Thursday, March 12, 2009

The Ultimate Chain Hook for Catmarans...

rev. 9-13-2016

The Problem. Catamarans use a long bridle, and monohulls should to, to reduce shock loading on the anchor and chain. Unfortunately, an ordinary hook falls off if it rests on the bottom in shallow water during light winds.

My first solution, not for sale anyplace I could locate, was a steel plate is 3/8" x 3" x 4 1/2" A-460. The left hole is 5/8" and generally holds a large stainless carabiner, the right hole is 3/8" and is a good fit for the 5/16" SS shackle that forms the pivot of the latch. The slot is 3/8-inch, over size to allow for an easy fit and because 1/4-inch chain is closer to 5/16-inch at the weld. The chain rode drops into the slot and can't get out once the second bridle line is attached. Very simple and idiot-proof in years of testing. The apex hole is 5/8" and also generally holds a 3/8" anchor shackle used to secure a sling that is prussic-hitched to a fiber rode.I don't use this feature and consider it a bad idea, since it is better to attach the second rode to the chain.

Calculations show that it should have a safe working load of 3200 pounds in any loading combination, including attaching only one bridle leg. I tested it to 5500 pounds on a test rig I once used for pulling rock climbing gear apart; there was no permanent distortion. My anchor chain is 1/4" G-4 and my governing working load is thus 2600 pounds.

But you can't buy it. Not yet. But there is a nice hook on the market now that you can buy....

The Solution. New on the market, the Mantus Chain Hook. Perhaps a real innovation. I used this for about 2 years and find if very handy. A locking plastic plate keeps the chain in place. Unfortunately, it is difficult to operate with one hand in sizes over 1/4-inch.

Another Solution. A friend in Australia made me one (he calls it a Barra) and had it ArmorGalv treated.I would love to see it commercialized. I've been testing it all season. Very nice.
The long shackle makes spinning the locking plate easier.

 Much stronger than the chain, can't come off, completely redundant attachments.

So which is the ultimate? I've got to say the ArmorGalv Barra because it works better in larger sizes. I can't claim that it is a complete original invention. Sea Dog made an inferior design for years, and I've seen crude versions here and there, but this iteration just does not have any obvious flaws. Simple, durable, scalable to any size with no fiddly parts to break. But I still like the Mantus Hook best for 1/4-inch chain.

Not a DIY type? The bridle plate by Sea Dog will do the job nicely for boats up to about 40 feet, if you add your own locking plate.  Larger catamarans have reported bending in extreme conditions (not enough meat at the bottom of the slot), and 1/4-inch chain is rattly and prone to falling out.