tjbrace
Active member
What are the possible consequences of motoring my boat with a dezinct bronze prop.
Prop dezinctification
- Thread starter tjbrace
- Start date
vyv_cox
Well-known member
As ever, it depends on the severity of the dezincification. Are you talking about a bit of surface pinkness? Or chunks of metal falling off? Dezinc commences at the surface and invades progressively. If blade tips have broken off there is a risk that the whole blade will fracture, rare but possible.
tjbrace
Active member
Thanks Vyv. I believe it is surface pinkness. New prop fitted when I bought the boat in 2006 but I think it is now worn out, lots of vibration at 2500 rpm, all ok at 2000 rpm, and silky smooth in reverse. Thinking I might refit the old prop for the time being.
Tranona
Well-known member
Props do not normally "wear out", although folding and feathering ones can get wear in the moving parts. However if it is a fixed blade yellow metal prop there is something wrong if it is dezincifying to the point where it is losing bits and causing vibrations. Even then would likely bee the same in forward and reverse.
tjbrace
Active member
The worn out one is a 3 blade folding prop, there is much vibration as in my original post. I won’t know if bits have fallen off until I can view the prop.
Looking to refit the old prop, 2 blade fixed, to get me by. It’s this one that is pink on its surface.
Tranona
Well-known member
More likely to be wear in the pivot pins than dezincification of the blades. Still a short life. My Flexofold was 10 years old when I sold it and zero wear - but some other designs have a less than good reputation in this respect. as Vyv says a bit of pinkness on a fixed blade is not normally a problem. It may well disappear with a dip in brick cleaner and a polish.
Mudisox
Well-known member
I had a pair of 3 bladed, fixed props which after 10 years and a few knocks on semi floating debris had suffered.
Removed, cleaned and thoroughly dried before coating with epoxy x2 coats. Hand sanded to smoothness. It has lasted 3 seasons further use so far.
Removed, cleaned and thoroughly dried before coating with epoxy x2 coats. Hand sanded to smoothness. It has lasted 3 seasons further use so far.
Boater Sam
Well-known member
There is no zinc in bronze! If there is zinc its brass, rubbish prop.
vyv_cox
Well-known member
The vast majority of original equipment propellers and P-brackets are made from manganese bronze, a 60/40 brass with a few minor additions of other metals. Replacement fixed props are the same.
Many after-market props are marketed as bronze, aluminium bronze or nickel-aluminium bronze but I have a collection of photos of some that are clearly suffering dezincification.
Boater Sam
Well-known member
I am not surprised.
Tranona
Well-known member
Although you may turn your nose up at them the reality is that they are fine in service. Hundreds of thousands in use and no real epidemic of early failures. folders and featherers are a different matter because they involve a mix of metals in their mechanisms so better alloys tend to be used.
Channel Sailor
Active member
I suggest get the prop inspected, the edges of the blades tidied up and importantly re balanced. If you have vibration it could be the prop shaft as well. Which in turn any imbalance could be wearing out the cutless bearing. I was told blades on props are very strong.
tjbrace
Active member
Thank you for all the replies.
I won’t know what is damaged until I can get to the stern gear, and the tides aren’t suitable at present.
The original fixed 2 blade prop which is ‘pink’ looks very robust whereas the newer 3blade folder is making all the noise and has done 18 seasons. I think it may be worn out and has taken my newish cutless with it.
So waiting for the tides now.
I won’t know what is damaged until I can get to the stern gear, and the tides aren’t suitable at present.
The original fixed 2 blade prop which is ‘pink’ looks very robust whereas the newer 3blade folder is making all the noise and has done 18 seasons. I think it may be worn out and has taken my newish cutless with it.
So waiting for the tides now.
rotrax
Well-known member
Even our high quality O/E prop on our island packet has a few pink spots, plus a 'comma' shaped pink bit near the root of one blade.
It is O/E, 16 years old now and when inspected in April during our two weeks ashore had no deteriation since I first inspected it in 2016.
The spec. says bronze, but founders use their own black art of 'when to piss in the crucible' additions of small amounts of other metals and chemicals to make casting better.
From direct experience of living next door to Walter Wilders foundry in Crowmarsh Gifford for ten years. The Foundry Foreman was a mate, one of my chums Ivor married his Daughter.
vyv_cox
Well-known member
It seems that there is no recognised specification for 'manganese bronze'. This USA company https://www.wbcastings.com/non-ferrous-alloys/brass-bronze/maganese-bronze/ says:
"The term “manganese bronze” which is used commercially to describe the high strength yellow brasses is somewhat misleading. Actually, they are not bronzes, nor does the amount of manganese they contain have any significant effect upon the structure of the alloys. The high-strength yellow brasses are basically alloys of copper and zinc to which varying amounts of other elements are added. These additions produce high strength combined with excellent corrosion resistance properties."
Some years ago I managed to find a composition list for it that contained no manganese at all!