Pitting on My Bronze MaxProp

[gettinthere]

My boat sits in fresh water. After the 2008 season (July to October), I hauled it and the prop appeared fine. After the 2009 season (April to October), the edges of the Maxprop were severely pitted, corrosion. The zinc on the prop showed minimal loss.

I sent it to PYI. The experts there think it was a sudden spike of heavy voltage. They say that low voltage doesn't go far in fresh water and the zinc was fine. The shaft zinc was perfect too.

There were no boats on either side of me the first half of the season. Both boats props are perfect after the second half of the season. I did travel for about 10 days staying in 4 marinas.

Any ideas as to what caused this rapid pitting of the prop?

[Jon D]

my bet is you had a transient in with an electrical problem. I had a similar situation where my max prop was fine for over 9 years then suddenly some pitting. There was a boat next to mine for a month or so that was not the best kept.. bet that was the problem.

[senormechanico]

While in a marina in Mexico, we had a very small bit of pitting (although nothing like yours) when a boat across from us had a welder building a cockpit arch. Several boat owners we talked to had similar damage.

[Joli]

Fresh water?

You should be using aluminum or magnesium anode. Zinc creates a zinc oxide that insulates the anode.

Go here for what you need. Magnesium Shaft Anodes

FYI, we have a Max Prop and use a mag anode. It's shot by seasons end on the Great Lakes.

Originally Posted by gettinthere

My boat sits in fresh water. After the 2008 season (July to October), I hauled it and the prop appeared fine. After the 2009 season (April to October), the edges of the Maxprop were severely pitted, corrosion. The zinc on the prop showed minimal loss.

I sent it to PYI. The experts there think it was a sudden spike of heavy voltage. They say that low voltage doesn't go far in fresh water and the zinc was fine. The shaft zinc was perfect too.

There were no boats on either side of me the first half of the season. Both boats props are perfect after the second half of the season. I did travel for about 10 days staying in 4 marinas.

Any ideas as to what caused this rapid pitting of the prop?

[gettinthere]

The PYI folks feel it was a VERY big load of power all at once to create this issue.
There's been no welding near me but there have been a very few transients stayed overnight early in the year.

[RSMacG]

Could the pitting and corrosion not be a result of prop cavitation? Given that the others in the marina were unaffected and there doesn't seem to be an obvious source of charge. The imploding bubbles will actually suck the metal right off the blades and you wouldn't have noticed any appreciable loss in power.

[s/v Jedi]

I think the first thing you should check is your own shore power installation. I understand that it is easier on the mind to look at other possibles causes first, but that is not the best for the boat.
When other boats in your marina do not have the problem, it's very likely that the problem is on your boat.

cheers,
Nick.

[gettinthere]

These are the things I thought of first.
But the maxprop in house experts felt that the cause was a very high voltage hit. The pitting is not on the face of the blades as would be the case from cavitation. The pitting is on the very edge. And I'm in fresh water where electricity does not flow nearly as easy as in salt. I will be checking for stray current when I get back in the water.

[s/v Jedi]

Okay, how does the color look like? Maybe the material has weakened?

ciao!
Nick.

[slowshoes]

Originally Posted by s/v Jedi

I think the first thing you should check is your own shore power installation. I understand that it is easier on the mind to look at other possibles causes first, but that is not the best for the boat.
When other boats in your marina do not have the problem, it's very likely that the problem is on your boat.

cheers,
Nick.

Nick,

How do you go about checking for stray current on a boat? I had some oxydation (no pitting) on my prop after hauling out this past fall. Usually when I haul out my prop is perfectly clean, so that left me wondering whether my boat has developed a stray current problem - I just have no idea how to determine whether it does or not.

[btrayfors]

Originally Posted by Joli

Fresh water?

You should be using aluminum or magnesium anode. Zinc creates a zinc oxide that insulates the anode.

Go here for what you need. Magnesium Shaft Anodes

FYI, we have a Max Prop and use a mag anode. It's shot by seasons end on the Great Lakes.

Joli,

Where did you find a mag anode for the Max Prop? They're not shown in the referenced catalog.

Thanks,

Bill

[s/v Jedi]

With oxidation you mean the prop turned green?

Testing for stray currents aboard is not difficult. Just hire a marine electrician or if you are handy with multi meters, read the books and do it yourself.

Are you on shore power? If so, do you have an isolation transformer or galvanic isolator?

cheers,
Nick.

[slowshoes]

Originally Posted by s/v Jedi

With oxidation you mean the prop turned green?

Testing for stray currents aboard is not difficult. Just hire a marine electrician or if you are handy with multi meters, read the books and do it yourself.

Are you on shore power? If so, do you have an isolation transformer or galvanic isolator?

cheers,
Nick.

No, the props not green but rather has a thin, hard white coating on it - something that has never happened before and is very hard to get off. (I didn't mention it before, but I am also in freshwater).

I am on shorepower but I have to plead ignorance on your isolation transformer/galvanic isolator question. As you have probably figured out, electricity isn't my forte, so i would probably have to hire an electrician to figure out if there is a stray current problem.

That being said, I like to at least give myself a chance at trying to figure things out for myself - do you have any recommendations on reading references that explain the steps to check for stray current?

Thanks for any info.

[Charlie]

Caulsers book has a good section on testing.

[s/v Jedi]

;-) I think Charlie meant Caulder as in Nigel Caulder.

The white stuff isn't corrosion from the bronze prop because bronze corrodes green. I still wouldn't take cavitation off the list of possible problems.

Also, while reading up or getting to hire someone to inspect the electrical system aboard, disconnect your shore power. And I mean physically disconnect the cord, breaking all electrical contacts between the boat and shore. If there indeed is a severe problem like you were told, you must assure that it stops now.

Also, in your case, I would just hire a good electrician and observe him on the job. This allows you to learn as well as deal with the problem quickly. I also think you should start saving for at least a galvanic isolator or better yet an isolation transformer. Discuss it with the electrician. These devices set you back a couple of hundred dollars.

cheers,
Nick.