronic properties and you no longer get a current passing between the two ( unless of course you add a dissimilar chunk of Zinc and crate a battery).

Just for clarity, Im not suggesting the anode is causing the damage from electrolysis, the shaft anode could be causing excessive bubbles.

I am interested to hear if the prop leading edge where it joins the hub was clean on lift out


Good luck with it Bart, I went through about 4 sets of props in 5 years and never did get mine sorted.

 

[MapisM]

IMO you must get that repaired, by weld not by filler.

+1.
Was the quoted price just for re-welding the holes, so to speak, or for an overall renewal, including a proper balance?
If the latter, it's still expensive, but not as outrageous as for the first...

 

[Latestarter1]

+1.
Was the quoted price just for re-welding the holes, so to speak, or for an overall renewal, including a proper balance?
If the latter, it's still expensive, but not as outrageous as for the first...

Yes I am with everyone on this except the price of repair!!!

There are at least three companies in UK which would be prepared to re-weld fettle and fettle for substantially less than price quoted.

 

[MapisM]

Well, I did say it's still expensive!
Just curious, for what sort of money do you think they could be done in the UK?
Mind, they are pretty substantial props, by heart I'd say around 20", if not more...

 

[Hurricane]

Yes I am with everyone on this except the price of repair!!!

There are at least three companies in UK which would be prepared to re-weld fettle and fettle for substantially less than price quoted.

Agreed
Hamble Props for example - good experience from them
Rewelding props IS expensive but not that much IMO

 

[BartW]

Is that little silver patch to the right a previous fill/repair do you think???

all patches, different colloration, are stains from the chemicals they have been using to clean the prop,
or just light reflections on grinded surfaces.. I think.
I didn't see any fillings / repairs when inspecting the prop myself.

 

[BartW]

I am interested to hear if the prop leading edge where it joins the hub was clean on lift out

really don't know,
didn't look at it in detail on lift out,
now I learned here what to look for on a next occasion.

 

[BartW]

Was the quoted price just for re-welding the holes, so to speak, or for an overall renewal, including a proper balance?
If the latter, it's still expensive, but not as outrageous as for the first...

good question MM,
I forgot to asc, as I was impressed with the price when he told me,
but wondered myself after considering doing the work here locally in B

I'll try to get a price indication from 2 prop repair co's, one in B and one in NL,
and then decide if I will pay the SOF inflated price (if ballancing is included)
or having all the hassle myself, taking them off, bringing and recovering them to the repair co.

coincidently the boat is coming two weeks OOW, and I have two travels by car (B-SOF-B) during that period of time

despite the fact that there are probably several good prop service co's,
I don't fancy sending the props to UK,
even more hassle, packing, arranging transportation, ...

 

[cryan]

That is certainly cavitation pitting. It can be bronze welded and dressed up but will probably require balancing. Have the whole prop polished. Cavitation can be caused by incorrect prop speeds, ie too fast. As for price? Well that depends on the size of the prop and the hours required. I suspect the welding, polishing and balancing will be the bulk of the cost as pulling it off and replacing is a faily quick job. Bronze welding is a speciality so the guys that do it can charge a fortune.

 

[jfm]

probably require balancing.

If done by skilled peole it won't require balancing. Out of balance effect is proportional to the square of the radius, and this work is near the hub, plus the thing is only spinning 800rpm, so if there is a gram too much or too little weld it wont make any difference ihmo

 

[MapisM]

J, I'd rather have them polished and balanced anyway.
Ideally, it would be a good idea also having them checked by someone who has the proper equipment for scanning the blades (as done in M2) and if necessary adjust them.
Not because I disagree with what you're saying, but because those props made their fair share of work, and cavitation might have something to see with them not being anymore 100% kosher, in some respect.

 

[BartW]

If done by skilled peole it won't require balancing. Out of balance effect is proportional to the square of the radius, and this work is near the hub, plus the thing is only spinning 800rpm, so if there is a gram too much or too little weld it wont make any difference ihmo

good point,
but pehaps it makes sense as MM sugests to have them checked anyway, because I think they are in use sinds very long...(?)


unless lots of hassle with transport arrangements, I'm afraid I have to byte the bullet in SOF

 

[jfm]

J, I'd rather have them polished and balanced anyway.
Ideally, it would be a good idea also having them checked by someone who has the proper equipment for scanning the blades (as done in M2) and if necessary adjust them.
Not because I disagree with what you're saying, but because those props made their fair share of work, and cavitation might have something to see with them not being anymore 100% kosher, in some respect.

Yup agreed - have them "100k serviced" due to age and use, rather than because of a tiny weld repair. It might help/cure the cavitation anyway, as you say. I dunno if lots of places have the "MRI scanners" or whether only the big boys like Clements have them. Anyone know?

The scans are very interesting (in a geeky way of course) and show lots of data- I will try to remember to post mine sometime

 

[BartW]

Yup agreed - have them "100k serviced" due to age and use, rather than because of a tiny weld repair. It might help/cure the cavitation anyway, as you say.

while I almost convinced myself to have a good local welder here at home, to do a small and cheap welding repair.
......decisions, decisions, ....

 

[jimmy_the_builder]

good question MM,
I forgot to asc, as I was impressed with the price when he told me,
but wondered myself after considering doing the work here locally in B

I'll try to get a price indication from 2 prop repair co's, one in B and one in NL,
and then decide if I will pay the SOF inflated price (if ballancing is included)
or having all the hassle myself, taking them off, bringing and recovering them to the repair co.

coincidently the boat is coming two weeks OOW, and I have two travels by car (B-SOF-B) during that period of time

despite the fact that there are probably several good prop service co's,
I don't fancy sending the props to UK,
even more hassle, packing, arranging transportation, ...

Bart, fyi there's a forum car going up from SoF to UK next week, so if BA is already on the hard, and you can get the props to PV, getting them up to the UK would be v easy. Just a thought.

Cheers
Jimmy