Aluminum Keel That Flooded

[msponer]

Hi Guys,

I just purchased an aluminum boat. At the end of the sea trial I noticed water coming out of the zinc bolt hole on the fin part of the keel. A very thorough ultrasonic inspection revealed no thinning of the plates on the fin or bulb, so I went ahead with the purchase.

Here is a video from the boroscope inspection, which I believe looks pretty good. The metal inside looks dirty, but I do not see any craters.

Boroscope inspection of keel - YouTube

The history is:

1997: Boat constructed

~2008: Plate on bulb deformed. Pinhole leak found in a weld on the deformed plate. Plate removed and rewelded. Zincs added to bulb and fin in case there are more leaks.

2011: Water poured out of zinc bolt hole when boat lifted out of water. We incorrectly launched the boat without a bolt screwed into a hole, and did not know that the threaded bolt hole for the zinc goes all the way through to the inside of the keel. We assumed the bolt holes were only as deep as the zinc mounting plates. There was silicone inside the hole, but without the bolt, the keel filled.

I'm trying to figure out what the "best" fix is, or if one is even necessary. I believe the external zincs protect the aluminum plate when the boat is in the water. I'd also like to keep the keel happy when the boat is out of the water: since it's aluminum, our plan is to keep the boat on the hard if we ever have to leave her, rather than a marina (and risk electrolysis from a new neighbor).

I am guessing that before I weld the boroscope hole shut, I could:
- Dry out the inside of the keel (how?)
- Fill the compartment with epoxy, or some other goo, to reduce the surface area of the lead that's in contact with sea water, in case the keel floods again or is always flooded?
- Something else?

If it's really important to have no water inside the keel: grind off the current zinc mounting plates, weld the bolt holes shut, and then drill & tap new mounting plates before welding them to the keel (so that the holes don't go all the way through to the inside of the keel).

Do you guys have any experience or ideas?

[gjordan]

I would think it would be important to not have water in your keel if there is any chance of you leaving it on the hard in a cold climate. Frozen water will easily distort aluminum and probably break your welds in the keel. Pre-threaded plates, welded to the keel is pretty standard, and should work good. Can you get to the top of the keel from the bilge? You might want to put an inspection plate, so that you could pump it if needed. Better yet, make sure the welds are perfect and use the keel as a fuel tank.___Good Luck____Grant.

[Lagoon4us]

Originally Posted by msponer

Hi Guys,

I just purchased an aluminum boat. At the end of the sea trial I noticed water coming out of the zinc bolt hole on the fin part of the keel. A very thorough ultrasonic inspection revealed no thinning of the plates on the fin or bulb, so I went ahead with the purchase.

Here is a video from the boroscope inspection, which I believe looks pretty good. The metal inside looks dirty, but I do not see any craters.

The history is:

1997: Boat constructed

~2008: Plate on bulb deformed. Pinhole leak found in a weld on the deformed plate. Plate removed and rewelded. Zincs added to bulb and fin in case there are more leaks.

2011: Water poured out of zinc bolt hole when boat lifted out of water. We incorrectly launched the boat without a bolt screwed into a hole, and did not know that the threaded bolt hole for the zinc goes all the way through to the inside of the keel. We assumed the bolt holes were only as deep as the zinc mounting plates. There was silicone inside the hole, but without the bolt, the keel filled.

I'm trying to figure out what the "best" fix is, or if one is even necessary. I believe the external zincs protect the aluminum plate when the boat is in the water. I'd also like to keep the keel happy when the boat is out of the water: since it's aluminum, our plan is to keep the boat on the hard if we ever have to leave her, rather than a marina (and risk electrolysis from a new neighbor).

I am guessing that before I weld the boroscope hole shut, I could:
- Dry out the inside of the keel (how?)
- Fill the compartment with epoxy, or some other goo, to reduce the surface area of the lead that's in contact with sea water, in case the keel floods again or is always flooded?
- Something else?

If it's really important to have no water inside the keel: grind off the current zinc mounting plates, weld the bolt holes shut, and then drill & tap new mounting plates before welding them to the keel (so that the holes don't go all the way through to the inside of the keel).

Do you guys have any experience or ideas?

Ok i'm a retired builder of both round bilge aluminium and steel yachts. The following is my opinion only. And i agree with gjordan.
1) Did you notice the whitish gooey gel inside? Thats disimiliar alloys electrolytic corrosion similar to a battery.
2) did you notice the extruded aluminium sections inside? They are made of a different alloy to the plating ie high in silicon low in magnesium.
3) The only way to connect a MAGNESIUM anode (not zinc!!!!!) is by welding a say 10mm backing plate to the keel then bolt the anode on by way of drill and tapping. Never ever through bolt into a void. Why? because as the anode deterioates or gets hit/damaged it does not void the hull.
When all welding is completed disc sand it and put three coats of epoxy resin over all ally areas other than the contact area of the anode. Then undercoat and antifoul.

INSIDE the hull on top of the keel plate put a couple of bungs in and use as a fuel tank or WASTE OIL or simply add some soluable oil into the keel BUT install vent,fill and pump out tubes, it will stop corrosion and if you ground heavily and void the keel you will get a harmless slick or oil (depending on your choice) around the boat confirming a repair being needed.
Has worked for me, here comes the criticism..............

[marc2012]

The Zn had me wondering as well,Seems the Al should do a pretty good job of saving the Zn though.

[Lagoon4us]

It pays to look up the metal nobility table, Cheers Frank.

[S/V Alchemy]

Purchase this to increase understand of your issues before you pour further time and money into a solution. I have a steel boat and it's clarified some misconceptions and has improved my understanding greatly.

[msponer]

Originally Posted by S/V Alchemy

Purchase this to increase understand of your issues before you pour further time and money into a solution. I have a steel boat and it's clarified some misconceptions and has improved my understanding greatly.

Thank you. I have it, and read it, but should probably read it again, since I still know very little about galvanic corrosion. My wife has a graduate degree in Chemistry and, when I try to figure these details out with her, she tells me that it's complicated to really figure out from first principles. That the electropotential only tells you the energy released by the reaction, but not the rate, and that the rate is the most important part. And that intermediate products, which are not on the simple galvanic scales, are very important, they can completely change what will happen. So that, really, the best way to know this stuff is to know what people have figured out experimentally and with experience. Understanding the science behind it is only the first step, because it's so complicated. I read a Navy paper that said stagnant sea water gets slimey, and that slimey sea water moves the galvanic series around -- that's something I would have never thought of, and may apply here (if the keel fills with water again and the water gets stagnant). Or the whole thing about over-zincing (or bringing the electropotential down too much) the aluminum: how it causes paint to peel off, that is something that'd be very hard to predict from first principles.

So, I guess my main questions are:
- How do I dry the inside of the keel out? Keep pouring acetone in there? Put an air compressor hose in there and let it blow through at a low rate for days?
- Is there something better than epoxy for reducing the surface area of the lead, if it gets wet inside again?
- If I do pour epoxy into the keel, is there a way to help it stick to the dirty sides of the aluminum and lead that I can't quite clean in there?

[noelex 77]

Originally Posted by Lagoon4us

3) The only way to connect a MAGNESIUM anode (not zinc!!!!!) i

Originally Posted by marc2012

The Zn had me wondering as well,Seems the Al should do a pretty good job of saving the Zn though.

Zinc is the recomended anode material for an aluminium boat in salt water.

[minaret]

Originally Posted by msponer

Thank you. I have it, and read it, but should probably read it again, since I still know very little about galvanic corrosion. My wife has a graduate degree in Chemistry and, when I try to figure these details out with her, she tells me that it's complicated to really figure out from first principles. That the electropotential only tells you the energy released by the reaction, but not the rate, and that the rate is the most important part. And that intermediate products, which are not on the simple galvanic scales, are very important, they can completely change what will happen. So that, really, the best way to know this stuff is to know what people have figured out experimentally and with experience. Understanding the science behind it is only the first step, because it's so complicated. I read a Navy paper that said stagnant sea water gets slimey, and that slimey sea water moves the galvanic series around -- that's something I would have never thought of, and may apply here (if the keel fills with water again and the water gets stagnant). Or the whole thing about over-zincing (or bringing the electropotential down too much) the aluminum: how it causes paint to peel off, that is something that'd be very hard to predict from first principles.

So, I guess my main questions are:
- How do I dry the inside of the keel out? Keep pouring acetone in there? Put an air compressor hose in there and let it blow through at a low rate for days?
- Is there something better than epoxy for reducing the surface area of the lead, if it gets wet inside again?
- If I do pour epoxy into the keel, is there a way to help it stick to the dirty sides of the aluminum and lead that I can't quite clean in there?

Questions-

1. We use a large diesel heater with forced air. It has a large duct attachment. I would drill a second hole saw hole and attach the heater duct to the lowest hole, allowing the upper hole to vent. That would dry it out pretty quick, usually a few hours but sometimes a day or two. If you don't have access to a 60k BTU forced air heater you could do the same with a different heater and just use much more time. Hi temp ducting is hard to find and expensive, but there are some lo-tech options like old fire hose. If you use a diesel heater be aware that the output can contain a little sooty exhaust, especially on start up and stop. This needs to be dealt with before adhering anything to the substrate.

2. Not really. You might look at pouring chockfast to cover the top of the lead. Use chockfast orange for this. It is a modified epoxy.


3. Acid etch the aluminum and lead at the same time. I suggest cleaning with alumiprep 33 followed by a nice coating of alodine. I realize access is minimal but if you can get a sprayer in there it could be done fairly thoroughly. Alodine is extremely thin and would spray nicely, a big enough cloud of overspray in the keel cavity might reach spots the sprayer alone couldn't. You should consider cutting an inspection plate first to give yourself more options for drying and spraying and pouring. Maybe a second vent hole would be unnecessary if you did this.

[msponer]

Originally Posted by Lagoon4us

2) did you notice the extruded aluminium sections inside? They are made of a different alloy to the plating ie high in silicon low in magnesium.

I am guessing that the box inside is the edge of a plate that pokes up from part of the bulbs internal structure. I do not think it is an extrusion, since it seems like it'd be part of the structure that fastens the bulb to the fin, and just doesn't look like an extrusion. But of course I have a limited knowledge of metal fabrication and boat construction and defer to someone (you!) whose actually made a boat. If it is a plate I am guessing it's the same marine grade alloy as the outside of the keel bulb.

Originally Posted by Lagoon4us

3) The only way to connect a MAGNESIUM anode (not zinc!!!!!) is by welding a say 10mm backing plate to the keel then bolt the anode on by way of drill and tapping. Never ever through bolt into a void. Why? because as the anode deterioates or gets hit/damaged it does not void the hull.
When all welding is completed disc sand it and put three coats of epoxy resin over all ally areas other than the contact area of the anode. Then undercoat and antifoul.

Yes, I agree completely, I think it's border line retarded that they welded the backing plate to the keel and then drilled and tapped through both. What is even the point of the backing plate, then? Boat yards....

Why magnesium? I read a little about it (in the book mentioned above), and I believe the widely accepted thought is to always use zinc. But I do not know the details well enough to talk about it intelligently or do more than just parrot back the conclusion. I'll pay attention to that part when I read the book again.

Originally Posted by Lagoon4us

INSIDE the hull on top of the keel plate put a couple of bungs in and use as a fuel tank or WASTE OIL or simply add some soluable oil into the keel BUT install vent,fill and pump out tubes, it will stop corrosion and if you ground heavily and void the keel you will get a harmless slick or oil (depending on your choice) around the boat confirming a repair being needed.

This is a hydraulic lift keel, so I can't use it as a fuel tank... But isn't a problem with filling it with oil or diesel that it would make welding on the keel later potentially explosive? I have limited knowledge, but I learned to weld from a guy that works on natural gas and oil pipelines. He said that before they could weld on a pipe that had oil in it they had to work pretty hard to clean the inside surfaces to make sure any trace of oil was gone.

[Cheechako]

I'm not sure i understand the whole thing entirely, but it seems you can drill a low drain hole and flush the keel out with fresh water. You might be able to add something in the water... baking soda?.... to neutralize the salt. Then , why not weld up all holes in the keel and put the zinc somewhere else.. ie: why does there have to be a zinc on the keel itself...? Problem I see with filling the keel with epoxy is if you dont get the corrosion goo and salt out of there... you may make corrosion worse by trapping it between the alum and epoxy....

[noelex 77]

Salt water will not corrode marine grade aluminium even without any protective coating. It will also not corrode lead, but put the two together and you will get corrosion so its important to get the water out.
A vacuum engine oil removing pump should work. They have long thin stiff tubes that you should be able to push down to the bottom. and suck any remaining salt water out.
Don’t use baking soda aluminium needs to kept near a neutral PH. Many aluminium boat keels are filled with diesel, usually as part of the fuel tank, but this may be a good option if there is no possibility of it leaking into the environment.

[Cheechako]

[QUOTE=noelex 77;854155]Salt water will not corrode marine grade aluminium even without any protective coating.
In a perfect world this is true, unfortunately it's not a perfect world. Otherwise, why put zincs and electrolysis monitors on alum boats?
Here's an example: A client had an aluminum trailerable boat. Because he didnt keep it in the water he decided to not put bottom paint on. He fresh water rinsed the boat and trailer after each use. The trailer had bunk boards covered with indoor /outdoor carpet. To his dismay, after using the boat for one season, he found fairly severe pitting in the aluminum... only where the bunk boards contacted the hull. A few of these pits were nearly .06 deep. The salt water was not getting rinsed out of the carpeted area, and the lack of fresh air flow etc caused this issue.
Actually I was thinking that using baking soda or something..... to make the water neutral ph... isnt salt water rather acidic? not sure.... that's where the chemist wife comes in handy!

[swagman]

We had an aluminium keel on a past yacht and recall the lead was encapsulated by a slow curing resin - they said this gave the resin the best chance to get right into every void twix lead and aluminium, before going off. Just like you are proposing with epoxy.
After six years it was apparent our encapsulation was not 100% successful, and if we had to do it today, I'd take the advice others have given and flood the void with oil.
CHeers
JOHN

[Matt sachs]

+1 on the water freezing and deforming the keel. Mine is 5/16 steel and it distorted 3/8 inch on both sides. PITA to repair. Doable but not fun.