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Zincs for Aluminum Boat

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theydrewa31

Regular Contributor
Hello again Gentlemen!

I am in the process of restoring a Starcraft Islander 221V. The hull material is 5052 riveted aluminum. I have a few questions about zincs.

The first is a stupid question. It is necessary to have zincs on an aluminum hull? My understanding was that they were necessary but the guy at the local boating supply store was telling me that they were not necessary. This did not seem right to me so I though I should ask you guys.

Is there a way to figure out the best size and shape for these the zincs? Also, how many zincs should be used, and where is the best mounting location? My boat is a 22' V shaped hull and I will be using it primarily in saltwater. The zinc that was previously installed was placed on the outside of the transom, below the water line. The previous owner did me the wonderful favor of painting every single zinc he could find with black paint, including the zincs on the outdrive! :eek:💩 I was told I might be able to save the old zincs by using paint remover on them to see if I can get the paint off. Is it a good idea to remove the paint, or should I simply replace them. This project boat has turned out to be far more expensive than I had realized so I am trying to save every penny that I can.

I removed the zinc from the transom as I am currently replacing the transom wood. I am including a picture of the zinc below.

zinc.jpg
 
So I went at it with some goof off and some elbow grease today. The result is below. It looks alright to me, so I think I'll put it back into use. that said, I'm still curious if this is large enough zinc for my vessel, and where the ideal placement would be as all of the old attachment holes in the transom have been welded up at this point. I'll take a rough opinion on size. I don't need an ultra scientific explanation with a math equation to back it up or anything. Just want to make sure I'm covering my bases before I start putting more holes into the boat.

zinc cleaned.jpg



Thanks in advance for any help gents!
 
Sacrificial anodes, (zinc or AL), by definition are sacrificial. Their surface area NEEDS to be pure, otherwise you are defeating their purpose.
Anything the impedes the flow of electrons, (which are produced by the weak battery effect of saltwater & non noble metals), will result in some other part being eaten away.
Only an idiot would paint an anode.
You can use paint remover, or simply strip them clean with a wire wheel.
 
If you keep it in the water all the time, yes you need zincs. The ones you have are fine. Heck you can still read the "PERKO" script. The hull itself, again only if in the water constantly, should be epoxy primed on the bare aluminum followed by a non copper anti fouling. Don't paint the zincs as that more or less kills the effect.
You could also use what's called a zinc "guppy" which is a sacrificial zinc on a conductive wire hung over the side. It should be attached to the hull in a way that allows it to conduct between the hull and the zinc. You can use one of those you pulled off. Wire it to the hull and chuck it over when tied up. Don't place it where it can get into the prop if you forget to pull it inboard when you go out. The commercially available ones use stainless steel braided wire not plain copper household wire.
If the boat lives on a trailer you don't really need to be concerned unless you plan to spend a lot of time tied up at a marina where there's plenty of stray current.
 
theydrewa31 said:
So I went at it with some goof off and some elbow grease today. The result is below. It looks alright to me, so I think I'll put it back into use. that said, I'm still curious if this is large enough zinc for my vessel, and where the ideal placement would be as all of the old attachment holes in the transom have been welded up at this point. I'll take a rough opinion on size. I don't need an ultra scientific explanation with a math equation to back it up or anything. Just want to make sure I'm covering my bases before I start putting more holes into the boat.

View attachment 34260


Thanks in advance for any help gents!
Click to expand...

What did you expect the Goof Off to remove? That stuff is for removing solvent-based materials, not organic or electrolytic deposits.

Sand them in an open space, while wearing a good dust mask. As posted, you need bare metal on all surfaces.
 
Edchris177 said:
Only an idiot would paint an anode.
Click to expand...
That was my thought exactly. Again, the previous owner didn't really seem to know what he was doing.
Edchris177 said:
You can use paint remover, or simply strip them clean with a wire wheel.
Click to expand...
I was considering something like a wire wheel but someone told me that the resulting dust that would be created is flammable. I didn't know if it was malarkey, so I used the goof off instead. But I am seeing some corrosion on the top layer so I was considering trying to sand it off a little more anyhow. Is wet sanding a good option? If the dust is in fact flammable I just wanted to cover my bases. Especially in Southern California right now where we are having wildfires left and right, I don't want to add to the problems we are having down here.
 
o2batsea said:
If you keep it in the water all the time, yes you need zincs. The ones you have are fine. Heck you can still read the "PERKO" script. The hull itself, again only if in the water constantly, should be epoxy primed on the bare aluminum followed by a non copper anti fouling. Don't paint the zincs as that more or less kills the effect.
You could also use what's called a zinc "guppy" which is a sacrificial zinc on a conductive wire hung over the side. It should be attached to the hull in a way that allows it to conduct between the hull and the zinc. You can use one of those you pulled off. Wire it to the hull and chuck it over when tied up. Don't place it where it can get into the prop if you forget to pull it inboard when you go out. The commercially available ones use stainless steel braided wire not plain copper household wire.
If the boat lives on a trailer you don't really need to be concerned unless you plan to spend a lot of time tied up at a marina where there's plenty of stray current.
Click to expand...

She won't be moored full time. Yes she will be used in saltwater, but when not in use she will live on a trailer. Clearly I wouldn't paint the zincs. That was done by the previous owner. At most this boat will spend 3 days and nights on the water when I visit the offshore islands, or perhaps when I spend a few days in the bay with my wife for a "stay-cation". It will probably not be often that she spends that much time on the water, but when that does happen she will be anchored or tied to a mooring ball. I think I'll stick with attaching this thing back onto the transom. That said, I'm curious if a guppy is more effective than simply attaching this to the hull?

Thanks o2batsea!
 
jimn said:
What did you expect the Goof Off to remove? That stuff is for removing solvent-based materials, not organic or electrolytic deposits.

Sand them in an open space, while wearing a good dust mask. As posted, you need bare metal on all surfaces.
Click to expand...
Well, the goof off did remove the paint, which was my first goal but I do see the deposits on there still. The only reason I haven't gone further is because I was told that the resulting dust is flammable. I was considering wet sanding it just to make sure I don't have any issues with that. Is wet sanding a bad idea?

Thanks jimn!
 
I have another question for you gents. The zinc from the hull had a strip of rubber on the back, which I assume was for isolation from vibration so that it didn't scrape the paint of the hull over time. Any thoughts on what I can replace that with?
 
o2batsea said:
The hull itself, again only if in the water constantly, should be epoxy primed on the bare aluminum followed by a non copper anti fouling.
Click to expand...
Being that this boat at most will spend a few days at a time on the water, is the anti fouling paint necessary? There are only a few bare spots on the hull as of right now which are the spots on the transom where I had to get some welding done, and a few spots on the bottom where the rollers have rubbed the hull down to bare metal over time (or perhaps it happened when I towed her 3400 miles across country). I have professional paint sprayers and all the necessary supplies for that and I was considering painting just the bare spots with some high build primer, followed by automotive base coat. I was considering topping it off with some 2K clear coat for strength but I wasn't sure if that was a good idea or not. I am trying to avoid the anti-fouling paint as it is insanely expensive and this boat project is far more expensive than I had expected already.
 
theydrewa31 said:
I have another question for you gents. The zinc from the hull had a strip of rubber on the back, which I assume was for isolation from vibration so that it didn't scrape the paint of the hull over time. Any thoughts on what I can replace that with?
Click to expand...
The anode has to be electrically connected to whatever you’re trying to protect. If it’s isolated, by any form of electrical insulation, it cannot protect. That’s why Obatsea said to use a connecting WIRE between the zinc & the hull. The wire has to be attached to the metal hull of the boat. If there is not continuity between the hull/outdrive & the zinc, the anode will do nothing, & the least noble metal on your boat will become the sacrificial anode.
All anodes on all my motors are secured directly to the outdrive. If you feel vibration is an issue, (I don’t, if it’s bolted securely it can’t vibrate), you can rubber mount the anode, BUT, you must electrically connected to whatever it via a conductive material to whatever you are trying to protect.
 
Edchris177 said:
The anode has to be electrically connected to whatever you’re trying to protect. If it’s isolated, by any form of electrical insulation, it cannot protect. That’s why Obatsea said to use a connecting WIRE between the zinc & the hull. The wire has to be attached to the metal hull of the boat. If there is not continuity between the hull/outdrive & the zinc, the anode will do nothing, & the least noble metal on your boat will become the sacrificial anode.
All anodes on all my motors are secured directly to the outdrive. If you feel vibration is an issue, (I don’t, if it’s bolted securely it can’t vibrate), you can rubber mount the anode, BUT, you must electrically connected to whatever it via a conductive material to whatever you are trying to protect.
Click to expand...
This makes perfect sense with your explanation. So no rubber backing on the anode. Note taken. If this zinc is mounted on the outside of the transom, should I attach a wire to one of the bolts attaching the anode on the inside of the transom to somewhere inside the boat (perhaps the grounding wire) or is that overkill? Or, should I remove the paint underneath where the anode will be attached to the transom to ensure contact that way? Sorry if these are dumb questions, just trying to gain full understanding of the subject matter. Clearly I want to do things right, just trying to figure out what the right way to do things!

Thanks for the help Edchris! Very much appreciated!
 
I would remove the paint under the anode. My manual, (Volvo), specifically states that, along with not painting the anode.
If you look closely at outdrives you will see several thin SS wires connecting different parts. That is to ensure the entire power train is connected to the anode(s).
Essentially all metas can be arranged with reference to a nobility scale. Metal such a gold, titanium, nickel are very noble. Zinc, magnesium, aluminum are at the other end.
Any situation that creates a galvanic couple results in erosion of the least noble metal, & there just happens to be quite a bunch of aluminum in most marine drives.
 
If someone looks at a stern drive or outboard, they'll see thin wires connecting the separate parts- they're called 'continuity wires' because if they aren't used, the pieces will be electrically insulated to some degree that would make anodes at the far end (lower gearcase) useless. Some gearcases have a Zinc cap on the propshaft for this purpose- it decreases loss of material due to galvanic erosion. If anyone sees that any of these wires are missing, it's best to replace them. Continuity needs to be tested from the propshaft to the battery negative and if high resistance is seen, it needs to be corrected.

DO NOT try this if the cable ends are lead and just set on the battery posts- there's no point. These need to be clean and tight- the Coast Guard no longer approves wing nuts on studs with ring terminals.
 
I am guessing that you have an outboard on it, yes? That will have anodes attached, yes? If it's a stern drive you definitely have anodes. Those should be sufficient to protect the boat for the few days you're in the soup. Be sure that there is a continuity wire going from the outboard or engine to the hull. It can be a small (like 1/16) length of stainless cable that you crimp terminals to the ends and attach to the hull with a screw or use an existing fitting. As long as the engine is bonded to the hull, the anodes on the lower unit should be plenty for the short duration wet. Keep an eye on the hull and running gear. Since you have it on a trailer, inspection isn't a thing. If you see corrosion, pitting, or anything suspect, get after it with a stainless wire brush and some paint. I'm surprised that you are reticent to protect your investment with proper bottom paint.
 
o2batsea said:
I am guessing that you have an outboard on it, yes? That will have anodes attached, yes? If it's a stern drive you definitely have anodes. Those should be sufficient to protect the boat for the few days you're in the soup. Be sure that there is a continuity wire going from the outboard or engine to the hull. It can be a small (like 1/16) length of stainless cable that you crimp terminals to the ends and attach to the hull with a screw or use an existing fitting. As long as the engine is bonded to the hull, the anodes on the lower unit should be plenty for the short duration wet. Keep an eye on the hull and running gear. Since you have it on a trailer, inspection isn't a thing. If you see corrosion, pitting, or anything suspect, get after it with a stainless wire brush and some paint. I'm surprised that you are reticent to protect your investment with proper bottom paint.
Click to expand...
Sorry, not an outboard. It is an OMC cobra inboard/outboard. And the outdrive does have its own anodes. There was a wire running from the engine to bare aluminum when I pulled the motor out.

It's not that I don't want to use the proper bottom paint, I'm just trying to keep cost down. That said, I do want to do things right, and I would value your opinion if you think its worth it for my situation. I was told by a fella at the local boat supply store that "aluminum boats don't need any paint at all", but I kind of thought that didn't seem right.

Thanks for the link, I am shopping their products right now. I'm thinking about using the Krypton.

Is the etch wash necessary? I'll be using a spray gun, If you happen to know how many coats of the barrier coat, and Krypton I should be using please let me know! Looks like I'll need at least 4 coats of the barrier?
 
theydrewa31 said:
Sorry, not an outboard. It is an OMC cobra inboard/outboard. And the outdrive does have its own anodes. There was a wire running from the engine to bare aluminum when I pulled the motor out.

It's not that I don't want to use the proper bottom paint, I'm just trying to keep cost down. That said, I do want to do things right, and I would value your opinion if you think its worth it for my situation. I was told by a fella at the local boat supply store that "aluminum boats don't need any paint at all", but I kind of thought that didn't seem right.

Thanks for the link, I am shopping their products right now. I'm thinking about using the Krypton.

Is the etch wash necessary? I'll be using a spray gun, If you happen to know how many coats of the barrier coat, and Krypton I should be using please let me know! Looks like I'll need at least 4 coats of the barrier?
Click to expand...

The stuff that makes bottom paint necessary doesn't care about your budget, it's all gonna do what it's gonna do.

Aluminum needs to be etched and it's a good idea to ground the hull before spraying, which creates static electricity.

THe wire to the hull from the battery- if it was like a typical power cable, it may have been for the gauges and accessories.
 
lots of excellent infor here.
I have aluminum anodes on my engine pod which is considered the hull. my outboard engine has like 3 anondes at differnt heights one of which is above the water line. the most important thing to know about electraliss's is never conduct electricy though the aluminum hull. ei: don't use the hull as a ground Like automobils use there bodies.
always connect grounds back to the battery.

edit: when to replace a anode is when it's completely disenagrated is this true or false?
 
TheBrain said:
.

edit: when to replace a anode is when it's completely disenagrated is this true or false?
Click to expand...
FALSE
One of my service manuals says replace when it is 1/3 gone.
Volvo “ Replacing sacrificial anodes 1. Inspect anodes every 14 days, or more frequently if used in extremely salty water. If an anode is 2/3 its original size (1/3 eroded), replace it.”
 
Last edited:
TheBrain said:
.

edit: when to replace a anode is when it's completely disenagrated is this true or false?
Click to expand...
From Evinrude service manuals,
“If any anode has been reduced to 2/3 its original size ( 1/3 eroded), it must be replaced! Test for proper installation of the anode.
Calibrate an ohmmeter on high ohms scale.
Connect one meter lead to a powerhead ground and the other lead to the anode.
Be sure the surface of the anode is clean to make good contact.
The ohmmeter should show a low reading. If not, remove the anode and clean the area where the anode is installed.
The mounting screws and the anode itself should also be cleaned. Install and retest.
NOTE Do not paint or coat the anodes or their mounting surfaces.”
 
TheBrain said:
lots of excellent infor here.
I have aluminum anodes on my engine pod which is considered the hull. my outboard engine has like 3 anondes at differnt heights one of which is above the water line. the most important thing to know about electraliss's is never conduct electricy though the aluminum hull. ei: don't use the hull as a ground Like automobils use there bodies.
always connect grounds back to the battery.

edit: when to replace a anode is when it's completely disenagrated is this true or false?
Click to expand...

If you have Aluminum anodes, ALL of the Aluminum on the boat is acting like an anode unless it's not in contact with the water or elctrical system and even then, it can erode, especially if the fasteners are steel, galvanized, or not. Aluminum seat hinges come to mind- I saw a lot of those with evidence of galvanic erosion when I worked for an upholstery shop.
 
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