The mast base and the the lower section of the mast on my H37 was very corroded, so last week I decided it was time to do something about it. After a close inspection, I figured out that I had to remove at least 4 inches down the bottom to get to sain material (as seen in the first pic). In order to remove 4 inches and still keep the mast at the same height, I designed a new mast base using 4''x4''x1/4'' to raise the foot. Plus, the old mast base plate was very corroded, I decided to go with a 1/2'' base plate instead of the original 3/8'' thick one. To avoid furter corrosion, I painted the new mast step with two coat of an epoxy paint, as with the rest of the mast. Hope this may help someone with the same problem.
Solving mast base corrosion
- Thread starter Mathurin
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I made the base myself outside work hours at work.
Costwise, the base plate was 50$ and the square tubing 14$.
The most significant investement was the new molded foot from Rig-Rite, the foot alone was around 250$ and it ended up costing me 100$ in custom fees because they sent it using UPS (I live in Canada), when I think about it, I should have reused the old one, it was still in good shape.
Total cost for me around 400$, but you would have to add around 2 hours of machining time and 2 hours of welding if you were to have that made, so probably around 700-1000$ if you can find someone willing to do it.
Costwise, the base plate was 50$ and the square tubing 14$.
The most significant investement was the new molded foot from Rig-Rite, the foot alone was around 250$ and it ended up costing me 100$ in custom fees because they sent it using UPS (I live in Canada), when I think about it, I should have reused the old one, it was still in good shape.
Total cost for me around 400$, but you would have to add around 2 hours of machining time and 2 hours of welding if you were to have that made, so probably around 700-1000$ if you can find someone willing to do it.
So I assume that you are removing the same amount of material off the bottom of the mast.
Needless to say, this is very innovative and a nice job. It is something that the mfg should have considered for a keel stepped mast.
Needless to say, this is very innovative and a nice job. It is something that the mfg should have considered for a keel stepped mast.
The mast was indeed cut 4 1/8'' shorter, I very pleased with the results. I used to be scared it might give away with all tha corosion, now the mast is almost as new. Here some pictures of the job. The mast was put back on today, the new base fit perfectly.
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Beautiful work. It sounds like you didn't pay much for the aluminum and it's certainly a bit lighter, but since you coated it with epoxy did you ever consider mild steel?
Since the original base was made of aluminium, I prefered going back with it. Plus, the cast foot is made of aluminium, and I found it more convenient to weld it in place like on the original. Finally, I would be afraid of galvanic corrosion at the bottom of the mast if I were to use mild steel, and I want to keep what's left of the bottom of my mast as intact as possible. Galvanic corrosion is already an issue between keel bolt and the mast base... Mixing materials never is a good idea... I'm even thinking about completly isolating the base from the keel bolt, and putting a grounding strap directly between the mast and one bolt to minimise bimetal contact to the maximum in order to reduce corrosion.
WOW, having been in the marina game, that is a beautiful piece of work. A marine workshop would charge an arm and a leg for that, IF you could find one to do it, WELL done. I also agree that anything to help further galvanic corrosion is a plus. I am with you that NO MILD STEEL should be in a bilge in contact with ANYTHING. You have shown that we can all do necessary repairs, just have to think about it and go from there, help is only a few keystrokes away. Thanks for the post, Happy Sailing, Cheers Jeff
I'm totally shocked at the level of corrosion you removed. I have just upgraded my electric system, and am now thinking about bonding the electric system and mast. So I'm very curious about what conditions caused the corrosion, and if you were able to resolve them. I know corrosion is caused by dissimilar metals, but electricity is also involved too?
I just noticed that your old mast base is different from mine ( I have an 83 cutter). I'm also in fresh water. 2 likely differences.
I'm going to check my zincs weekly from now on, and re-read Nigel Caldur's opinions on this. Yikes!
I just noticed that your old mast base is different from mine ( I have an 83 cutter). I'm also in fresh water. 2 likely differences.
I'm going to check my zincs weekly from now on, and re-read Nigel Caldur's opinions on this. Yikes!
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I think my mast base is different from yours because I have a shaol draft, my bildge is about 14inches deep maximum, yours look a lot deeper than mine...
If you think that's a lot of corrosion, well to be honest, it looked a lot worst than that when I bought the boat... I used a little bit of putty to hide most of it at the time of the first survey, because I knew it would catch the surveyers attention, and insurance compagny are very hard to deal with in my area... Furtermor, it was in my plan to repair it.
As for the electrical system, my ground on the 12v system is throught the engine. My ground on the 115V is throught a dynaplate. I've attached a grounding strap that goes from a bolt on the mast to one of the keelbolt to protect against lightening, if I had the buget, there would be a diode in between the two to eliminate the flow of electricity in normal conditions (the diode would let the electricity flow in cas of a lightening strike)...
As for most of the corrosion, I think it probably comes from the facte that the aluminium base is linked to a big mass of lead with the keel bolt. So the lead eats up the electrons from the aluminium base making it corrode (plus add water in the bildge and you got yourself a battery).
As for galvanic corrosion, whats to be remember is that you should always avoid putting two material that are far away in the galvanic index togheter (see the chart in the wikipedia link).
http://en.wikipedia.org/wiki/Galvanic_corrosion
That is unless you want a sacrificial anode.
And you got to be even more careful not to put a small amount of a material lower on the table with a big amount of material higher in the table. In other therm you could put steel rivets in aluminium sheet metal, put putting aluminium rivets in steel sheet metal is very dangerous !
If you think that's a lot of corrosion, well to be honest, it looked a lot worst than that when I bought the boat... I used a little bit of putty to hide most of it at the time of the first survey, because I knew it would catch the surveyers attention, and insurance compagny are very hard to deal with in my area... Furtermor, it was in my plan to repair it.
As for the electrical system, my ground on the 12v system is throught the engine. My ground on the 115V is throught a dynaplate. I've attached a grounding strap that goes from a bolt on the mast to one of the keelbolt to protect against lightening, if I had the buget, there would be a diode in between the two to eliminate the flow of electricity in normal conditions (the diode would let the electricity flow in cas of a lightening strike)...
As for most of the corrosion, I think it probably comes from the facte that the aluminium base is linked to a big mass of lead with the keel bolt. So the lead eats up the electrons from the aluminium base making it corrode (plus add water in the bildge and you got yourself a battery).
As for galvanic corrosion, whats to be remember is that you should always avoid putting two material that are far away in the galvanic index togheter (see the chart in the wikipedia link).
http://en.wikipedia.org/wiki/Galvanic_corrosion
That is unless you want a sacrificial anode.
And you got to be even more careful not to put a small amount of a material lower on the table with a big amount of material higher in the table. In other therm you could put steel rivets in aluminium sheet metal, put putting aluminium rivets in steel sheet metal is very dangerous !
My '79 mast and base have minor corrosion compared to your pictures. I have seen masts like yours but always attributed it to the difference between salt water boats and fresh water boats. But maybe not. I remember when Tom Hadoulias, an '82 I think and in salt water, fixed the same problem. He had someone machine a four inch base out of solid aluminum. It was beautiful. And yours reminds me of that. Nice job.
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