mast step rot

[eustace]

Hello - lurker here, first post,

I took this picture...

http://cruisersforum.com/photopost//...php?photo=1100

of the step of a keel-stepped mast on a boat I inspected today.
Has anyone seen something like this before?
It was brittle and chalky in texture. I thought it may have been some sealant paint, the aliminum itself couldn't corrode this badly, right?
The step is not at the bottom of the bilge, so if it is water that is causing this corrosion, I wonder if it could be seeping out the bottom. Maybe be it isn't water related - I clearly don't have a clue! If anyone else does, I'd appreciate you sharing the knowledge.
Cheers,
-eustace

Looks like electrolosis to me. Bad news.

[Alan Wheeler]

That's a major. Certainly a corrsion problem. I don't think it is electrolysis. Electrolysis is usually contact area affected. It would have to be submerged in salt water or touching the other metal it is working against. If the mast is stepped on something metal, that could be the issue and the corrosion is working up the mast.
What material is the step fixed to, fiberglass, metal, Wood?
I presume SST bolts all round? SST bolts need to be insulated from the Aluminium.
What is the cable attached, earth strap? Firstly, the cable isn't really heavy enough for the job. The connecting terminal needs to be heavier and coated in Lanocote or similar to protect it from corrosion.
OK, you need to wire buff this white stuff away and see what you have left to play with. I suspect very little, but here's hoping the best for you.
Keep us up to the play and when you post again, please include another photo just a little further away, so as I can see a little more of the area.
Good luck

[capt lar]

that was aluminium. appears the boat sat with mast in for some period of time with water in the bilge high enough to submerge the base of the mast. you need to pull the mast and determine how much is gone. if lucky, you can trim mast and install a shoe @ keel that will make up the loss.
any quality yard can help.
capt. lar

[eustace]

Thanks for the helpful replies everyone.
The good news is that I don't own this boat, I was just inspecting it. Because of this and other problems with the boat I am not going to pursue it further. It is listed at a very low price, and I guess you do get what you pay for.

The step where the corrosion is ocurring was raised about a foot up from the bilge, just under the cabin sole. It was mounted on metal, which at the time I presumed to be aluminum after some gentle scraping, could be wrong.
It seemed too high to be sitting in bilge water, maybe water was seeping from inside - which would suggest it is even worse underneath and inside the step.

I will upload more pictures when I get home in case anyones interested to see them.

Thanks again all,
-e

[Alan Wheeler]

If the base is sitting on a metal plate, and if by some chance that plate is SST, then there is your culprit. Water most likely is coming down from above. Sometimes difficult to stop, especially if a boot is not used. But if it can freely drain to the bildge, it still shoudn't cause what you have seen, UNLESS, a dissimilar metal is in contact.
Still, if the boat is cheap enough, the repair is not tooo major and you could end up with a good deal at the end of it.

[capt lar]

i, too, would not be scared off by this alone. every boat will have issues. my boat had the same problem and repair, and surveyor signed off on it.
i once owned a boat that had the engine fail shortly after purchase - no oil - thats bad. figured out the boat had partially sunk at the dock prior to purchase. yard pumped her out and since high water was below floorboards - no harm - no foul. unfortunately someone had made a large custom copper drip pan and the sides came up beyond the engine, back where you could never get to it anyway. pan filled with saltwater when boat took on water at dock- engine / transmission sat in salt water from then on - found a nice hole the size of a quarter when we hauled it out. copper pan was in good shape when i ripped it out of the boat.
capt. lar

[delmarrey]

I have the same problem except that mine has not progressed very far. One of the major problems with keel stepped masts. Most have a SS plate under an aluminum mast, bad combo! And add salt water, and Wa-la.

Fortunatlly, mine has a salt free bilge, unless I screw up, like leaving a forward hatch open while in foul weather (don't ask) . Most of the water I get (rain) comes down the internal halyards of the mast. There are a couple of notches at the base of the mast so the water can drain out. I keep those cleaned out regularly. And then I have created some small levee's to direct the water away from the mast. Just hope there's no hurricanes

One of these days (Ha) I'm going to manufacture a Phenolic shoe about 2" high to go between the keel plate and the mast. That should stop the errosion problem.

What you have here is repairable. Just cut off a couple inches and add a shoe like I discribed above. The shoe just has to be bolted to the keel plate and inserted into the mast a substantial distance to prevent the mast from sliding.
Depending on the brand of mast, you can buy a shoe that already fits inside and add a spacer to take up the rest of the distance removed.

My guess of electrolisis was based on the likelyhood that the mast was stepped on steel. A very common procedure in 70's-80's boats. The set-up you describe sounds like what I am thinking. With the steel step, the aluminum mast, and the copper wire with the cheap automotive lug connector, I think it is a safe bet, but... I also agree about not letting that stop you. You may just have a diamond in the rough. I guess it depends on how much of a project you are willing to take on. Sometimes a deal really IS a deal.

[Mr. Fixit]

I am in the process of correcting the same problem. On my boat the mast was inserted into a "shoe" of cast aluminum. The first 2 inches I would estimate approx. 25% 0f the mast was completely gone. I was surprised that the first few inches didnt collapse. The shoe was likewise corroded. I am in the process of using "Black Locust " blocking to raise the step 4". ( I cut 4 1/2" inches off the mast) Using the cut off portion as a form I will make a shoe using fiberglass reinforced epoxy, that the mast will sit inside of. I intend to provide plenty of drainage to get water inside mast to drain.. The epoxy "shoe will have 4 tabs" to fasten to Black Locust blocking that is lagged to the keel. I feel by raising mast above water level in bilge and providing drainage my problems will be over
I have and advantage over all you younger sailors, My fixes do not have to last as long !!!!! sad but true.

[JGI417]

Electrolysis would be my guess, however I would ensure that the mast drain is clear,
From what I am reading from these posts, if this is such a problem, is is possible to use a zink on the base of the mast,
Hope this is not a stuip question

[Alan Wheeler]

Not a stupid question JG, but the answer is no. There are two forms of corrosion. One is Galvanic and the other is electrolytic. For an anode to work, it must be placed along with what ever metalo it is protecting, in an electrolyte. Thus under the water. This Corrosion we are observing here, is Galvanic and is caused by another metal actually touching the Aluminium. The corrosion is happening at the joint itself. The reason why the Oxide is traveling, is due to several reasons, but mostly, because aluminium needs oxygen to generate it's protective layer. But oxygen is the same gas that makes it corrode. With clean Aluminum and balance is meet. But in this case the oxide is stopping that protective layer from forming and staying on the surface and thus exposing the ally to more oxygen in an uncontrolled way and thus is corroding away.