Choice of Material for Snubbers

[sabray]

I'm thinking ill try ace hardware clothes line. This stuff can go from taught as hell to droopy with only a few towels on it. Yet survives day and night exposed to the elements. I think the one at the lake house has been up for 8 years. Still it maintains its springy composition.
If I recall gramma tied it up there with a few of her crotchet knits knots. Grand grand kids tried to tite rope on it. Still it won't fail. I'll check with gramma on the knit knot we may use.

[Andrew Troup]

Originally Posted by estarzinger

No, actually you should only be concerned with the velocity vector component pointed at the anchor. ....

I'm relieved you made that point, at a level which struck the perfect balance between authentic adherence to the laws of physics and accessibility to the informed lay person ...

I was struggling to think how to put it concisely, let alone walk this tightrope; I reckon you nailed it!

[estarzinger]

Originally Posted by colemj

Is there reasoning behind this? A bridle is about the only option multis have.

Mark

I am looking at failure history and resulting recommendations. They are pretty clear. But unfortunately I have not yet found a really compelling analysis which explains the cause of the higher bridle failure rate (vs. the primary and back-up set-up).

Just to be clear . . . bridles are better (lower failure rate) than single lines (comparing bridles with single lines the same size as the individual bridle lines) but just not as good as the "shorter primary plus longer back-up" set-up.

How do multi's ride to their bridles? In strongish winds do you sit with both sides of the bridle roughly evenly loaded? Or do you sail, with first one side of the bridle fully loaded and then the other side? This latter is what a mono does. That dynamic must (I think) be part of the cause, but it's certainly not a complete explanation.

[bobsadler]

Evan: how do you link the dyneema part of your snubber with nylon part ? I'm sure you described this previously but when I went back I couldn't find the info.

Regards,

[Andrew Troup]

Here's my off the cuff thinking about reliability of equal-leg bridles vs long/short snubber pairs:

With the latter, the short element of the pair will limit the stress in the long element to a low proportion of the long element's breaking load.

Stress is (very roughly) proportional to % extension: the long element's extension will be a fixed fraction of the short one's, hence so will the tensile stress.

Hence the breaking of the short element leaves the long one in a relatively fresh condition. That buys time to replace the short element without the long one immediately failing.

In the equal bridle case, when the first element breaks, the second element will be similarly at the end of its fatigue life, and the extra loading will cause it to break immediately, if the load regime does not immediately moderate.

Does that make sense?

[estarzinger]

^^ two cow hitched eye spliced loops is the best/recommended way - strongest and least chafe.

I personally think any of a number of knots will also do the job - I have used a sheet bend previously, while others have recommended the zeppelin bend and a double fisherman should do the trick. These will definitely reduce the strength more than the spliced loops, but I have never had them break at the knot.

[JonJo]

Bridles,

Our experience is that we load one arm or the other. We must load both equally as we swing from one side to the other but basically the load is on one side at any one time. Mono single snubbers are in a straight line, roughly, ours are always loaded at an angle. When one breaks the other might break soon after (we have never tested this) - when one breaks we replace both. Ours break in the 'middle' not at the splice or knot. But they can touch the kicker wire (bob-stay) that holds the prodder (bowsprit) - which might be where they fail. we have never seen wear - they just fail, unexpectedly, with a bang.

Since we moved from a bridle off the cross beam (about 4m each side) to first braided nylon and now climbing rope but of about 14m we have not broken anything, yet (but the loading - first one side then the other, stays the same) but (I have not checked) it is possible we have evened the loading out a bit as the better, longer, stretch (of the loaded side) might mean the 'unloaded' bridle takes up some of the load.

This is all single anchor experience in shelter anchorages where winds can gust from side to side. In wide open anchorages we still veer, but not so much, as the wind tends to be more stable and wave action (even if slight, 1' waves) might have a steadying influence.

Jonathan.

[Kettlewell]

In my previous boat, a 32-foot cat, we always used a bridle and the legs stayed evenly tensioned--more so the higher the wind. It was rather interesting watching the difference during hurricane Bob between our cat riding to a bridle and the monos all tacking back and forth. The tacking was the direct cause of the boat ahead of us breaking loose--it was a light Hunter, and the boat tacked around the harbor almost like it was sailing--back and forth until the pennants parted. I found I could even cant the bows of the cat off to one side or the other a bit by adjusting the lengths of the bridle legs, which was useful anchored in some places in the Caribbean where the swells weren't in alignment with the wind.

On the mooring chafe issue during a hurricane I would be very curious as to what exactly they were using for chafing gear and how it was held on--most boats I have observed on moorings had woefully inadequate chafing gear (if any), and did not put out extra scope. What I usually do is extend the mooring painter so that it is attached to the boat with multiple very heavy lines extending beyond the edge of the deck, all with bulletproof chafing gear, of which I have never had a failure. Then I will also have backup lines that extend all the way to the mooring chain that are slightly slack to take up any strain, plus I usually also put out at least two anchors to back up the mooring, with a third anchor over the side and ready to go if needed.

I don't like to depend on any single line or anchor.

[s/v Jedi]

I often see cats move straight backwards and forward while keeping pointing into the wind. Jedi does the same as do many ketches and schooners, while the sloops and cutters sail and tack. I have seen light mono's with rope rode sail up and down so violently that they end up over the anchor with the rode slack and the stern in the wind. This lasts seconds before they accelerate downwind until the rode come tight again which works out better than I would expect.

[colemj]

Originally Posted by estarzinger

How do multi's ride to their bridles? In strongish winds do you sit with both sides of the bridle roughly evenly loaded? Or do you sail, with first one side of the bridle fully loaded and then the other side? This latter is what a mono does. That dynamic must (I think) be part of the cause, but it's certainly not a complete explanation.

Speaking only for our boat, we ride dead steady pointed into the wind with loads equal on both bridles. Many catamarans use too short of a bridle and these sail around quite a bit, and most likely load one leg then another. Our two 25' legs 20' apart serve to keep us steady (and for the depths we are usually anchored in, serve as a mixed rode).

Mark

[colemj]

Originally Posted by Andrew Troup

In the equal bridle case, when the first element breaks, the second element will be similarly at the end of its fatigue life, and the extra loading will cause it to break immediately, if the load regime does not immediately moderate.

Does that make sense?

In the equal bridle case, assuming the legs are loaded equally, the load at failure will be greater than a single line because the load is divided by the Sine of the angle (I think - my trigonometry and physics is way past its expiration date).

So the bridle is only seeing ~70% of the force of a single line.

Mark

[Kettlewell]

There may be a practical reason why boats on moorings using bridles have a greater failure rate in hurricanes than boats using single lines, if it really is the case (how much accurate data exists?). A lot of boats I see with bridle rigs to their mooring are using two lighter lines for the bridle as the side cleats they lead to are smaller, often with poor leads to the main mooring painter too. For example, one boat I inspected closely after Hurricane Bob (she was on the beach) had a bridle set up to port and starboard bow cleats, but they were just inside of an aluminum toe rail which acted like a knife edge on the lines. Other boats I have observed using bridle rigs have issues with the lines snagging or chafing on the anchor, which is left on the roller often. Sometimes this only occurs in severe conditions when the bow is pitching, so isn't apparent to the owner until it is too late. MaineSail has a good video showing this problem on his site. I tried rigging a bridle on my mooring and I found there were serious issues with chafe when the wind was against the tide, forcing the bow off at an angle to the mooring. I wanted to get away from having to take the anchor off the roller to use the mooring, but I found there was too much chafe.

Even with a cat on a mooring I found there were serious issues with chafe under certain circumstances of wind against current, and there was a possibility of catching one of the bridle legs under the mooring ball, where it could be chafed by the chain and/or cut by sharp cotter pin ends. I ended up attaching my mooring to a single bow roller on my cat--the boat would angle off the wind a bit, but overall it was much better for chafe in my situation.

[cfarrar]

Anyone have this issue? Our boat sails somewhat on the anchor or mooring, and if we use a bridle snubber or pennant the sides of the bridle alternately rub across the bow and contact the forestay chain plate, which is a beefy stainless strap with square corners - a chafe point. So we use a snubber or pennant over the anchor roller instead of a bridle via the bow chocks.

[Dockhead]

Originally Posted by cfarrar

Anyone have this issue? Our boat sails somewhat on the anchor or mooring, and if we use a bridle snubber or pennant the sides of the bridle alternately rub across the bow and contact the forestay chain plate, which is a beefy stainless strap with square corners - a chafe point. So we use a snubber or pennant over the anchor roller instead of a bridle via the bow chocks.

My boat lies better if the snubber is attached to a bow cleat and led over one side. But I don't have a fair lead that way, for the reasons you state. So I run my snubber through the spare bow roller.

[s/v Jedi]

My single snubber always goes through the starboard fairlead on to the starboard bow cleat.