January 2, 2016
No matter if your anchoring religion tends to the church of Rockna or some other denomination, while gathering information to replace my chain, I found a very nice resource Rockna’s website here:
I thought it would be simple to replace our rusting, ten year old chain, but no. First, what kind of chain did we have? It turns out it might not have been the 1/4″ high test that we thought it was. It seems that “High Test” and “High Tensil,” terms that represent very different animals, are often used interchangeably by marketers.
I’m resigned to replacing the chain wheel on our anchor windlass to fit the metric chain available in New Zealand. What chain wheels does Maxwell actually make? Which can be readily sourced?
Will I be able to maintain the same strength in our anchor rode (and since I’m now not sure what chain we had, what working load or breaking load numbers should I look for?)
Oh yea, to complicate that issue, working load seems to be nothing more than another marketing team invention. In the US, working load is often chosen to be 1/4 or 1/3 the breaking strength (which looks more impressive). In New Zealand, it can be 1/5 or even a smaller fraction. That leaves only one choice: just look at breaking strength. Easy right? Nope. I can’t seem to find any breaking strength numbers on the chain available from local marine stores.
And now there’s the weight issue. Legacy is very sensitive to weight in the bow. Add a little too much and the ride gets much wetter. How much weight will we gain with new chain? How will I offset that weight gain in the bow? Can I stow the secondary anchor rode further aft?
Old school says as much as you can carry of the largest chain possible without completely sinking the boat. It turns out that maybe with modern anchors, this might not be necessary. Here are two great articles on Rockna’s web site:
Rode Optimizations
Scope vs. Catenary
Anyway, I’ll muddle through it all. The point of this was that I am really impressed with the info on Rockna’s website. There’s also good info about shackles. That’ll be the next part of our new chain saga. -Rich
Update, February 22, 2016
We found and bought new chain! It’s Acco 7 mm Grade 40 chain and it’s almost exactly the same size as the 1/4″ chain we had. It fits in our chain wheel perfectly. We bought it at Bridon Cookes in Tauranga. What great people. They know their stuff!
Acco 7mm Grade 40 Chain (A4, DIN 766):
Working Load: 750 kg = 1,653 lbs (meaningless marketing stuff, see above)
Breaking Load: = 30.8 KN = 6,924 lbs
We took the old chain to Bridon Cookes and they tested a sample of our old chain to the breaking point, which turned out to be 4,050 kg, or 8,928 lbs. This surprised me and was much higher than expected from it’s outward appearance.
Above is the chain before and after the test. I was amazed at how much it stretched. The bright silver is what happened to the galvanizing. The chain at the top shows the worst of the rust.
The above image shows how dramatically the chain narrowed during testing at the points where it meets the adjoining link. I think I’ll take a lesson from this and inspect these spots in our new chain periodically.
OK, lets do the math. Did I really need new chain?
cb = curb weight of a ’68 Cadillac Coupe DeVille = 4,900 lbs
bs = breaking strength of our chain = 8,928 lbs
ce = Cadillac Equivalents
bs / cb = ce = 1.822 ’68 Cadillac Coupe DeVilles
I’m pretty sure that they’d pull the bow off legacy before the chain would break.
But seriously folks. I probably could have re-galvanized our old chain and gone another ten years. I read that re-galvanizing reduces the strength of the chain but I don’t know how much. Live and learn.
Shackle were another issue. The only shackles I could find that were load rated, and with a high enough load to match the chain where stainless Wichard forged bow shackles.
Working Load: 3,350 lbs
Breaking Load: 11,465 lbs
The pin was too tight in the chain links but a tiny fraction. I was able to expand the link that tiny bit needed by brute force, a hammer, and a now ruined socket used as a wedge. (I don’t want to think about what that might have done to the strength of the chain!)
Update: September 3, 2021
The chain we bought from Briden Cooke, supposedly Acco, was trash. In two years it was badly rusted, so bad that we replaced it in May of this year.
Chain is really hard to come by in New Zealand (thanks Covid!) and we had to go up a size – from 7mm to 8mm. Fortunately, or chain gypsy is so worn that the new chain fits great.
Unfortunately, the new chain is heavier and Legacy is very sensitive to weight in the bow. For this reason, we went down to 61 meters of chain from 70 meters. Oh well.
