Keel bolt corrosion

[Gary Wilson]

I've discovered that three of my keel bolts are leaking.  This problem has been masked because my bilge is normally full of fresh water from rain coming down the mast.  During a couple of months of inactivity, I noticed there were deposits of black "dust" that collected around the three.  One had small white specks scattered in the black dust.  There was also a "blob" about the size of a grape that "grew" on one of them.  It looked like mold growing on a pumpkin. I dried out the bilge and observed it over a couple of weeks.  A small amount of salt water has collected around each of these three, and no others.  They are the front one, the port one in the second row and the starboard one in the fourth row.

When we first bought our boat in 1998, I torqued the keel bolts to 105 ft lbs and repaired the "Catalina smile" at the front of the hull/keel joint.  At our last haul out and bottom job in 2003, the joint was still closed.  I think I will send a diver down to check on it.

I'm concerned that I may have some crevice corrosion taking place.  Does anyone know what stainless steel alloy is used on the keel bolts (304 or 316)?  I have saved a sample of the deposits.  Can this be analyzed to see what caused it?

As a solution, I am wondering if bonding these keel bolts to my engine ground (and therefore to the shaft zinc) would stop the process.  If I merely seal them off in the bilge, they will be out of sight and mind, but will the corrosion stop?   I wonder if I could remove the nuts and washers and inject some kind of corrosion proofing substance into the leaks?

What if my Catalina smile has opened up?  If I repair it and the leaks stop, will the corrosion continue to occur in the stagnant sea water trapped in the wooden keel insert?

Any knowledge or experience from the group on this issue would be greatly appreciated.

Thanks,
Gary Wilson
Childsong #138 1986

[Ron Hill]

Gary : To re bed and re tighten your leaking keel bolt nut you first need a haul out and get the weight of the keel off of the hull.  Then you'll need to clean out and dry the area around the leaking nuts.  Remove the nuts & washers and chip away the old bulged out caulk.  I'd try to "V" out a SMALL grove between each leaking keel bolt and the bilge/hull "floor".  I used 3M 4200 although you can use 5200.  I know about the 105/7 ft lbs of torque.  If you are doing the tightening by hand I seriously doubt that you can over torque - unless you're King Kong!!  Then clean up the excess and don't splash the boat till the caulk is 100% cured.

Hint - Anytime you caulk a bolt/screw hole only tighten it down 3/4 of the way.  Then let it cure for about 8-12 hrs.  Then tighten it down all of the way.  If you tighten down fresh caulk all the way immediately, you squirt all of the caulk out. 3/4 tightness will let some of the caulk cure and then when you tighten to 100% you'll force some (cured) caulk into the hole instead of all of it out of that area.  

[Gary Wilson]

Thanks, Ron.  This sounds like a good procedure.  I did not realize the keep bolts were caulked.