Saturday, June 3, 2017

Cast iron keels and keel bolts


...after sand blasting, epoxy filling and sanding, then three coats of epoxy primer the cast-iron keel of our Columbia 43 is ready for bottom paint. It has a complex and beautiful shape that you could only achieve with a strong, durable materal like iron.
I get a lot of questions about keel bolts. Almost every potential owner and owner of a Columbia 43 worries about them.

I only really know about my boat, a Columbia 43 Mark I, but I think it is like most of Tripp-designed boats Columbia built. They had cast-iron keels attached with galvanized keel bolts. The keel was set in a socket in the fiberglass hull with an industrial adhesive called Furane Epibond, which is still made today.
The keel installation page from the Columbia 43 plan set. Note the beautiful drafting, which was all done by hand. Tripp was a consummate artist.

Here's an interesting paragraph from a 1971 article in Boating Magazine describing in detail how the keel on a Columbia 43 is attached:

"With a 10,250-pound cast iron fin keel hanging on the bottom of the boat, we were interested in the method used to secure same. We found that the keel flange is flushed into a recess or pocket in the hull. Prior to attachment, the keel is given a dry run to check for accurate fit in the recess. If all is not well, the flange is ground to suit--the pocket is never ground except to remove gel coat. When the fit is satisfactory, the recess is coated with a thick application of Furane Epibond, and epoxy compound. With the entire weight of the boat resting on the keel, ten 3/4" diameter cotton-wrapped bolts, nuts, flat washers and lock washers are installed. Internally the keel weight is distributed by a heavy, glassed-in platform and a series of steel transverse channels that pickup the keel bolts. We were convinced that the keel is there to stay."

The article didn't specify that the bolts were galvanized steel, but the plan sheet for attaching the keel does. That's what is on my boat too.

Galvanized bolts were exactly the right thing to use. They start out being 18 percent stronger than the same sized stainless bolt. From there the stainless bolt has nowhere to go but down. I would not trust any stainless bolt more than 10 years old. They can look perfect and yet fail catastrophically with no warning.

Galvanized bolts, on the other hand, retain their strength even when they are rusty. So a 50-year-old galvanized bolt that is 18 percent rusted away is about the same strength as a brand new stainless steel bolt. I won't even get into crevice corrosion in stainless steel. Let's just say a damp bilge provides the perfect environment for crevice corrosion.

If someone, I'm thinking a boat buyer here, looks in a bilge and sees some rusty keel bolts they totally freak out! I've had more than one person tell me that they once considered buying a Columbia 43, but didn't because of the condition of the keel bolts. I also had a C-43 owner bemoan the fact that she almost had her boat sold until the potential buyer looked in the bilge and saw the keel bolts. I told her to get a wire cup for her drill and go to work on them to get the loose rust off them, wipe them down with acetone, prime with a rust converter and then spray paint them white. I hope that was good advice. (While you're at it GET RID of all the old useless wires, pumps and junk in the bilge.)

The keel bolts on the Columbia 43 Mark I were studs and can be backed out (theoretically). I wouldn't do it. I might sister them, but I would not do that either unless the bolts -- all or most of them -- had all but disappeared. I can think of all kinds of things that could go wrong. You could get the new bolts torqued wrong and start a leak, for example. (More about this later.)

The thing is, there are no cases where a Columbia 43 has lost her keel. If there were, we would hear about it. (Think Cheeki Rafiki.) Also, Columbia tested the adhesive system they used on these keels using it alone without any keel bolts. It worked fine, or so the story goes. I don't know if they went back and added keel bolts later or not. Let's just say I trust my 46-year-old keel attachment more than I would most new boats.

Now for the Columbia 43 Mark III: The Mark III was a later development of the original Mark I. One of the biggest changes Columbia made was a smaller keel (same depth, 6'11", but a much shorter chord) to reduce wetted surface. I haven't seen a Mark III out of the water nor have I seen the design drawings. From what I can gather the keel had external lead ballast on a fiberglass keel stub. I don't know what kind of bolts they used. I also don't know who did the redesign, since Bill Tripp (the Columbia 43's designer) was dead before Columbia came out with the Mark III.

One of my friends who has a Mark III in the Sea of Cortez had problems with his where it developed a smile (in boatyard parlance, it's called a "Catalina smile"). It looked like the keel was starting to become detached. He had a yard in Mexico fix it -- I don't know the details -- but so far he's happy with it.

Stumpy J, the Columbia 43 Mark III that competed in the 2013 Transpac and finished 6th in Division 8, the same division that Dorade won that year, also had problems with her keel. When the owner was getting her ready for the race someone recommended that he re-tighten the keel bolts. He did that and it caused leaks that plagued the boat throughout the race and afterward.

That's about all I know about Columbia 43 keels. I believe a lot of the Tripp-designed Columbia's had cast iron keels similar to the 43 Mark I. One notable exception is the Columbia 50, which has lead encapsulated in the fiberglass hull. (This, to me, is the most trouble-free method. I hesitate to say "best" because other things come into play.)

I generally think Columbia 43 boat owners worry a lot about keel bolts because they look bad, not because there is any real danger of losing a keel. Should I be worried? Comment below. You'll have to cite actual examples of keel failures if you want me to pay attention.


  1. I'm renovating my Columbia 43 Mk I. The keel is fastened as described by Brandon, with threaded rods. My bilge has been wet for years from multiple causes, including a terribly leaking hull-deck joint and a leaking water tank. I have resolved all those issues only to discover a hideous flaw in the keel fastenings. As depicted in the accurate drawings, the galvanized rods have a galvanized nut and washer bearing down on a steel channel that runs athwartships, bonded to the fiberglass bilge. The steel channel is maybe 30" wide, and was designed, no doubt, to spread any bending forces widely rather than have the nuts and washers bear the load. The tragic design flaw is that the steel channel is mild steel. This caused two major failures. First, the steel channels have turned into flakes of blackened slag. They are almost completely gone. Second, the galvanic interaction between galvanized steel and mild steel is such that the galvanizing zinc is the less noble, and is therefore attacked by the steel channel. Worse, the steel channel is hundreds of times the area of the galvanized washer and nut, accelerating the corrosion. The nuts are completely compromised. I could break off one shoulder of a nut with my fingers, like it was made of dried mud. I have not yet split the nuts to examine the galvanized rods, but they must surely be compromised in a similar fashion. In other words, my keel is being held on by the glue Brandon mentions.

    Fortunately, my boat is on the hard while I rebuild my 4JH2-TE and velvet drive transmission -- all in my garage at home. My remedial plan for the keel is simple: I'm going to sister the threaded rods with 3/4" galvanized bolts (easier to install than threaded rod). I will order steel channels similar in size and shape to the originals, with holes pre-drilled, and then have them hot-dip galvanized. I will install the new channels and bolts about 6" from the existing relics. Fortunately, long cobalt drill bits and long bottoming taps are easy to come by, and remarkably inexpensive. I'll probably order a couple of each in case of breakage.

    What I can't figure out from the drawings is how long the existing threaded rods are. I'll drill a test hole to see how far down I go before hitting the cast iron, then add --- how much? Would 4" penetration into the keel be enough, or should I go for more?

  2. I have a Columbia 43. I am on. The verge of bolstering the hull section by section and removing rust from the top of the keel (so I am not forced to drop the keel. I will be able to access it from inside the boat, God willing!

  3. Hi all..I have a 34 mark 2 columbia ..and yes the same issues as above..any solution as to the hull and deck joint

  4. This comment has been removed by a blog administrator.