Mast Step Repair Articles for a Cape Dory 27

[psjanker]

I took this two part series on a Cape Dory 27 mast step repair from Sailfeed. Thought it was interesting since I always wondered what was under the mast on my CD 28. Note that 40 years after the point that CD made the engineering decision to put in the mild steel tube, the author decided to leave it as is with the slight modification of filling in the tube....I would have painted with POR 15 also.

V/r

Pete



Mast Step Repairs with the Telltales Sailing Collective
Posted by Paul Calder // September 15, 2015
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Yep folks, that’s forty-year-old mild steel holding up the mast!
I’ve written before about bizarre and highly questionable design elements in 1970’s Cape Dorys (Side note: I always hesitate when I pluralize Cape Dory, like I want to write ‘Cape Dories’ but I know that isn’t actually right). Now that the Telltales Sailing Collective has been given a nearly identical Cape Dory 27 I’m getting a trip down memory lane. But I’m pleasantly surprised to find that this time around is a little different. That rebar and mild steel isn’t pretty and from a technical perspective it’s fairly artless but on this boat it has held up to the test of time surprisingly well. This wasn’t really true on my boat, where much of the original steel ‘chainplates’ had rusted into dust, but much of the blame for that lay on foolish DIY fixes, like when someone tried to stem water intrusion with duct tape!

Apparently they tried to make up the difference in size between the hole in the deck and the fill fitting by wrapping a few turns of tape around the fitting
The current boat, our Collective’s CD27, has been better cared for, or at least less abused. I was pleasantly surprised to find the chainplates/backing plates in good enough shape that I don’t think we’ll need to replace them anytime soon. Unfortunately the mast step is more of a concern; it was showing signs of distortion and possible sinking and we decided that we had better cut into it and see what state the internal structure was in. What we found was surprising in a few ways.
First, a note on the (’70’s-era) Cape Dorys’ construction, which included a fairly unusual way of transferring loads from the mast to the keel. In the mid-70’s when these boats were built Cape Dory Yachts had only just jumped into the ‘big’ boat market after ten years developing a reputation building ten and fourteen-footers (of note: in the mid-70’s a builder producing seaworthy 27-30 footers was in the ‘yacht-building’ business!). Around this time Cape Dory got into in-house fabrication of its own hardware, under the moniker Spartan Marine. Cape Dory has long since folded but Spartan are still around, now located downriver from my family home in Damariscotta, Maine and still making very high quality bronze hardware. Back then their hardware appears to have been of a similar caliber. These 70’s era Cape Dorys carried a smattering of really impressive cast bronze pieces, including the heel fittings and the massive castings which anchor the forestay on the 27’s and 28’s. It is this no-expense-spared approach to certain aspects of construction which makes the extensive use of low-quality mild steels elsewhere on the boat all the more inexplicable. I suppose these were still the chaotic early days of fiberglass boatbuilding when even major builders were more-or-less winging it.

Just for fun, take a look at this chainplate diagram from the original owners manual: XX
Compare the proud specificity about the “manganese bronze chainplate casting” with the suspiciously unspecific note about “metal reinforcement” on the inside of the hull. “Metal reinforcement” actually means a honkin’ big chunk of 1/2″ mild steel running along the underside of the deck and welded to three pieces of mild steel rebar (!) which are bent in a fishhook shape along the inside of the hull and glassed into it. Which brings me back to the mast step. On the 27’s and 28’s the bulkheads dividing the head from the v-berth and the main cabin were of course structural elements which held the hull in shape but through the addition of beefy 2″x 2″teak or mahogany ‘trim’ on the door frames they also served as compression posts for the mast, eliminating the need for a big wooden post cutting through the already slim walkway in the center of the boat. Of course the door frames aren’t located right under the mast so the yard needed a way to distribute that load. This is where things get weird. Here’s a shot of the mast step after we chopped it open:

It’s a little confusing but I’ll do my best to explain. The mast rests on a rougly two foot long chunk of 5″ x 2″ mild steel rectangular tubing. Very economical this, you can buy it at any steel yard for a couple bucks a foot. Being tubing it is hollow, but the walls are fairly thick and it’s a serious piece of metal. On my 28 I believe that this piece is welded to two similar bits of rectangular tubing which extend over the doorframes. On the 27 they simplified a bit, opting instead to weld the rectangular tubing to what looks like a piece of flat steel which runs the length of it and presumable stretches out over the door frames. We didn’t cut enough away to be certain how far this piece extends.

The rectangular tubing is resting on and welded to a piece of flat steel
The air space around this construction has been filled with what looks to me like polyester resin mixed with sawdust and then fiberglass has been laid over the top of it all to a thickness of about 3/8″. When new this construction was probably strong enough for a fifty footer. Now that these chunks of mild steel have spent forty years in a marine environment the questions is how much of the original metal is left to hold up the mast. From the cracking we observed around the mast step I was expecting the answer to be ‘not much’ but when cut in with a grinder and chisels to expose the steel I was surprised to find nearly all of the structure still intact with little more than surface rust.

Freshly exposed
The single exception is in the are where a hole was drilled for the (poorly sealed) mast wiring and rust had chewed through about half of the thickness of the steel over an area of an inch or two square. This rusted area was the cause of the visible cracking which had us worried that the mast step was sinking. It turned out that the opposite was true. Mild steel expands as it rusts, sometimes to something like double its original thickness, and this expansion was pushing the fiberglass upwards and creating cracks.

The one area showing significant corrosion damage
At this point we sat back to think, and I took a minute to check in with the always helpful folks at the West System technical hotline. Really we were quite lucky. Our fears that the structure of the mast step had deteriorated enough to cause sagging were unfounded and actually the only significant structural differences between the boat as constructed and at present seemed to be the rust in that small area where the wires passed through and, of course, the fiberglass we cut away to expose the internal structure. Now then, how to make our repair?
Mast Step Repairs with the Telltales Sailing Collective (Part 2: What is the ‘correct’ repair?)
Posted by Paul Calder // September 19, 2015 // COMMENT (0 Comments)
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Mast step structure exposed
Well, we’ve got the mast step on the Telltales Sailing Collective’s first boat opened right up and now we’re deciding how to put it back together. Working on boats I often find this the hardest part of the repair- there are so many materials and approaches available that it can be overwhelming, especially in a case like this where there is no ‘standard approach.’

The fiberglass we cut away to expose the internal structure
Fortunately with a little critical thought we came up with the correct repair. In the first case, mild steel has no place on a sailboat, particularly in a role as critical as distributing compression loads from the mast, so the first step will be to remove the piece of steel tubing which the mast was resting on. Unfortunately it is welded to flat steel plates at either end so we will need to cut these welds and quite likely to extend our deck surgery out until we find the edges of these plates and are able to remove them. Then this structure will need to be replaced with a material which is equally strong but more appropriate to a marine environment. Stainless steel is a reasonable candidate but introduces potential issues of crevice corrosion, especially in an anaerobic (oxygen free) environment, such as being glassed into the deck. A better candidate would be a marine grade bronze, but the cost of fabricating in bronze is immense. A third option is to use a modern fiberglass composite such as G-10.

G-10 Fiberglass Board
G-10 is immensely strong, immune to corrosion, relatively light and easy to work with, and cheaper than bronze. Rather than replicating the existing hollow metal box-section we could use G-10 to fabricate a solid ‘beam’ which would have the added benefit of eliminating any air spaces where water might collect. We can then rebuild the fiberglass deck over the top of our new mast step structure and have a stronger-than-new repair. Certainly this is a serious endeavor, maybe twenty or more hours of work and upwards of $500 in materials, but we’ll have the security of knowing we’ve done this the ‘right’ way, using modern materials and techniques.
Oh, except we’re all volunteers and we don’t have any money… So on second thought…

Cleaning off rust with a wire wheel on an angle grinder
This boat is forty years old, as are these mild steel structural elements. For at least the past few years a poor seal for the mast wiring has allowed rainwater intrusion into this structure. In spite of this there is surprisingly little visible deterioration of the steel, aside from the approximately two inch square area where the hole for the wires was drilled. Luckily this is not directly under the mast and shouldn’t weaken the rest of the structure a whole lot. Aside from the relatively minor fiberglass cracking from rust expansion there are no telltale signs such as extensive gelcoat cracks or sagging of the cabin ceiling which would indicate a loss of structural integrity. There is also no history of mast step failure in these boats that I’ve heard of, despite there being hundreds produced. Given this, and the fact that these boats are massively overbuilt to begin with, it’s clear that there is no real need for repairs or structural reinforcement at this point. Actually we’ll be just fine if we leave this structure as is, maybe with a protective coat of epoxy to delay any future corrosion and glue back on the fiberglass that we removed to expose it.

See, it really doesn’t look bad with all the rust cleaned up
Now you see what I mean about settling on an approach being the hardest part of the repair? Despite being polar opposites I’m fairly confident that in this case either of these approaches would work out. The first, done right, is obviously a superior repair but it’s also a far greater expense of resources. The second is a bit of a gamble but I suspect that even doing nothing we would be just fine. At any rate after taking a good look at this internal structure I’m confident that any future problems would manifest gradually and visibly rather than catastrophically.
This brings me (finally!, you might be thinking) to my point, which is that the ‘right’ repair in this and many cases is the one that best balances expectations of security and longevity with available funds and supplies. When you’re on a budget, as I nearly always am, you can’t always do things in keeping with industry standards. In my experience a critical eye and an open mind is more valuable (and a lot cheaper!) than slavish dedication to anyone else’s rulebook. With this in mind, let’s take a final (serious) look at our repair.

That weld connects the rectangular tubing to an underlying steel plate the shows minimal if any corrosion
The big variable here is the mild steel support member.Nearly everything I’ve ever learned about sailboat construction tells me that relying on mild steel for a critical structural member is a very bad idea. But, like I noted, this piece is overbuilt, has done its job for forty years and appears to have lost very little strength in that time. As far as I know this unusual construction technique was standard on all Cape Dory 27’s, 28’s and probably others. Hundreds of these boats were built and a great number are still in service thirty and forty years later. Quite a few have crossed oceans or even circumnavigated. There is also an active owners group with an excellent forum in which the common issues with these boats are well covered. Fortunately the mast step is not one of these issues and the
general consensus among internet-savvy owners seems to be that this part is rarely, if ever, an issue.
Despite going against all my learned wisdom about boats it seems that mild steel was a perfectly adequate material for this job and I don’t see any compelling reason to replace this structure with something more ‘marine grade’. That said, having already gone this far with grinder and chisel to perform an important visual inspection I think it would be foolish to put this structure back together without making some improvements and repairs.
First, there’s that rust spot. An easy reinforcement is epoxying a new piece of reinforcing steel over the damaged section. Since weight is no major concern and steel is cheap we decided to cut a larger piece which extends over the area that the mast rests on.

The damage section before rust cleanup. We enlarged the hole for the mast wiring so we could better inspect the interior. This will be covered with a piece of flat steel reinforcement
Next, there’s the airspace created by the use of hollow box-section steel. I don’t like internal air pockets and I especially don’t like them in proximity to steel of any type. One misplaced hole and an air pocket becomes a water reservoir. So, while we have the chance we’re going to fill all the air space in this structure. Since the filler ought never to be structural it doesn’t really matter what we use although it makes sense to use something with high compression strength, just in case. Neat (unthickened) resin flows nicely and has high compression strength, making it an excellent choice. In this non-critical role we decided to use polyester, to save costs. We also decided to add some debris filler to save on weight and cost. Almost anything incompressible would be suitable here so we chopped up some otherwise useless scraps of ironwood that I had saved. In this case the selection is mostly based on making me feel better about being a bit of a hoarder. This mixture of resin and debris will be used to fill all the air spaces in a series of pours.
With the steel structure reinforced and the air spaces filled the last step will be re-bonding the fiberglass cap which protects and strengthens the internal structure. For this fairly standard repair we will use epoxy resin and fillers.
It may seems crazy to talk about repairing a mild steel structure with polyester resin, a little more mild steel and some random debris but if this boat’s 40-year history is anything to go by I think our budget repair will hold up just fine. Of course it helps that there wasn’t actually much that needed fixing in the first place.