Macgregor 25 1982 Keel What should I do?

[patrickfarley]

The boat sat for years in fresh water. It had encrustations of mud and iron 2" thick. I scraped it and gave it a quick wire brush.

I have the feeling it was made in Mexico.

I had no idea that there was so little metal around the pivot hole. The pivot hole is 11/16" round in the center of the keel. As the hole nears the edge of the keel it gets bigger and becomes 13/16". I hope I explained it clearly enough. It does not show in the pictures. The pivot bolt showed no wear at all.

I plan to take it to a welding shop on Monday and find out what they can do about strengthening that little piece of metal between the hole and the edge. I am hoping someone can give me some ideas to bounce of the welding shop. I don't want to have something done that will weaken the area and I really really don't want to loose the keel.

When that is done I am going to have it blasted, paint it with a barrier coat and bottom coat.

By the way. I am trying to figure out what bottom coat to use. I plan to spend June on the Florida coast every year and two weeks around Christmas. The rest of the year I am in fresh water. I want to keep it at a dock July to November in Lake Lanier, fresh water. Any suggestions?

 

[centerline]

the pivot hole is easy if you can weld. there are several ways to go about it, but the best would be to bore it out bigger and then weld a slug in the hole.... then redrill a new hole of the right size and in the proper spot. the hole as it is could probably be welded closed and redrilled, but thats hard on tools and you have a chance of breaking a bit off in the hole trying to drill thru the weld...... or..... for someone that doesnt have a boring bit, you can cut a rectangle out where the hole is, turn the rectangle over so the existing hole is located in the wrong spot, and weld the rectangle back in.... and redrill a new hole in the right spot where the fresh metal is. then weld up the old hole, or not.... it wont matter

 

[patrickfarley]

The keel is cast iron. I have never welded cast iron. Grew up on a farm welding tools and took a welding class in college. Cast iron is beyond me. Can one just weld the hole closed? I like this idea. It sounds like it will not weaken the surrounding area. Sounds like a good idea to run by the welding shop.

 

[centerline]

if the welding is done correctly it will be as strong as it ever was or will be. cast is a little tricky but its just a different procedure. any experienced welder can do it.
its an easy fix either way and shouldnt cost much to have it done.

 

[caguy]

The keel was meant to have a 1/16 inch clearance witha 5/8 bolt. If you want to tighten up the tolerance you could drill the hole out to just under 13/16 and use a bunting bearing. Freeze the bearing and heat up the keel it should press fit right in.

Or do nothing and wait another 120 years for the hole to open another 1/2" and worry about it then.

http://www.globalindustrial.com/p/m...e-Bearings-google_pr&infoParam.campaignId=T9F

 

[patrickfarley]

Ok, I always thought cast iron took special skills. I guess the skills are special if you don't have them.

What is the correct diameter for the hole on a 1982 keel pivot hole and any recommendations on the barrier paint? Trailer, fresh and salt water.

 

[patrickfarley]

Thanks for all the great information

 

[caguy]

I used red oxide paint and it looks as good now as it did 5 years ago. If I did it over again I would probably use zinc chromate.

 

[Phyrexii]

I wouldn't worry about it. There's more material between the edge of the keel and the edge of the hole than there is in the bolt holding it in place. The shear strength of the iron in the keel between the hole and the edge is in the many thousands of pounds (the shear strenth of cast iron is aprox 58,000 lbs / in^2). The keel only weighs aprox 650#. Plus, there's very little load in that direction, even in a grounding. Besides, your fiberglass hull around the bolt will yeild before the iron will. Unless it's cracked, I wouldn't touch it (in fact, welding cast iron is more likely to cause a crack).

My $.02

 

[Phyrexii]

Lincoln welding has a page about how to weld cast iron. Thought you may findi it interesting:
http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/welding-cast-iron-detail.aspx

 

[centerline]

Ok, I always thought cast iron took special skills. I guess the skills are special if you don't have them.

you are correct, that is the only thing special about it. people are scared of it cuz they dont understand it. as with anything else, follow the procedure correctly and it is all good....

 

[patrickfarley]

Lincoln welding has a page about how to weld cast iron. Thought you may findi it interesting:
http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/welding-cast-iron-detail.aspx

Sealing Cracks
Because of the nature of cast iron, tiny cracks tend to appear next to the weld even when good procedures are followed. If the casting must be water tight, this can be a problem. However, leaking can usually be eliminated with some sort of sealing compound or they may rust shut very soon after being returned to service.

After reading the procedures and then this section I am reluctant to have any welding done on the cast iron keel.

 

[patrickfarley]

I wouldn't worry about it. There's more material between the edge of the keel and the edge of the hole than there is in the bolt holding it in place. The shear strength of the iron in the keel between the hole and the edge is in the many thousands of pounds (the shear strenth of cast iron is aprox 58,000 lbs / in^2). The keel only weighs aprox 650#. Plus, there's very little load in that direction, even in a grounding. Besides, your fiberglass hull around the bolt will yeild before the iron will. Unless it's cracked, I wouldn't touch it (in fact, welding cast iron is more likely to cause a crack).

My $.02

Ok. You made me start reading. I did not understand your equation for the sheer strength but from what I read you are correct. I also read that cast iron fails in tensile strength and found: Tensile strength of cast iron is 50ksi or 50,000psi. I have at least an inch of cast iron left around the pivot hole. I read another site that stated 40,000 psi.

Based on all this information I am not going to have any welding done on the keel. I really don't want small cracks that will allow water intrusion around the pivot hole and the amount of metal left should easily hold the weight of the keel. .

 

[patrickfarley]

What failed to cause the keel to fall off of a Macgregor 25? What is the cause/ are causes of keel failures?

 

[centerline]

Sealing Cracks
Because of the nature of cast iron, tiny cracks tend to appear next to the weld even when good procedures are followed. If the casting must be water tight, this can be a problem. However, leaking can usually be eliminated with some sort of sealing compound or they may rust shut very soon after being returned to service.

After reading the procedures and then this section I am reluctant to have any welding done on the cast iron keel.

I am sure from the pictures you have posted that it will be fine the way it is, but to clarify.....
the cracks they speak of are cosmetic surface cracks.... it is because the weld deposit cools faster with the exposure to air.... and slightly pulls away from the base metal as the deposit shrinks. they may go as deep as a 1/64 of an inch along the edge of the weld. you will sometimes get them with the cold weld process, but not with the hot weld process. normally you cannot even see the cracks unless you use a dye solution made specifically for finding impossible to see cracks.
water cannot possibly get into your keel after welding... not now, not after welding on it, or ever. it is a solid piece of iron with absolutely no place for water to go or collect.... inside or out.
the crack, if it should develope, would fill itself with oxidation within a couple weeks.... or if you painted it, the paint would seal it forever. no worries....

 

[THECUSCUS]

My pivot hole was enlarged also. I reamed the hole to 3/4" and put a bronze bushing in there (3/4"od x 5/8"id). I got it from Mcmaster-carr for afew dollars. Here are the links to how I rebuilt my keel. I only wanted to mess with it once in my lifetime.
http://www.macgregorsailors.com/modt/index.php?view=1483
http://www.macgregorsailors.com/modt/index.php?view=1484

Hope this gives you some food for thought.

 

[patrickfarley]

My pivot hole was enlarged also. I reamed the hole to 3/4" and put a bronze bushing in there (3/4"od x 5/8"id). I got it from Mcmaster-carr for afew dollars. Here are the links to how I rebuilt my keel. I only wanted to mess with it once in my lifetime.
http://www.macgregorsailors.com/modt/index.php?view=1483
http://www.macgregorsailors.com/modt/index.php?view=1484

Hope this gives you some food for thought.

Thanks. I think I will paint it with an epoxy barrier coat and then an ablative bottom coat. Other than the big MEXICO cast into the side of the keel it looks quite smooth. There is one void near the bottom that I will fill. Other than that I think I will just blast it and paint.

 

[patrickfarley]

Took the keel to two different shops. The welding shop I usually use was not sure about what would work. I then went to a big shop that is usually too expensive and they said for $50 they could weld a hard bead around the inside of the hole and drill it out to the correct size. They said the weld would be stronger than the original hole and harder than the original cast iron. They wanted $150 for sand blasting the keel.

I think I will have them do the work on the pivot hole. $150 for removing some rust seems a bit too much.

What diameter should I have them drill the hole. I saw it on the site before but forgot and cannot find it now. I think it is 11/16" Is anyone sure?

 

[Sumner]

The repair sound like a good deal to me and the blasting a little high. Try a couple other places. We got the whole trailer done for $275 if I remember right.

Can't help on the hole size, but look up a couple posts and see what was used on another 25,

Sum

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[THECUSCUS]

The pivot bolt is 5/8", and the prints I've seen say 11/16" for the hole. But unless you're going to bore it with a mill, hand drilling a 5/8" hole with a drill bit will be sloppy enough. Personally, I wouldn't weld on the thing, if its not done correctly you will have other issues. These keels are of questionable material, made in Mexico and are metalurgically challenged to begin with ( they are full of casting pourosity and I've even seen pictures of a keel that that still had some "unmelted" junk in the keel casting) and I wouldn't subject one to the heat/stress of welding. Drill it and use a bushing. I think that the keels we hear of that just "fall off" are mishaps due to the poor castings.
Just my thoughts, do what you are comfortable with.