Anchor bridle length

[StuM]

Originally Posted by kmacdonald

2.5 times the boat width. That's what is recommended for a Jordan Series Drogue bridle.

If it were me, I would use 2.5 times the beam for each leg of the bridle.

Now I see the problem. That's a recommendation for attaching a storm drogue to a monohull.

Do you understand why and how we use mooring bridles on catamarans?

[kmacdonald]

Originally Posted by StuM

I see from your profile that you sail a 22ft monohull.

I do on occasion but I prefer to sail my 15' home made cat boat. (not catamaran)

[StuM]

Originally Posted by kmacdonald

Where did I suggest 70 metes? I said 2.5 times the beam. I am guessing the 14m beam cat was a typo. If not it's totally out of our league to even make a suggestion for something that large. The rules of thumb would not apply. A bridle or a snubber would need to use the same design parameters for storm or hurricane force winds.

Why would the 14m beam be a typo. It's about what we would expect from the fact that the OP has a 78ft ex racing cat according to his Avatar info.

And while it might be out of your league, we are not all in your league.

Plenty of people here have experience with boats that size.

[kmacdonald]

Originally Posted by StuM

Now I see the problem. That's a recommendation for attaching a storm drogue to a monohull.

Do you understand why and how we use mooring bridles on catamarans?

That's not a problem. It was a very specific recommendation in plain English and more or less supported by the article in Practical Sailor. What else don't you understand?

[StuM]

Originally Posted by kmacdonald

That's not a problem. I was a very specific recommendation in plain English and more or less supported by the article in Practical Sailor. What else don't you understand?

I take that as a "no"

[kmacdonald]

Originally Posted by StuM

Do you understand why and how we use mooring bridles on catamarans?

What's a catamaran?

[Lucky Larry]

So if each leg of the bridle is 2.5X the 14 meter beam that's 35 meters or approximately 105ft. And if he anchors in 10ft of water with another 5 ft up to the bridle attachment points with a 5:1 scope that is 75ft of scope. The bridle would be attached at the anchor and unless there was strong current or winds there would be about 75 ft of bridle dragging on the bottom.

Our beam is approximately 8M, each leg of the bridle is approximately 10M and we shorten it by wrapping it around our cleats to keep it from touching the bottom.

[kmacdonald]

I guess I should mention that it's best to anchor from the stern if the boat yawls back and forth when anchored from the bow. Monohulls almost always benefit from anchoring from the stern.

[kmacdonald]

I don't mean to be argumentative here but what's the problem with the bridle resting on the bottom? The overwhelming number of boats use a short section of chain followed by 3-strand nylon anchor rode. The line rests on the bottom when there isn't much or any wind or current. It's not the end of the world if it touches the bottom. Adjustments can be made for anchoring in coral (god forbid) or rocky areas.

[damianham]

Thanks for everyone's input - it is really appreciated. No the 14m was not a typo. My boat is the famous racing cat Commodore Explorer. She was left abandoned in Sweden for 7 years stripped of all parts except engines. Over the past 2 summers I built some beams and a jury rig and built an anchoring system as well as install a whole host of other stuff in order to sail her to Portugal where she is now waiting to come out of the water so I can convert her into a fast cruising catamaran. The 12m jury rig which worked quite well downwind, we achieved speeds of 13 knots in a gale from Dover to Weymouth.

Unfortunately we broke the 12m rig near Belle Isle and what followed were 3 more jury rigs using what was left of the initial rig from Belle Isle to Nazare Portugal. She now has a new record - 4 jury rigs in 1 trip

I built an SS anchor cradle that sat on the longeuron just behind the front beam and I bought 2 x 11m lengths of 25mm multiplait nylon for the snubber bridle with eyes spliced in each end and they are shackled to the front beam mount points.

In benign conditions I shortened the 11m to about 6m using a sheepshank knot and deployed a 35kg bruce with 35-40m of chain on the snubber. In fresher conditions I deployed a 75kg bruce on the shortened bridle. In strong conditions I let out the sheepshank knots to lengthen the bridle and deployed 50m of chain on the snubber. I mostly anchored in 5m and no more than 10m of water. These lengths and weights were all guesswork on my part with a bit of prior reading for guidance.

It seemed to me that the yawing increased a lot with the longer bridle so I was wondering what bridle lengths other cat users deploy. With the 6m length the snubber is on the chain just below the water just forward of the boat and was very comfortable at anchor, albiet in benign conditions. Near Cap Finisterre we were anchored in strong winds, with 50m of chain and 11m bridle. No waves to speak of but the boat was dancing around like rudolph valentino. I have dagger boards and with the dagger boards down the effect of the wind taking the high bow downwind is worse as it pivots on the daggerboards

The serial drogue info is very interesting and I think it raises the point that in very strong winds I should consider anchoring from the stern - especially if there are no big waves. Any cat owner here with experience of anchoring from the stern ?

[StuM]

Yes, the yawing does increase with a longer bridle. You need to balance this against the additional stretch needed in strong winds.

You also need to consider the side loads imposed by a shorter bridle - once you get beyond about 45°, the "sweating"or "swigging" effect on the line puts significant extra strain on your anchor points pulling the bows together in heavy conditions.

Your current choice sounds about right to me.

I wouldn't advise anchoring by the stern in strong winds. Your windage will increase for one thing and retrieving the anchor will be a lot trickier if your winch is forrard

[noelex 77]

Originally Posted by StuM

Yes, the yawing does increase with a longer bridle. You need to balance this against the additional stretch needed in strong winds.

One option is to attach each leg of the bridle near the stern leading it forward to the bow cleats. The bridle has the advantage of a longer length for more stretch, but with the angle of a shorter bridle and less chance of the bridle abrading on the bottom.

It is not possible on all boats but is worth considering.

[kmacdonald]

I have heard that a polyester bridle may work better in the longer lengths. Less stretch and rebound may reduce the yawing but still have enough stretch to reduce shock loads. I have even heard of series drogues being made with dyneema line to reduce size and weight of drogues. Polyester also has a number of mechanical advantages over nylon that make it more suited to anchor lines----abrasion resistance being one of them. No reduction of strength when wet, less internal friction of fibers under load are some of the other advantages.

It should be noted that it takes very little stretch to significantly reduce shock loads.

[belizesailor]

Originally Posted by kmacdonald

I benign conditions anything will work. In storm or hurricane conditions 2.5 times the beam is what should be used. From the responses here it comes as no surprise that most people lose their boats (and often their lives) when anchored in hurricane conditions. There really isn't any excuse for it other than stupid.

I've yet to see you post any information actually supporting your position of 2.5. Calling others stupid does nothing to add to the credibility of your statement.

How much experience do you have actually anchoring/mooring cats?

[belizesailor]

Originally Posted by kmacdonald

Looks like they agree with me for the most part.

The article is actually about snubbers, not specifically about bridles. There is a difference, you know?