Adjustable Snubber Bridle and Chain Hook

This report focuses on multihulls, because that is what we sail, but most of what we learned from this project can be applied to monohulls, as well. Our catamaran Josepheline is 38-feet with a 22.5-foot beam and draws 3.25 feet, weighing in at about 7 tons in full cruising mode. To put this into context our cat is the equivalent in windage to a 45-foot 13-ton monohull.

The current bridle system, as described below, can be modified to use on a monohull, where bridles are not common but could and should be used more often (see PS March 2016, “What is the Ideal Snubber Size?”).

Important note. You should never rely on the chain on the windlass to hold if your snubber fails. You need some form of chain-stop that isolates the windlass from load. We use a Dyneema strop attached to a strong point with a galvanized chain hook. We use the same hook and strop to secure the anchor (and chain) on passage. You can also use chain locks, Dyneema strops, or secure the chain using existing bow cleats. There are usually lots of options. Just don’t rely on the windlass.

Why a Bridle?

Bridles, as opposed to single-line snubbers, help to ‘share’ the load (see PS November 2013, “Anchor Snubber Shock Load Test”).  This reduces the tension imposed on the securement point.

Nylon, the cordage commonly used for snubbers and bridles, has a finite lifespan, in part dictated by the load cycles. By sharing the load on two legs, you prolong the life of the rope. Sharing the load also helps reduce yawing, which can hinder holding (see PS February 2020, “Yawing and Anchor Holding”).

Our bridle arms are made of climbing rope, each 30 meters long with about 40-percent elasticity to breaking point. They quell chop, subdue yawing, and absorb large snatch loads.  In our case, they do all this with a rode of 6mm G80
galvanized chain (see PS June 2016, “Pencil Thin Anchor Rode,”).  The chain was treated with Armorgalv, a thermal diffusion galvanizing (TDG) treatment (see PS March 2015, “Armorgalv vs. Hot-dipped”).

The Chain Hook

We had looked at hooks, methods of attaching snubber-to-chain, and found many of them wanting.  The best hooks undoubtedly come from the lifting industry where hook design is considerably more advanced than anything the marine industry offers. Lifting hooks are painted steel, powder-coated steel, or very expensive duplex stainless. We’ve not found a high-quality galvanized lifting hook.

It is possible to have an industrial lifting hook galvanized. We had a number treated with Armorgalv, but for most galvanizers, treating only a small hook is a nuisance—and you pay accordingly.

The problem with most hooks sold to the leisure marine industry is that they can stress the individual chain link or damage the galvanizing of the link to which they are attached.(see PS January 2017, “). Many of the devices designed to join a snubber to chain are not strong enough for the job. For example the ‘retaining’ pin on the popular Wichard hook is prone to bending, and once it is bent it can be hard to detach. Ketten and Waelder make a line of “Cromox” eye hooks and clevis hooks, but these duplex steel hooks are expensive.

Many people find success using Dyneema soft shackles to join the snubber and chain (see PS April 2015 “Going Soft on Shackles”), but we found them too fiddly to use on our 6 mm chain. (Even 8 mm chain can be too small to easily thread the Dyneema.)  Link holes on imperial chains are bigger—and it maybe easier to insert a soft shackle.  In our view, a chain hook is simple, effective, and quick to attach—even in the dark with a deck awash.

SHOCK ABSORPTION

One of the incentives behind the development of a better snubber came when we switched from 8mm G30 chain to the 6 millimeter high-tensile, Armorgalv-treated G80 chain. Lightening the rode reduced our loaded weight, but it also meant less shock-absorbing catenary.

One of the easiest ways to add shock-absorbing capacity is to lengthen a snubber. With our demands of frugality we searched and found a climbing gym where we obtained some 30 meter lengths of used single dynamic climbing rope, which offers more stretch than conventional running rigging.

For safety reasons, climbing rope is routinely retired at relatively short intervals, when it is still perfectly suitable for less critical applications. Make sure you understand what you are getting, as not all climbing ropes share the same specs (see PS January 2016, “Testing a Dynamic Traveler”).

Running the Lines

The images and captions below illustrate the setup (see “Running the Lines on a Multihull Bridle”). Each bridle leg has a sewn loops at one end (see PS October 2014, “Stitching instead of Splicing”).

This eye is shackled to extra-reinforced pad eyes, which also serves as the chainplate for the prodder (bowsprit) bobstay.  Each snubber leg leads through low-friction eyes in the chain hook (see adjacent photos), to a swivel-mount lead block on the bow.

From the turning block at the bow, each snubber leads aft through the struts in the stanchion bases. The snubber then passes through a clutch near the transom, then through a turning block on the transom (a spinnaker or screecher block is ideal), and then to a cockpit sheet winch. You don’t need a clutch. You could secure the snubber to cam cleat, a clam cleat, or even a horn cleat. The ‘spare’ end of the rope we stored as we would a sheet, in a bag hung from the lifelines.

Normally we simply deploy 15-20 meters. If the anchorage is exposed to chop or swell, it is easy to deploy more snubber. We leave our snubbers permanently attached at the bobstay chainplate. They are not obtrusive.  With this new arrangement and extra length we can have about 15-20 meters of snubber in use on each leg. If the wind picks up—we can deploy the full 30 meters.

Prior to the new design, the hook would sit on the bottom when we were anchored in calm, shallow water. This could even cause the hook to disengage, something we observed with the first Mantus chain hook (see January 2014, “Mantus Upgrades Snubber Latch”). Reducing this excessive length was the final part of the puzzle.

In the new arrangement, with only five meters extending from the bow, the hook won’t sit on the bottom. Even if we terminated the line at the bow instead of running most of it aft, we’d still have the shock absorbing capacity of 10 meters on each leg, since it is doubled back.

Low Friction Rings to the Rescue

The key to creating a long snubber that wouldn’t sit on the bottom was our addition of low friction rings (LFR). LFRs are commonly attached with soft shackles or Dyneema strops but we wanted something that wouldn’t flop around. Snatch blocks would also work, but we chose to incorporate LFRs into the bridle plate.

We found two-part threaded LFRs used for fairleads through bulkheads, but they cost more than $100 plus per pair. To save money, we drew up plans for threaded LFRs and had them custom made in China. We ordered two sets, one set in a 6xxx alloy (magnesium and silicon) and another set in 316 stainless. The former would be used with redesigned bridle plate made of anodized 7075 aluminum alloy. The 316 eyes would be used in a bridle plate made of 2205 duplex stainless steel.

While we waited for our custom LFRs to arrive, we used stainless steel tubes to serve as a bearing surface on an ordinary clevis pin shackle. With one short tube inside the other, the pair of tubes were slid onto the  shackle’s clevis pin like a crude roller bearing. This prototype gave us the chance to test the design and modify it as needed before we created the finished product.

V-Shaped Shock absorber

The system works surprisingly well. The vertical v-shaped portion of the bridle forward of the bow—between the bobstay chainplate to the turning block on the bow—creates an effective tensioner which noticeably cushions some of the movements generated from chop and swell.  This works in the same way that a normal bridle (forming a horizontal V) helps reduce veering.

Additionally, the setup had the unexpected effect of reducing the angle of pull (increasing scope) under a snatch load. When a big wave lifts the boat and creates a sudden snatch load, the chain hook is pulled downward on the snubber. This significantly lowers the connecting point, which in turn reduces the angle of pull (angle between the anchor rode and the seabed). In deep water this makes little difference, but in shallower water the actual scope ratio improves noticeably.

This brings up another comment related to scope while using this bridle hook arrangement. For a more accurate picture of required scope, use the snubber hook height above water to determine the vertical factor in your calculations, not the deck level. Again, the difference is insignificant in deep water.

Normally we would deploy 20 meters of snubber, 10 meters up the side decks and 10 meters (two five-meter legs) beyond the bow.

If you expect the wind to pick up the best idea is to plan ahead and have a long enough ‘lazy’ loop of chain between bow roller and bridle plate. Then you can simply release more snubber  using the sheet winches. You can do all this from the safety and comfort of the cockpit (in your pajamas if its 3 am).

If the lazy loop is too short you will need to venture to the bow, release the chain-stopper, deploy more chain, replace chain-stopper, retire to cockpit and deploy more snubber. We have found it is quite possible to release the snubbers ‘bare handed’ since the tension – at the cockpit – is surprisingly low. Using a sheet winch ensures anyone can do it. When you release extra snubber, the rope slips easily through the LFRs.

Better holding?

Another benefit of a stretchy bridle is a phenomena that has largely gone unreported, probably because you have to dive on the anchor to observe it. Without a bridle, and when all the chain has lifted off the seabed, we can feel the anchor noticeably twitching with every movement of the chain (and yacht).

In fact all the movements of the catamaran, yawing, horsing and vibration of the rigging is transmitted along the chain. To see for yourself how this works, wiggle a trowel in wet cement and watch the cement around the trowel refuse to consolidate. Leave the trowel alone and the cement will settle and “grab” the anchor.

This is exactly what happens as your chain rode is lifted off the seabed. This unwanted twitching increases in a short-scope situations. Arguably the lower shear strength of the seabed around the twitching fluke would help your anchor to set more deeply with shorter rode. This might be true, but only  until the anchor meets an inconsistency in the seabed— trash, shell, or a buried kelp stalk. When that happens, you’ll begin to drag. In general, you don’t want the anchor moving about after it has set.

There are other ways of reducing twitching. For example, having a deep-setting anchor that buries chain will help. Buried chain reduces the vibrations along the chain to the anchor. Smaller diameter chain tends to bury more deeply (another reason we downsized).

Conclusion

We were so impressed with our new arrangement that we invested in two 30-meter lengths of new 12mm dynamic climbing rope with sewn loops at the end of each one (10mm would have also served well).  The sewn loops attach to the waterline bobstay padeyes.  We retired the ‘free’ ropes, which we now carry as spares or shore lines. Snubbers should be replaced with running rigging, or as soon as they show obvious signs of wear.

One advantage of having a free end to each bridle arm at the cockpit is that you can alter the orientation of the yacht, have one arm longer than the other, to suit conflicting wind, tide, or wave direction. This allows you to better balance the vessel and makes it considerably more comfortable at anchor.

One of the fears of long, elastic snubbers or bridles is that the yacht will yo-yo—surging fore and aft like a demented dinghy being towed in following seas.  So far this has not, in any way, been our experience, and we have obviously been able to test it.

Our bridle development is very much a work in progress. We know we can improve the basic design of the plate itself. Some of the dimensions are obviously critical—the slot needs to fit the chain diameter, for example—but other important dimensions, like plate thickness to match the low friction rings, are not so obvious.

We also think casting the plate as one piece, all 2205 duplex and, possibly, polished, would be more sensible and attractive and will more easily allow incorporation of the developments of lifting hook designs.  The whole system is thus a project in development.  It works as it is, but it will be better!

The system can, relatively easily, be installed on a mono hull—in whole or in part.  Most yachts have some form of fairlead at the bow or amidships and these, with judicious use of LFRs and short strops, can arrange a sensible ‘V’ for a horizontal bridle.  Having a pad eye on the stem is obviously critical to accessing the advantageous ‘vertical’ component. A dedicated padeye could easily be installed—with careful use of reinforcing. If your boat has a bowsprit, you are probably already set.