A more recent Mantus write up (2018) with their stronger M2, and why the hook doesn’t need to be as strong as the chain.
Why we think it’s acceptable to use a stainless steel chain hook inline with a snubber/bridle even if it’s not as as strong as the chain?
M2 Hook Size M2 Hook WLL M2 Hook UBS G3 Chain UBS G4 Chain UBS G7 Chain UBS
1/4 in (6-7mm) 1,686 lbs 6,744 lbs 5,200 lbs 7,800 lbs 13,650 lbs
5/16 in (8mm) 3,788 lbs 15,154 lbs 7,600 lbs 11,700 lbs 20,475 lbs
3/8 in (10mm) 5,516 lbs 22,066 lbs 10,600 lbs 16,200 lbs 28,350 lbs
1/2 in (12-13mm) 9,271 lbs 37,085 lbs 18,000 lbs 27,000 lbs 48,300 lbs
The Mantus M2 Hook is stronger than most chain grades on the market. Most stainless steel chain hooks are weaker than Grade 40 chain.
At first look, one might make an argument that stainless-steel hooks are too weak to use on snubbers and bridles, especially when using hi test chain. However, if you look at how a snubber is stressed and how these loads differ from the chain’s experiences in the absence of the snubber, we can see it is not. A typical 35-foot boat, according to ABYC loads table (see below), at 42 knots of wind can expect a load of 1800 lbs on its anchor rode and at 60 knots of wind a load of 3600 lbs. A typical 35-foot sailboat will be outfitted with 5/16″ chain WLL 1900 lbs and breaking strength of 7600 lbs. Most experts agree that these ABYC loads already include a 3-fold allotment for shock loading.
Therefore, the loads that use a properly sized snubber are a third of the loads reported below. This illuminates the importance of using the snubber line and explains why snubber design parameters are different than the design specifications for chain.
Shock loads produced without the use of the bridle or a snubber can create loads on the chain that are 3+ times the average load experienced by the chain. Worst case scenario, in a 60-knot blow, the shock load on the chain would produce an estimated load of 3600 lbs. The chain would be tasked with having a breaking strength 4 times the recommended working limit. If we were using the hook to connect two pieces of chain, the same requirement would be necessary.
Wind
Speed
(Knots) Anchor Name
Boat Length – Feet
20 25 30 35 40 50 60
15 Lunch Hook 90 125 175 225 300 400 500
30 Working 360 490 700 900 1200 1600 2000
42 Storm 500 720 1400 1800 2400 3200 4000
60 Violent Storm 980 1440 2800 3600 4800 6400 8000
Since we are using the hook to connect an elastic snubber to the chain, the shock loads are dissipated, and the snubbing hook will maintain loads a third of those reported in the ABYC table (1200 lbs vs 3600 lbs.)
Since the M2 Mantus Chain Hook is made from Duplex Stainless Steel, it has the Ultimate Breaking Strength somewhere between G4 and G7 chain. However, since its intent is to be used with a snubber, it is way over designed for the job. As an example, the 5/16″ M2 Mantus chain hook has the ultimate breaking strength of 15,154 lbs and has a working load of 3,788 lbs, which means it can be used on a 50-foot boat in 60 knots with a 5/16″ G70 Chain.
