Anchor Chain Hooks: How to Choose One That Won’t Fall Off

Most chain hooks only stay put while the snubber is loaded. Here is why that matters, how to size a hook properly, and what our published test data actually means.

A chain hook connects your snubber or bridle to the anchor chain. The single most important property is whether it stays attached when the load comes off — because that is exactly when most hooks let go. A conventional open chain hook relies on tension to keep the link seated. In a lull, a wind shift, or the slack moment after a gust, the hook can drop off the chain, and the first you know about it is a bang as the load comes back onto bare chain.

This is a guide to choosing and sizing a chain hook. It covers what goes wrong with the common designs, how to read a strength rating, and how our M3 chain hook is built differently.

What a chain hook has to do

A snubber or bridle exists to take shock out of the rode. Chain has almost no stretch, so without a nylon snubber the loads that arrive at your bow roller are not the average wind load — they are the average plus a shock spike, and those spikes can run to three times the steady load or more. The snubber absorbs the shock loads. The chain hook is what attaches the snubber to the chain.

• Stay attached under all conditions – If it needs tension to stay on, it will come off at some point during the night.
• Survive the environment – Ocean is a harsh environment, thus long term integrity depends on the quality of the materials used
• Fit through the bow roller – Ideally you want the chain hook to be able to travel through the bow roller on deployment and retrieval
• Be strong enough with a real margin – the chain hook has to be strong enough to survive the expected loads on the snubber

How the M3 differs

The M3 latches around the chain link rather than hooking into it. Once the hook is closed, the link is securely held.

It is made from 2205 duplex stainless steel, not 316. Duplex has roughly twice the yield strength of standard austenitic stainless and markedly better resistance to chloride stress-corrosion cracking — which is the specific way stainless fails in warm salt water, in crevices, under sustained load. All three of those conditions describe a chain hook. The higher strength is also what allows the M3 to be physically smaller than the strength rating suggests, which is why it passes through most bow rollers.

It fits BBB, Proof Coil, High Test and stainless chain, in sizes from 1/4 inch (6 mm) to 5/8 inch (14 mm)

Sizing and strength

UBS is ultimate breaking strength — where the assembly fails. WLL is the working load limit, what you design around. We divide by a safety factor of 4, which is more conservative than several manufacturers use, so compare like with like before comparing numbers.

Is that strong enough for your boat?

Work from expected rode loads rather than from chain strength. Using the ABYC design load tables, a 35-foot boat sees roughly 1,800 lbs of rode load at 42 knots and about 3,600 lbs at 60 knots. That is without the use of the snubber, these loads are about a third with a proper snubber in place, 600 lbs at 42 knots and 1200 lbs at 60 knots. That boat typically carries 5/16″ chain and would take an M3 CH1 or CH2 — a working load limit of 2,507 or 3,344 lbs respectively, that is why we recommend using the smallest M3 chain hook that can fit on the chain.

Matching a hook to a snubber or bridle

The hook is sized to the chain; the rope is sized to the boat. If you are buying a complete system, our bridles ship sized as a set:

Common questions

Why do chain hooks fall off?

Because most designs are open hooks that rely on tension to keep the chain link seated. Any moment of slack — a lull, a wind shift, the boat sailing at anchor, retrieving a little chain — can let the link escape. A hook that latches closed around the link removes that failure mode.

Is it strong enough?

Yes, M3 Chain hooks are made from 2205 duplex Stainless Steel and are rated to be 80% – 100% the strength of your chain depending on the grade of chain on your boat.

Should I be concerned with Galvanic Corrosion if using with Galvanized chain?

Zinc is sacrificial to Stainless Steel, so yes using a stainless steel chain hook does contribute to loss of galvanization on your chain. However the chain hooks gets attached to a different link with every use thus in practical sense it does not decrease the life of your chain.

What size chain hook do I need?

Size it to your chain, not your boat length. 1/4″–5/16″ chain takes the CH1, 5/16″–3/8″ the CH2, 3/8″–1/2″ the CH3, and 1/2″–5/8″ the CH4. If your chain sits at a boundary, we recommend going smaller this will ensure that your chain hook travels easier through your bow roller, that only time to size up is if you have Grade 60 or Grade 70 chain.

What is the difference between UBS and WLL?

UBS is where the assembly actually breaks. WLL is the load you should design around, arrived at by dividing UBS by a safety factor. We use 4 as a safety factor. Some manufacturers use 3 or less, which makes their WLL look better against the same physical part — so always check the safety factor before comparing two published numbers.

Can the hook pass through a bow roller?

The M3 is designed to. Using a higher-strength alloy meant the same strength could be achieved in a smaller package, which was the main goal of the design.

Do I need a snubber at all if I have all chain?

Especially if you have all chain. Chain does not stretch, so without a nylon snubber every gust arrives at the bow roller as a shock load — the same reason your chain has to be so heavily specified. A proper snubber absorbs those load spikes into something the boat, the ground tackle and the crew can live with.

Keep reading

• M3 chain hook — sizes, dimensions and specifications
• Mantus bridle and single leg snubber
• Snubbers and bridles in the knowledge base
• Chain hook load testing data — the published results
• Understanding shackles — sizing the rest of the connection
• All guides and the knowledge base