Sunday, September 1, 2013

Long Bridles

Rev 10-29-2013

I'm still working my way through this topic--I think many cat sailors are--so this post is a work in progress.

There are 5 conflicting requirements asked of a catamaran mooring bridle and I have yet to hear of a perfect solution. Partial solutions that work, but always prone to some critical flaw.

  1. Turning Leverage. First, cats need a relatively long triangular bridle to keep them into the wind at anchor. If anchored to the center beam they skate all over, with a bridle they are placid. Legs equal to the beam provide sufficient leverage and allow working from either bow, if needed. Longer legs also place less stress on the bridle (basic statics/trigonometry).
  2. Shock Absorption. Actually, this applies to all boats, but more so to cats as they are more inclined to anchor in shallow water. Waves, particularly if breaking or simply steep, impart tremendous energy that the typical all-chain rode cannot absorb. Folks say the catenary absorbs shock, but only true in deep water with several hundred feet out; in a 50-knot squall anchored in 6 feet of water (60-70 feet of rode would be conservative) the rode is so close to straight--within 1 foot-- that chain has no absorptive capacity. What is needed is a nylon bridle long enough to absorb a wave, that is to stretch 2-4 feet. That will require a 30-foot bridle leg. This is even more vital for monhulls, which see severe impacts if a wave strikes the front beam or bridge deck.
  3. Apex of Bridle Must be Off the Bottom. If a very long bridle is used the apex will be on the bottom during slack conditions, subject to chafe. While this is not critically important in the Chesapeake mud bottoms, with rock or shell it would be. Even on the Chesapeake oyster shells eventually take a toll.
  4. Chain Hooks Like to Stay Off the Bottom. Even the the Mantus hook, one of the most resistant to getting flung off, stayed on when I used a short bridle but frequently fell of when I used a long bridle.
  5. One-size-fits-all Would be Nice. What boat has extra room for extra stuff?

In a recent Practical Sailor Magazine one multi-huller suggested using a long bridle, but anchoring the legs far back on deck, to the midships cleats or behind. The bridle then goes through a turning block and forward to the rode. The legs are thus over 30' long for shock absorption, but the legs between the hulls not so long that the apex of the bridle rests on the bottom. Another experienced contributor poo-pooed the practice, citing extra chafe points and rigging. True enough. He was a monohull sailor, of course.

I thought I would try it for a night.  My new Mantus Hook testing bridle is long enough and the wind was gusting over 20 knots. I was protected from waves but not the wind. It kept the bridle off the bottom.
  • The boat rode well, without any jerking or surging.
  • There was certainly movement of the rode through the chocks during the gusts--4-6 inches in the stronger puffs--proof the stretch was working. Webbing chafe gear seems to work, but anything that generates friction also reduces the effectiveness of the side deck portion of the bridle. Additionally, the line could jump out of the chock in rough conditions. A turning block is the right answer, but it must be well placed. For my boat and circumstances it is not needed.
Food for thought. It looked neat and it worked, but with turning blocks there is really too much to set up nightly and there is no go location for a turning block on my boat anyway. For now, it has become my standard method.

1 comment:

  1. Unfortunately on this new cat the bridle is fixed under the tramp. There is no way to adjust it easily. I preferred the bridle we had on the PDQ.