Corrosion on Propellor

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Your Flexofold propeller is made out of bronze, which is a relatively noble and seawater and corrosion resistant material. However, the saildrive version of this propeller (and most other brands of fixed and folding propellers) are electrically isolated from the saildrive shaft by means of a vulcanized rubber bushing construction in the propeller hub. This rubber construction is meant as isolator and to reduce the forces on the saildrive during engaging the clutch forward/reverse. Gori has e.g. exchangeable zinc anodes mounted on the propeller hub, I cannot recall how this was with Flexofold, when I remember correctly it has none. Looking at the pictures I suspect indeed galvanic corrosion, but then there must be a source close or connected to the propeller of material more noble then the propeller. The reason that your saildrive anode is still intact and your saildrive leg too indicates to my opinion the propeller is electrically isolated from the propeller as these would sacrifice itself for the more noble propeller.Also don't underestimate the influence of more hot seawater, which is more corrosive then colder seawater.
The reason that your hull anode (connected to keel, rudder stock, ground, engine block etc.) has been gone in a relatively short time period (mine is hardly attacked after two seasons) indicates that the area where your boat is moored seems to need proper cathodic protection. Am afraid your prop needs this too, but strange why your saildrive anode is still in relative good condition compared to the one on the hull. And: what props do other boats around have? Is your boat moored in water with a tide current, so flow around the hull? (Galvanic) corrosion can be a complex issue, you need to know the source as a new prop may otherwise end up the same.

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André Members Profile Send Private Message Find Members Posts Add to Buddy List Sub Lieutenant Joined: 16 June 2011 Location: Netherlands Status: Offline Points: 9	Post Options Post Reply Quote André Report Post Thanks(0) Quote Reply Posted: 12 June 2012 at 20:50
	Your Flexofold propeller is made out of bronze, which is a relatively noble and seawater and corrosion resistant material. However, the saildrive version of this propeller (and most other brands of fixed and folding propellers) are electrically isolated from the saildrive shaft by means of a vulcanized rubber bushing construction in the propeller hub. This rubber construction is meant as isolator and to reduce the forces on the saildrive during engaging the clutch forward/reverse. Gori has e.g. exchangeable zinc anodes mounted on the propeller hub, I cannot recall how this was with Flexofold, when I remember correctly it has none. Looking at the pictures I suspect indeed galvanic corrosion, but then there must be a source close or connected to the propeller of material more noble then the propeller. The reason that your saildrive anode is still intact and your saildrive leg too indicates to my opinion the propeller is electrically isolated from the propeller as these would sacrifice itself for the more noble propeller. Also don't underestimate the influence of more hot seawater, which is more corrosive then colder seawater. The reason that your hull anode (connected to keel, rudder stock, ground, engine block etc.) has been gone in a relatively short time period (mine is hardly attacked after two seasons) indicates that the area where your boat is moored seems to need proper cathodic protection. Am afraid your prop needs this too, but strange why your saildrive anode is still in relative good condition compared to the one on the hull. And: what props do other boats around have? Is your boat moored in water with a tide current, so flow around the hull? (Galvanic) corrosion can be a complex issue, you need to know the source as a new prop may otherwise end up the same.

skipper Members Profile Send Private Message Find Members Posts Add to Buddy List Vice Admiral Joined: 16 February 2008 Location: Sweden Status: Offline Points: 825	Post Options Post Reply Quote skipper Report Post Thanks(0) Quote Reply Posted: 12 June 2012 at 21:45
	I am so sorry when reading this serious problem. It sounds very strange that you have got those damages without being connected to shore power, an isolated propeller should not get those damages. When seaking for information how to solve this in short and long term you could get in contact with the manufactor of the propeller. My experience is that the Danish Flex-O-Fold company has helped myself and friends so if you ask them about guidelines they might have some ideas about the possible root cause in your harbour. http://www.flexofold.com/contact/ Edited by skipper - 12 June 2012 at 21:51
	Cheers, Skipper Former owner of Hanse 342 2005 (Sparcraft mast, white hull, wheel steering, deep draft keel, short rudder)

Xantos Members Profile Send Private Message Find Members Posts Add to Buddy List Sub Lieutenant Joined: 09 March 2012 Location: Mumbai Status: Offline Points: 7	Post Options Post Reply Quote Xantos Report Post Thanks(0) Quote Reply Posted: 13 June 2012 at 06:33
	Hello Andre, Thanks for the reply. Looking at the damage that is limited to ONLY the prop I tend to agree with your theory that possibly the prop is completely isolated exposing it to corrosion. You are correct - The Flexoflod does not have exchangeable anodes like the Gori. My earlier posts did indicate that the hull anode was completely gone because I didn't see one when I inspected the boat , I now understand that the 325's do not have an additional hull anode-atleast hull #079 had no hull anode. There is a Ground cable connected to the Keel and one to the rudder stock. Hanse has subsequently sent a Technical Dealer Bulletin (TDB) dated 24th Feb 2012 advising that the rudder stock ground connection to be disconnected. I completely clueless as of now what to do. Nandan

Brufan Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 16 December 2010 Location: Belgium Status: Offline Points: 672	Post Options Post Reply Quote Brufan Report Post Thanks(0) Quote Reply Posted: 13 June 2012 at 09:55
	[QUOTE=Xantos] There is a Ground cable connected to the Keel and one to the rudder stock. Hanse has subsequently sent a Technical Dealer Bulletin (TDB) dated 24th Feb 2012 advising that the rudder stock ground connection to be disconnected. My yacht was recall by the dealer for wrong heater installation. When they fixed it they also remove the ground cable from rudder shaft according to yard's instruction.
	Bruno hanse 355 - 57 S/Y Spicy Ginger White hull, 2 cabins, Volvo D1-30, Selden rig, removable mainsheet track system, Simrad (now B&G)-Jefa autopilot.

341 Agathe Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Commander Joined: 10 August 2010 Location: Denmark Status: Offline Points: 68	Post Options Post Reply Quote 341 Agathe Report Post Thanks(0) Quote Reply Posted: 13 June 2012 at 19:58
	It's a bit of a mystery why the Hanse yacht has installed ground cable on the rudder shaft keel and sail drive. According to the experts, it will result in korrrosion which also occurs. On this link http://www.myhanse.com/forum_posts.asp?TID=6193&title=rudder-stock-corrosion there has been a lively debate concerning same topic. Corrosion attack the vital parts, and generates high Repairing expenses.
	Agathe 341 2003, white hull, tiller steering, deep draft keel, long rudder

341 Agathe Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Commander Joined: 10 August 2010 Location: Denmark Status: Offline Points: 68	Post Options Post Reply Quote 341 Agathe Report Post Thanks(0) Quote Reply Posted: 13 June 2012 at 20:00
	It's a bit of a mystery why the Hanse yacht has installed ground cable on the rudder shaft keel and sail drive. According to the experts, it will result in korrrosion which also occurs. On this link http://www.myhanse.com/forum_posts.asp?TID=6193&title=rudder-stock-corrosion there has been a lively debate concerning same topic. Corrosion attack the vital parts, and generates high Repairing expenses.
	Agathe 341 2003, white hull, tiller steering, deep draft keel, long rudder

André Members Profile Send Private Message Find Members Posts Add to Buddy List Sub Lieutenant Joined: 16 June 2011 Location: Netherlands Status: Offline Points: 9	Post Options Post Reply Quote André Report Post Thanks(0) Quote Reply Posted: 13 June 2012 at 21:05
	Xantos, I think it would indeed be a good idea asSkipper describes to ask advise from Flexofold on your issue. Such an amount of corrosion is abnormal, there must be an explanation. What also is typical is the corrosion looks worst on the blade tips. The price of a flexofold is high enough to let them assist you. You could at least give it a try. I have 320 and it has an additional hull anode connected to ground, keel, rudderstock and probably also engine block. If the 325 doesn't have this, I would indeed consider to disconnect the aluminium rudderstock and leave it on its own, as it otherwise may sacrifice itself against the cast iron keel (is more noble) and can therefore understand why also Hanse in the meantime recommends this.



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