Anchor Chain Lessons

When we bought our boat there were two windlasses and only one anchor rode.  It was fairly new G4 Imperial sized 3/8" chain.  I asked the owner how long a chain lasts in the tropics.  "One season, sometimes two, then you just have to buy another one.  It's part of the cost of cruising," was his reply.

I took that as pretty much gospel, and it's certainly true.  Tropical waters, warm and saline, eat metal for lunch, stainless included.  The ideal anchor rode would actually be a stretchy line, like nylon except for one minor problem.  Coral can be very sharp and abrade through a line rode in one lively night at anchor.  There's just no way you can sleep with fabric alone keeping your family off the rocks.

Dual windlasses was one of the attractions to the Lagoon 47.  I wasn't aware of any other production cats that featured dual Lofrans wired and ready.  I asked the owner if the second, unused windlass worked.  "Don't know, I never used it."   But then, he didn't have three kids aboard.

I determined to test the second windlass.  There was a dangle of wires in the locker.  After some tracing and testing, it turned out to be a simple task to install a new controller.

Fast forward a couple years.

Now it's time to buy some replacement chain.  Because we foolishly put off fixing our watermaker for over a year, fresh water was scarce.  The boat is plumbed with an anchor locker fresh water wash-down, but we never used it.   In hindsight, that was probably false economy.  Even a gallon of rinse per cycle would most likely have helped extend the life of the chain.

Then the time came to buy chain, but which to choose?  Here things got sticky.  First off, Lofrans, who makes our windlass, is in financial trouble so new parts, such as gypsies (the wheel that actually interfaces with the chain and must be sized to match the link width, length and spacing), are getting hard to find.  A gypsy for the G4 hi-test imperial chain that was on the boat when we started is just no longer available and the one on board is pretty battered.  Investing in new chain with only a single rough gypsy available didn't sound like a great idea.

This meant using non-hi-test chain was really the only viable option.  This chain is sold as G30 or Din 766 or ISO4565.   The specs don't sound nearly as impressive as they do for hi-test.  Working load limits are just about half of what they are for high test chain, 5,400 versus 2,750 lbs.  

I wasn't really happy about this until reading some additional details on the chain, namely that the WLL for G30 is actually 1/3th of its average load at first distortion.  This means standard chain should deliver holding power in the 8,000+ range or, for out boat, wind speeds to about 140 miles per hour.   Add to this, the findings that most G30 Chinese chains were breaking at G40 strengths.

Of course, hi-test would be great, but it just wasn't an option and with these numbers in my head.  I'll still sleep like a baby through the average 45 knot squall which produces about 1,200 lbs force on the anchor rode, or half the WLL of standard G30/DIN 766.

The calculation I use for this is:

  • Force (lbs/square foot) = (wind speed (miles/hour))*.868)^2 x .0027 x resistance area (sq feet).
    • We reduce the wind speed by .868 to make it nautical miles per hour of wind since that's what boaters use and for which most wind instruments are calibrated.  If you are using a nautical mile wind speed measurement already, then skip that step.
    • Resistance is a wild card.  An actual calculation would take an engineer many hours factoring all surface areas, parasite drag, the drag coefficient (a measure of aero dynamic qualities) ad nauseam.
    • I take a much simpler approach to arrive at a workable estimate.  I look at the front profile of my boat, the part facing into the wind.  I cover that profile with sheets of plywood at 32 square feet per sheet, not even bothering to cut out the actual shape, just cover the entire hull silhouette so, for wind load purposes I am treating my boat like a billboard.  
    • Since we have a catamaran, that amounts to quite a bit of plywood, 5 sheets for 160 square feet.  Our boat is pointy though, not flat across the wind, so it cuts through the air a lot better than a billboard.  On the other hand, the boat has a lot of stuff sticking out, like a mast, boom bag full of sail, life lines, etc, that all snag a little piece of wind.   Do these cancel each other out?   Probably not exactly, but they do counteract each other so, for the purposes of not being an engineer, we say they do.

The next question was chain pitch.  European windlasses, like Lofrans, generally accept 30mm pitch (the inside dimensions of a single link) while Quick from Italy ships their windlasses with gypsies for 28mm pitch chain.  I checked my gypsy with some sample lengths generously loaned me by Ian from St. Lucia's Island Water World.   It became clear pretty quickly that the backup gypsy I have been stubbing my toes on for three years is designed for 30mm chain.  And, surprise, the gypsy that has been used for the last few years with 31.5 mm pitch imperial chain is actually also a 30mm gypsy.  This would explain why the chain didn't always feed properly and why it's so rough already.   I have been using a mismatched chain-gypsy combination the entire time.

While in Martinique we did some boat parts shopping and I saw barrels of chain in the corners.  I asked about it and learn two things:

  1. The anchor chain was made in France (I asked multiple stores and all got the same response).
  2. The chain was about 50% cheaper than chain sold by Island Water World and Budget in the formerly British islands.  In 2013, this was about 7.10 Euros per meter versus 4.50 per foot.   Per inch costs calculate at 23 cents versus 37 cents.  Ouch.  French chain started to look mighty attractive.

I had a sample of the French made anchor chain that we had purchased in Martinique a few days ago.   I compared this to a sample link of the Canadian Metals chain stocked and sold by Island Water World.  The Canadian links are made in China, but they insist that quality is tightly monitored and is as good as the old stuff that was made in Canada.  We'll see.

I started by cutting the non-welded side of the link.  Based on my house construction rebar experience, I know that a stiff start and a quick "pop" were a bad, brittle sign.   Both the French and CMP chains were nearly identical in this regard.  A nice slow squeeze with the bolt cutter with slow building resistance and then a mushy 'bump' when the link was cut 95% through and the remaining strands failed under tension.

So far so good.   Now for the acid stress test.  Using vice grips and a huge screw driver (wouldn't a vice have been nice?!) I twisted the links apart, putting maximum torsional stress on the weld.   Like people, you don't know what something is made of until you stress them beyond all reason.

My goal was to cause weld failure.  Of course, pure tension would be ideal, but I just don't have a 50 Ton Denison tensile tester handy.  The results were surprising.

Both French-made links failed fairly quickly with the weld itself splitting open pretty much right down the center.  Good adhesion, weak weld.  The first failed after about 60 degrees of twist, the second at about 120 degrees.  The Chinese-made CMP chain withstood 180 degrees of twist and still held, although noticeably weakening.   It was interesting to note that the weld itself didn't move, but that the torsional movement was occurring on both ends of the weld where it mated with the link ends.  This meant that twice the area is absorbing the same load.

The CMP is going to cost about 50% more (amounting to several hundred dollars) but, now that I have seen the French links fail so easily, it seems a worthwhile investment.   If I purchased the French chain, all I could see in my mind's eye during a freak squall would be those split links.

Maybe the French should stick to baguettes.

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