Anodes. Anyone familiar with Navalloy anodes ?

[About Time]

I have always used zinc for my sterndrives (VP DPG) - I am boating in saltwater and have always had the understanding that I should go for zinc anodes. However after 6 months in the water the zincs are 80-90% gone!!! .... I have recently read about the Navalloy anodes. More expensive but an alloy, zinc and indium blend that should last 30% longer...

The company is Performance metals (US based) ... they have two very interesting articles online.

http://www.performancemetals.com/anodes/navalloy.shtml
http://www.performancemetals.com/anodes/AnodeFAQs.shtml

Would anyone recommend this change from zinc ?

I guess one reason for the short life could be that I stay connected to shore power all the time. I have a friend who toldme that .... I may consider trying a year not doing that - even I feel it is nice always to come to the boat knowing all batteries are fully charged and ready to go

What do you guys do ?

 

[rafiki_]

Do you have a Galvanic Isolator? This will reduce anode erosion rates.

 

[About Time]

Do you have a Galvanic Isolator? This will reduce anode erosion rates.

Googled this .... Will this 'plug in Galvanic isolator' work for me. Seems simple and with no new wiring required. I see it is offered as a 16a and a 32a so need to check which one I need ... if this is what I need

http://galvanic-isolator.co.uk/divi/product/galvanic-isolator-plug-in-16a/

 

[rafiki_]

Googled this .... Will this 'plug in Galvanic isolator' work for me. Seems simple and with no new wiring required. I see it is offered as a 16a and a 32a so need to check which one I need ... if this is what I need

http://galvanic-isolator.co.uk/divi/product/galvanic-isolator-plug-in-16a/

Yep, I have a plug-in 16A on my Azi 39. Works great. Mine is a Safeshore isolator. Cost £100 iirc.

 

[About Time]

Much appreciated

Do you think I should stay with zinc or switch to Navalloy or Aluminium for salt water ?

 

[rafiki_]

Much appreciated

Do you think I should stay with zinc or switch to Navalloy or Aluminium for salt water ?

I don't know anything about Navalloy, zinc is the goto for salt water. If your anodes are eroding, good, as they are saving your engines and drives.

 

[About Time]

A galvanic isolator has been fitted. One follow up question. The O-ring zinc around the driveshaft is always eroding the most while the zinc bar on the transom erode slowly. Guess it takes more to protect the drive leg than the transom due to weight or surface. Would it be a good idea to ground the drive leg to the transom so the transom bar zinc could 'help' the O-ring zinc ? I guess Volvos DPS drives are wired up so transom and leg is grounded together.

 

[VicS]

The galvanic isolator should reduce the rate of loss of material from anodes on structures which are boded to the shorepower earth caused by the "stray" currents conducted by the earth connection.

Either zinc or aluminium anodes can be used in salt water. Aluminium can also be used in brackish water where zinc is not suitable.

Aluminium anodes are made of an alloy which crucially contains a small quantity of indium. Navalloy is simply a brand name for aluminium anodes from Performance Metals.
Zinc anodes are made from a grade of zinc with a very low iron content and a small quantity of cadmium

On a weight for weight basis, taking into account the relative atomic masses of the two metals and the fact that zinc is divalent whereas aluminium is trivalent it is possible to show that aluminium should last theoretically about 3.6 times as long as zinc. However aluminium is much less dense than zinc meaning that aluminium anodes are much lighter than zinc anodes of the same size. Once this is taken into account you find that you should get about 1.4 times as much life from an aluminium as you would from a zinc anode of the same physical size.
You can see from the electrode potentials quoted that aluminium anodes are slightly more reactive than zinc anodes. This probably reduces the "advantage" of aluminium anodes further with the result that they can be expected to last for about 1.3 times as long as zinc anodes.

To complete the comparison you should also take into account the difference in cost, but that's a calculations for the accountants.

You should check the earth bonding of the drive leg and transom but not add any other than that which the manufacturer provides.

The external anodes offer no protection to the engines. The salt water part of the engine cooling system may be protected by internal anodes. If so these should be inspected as part of the routine engine servicing and replaced when necessary.

 

[About Time]

Thanks a lot VicS. I will try out aluminium anodes and check earth bonding on the drive legs and transoms. With the galvanic isolator added on top hopefully I will see improvements next year.