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Old 14-02-2016, 14:43   #1
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Catamaran mooring bridle

Hi all,

Yesterday, while reviewing my ground tackle, I noticed that my anchor bridle has begun to show some signs of chaffing.

I initially started looking for some three strand nylon to replace the existing bridle. While researching I came upon the following article...

http://www.passagemaker.com/articles/lifestyle/safety/sizing-the-capable-snubber/

As I read the article the OP seems to suggest that low stretch, low chafe, high strength material is a better option than the traditional nylon.

I would be interested in your thoughts.
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Old 14-02-2016, 15:23   #2
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Re: Catamaran mooring bridle

Quote:
Originally Posted by mastequila View Post
Hi all,

Yesterday, while reviewing my ground tackle, I noticed that my anchor bridle has begun to show some signs of chaffing.

I initially started looking for some three strand nylon to replace the existing bridle. While researching I came upon the following article...

Sizing the Capable Snubber | | PassageMaker

As I read the article the OP seems to suggest that low stretch, low chafe, high strength material is a better option than the traditional nylon.

I would be interested in your thoughts.
I suggest reading the article again, more critically this time through.

Length. They mention 30-40 feet. Because stretch is important. They then mention that they sometimes snub at 15 feet, but ONLY if someone is around to lengthen if the wind picks up. The best way to break a snubber is to use a short one (too much energy to absorb).

Loading. they mention that the working load should not exceed 15% of the BS. That is because this is, more or less, the fatigue limit. Additionally, so long as the load is below 15% there will be no heating; that ONLY happens at higher load factors. Obvious. Additionally, they talked about load but never explained how they actually measured it or any data collect effort. Had they done so, they would have said so. I suspect they were guessing based upon tables or something similar.

They dismiss peak loading as a cause of anchor tripping rather flippantly. Yes, you can always accuse an anchor of being too small. I think if you re-read that paragraph you will see it is indefensible and contributes no knowledge. A better analysis is that they simply do not know.

I do know from instrumented testing (Practical Sailor next month) that is shallow water, low stretch is a terrible recipe. There was also a good article in Sail last month that explained why short scope works in deep water. BOTH are true; in deep water catenary works, but in shallows only a long snubber works. There is no one answer.

As for chafe and low-stretch, an argument can be made for having a short non-stretch leader through the chocks. A mooring pendant, for example. should generally be low-stretch for this reason. But for most people, So long as the snubber is long enough and sized reasonably (15% BS), good chafe gear will easily see them through.

----

Al of this depends on whether you ever anchor in relatively shallow water (<20 feet). Deeper that that, chain catenary is pretty useful. All of my testing was in shallow water, intentionally so, to collect data.
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Old 15-02-2016, 12:29   #3
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Re: Catamaran mooring bridle

Thinwater,

Thank you for the comprehensive reply. I am certainly looking forward to your article in Practical Sailor.

The reason I asked the question regarding this article is that the implied that if I overloaded my nylon bridle that it could be damaged. If I was unaware of the overload I would then basically be hanging off of damaged equipment and be unaware of it.

You are correct in saying that he has really not given any figures other than percentages to work with and therefore (after re-reading) it makes me less inclined to accept his observations. It reads more of an opinion article. I will however take care that my bridle is of suffecient strength.

I have calculated the applied force to my catamaran in 60 knot winds, while facing 30 degrees to the wind, to be 2331kg (5138lbs). My current anchor bridle is around 40' with an apex angle of 60 degrees. All of my ground tackle can support the appied force. The estimated peak holding of my anchor is 3200kg (6400lbs) in good holding. I will now ensure the new bridle material exceeds that by 15%. Anything beyond that force and we will be dragging the anchor anyway.

I will look forward to the article in March. I do anchor in shallow water more often than not so I will be curious about your findings.
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Old 18-02-2016, 16:07   #4
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Re: Catamaran mooring bridle

Nylon, each leg of the bridle at least equal to the beam of the boat attached as far as possible to the extremity of the bow.
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Old 18-02-2016, 16:44   #5
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Catamaran Anchor Bridle

Mastequila,
Anchor Bridles do wear out and should be replaced from time to time.
They are very easy to make yourself “DYI”
You want at least 20 feet out from the bow
3 strand nylon works the best and last the longest
Add rubber snubbers to give you even more comfort at Anchor.
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Old 18-02-2016, 17:04   #6
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Re: Catamaran mooring bridle

See underlined text. What is your boat size? That would help.

Quote:
Originally Posted by mastequila View Post
Thinwater,

Thank you for the comprehensive reply. I am certainly looking forward to your article in Practical Sailor.

The reason I asked the question regarding this article is that the implied that if I overloaded my nylon bridle that it could be damaged. If I was unaware of the overload I would then basically be hanging off of damaged equipment and be unaware of it. Obviously? The key to not damaging the snubber is, as they stated, not loading beyond 15% BS. Remember, of course, that the maximum load with a snubber is much lower than without one.

You are correct in saying that he has really not given any figures other than percentages to work with and therefore (after re-reading) it makes me less inclined to accept his observations. It reads more of an opinion article. I will however take care that my bridle is of sufficient strength. Sufficient strength will be

I have calculated the applied force to my catamaran in 60 knot winds, while facing 30 degrees to the wind, to be 2331kg (5138lbs). My current anchor bridle is around 40' with an apex angle of 60 degrees. All of my ground tackle can support the applied force. The estimated peak holding of my anchor is 3200kg (6400lbs) in good holding. But bad holding is what you need to worry about. The snubber will reduce the load. I will now ensure the new bridle material exceeds that by 15%. Anything beyond that force and we will be dragging the anchor anyway.

I will look forward to the article in March. I do anchor in shallow water more often than not so I will be curious about your findings.
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Old 20-02-2016, 14:00   #7
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Re: Catamaran mooring bridle

Thank you all for your replies.

ZipTie, that is a really nice looking rig.

The boat displaces 8 tonne and is 13 meters long by 7 meters wide. It is 6.5 meters at the fixtures for the bridle, at the very front.

The two sides of the of the bridle are each roughly 7 meters long. The current material is 3 strand nylon 9/16" (14mm). I will talk with the local rigger but most likely will stay with that. I am able to move to 5/8" (16mm) if the numbers work out. I need to see his specifications for the specific rope.

Cheers.
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Old 24-02-2016, 05:18   #8
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Re: Catamaran mooring bridle

Have you looked at something like Liros Handy Elastic for the bridle yet?
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