Mooring Bridles

6-16-2016, Rev.7-8-2015, rev. 8-1-2024


Why the post? Mantus Anchors has given me a bridle and chain hook to test for Practical Sailor Magazine. The quality of construction and detail work is exemplary; good splices, good hardware, and good chafing gear well secured with stitching. The design of the hook is both simple and elegant and may be the new "best"  design at any price. I will spend this summer finding out.

At the same time it is apparent to me that there is no single right answer for the bridle itself. While the Mantus construction is absolutely first rate, every situation has a best answer. They have made conservative design choices, and I respect that.

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For monohulls, a bridle is often used to take the chain load off the windlass, the surge load off the roller, absorb the wave shocks that chain can't, and perhaps keep the boat a little better into the wind. For catamaran bridles are a daily essential, since moored to a single bow they sail at anchor.

The Basics

The Need

• Multihulls must be moored on a bridle or they sail all over the place. With a bridle they sit steady like a rock, the long legs providing the leverage required to keep the nose right into the wind.
• Multihulls with all-chain rodes need the shock absorption. They often anchor in water more shallow than monohulls; a relatively short rode and steeper waves increases the tendency of steep waves to snap the rode tight, creating forces far beyond anything the gear can handle--boats have been lost this way. To prevent this, the legs must be long and sized correctly.
• Some bottoms provide poor holding and anything that can reduce forces will help keep the hook in the bottom.
 

The carabiner hook is for moorings.

The Requirements

• The legs must be at least 1 X the beam or they can be difficult to rig in rough conditions. It is good to have the option of working from either bow. This is also a good minimum for keeping the boat straight.
• They must be adjustable if needed. When tying to a mooring ball it can be very handy to shorten them, to hold the ball between and away from the hulls. If the waves are coming at an angle, for example around a point of land, it can be helpful to angle the bow.
• For permanent moorings they only need be strong. Nylon will stretch enough.In fact, often it is desirable to limit stretch to reduce movement in the chocks and chafe. Polyester and even Amsteel can be good choices.
• For anchoring they need be long enough and thin enough to provide stretch. One size lighter than the anchor rope is probably a good starting point, since there are 2 legs carrying the load (though there is some angle). Even smaller can make sense and give a smoother ride, if they are longer (1.5-2 X beam) and replaced more often.
• 3-strand, braid or even climbing rope. Braid and climbing rope have considerably better fatigue life when loaded heavily, particularly in smaller sizes.
• Chafing gear.
• A means of attaching the bridle to the chain that will NOT fall of when the chain is bounced slack on the bottom (back to that shallow draft thing). Ordinary chain hooks can and do come off. A plate is a good method. So is the Mantus chain hook. Or rather I will find out. 
• Rolling hitches and cow-hitched slings also work well, for attaching the bridle to the chain and have advantages: easy to release, feed through rollers better, easy on the chain (no wear on the galvanizing) cheap, and totally dependable. I prefer a hook simply because it is a little faster, but that doesn't make me right about this. I use these methods when setting a second anchor (to connect the rodes) and have never had a problem.
• The best method may be a Dyneema soft shackle through the chain. This has the advantage of being retrievable over the roller.

The Engineering

What line, how long, and how strong? Like most things, there is not one answer, but I will describe what makes sense for me. Your situation may differ.

For permanent moorings--something I very seldom use--the answer seems relatively simple; plenty strong, at least as heavy as the anchor line but more likely up one size, any rope type, and just sort enough that the ball cannot touch the hulls. Lots of chafe gear. If storing my boat on a mooring I would favor over size line and preferably limited-stretch line to limit movement in the chocks. But like I said, I have no extended real world experience.

The Mantus bridle package. Heavier line than I use on the Chesapeake, but better for durability and rough use.

For anchoring in open areas. I avoid them, and avoiding them is generally easy on the Chesapeake.

• One size smaller than the anchor line (if rode is 1/2", use 7/16" bridle). The load is shared by 2 legs and we can use some stretch. Has to be strong enough to endure full chain working load,  but remembering that it is backed-up by the chain and will be replaced every few years.
• Minimum 1X beam length per leg, and preferably more. If there is ANY risk of serious swell in shallow water, 2X beam is prudent. While the chain can absorb gusts and veers, only the bridle is available to absorb a quick rise of the bow caused by waves during gusts that already have the chain straightened out or effectively straight. The chain may not be in a completely straight line, some few feet may even remain on the bottom, but further strain provides no significant lengthening in the few seconds it takes for a wave to pass.  If this bow rise is 4-6 feet, then the bridle must stretch perhaps 1/2 of this, or perhaps 3 feet. Thus, at least 25 feet of bridle are needed.

For anchoring in soft mud. An even softer catch is needed. By far the most common anchoring hazard of the Chesapeake Bay, dragging is common and rode failure is VERY rare. Additionally, this soft catch makes setting the anchor easier, even with new-age anchors; I have a Manson Supreme and previously used a Delta. While chain help keep the shank down, the extra cushion of rope helps too, particularly in shallow sets.

• Two sizes lighter than the anchor line with separate eyes for each leg. Where I might use 1/2-inch anchor line, 3/8-inch is perfectly acceptable for a bridle/snubber. I've used old rock climbing lines and been very satisfied, replacing this every 100 uses or so. Alternatively, a longer bridle will do the same thing with greater strength.
• Replace more often. This is not just for wear. The ability of line to stretch fades after a few thousand hard cycles. When the line stiffens noticeably and it is time for replacement. The change in hand is often apparent.

What about strength? The apex is formed by an eye-splice with a thimble and then a Y-splice about 16 inches further down, all professionally executed and covered with hollow webbing for chare protection. The question is, how does a Y-splice react to broad Y angles? While I'm sure it is 100% strength at shallow angles, when shortened for mooring balls what happens? Given that the Mantus bridle is conservatively constructed this is only an engineer's curiosity.

And what about double braid? The apex will then be formed by either a figure-8 knot (80% strength at low angles, 60% strength at 90 degree angles) or a seizing.

What about 2 legs joined with a shackle? This is quite prone to failure as the angle becomes too wide. I'm sure many of us have destroyed a shackle when it shifted such that the load came on cross-wise and the threads stripped. Two legs to a plate is tough on the plate but can be designed for. Mine is.

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So do your own math. Your anchoring habits may differ.

Rev. 6-16-2013

Initial testing.

• Deploying. the bridle can be fed through the roller to the chain and deployed from on-deck, no problem. It will not bounce off going over the roller; I tried this repeatadly and it never shifted. No tendancy to hang-up either.
• Flipping the hook off accidentally while lowering. I violently flipped the chain every way I could think of, repeatedly. I lowered the anchor in every sloppy way I could think of. It seems unlikely in the extreme that the hook will ever come off while deploying, and FAR less likely than a conventional hook.
• Flipping of when setting on the bottom. Improbable in the extreme.
• Retreaval. While it's possible to flip the hook off with just the right sequence of flips, reaching over may be easier. It is not generally practical to bring it up through the roller, at least not on my boat; jamed every time. But it comes off very easily if I reach over with one hand.

Rev.  7-7-2013
After 8-day trip.

• Hook is fast and easy.
• I spliced a new bridle from 1/2-inch medium lay 3-strand (the Mantus unit was 5/8-inch hard lay) and for my purposes it is much better; easier to stow, shock absorption better matched to the boat, and is still plenty strong enough (the stock anchor cable is 1/2-inch). I did use 2 independent eyes at the apex to slightly increase strength. I used 25-foot legs (I had 15-foot legs before); these definitely gave better shock absorption in open anchorages, greatly reducing the load on the anchor and the passengers.
• Though I'm not a fan of 3-strand, it certainly seems to stretch more than double braid (generally) and that gives it the nod in this application.

I'm not yet certain I would use it on a mooring for permanent attachment, for months unattended. I think it would be fine, but I prefer the 100% security of a chain plate with a latch. But for typical cruising, I think it is my new favorite.

Rev. 7-12-2013
Yup, it does come off on its own. The 50th trial. And then it came off 2 more times, always when lying on mud under very light to zero winds.

I'm sure it was a very specific anchoring scenario, but I went to up-anchor and the hook came off while the chain was still on the bottom. I still like it, I still use it as my primary, and I have a number of designs available to me. Just sayin.... I believe that unless the hook rests on the bottom the chance of it coming off is VERY nearly zero. Would it have come off if we were not weighing anchor? I doubt it but only time will tell.

Rev. 8-10-2013
Yes, it will come off on its own. Yesterday we came back to the boat only to find the boat hanging from the chain. It had been on, since we power-set the anchor.

Rev. 8-19-2014
I've been testing the new plastic retainer for the hook since fall 2013. The new retainer easily locks on and off with the thumb, allowing easy one-hand operation and complete security. Problem Solved! 

 

  

 

Maybe. The Mantus MKI chain hook has two shortcomings:

• It weakens the chain (breaking strength) about 30%. We're not sure if this applies to the WLL as well and how serious the problem is when used on a snubber. 
• Does not scale up well to chains larger than 1/4-inch. The wonderful one-hand operation goes away.  Thus the recommendation is now either a bridle plate (below), a prusik hitch, or a soft shackle.
  

 

Rev. 7-8-2015
I've switched to an 8mm climbing rope snubber, 35' long, attached to the chain buy a 3/16" Amsteel soft shackle. A very soft ride, less stress on the anchor, and the soft shackle is easily deployed over the rollers. Because of the skinny line, I have 1" tubular webbing covering it at all vulnerable spots.