Some time ago I posted a topic relating to anodes and made mention of the fact that I was getting a significantly increased amount of marine growth in the area surrounding the anode. I searched for but could not find the original thread but having just had my yacht out of the water again over the weekend I took the opportunity to snap a pic or two of the situation before we cleaned it all off again. The growth does not occur on the other side of the hull away from the anode.
The pictures below are after a little over 12 months with the hull having had a rub down a couple of months ago that also involved a bit of scraping at the growth around the anode.
My questions are as follows;
Can anybody explain why this occurs? I am guessing it is something about what the anode gives off as it is dissolving that promotes the growth - but what exactly?
Any ideas on how to prevent this happening?
Where all the growth occurs the process of cleaning it off ready for new antifouling leaves the surface underneath very rough (which I suspect makes future growth more likely). as far as I can tell this rough surface is only as deep as various layers of antifouling. What would be the best way to approach the smoothing out of this surface? A good sanding with some course wet n dry or something with a bit more grunt?
Does that side of the hull get shade or sun while moored? That might have more to do with the growth?
She is on a swing mooring so I figure that with time of day and prevailing wind there is a good randomisation of the sun exposure around the hull.
My cat had more growth on one hull...it's on a swing. The starboard side from memory...might be your answer. Swap the anode over,would provide more proof of the theory
The anode looks a bit sus. What's the growth on the anode? Is the anode connected to that skin fitting, prop shaft, rudder bearings electrically inside? To me it looks like its been there awhile and doing very little. Is the prop looking a little pink? The Swanson 32 has no room for a shaft anode and I reckon the anode should be as close as possible to the prop, that skin fitting with a good coat of paint probably needs nothing.
It may need the area scraped back to get a smooth surface. Buy a new anode and ensure the bolt surface is clean.
Is the anode connected to that skin fitting, prop shaft, rudder bearings electrically inside?
It is connected to the prop shaft inside the hull. The bolts go all the way through and then there is a wire connection to a devise that runs a flexible mesh/wire strop around the prop shaft. That is the only thing connected to the anode.
Not sure about the growth on the anode but the anode was definately depleted (sacrificed). That anode was installed just over 12 months ago and it was probably about half the size it was when new. I replaced it again at this haul out so should be good for another 12 months. No doubt along with another forrest of growth.
If that's 12 months old that's not too bad. I just came past my mates Swanson 32 a few minutes ago and meant to check whether he had the same growth but my mind wandered. I'm fairly sure his anode is in the same place. I would prefer to have it as close as possible to the prop. A few weeks ago his prop snapped a blade. Looking at the stub there was probably only about 5 square mm of bronze left, the rest was like pink cheese. We had a similar discussion to this! That photo of your prop seems to have a fair bit of pink showing. May be a bit of marine growth but I would be checking that.
I know what you mean Ramona. That prop is about 2 years old after I snapped a blade myself. Prior to that there had been no anode connected to the prop as far as I could tell. The pink you can see on the prop in the photos is ( I hope) the red etch primer that was showing through after the anti fouling wore away
could it be that the copper in the anti foul is reacting with the anode and breaking down faster in the immediate area surrounding the anode?
Select to expand quoteMatM14 said..
I know what you mean Ramona. That prop is about 2 years old after I snapped a blade myself. Prior to that there had been no anode connected to the prop as far as I could tell. The pink you can see on the prop in the photos is ( I hope) the red etch primer that was showing through after the anti fouling wore away
What was the antifouling?
Hello MatM14, are you sure it is the anode causing the problem. You say you have an anode on this side of the boat only, is this also the case with the skin fitting? If so I would be more inclined to say what comes out of that fitting could be the cause. Either a lot of nutrients that promote marine growth or chemicals that are relieving the anti fouling of the ability to work effectively. AS for cleaning the growth away a decent water blaster should remove the growth then give it a scrape and wet rub with a coarse rubbing block, coarser=faster removal of anti foul. Remove any flaking anti foul and use the recommended primer on any areas that need doing. Replace the anode and make sure all of the connections between the anode and prop shaft have good contact. I cant see from the photo's but is there provision for an anode on the end of the shaft where the nut is? This can also help protect your prop and shaft, just keep in mind you can also over do it with the anodes. If in doubt consult a marine specialist. If nothing else peace of mind.
Mate with the Swanson 32 turned up today as I was trying to check the side of his boat. Black antifoul and I could see nothing. He has an anode on the other side in the same place and on the inside of both he has two anodes !!!!!! He reckons these two anodes in the air are getting eaten away! He is a Pom. I reminded him it was he who snapped a prop blade a few weeks back.
Both sides around the anodes are clean.
Hello MatM4, In the picture it appears that the anode is painted. I never paint the anodes (8 anodes from memory) on my steel hulled Adams 40. The anodes were in such good condition, I never changed them last time I slipped the boat. Is the anti-foul paint hard or self-abrading? Do you take you boat out very often? I'm assuming your hull is glass. If it is glass, what do you do with the internal connection for the anode. Is it bonded to all the other metal protrusions on the boat. Is this the only anode? What is the skin fitting used for? What is the skin fitting made of? (So many question, sorry)
To answer some of the questions;
The skin fitting adjacent to the anode is the cockpit drain so I wouldn't expect that there would be much coming through it that is causing the growth.
The skin fitting is bronze (I think).
Anti foul is Altex No 5 - ablative.
There is no room on the prop or prop shaft to attach an anode directly
The anode is not painted
There is an electrical cable that is attached to the bolt holding the anode in place in the inside of the hull. This cable connects to a flexible strop arrangement that circles the prop shaft.
The hull is glass
Boat gets out intermittently, more frequently in summer months (average would be fortnightly). She tends to sit a bit idle over winter.
I use Altex No 5 as well so I would say nothing wrong with the paint, maybe the preparation may have been sub standard! I use one anode. shaft anode just ahead of the bracket. I would hazard a guess that the anode has had no effect on the growth. It looks like the antifoul has just been worn off or too thin and the paint has lost its effectiveness. I would prefer to see the anode close as possible to the prop though. Breaking blades gets expensive.
I tend to agree with Ramona that the problem may have nothing to do with the anode. The text below is from the Altex No 5 Data Sheet. It may be worth while making sure you are getting enough of the anti-foul on. It seems rollers and brushes just don't put enough on in a single pass if you want 12 months of life. You may need up to 4 coats with a roller just to get the correct thickness and then some more around the leading and trailing edges.
Application:
No.5 Antifouling can be applied by spray, brush or roller. However, it is strongly recommended that heavy duty airless spray equipment be used to ensure the specified film thickness per coat is applied. Film thickness control is critical to the performance of the coating, as service life is a direct function of film thickness. Additional coats will be required to attain the correct film thickness if the coating is applied by brush or roller.
Important:
Film thickness control is critical
.
Service life is a direct function of film thickness
Theoretical Coverage Rate: 6.7 sq metres per litre at 75 microns dry
Recommended Film Thickness Per Coat: 150 microns wet to obtain 75 microns dry.
Two coats recommended
Hello MatM14, Just another thought. Is there any possibility of an electrical (metal) connection between the swing mooring (is it rope or chain) and the engine/prop shaft/prop and also the anode via an anchor which with a permanently connected battery earth? If there is, this may explain why you have lost half your anode in 12 months. Your anode may be sacrificial for the swing mooring as well
Hi Crusoe - good point but there wouldn't be any connection that I can think of. The only part of the mooring aparatus that is in contact with the boat is rope. We have no anchor winch.
