Wednesday, October 26, 2011

The Rigging
By Michael


Here is the port-side upper chain plate, visible with the wood
trim removed. Note the tell-tale signs of long-term water
intrusion. Note the Japanese characters penned on the plate;
it's likely this thing had never been removed and cleaned
in the past. After 33 years, I was afraid of what I would find.

Sailboats are characterized by masts, those tall sticks used to hoist and support sails. Like most, our aluminum mast is not built strongly enough to both support itself and to bear the enormous forces imposed by the wind in the sails (this is by design as the weight of an aluminum mast capable of such loads, would be prohibitive). So, heavy cables (called stays) are attached to the mast and led to the deck, three on each side and one each at the bow and stern. Stays, in turn, are connected to large solid points attached firmly to the hull. These large solid points are called chain plates. Collectively, this whole system is called the rig.
A nightmare for any boat owner is the prospect of losing the rig, meaning losing the mast. If this happens, the sailboat loses its primary means of propulsion and likely sustains damage (or injury to the crew) from the mast and stays crashing down to the deck and cabin top. And once down, the whole heavy mess of twisted, broken metal has to be either discarded or secured to prevent further damage, such as puncturing the hull and sinking the boat.
Unfortunately, potential failure points are often difficult to identify: hidden where a stay attaches to a fitting, aloft where stays attach to the mast, or in the dark places where chain plates pass through the hull.
We had our rig inspected before we bought Del Viento and knew we had likely failure points: distorted connections where wire cable attached to fittings (swage fittings), visible cracks in the same connections, and evidence of water penetrating the sealed areas where the chain plates pass through the deck. The first two problems we addressed by replacing all eight stays. Total cost was about $3,900. This includes labor costs in Mexico and 16 Norseman mechanical fittings, all new turnbuckles, and hundreds of feet of wire cable we brought down from the States.
The top of the chain plate extends through the
deck and attaches to a turnbuckle fitting. In this
picture, I've removed the deck collar plate and dug
out all of the bedding from around the chain plate.
The rust staining you see on the chain plate here,
combined with what I saw on the collar plate, and
the evidence of water leakage below, were the
causes of my concern. 
But all new standing rigging does nothing to prevent a dismasting if there remains a weak link in the proverbial chain. Our remaining potential weak link was the chain plates.
Chain plate failure is uncommon. On a good, solid boat chain plates are overbuilt. On a well maintained boat chain plates are re-bedded on occasion to prevent water from seeping and weeping into the sealed space where the chain plate passes through the deck. The danger is that water here can cause and accelerate crevice corrosion of the stainless steel. Unchecked over time, this corrosion (totally hidden from view) can lead to a catastrophic failure of the rig.
Our rigger (Rob) noted that the bedding around our chain plates is an old product (popular in the 1970’s and 1980’s) called Dolfinite. It is still available, but I suspect its use to seal our chain plates is an indication that they’ve not been cleaned out and re-bedded in a long time. Also, there is rusty evidence of water leaking on most of our chain plates. Topsides, where the through-deck holes are sealed with a plate around each chain plate, more rust is evident.

The heavy fiberglass strut with the
chain plate removed. The rust stains
are superficial. Note the through-
deck hole at the top.

All of this led me to believe we may have serious crevice corrosion on our chain plates and may have to replace them before we can sail anywhere. To determine whether or not we have a problem, I had to remove the chain plates. (Note: the fore and aft stays on our boat are external, meaning they do not pass through the deck, creating the need for a collar of sealant, devoid of oxygen and where water may penetrate, causing corrosion. For this reason, problems with these chain plates are less likely to be hidden.)
I started with the uppers.
Uppers?
Stays on the sides of a mast are called shrouds. Shrouds generally extend either from the deck to the top of the mast (uppers) or from the deck to about halfway up the mast (lowers).
I first loosened the port side upper stay, until there was no longer any tension on the plate. Then I went below and removed the pretty wood trim that hides the port-side upper chain plate from view. Rust stains were on all the bolts and on the chain plate itself. Up around where it passed through the deck, there was additional rusty evidence of long-term water penetration. Then I removed the six massive 15/16” bolts used to attach the plate.
I learned that these bolts pass through nuts that are fiberglassed to the back of the strut to which the plate attaches and completely inaccessible. This is fine, but what if one of these is stripped or breaks free? Remedying that would be a major undertaking.
Once all of the bolts were removed, I went back out topsides and pulled the chain plate up through the hole in the deck. There I was, holding the heavy thing in my hand. I was pleased. I am going to have it polished so that I can be certain, but it appears to be one solid, intact piece of metal. I will pull the starboard upper today. If both of these uppers look good, and if the bedding material I dig out from the lowers is dry, I will re-bed all six shrouds from on deck and not pull the lowers at this time.
Once this re-rig project is complete, we can take our first sail as a family. It's been a long time coming.
--MR
This is Rob, an expert gringo rigger who helped us replace ours.
Above and behind him is Fisher, his expert gringo rigger
assistant.


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