Strange Activity Around Anodes

Shame on me. I backed into a rock is shallow water and damaged my prop. Prop is off and being repaired. My question is, what's going on around my aluminum anodes on the rudder and rudder shoe ?

After being on a salt water mooring for years, this season, I moved to a fresh water slip up in a river. As I mentioned, my anodes (divers plate, rudder, rudder shoe, and thruster), are all aluminum. I've been plugged into properly grounded shore power, with Xantrex battery charger running 24 X 7 for the last 2 months. I have a Charles battery isolator, and I installed a ProMariner ProSafe galvanic isolator. For the past couple of years, I've been using Trilux 33 bottom paint on the prop, rudder, and shoe. With winter and rain runoff, the river water is the color of a strong tea, therefore the stained color.

When I hauled for repairs, I noticed the Trilux 33 was relatively soft. Expand the photo and look what's going on around the anodes. The Trilux has flaked off. Prior to using the Trilux, I painted hull, rudder, and shoe with Pettit's Hydocoat, without any issues. I've striped off the Trilux, and I'm going back to repainting the rudder and shoe with Hydrocoat (other than water stain, hull looks good). I will spray the bare prop with 3 light coats of Pettit's 1792 Zinc Coat Barnacle Barrier. Is this deterioration some kind of Trilux and fresh water reaction?

Any pitting to the metal or just paint issues?

Ted

Put a meter on your grounds and check to see if it is high. I had one read out at 16 yesterday. Yes I took care of it quickly as it was a brand new thru hull fitting that was just replaced 3 weeks ago so luckily no damage done.

Looks like paint went galvanically active. Anode looks like it went cathodic due to coloration. Scrape the crud off the anode and see if it is pitted at all. If no pitting, that aids my theory.

Isn't trilux meant for aluminum? What mat'l is the rudder? Presume SS.

Second your idea to go back to what worked previously.

What is the logic with using an Al anode?

Ski in NC said:

What is the logic with using an Al anode?

Click to expand...

Zinc doesn't work in fresh watet and aluminum is preferred for brackish. The lower the salinity the less effective zinc is as an anode, or so I have been told.

Ted

Aluminum lasts 30% longer, is cheaper to buy and is one number removed on the galvanic scale from zinc.

Trilux IS intended for aluminum. You have stainless, zinc, copper and possibly a bronze wheel - what could go wrong? I wish I could get Trilux up here, the crap they sell us here has no biocides in it so the Trilux 2 we get is good for maybe one year, if you are lucky.

Send your picture to boatzincs.com

Freshwater, brackish or salt, there is still an amount of electricity in the water. It is most prevalent around marinas or other boats with improper grounding/bonding.

This issue has been a thorn in my side for quite a while and I do believe it is now under control. If you think this could be your problem, it takes 15 minutes to put a meter on your grounds. Reading should be, (salt) 0.4-1.6 is acceptable. Like I mentioned above, one of my ground reading was a 16. It needed to be addressed immediately.

To answer a few questions:
1. There is no metal pitting. Rudder and shoe are stainless steel.

2. Coloration on anode is due to the highly stained water. Brushed off stain
to expose anode. After 2 months underwater, there is some deterioration
starting on all anodes, including thruster anode.

3. Why aluminum ? Current consensus (including marine guru Steve
D'Antonio) is that aluminum anodes are the best material in salt, brackish,
and fresh water. Side Power thruster's anodes changed over to aluminum
anodes a couple of years ago.

4. Put meter on grounds ? Nordic Tugs have a grounded system. Only 3
thruhulls on boat... raw water inlet, thruster, and black water tank
macerator thruhull. All are grounded. No paint deterioration around
thruhulls, which are painted with Hydrocoat. Only paint deterioration is at
Trilux paint around rudder and shoe anodes. What, how am I testing for
on thruhulls?

5. About 5 years ago, to improve ground at rudder, I ran a ground wire from
inside attachment bolt of divers plate to the rudder shaft. Over the years,
I've never had a 100% lose of any anode after 6-7 months in salt water.

6. Three years ago, I wintered in the water at the same slip and had no
issues. Boat was in the water for 13 months. I was plugged in BUT the
rudder and shoe where painted with Hydrocoat. No issues. I'm thinking
this is just a Trilux/fresh water issue. From Trilux can... "developed for
use on aluminum hulled vessels but can be used on fiberglass, wood, and
steel surfaces". Directions on can also states that Trilux can be used in
fresh, salt, and brackish waters.

My experience with Trilux is its expensive but its marginally better for protecting the bottom than house paint. Emphasis on the marginally. I'd put the blame squarely on the Trilux.

Seems like the Trilux has set up housekeeping with your aluminum anodes.

Meter

Hi Donna
Could you describe what kind of meter and how to test this, Perhaps what you are looking for?
Please
Gregg

Wataworld said:

Hi Donna
Could you describe what kind of meter and how to test this, Perhaps what you are looking for?
Please
Gregg

Click to expand...

Yeah that wasn't too clear to me either. Put the other meter lead to where? 16 what? Volts? Current?

Wataworld said:

Hi Donna
Could you describe what kind of meter and how to test this, Perhaps what you are looking for?
Please
Gregg

Click to expand...

A simple multimeter to your ground and in my instance, thru hull fitting. in salt water an acceptable reading would be 0.4-1.6 Mine was super high at 16.This led me to check the whole grounding/bonding issue. It doesn't last forever. Checking for proper grounding is important or it will eat up your zincs and eventually metals. If you are changing zincs either on the engine or exterior with a diver at a rediculous time frame check your grounds.

The fitting I tested was just replaced 3 weeks ago when she was hauled in the Bahamas.

I also thought my grounds/bonding were good. Surprise! I'm learning as I go so technicality of words is not my strong point. I know basics on electricity and how it gets in the water and where it is more likely to occur.

It really doesn't matter what kind of boat you have, it should be checked periodically. Not a fun job.

Donna said:

A simple multimeter to your ground and in my instance, thru hull fitting. in salt water an acceptable reading would be 0.4-1.6 Mine was super high at 16.This led me to check the whole grounding/bonding issue. It doesn't last forever. Checking for proper grounding is important or it will eat up your zincs and eventually metals. If you are changing zincs either on the engine or exterior with a diver at a rediculous time frame check your grounds.

The fitting I tested was just replaced 3 weeks ago when she was hauled in the Bahamas.

I also thought my grounds/bonding were good. Surprise! I'm learning as I go so technicality of words is not my strong point. I know basics on electricity and how it gets in the water and where it is more likely to occur.

It really doesn't matter what kind of boat you have, it should be checked periodically. Not a fun job.

Click to expand...

Lets back up a little.
The meter is on Volts DC or Ohms? Guessing Ohms?
One meter lead is connected to the thruhull in question and the other is connected to what? Guessing battery negative post?

Donna said:

A simple multimeter to your ground and in my instance, thru hull fitting. in salt water an acceptable reading would be 0.4-1.6 Mine was super high at 16.This led me to check the whole grounding/bonding issue. It doesn't last forever. Checking for proper grounding is important or it will eat up your zincs and eventually metals. If you are changing zincs either on the engine or exterior with a diver at a rediculous time frame check your grounds.

The fitting I tested was just replaced 3 weeks ago when she was hauled in the Bahamas.

I also thought my grounds/bonding were good. Surprise! I'm learning as I go so technicality of words is not my strong point. I know basics on electricity and how it gets in the water and where it is more likely to occur.

It really doesn't matter what kind of boat you have, it should be checked periodically. Not a fun job.

Click to expand...

Where and what are you measuring with an ohm meter? Your metals should all be bonded together so the DC resistance will or should be small. Those metals that are not properly bonded require separate anodes. The only way I know to determine proper bonding is with a half cell where exposed metal's voltage is measured between the half cell and the particular metal being tested.

Prop repaired. Ready for paint (sprayed 3 light coats of Pettit's 1792 Prop Coat). Striped Trilux off rudder and shoe and repainted with Hydrocoat. Relaunched. With prop retuned, actually picked up a one knot increase at WOT (19 knots, 2600 RPM). No definitive answer to Trilux breakdown. I'll write it off to Trilux and fresh water.

The best way to test for galvanic action is to use a silver chloride anode connected to a multimeter and drop it overboard. The silver chloride, not the multimeter. Overboard. Then use the other electrode to probe various metal parts on your boat to find out how much current is moving into the water. All the places you touch should all be bonded and produce similar readings and all should be in the proper range.

Or was that volts? I'll have to go to the boat to look at my meter - sorry, temporary loss of lucidity. Need more coffee.