Line size for anchor bridle

[wrwakefield]

Originally Posted by cabo_sailor

5/8 fits the cleats easily. My concern is attaching two such lines to the Mantus hook without it being too cramped. Our boat is around 24 K lbs but our waters are shallow. Typical anchorage is only about 10-20 ft.


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Hi Rich,

Safe, shallow anchorages [something rare up here...] would require us to rig our bridle as we do for inclement conditions: fair lead from bow to primary winches [with anti-chafe covering at bow fairleads. (Or maybe hi-mod line in the future.) ] This way the bridle legs are long enough to do some good, and the attachment point doesn't have to contact the bottom...

In case this might work for you...

Cheers!

Bill

[Delfin]

Originally Posted by zboss

It does... lots more stretch. I can't explain it but the boat doesn't bounce around nearly as much with the 3/8" nylon vs. the 5/8" nylon. With that said, if we are expecting weather we usually switch to the 5/8" or preload the 5/8" behind the 3/8" so if the 3/8" breaks we have the 5/8" that can take the load.

I use 50 feet so I can periodically move it to avoid chaffing a single spot - we start out at 25 feet on each side then move out 1 or so feet at a time. If we only had 25 on each leg we would not have that option. The 3/8" is very easy to manage at 50 feet long (its actually probably closer to 45 on each leg because I put an eye at the end).

The reason the 3/8" settles the boat better is because the force of wave and current against the hull is dissipated over a greater distance due to the stretch. The force declines pretty significantly the more stretch there is. IMO the key to building the right snub line is to use the lightest line that will hold up to the loading expected, so having two of them makes a lot of sense. By way of reference, my boat weighs 68 tons or so, and for everyday use 5/8" has worked great for years. For more vigorous conditions, I have a 3/4" snubber.

The OP might want to think about just using a single line of around 30' and not a bridle, with attachment to the chain via a soft shackle.

[CAELESTIS]

Ditch the Mantus hook and use a soft shackle.

http://www.cruisersforum.com/forums/...-155714-3.html

[thinwater]

I did a bunch of instrumented testing for a magazine article, everything from very long and thin to Dyneema. A few thoughts:

a. Because you are absorbing energy as much as force, length matters almost as much as strength. A long 3/8" snubber will outlast a short 5/8" snubber, because it sees MUCH less force.

b. If the gate on the Mantus snubber is failing from UV, your snubber is too short (it should be well underwater). I have one of the first prototypes. That said, the users should suggest they use a softer plastic (I have).

c. Other than faulty deployment (keep tension on it) the only way any hook comes off is if it lies on the bottom. I've seen broken snubbers stay on the chain.

As for the OP, 1/2" should be plenty. I use an 7.8 mm climbing rope (5/16") x 35' bridle on a 34' cat (nearly the same windage, less weight). 5/8" is certainly too much at 25 feet long. The point is that it should be at least 1 boat length to absorb shock in shallow water.

[model 10]

Originally Posted by thinwater

I did a bunch of instrumented testing for a magazine article,
c.the only way any hook comes off is if it lies on the bottom. I've seen broken snubbers stay on the chain.
The point is that it should be at least 1 boat length to absorb shock in shallow water.

How can it be a boat length long and not end up on the bottom? I see lots of stretch in our 5/8" snubber that is only 25" long . There has never been any shock loading and we weigh only 18,000lbs .

[Hudson Force]

Originally Posted by wrwakefield

...............................
................... Safe, shallow anchorages [something rare up here...] would require us to rig our bridle as we do for inclement conditions ............
...........

I was confused by this. I was thinking just the opposite and considering a safe anchorage as being one with little fetch and no waves or swell. This would mean no surge or changing tension on the bridle and therefore, no need for a long length or stretch.

My practices are influenced by spending most of my anchored times at 10 to 20 feet with no more than a half mile fetch, often far less, so I'm usually using a bridle with a pair of 5/8" lines no more than 20' and often just 10' deployed.

[Hudson Force]

Originally Posted by Guy

................... I see lots of stretch in our 5/8" snubber that is only 25" long . .................

Wait! You mean 25 feet! right? typo?

[model 10]

Originally Posted by Hudson Force

Wait! You mean 25 feet! right? typo?

No! 24" was too short, had to go 25"

[thinwater]

Originally Posted by Guy

How can it be a boat length long and not end up on the bottom? I see lots of stretch in our 5/8" snubber that is only 25" long . There has never been any shock loading and we weigh only 18,000lbs .

a. If it is under load it is not on the bottom. And though I do not like having the snubber on the bottoms, on most bottoms there is no great harm.

b. When I am in shallow water the bridle terminates at the midships cleat, over bow chocks through chafe gear, and to the rode. It is free to move in the chafe gear. Others have used blocks for this purpose.

c. 25' is a good length. It is really the little 5-8' snubbers that underperform.

d. Just because you do not feel the shock does not mean it does not exist. The loads on a 1/2" snubber would be 25% less than you have now. The loads on all-chain were as much as 4x higher than with a long thin snubber.

I bet your snubber could be thinner without any loss in durability, but it sounds OK to me.

[wrwakefield]

Originally Posted by Quote:
Originally Posted by wrwakefield View Post
...............................
................... Safe, shallow anchorages [something rare up here...

would require us to rig our bridle as we do for inclement conditions ............
...........

Hudson Force;1992151]I was confused by this. I was thinking just the opposite and considering a safe anchorage as being one with little fetch and no waves or swell. This would mean no surge or changing tension on the bridle and therefore, no need for a long length or stretch.

My practices are influenced by spending most of my anchored times at 10 to 20 feet with no more than a half mile fetch, often far less, so I'm usually using a bridle with a pair of 5/8" lines no more than 20' and often just 10' deployed.

I'm sorry to cause any confusion, Hudson.

What I was trying to describe is how we would keep our longer anchor snubber/bridle length without letting the chain attachment point hit the bottom in a shallow anchorage: Instead of attaching at the bow and only have 15ft or so of bridle/snubber length, we would lead through bow fairleads back through return blocks near the stern, then to the primary winch(es) so the line is much longer, and chain attachment point just below the water surface. [This is also what we do if expecting inclement conditions so we can adjust the bridle from the cockpit...]

One possible difference with us is we always set the [overnight] anchor and bridle as though we are expecting storm force conditions. [And this has occurred several times over the years- once being blown off my anchor in unanticipated williwaws. (Think zero to Force 11 in under 15 seconds... then back to zero again...) Hence my conservative approach in higher latitudes...] It doesn't take any longer to do so and- being inherently lazy myself- I don't feel compelled to get up in the middle of the night to check things if the predicted conditions deteriorate. [And, in the case of williwaws, there is no time to take additional preventative measures...]

RE: Protected anchorages- your point is well taken, and I agree with seeking them out wholeheartedly. Though our average anchorage may be deeper than we usually read about, we only select those that are well protected from anticipated winds, with little fetch or wave/swell potential.

RE: Snubber/Bridle length: We choose to use a longer bridle because of our tidal variations of 15-20+ft; our scope ratio changes several times over the course of 24 hours. We keep the longer snubber to help ameliorate the smaller scope ratio [i.e., at higher tides in deeper anchorages we approach a 4:1 ratio- sometimes slightly less- with our 360ft of chain (+ 100ft of nylon rode for Hail Mary scenarios)...] The idea with the longer snubber/bridle is to reduce sudden forces on the anchor [and vessel attachment points...] in high-wind and/or gusty [e.g., williwaw] conditions- especially when at reduced scope due to high tide in a deep anchorage.

So far, so good... knock on wood...

I hope this helps clear up any confusion I may have caused.

Cheers!

Bill

[Hudson Force]

Thanks, Bill, for allowing me to better understand. We are in such different environments of latitude, tide, depths, anchorages and weather.

[Don Pedro]

On the lighter side of life, we sell Mantus chain hooks in Australia, one inquiry we had, I asked the chap how long his bridle/snubber was, he replied 'about 5ft' I don't want to get the rope wet!

[Group9]

Originally Posted by zboss

We have two bridles. Both use the mantus chain hook. One uses 25 feet on each leg of 5/8" 3 strand. The other uses 50 feet of 3/8" 3 strand on each leg.

The 3/8" has a LOT more stretch. We have had that line in 40 knots winds with our spade anchor and pretty high standing waves and its a champ. The boat hobby-horses less in heavy wave action than using the 5/8" three strand.

I would add... the 3/8" line is very cheap to replace, so we do whenever it occurs to us that it may be needed.

We use 3/8s for the same reasons you state.

[Jim Cate]

A point not often raised in these discussions:

Snubbers with extreme stretch do reduce instantaneous loads more than less stretchy ones, this is certainly true. What is not clear is whether this additional stretch makes very much difference in reality.

What I have observed is with very stretchy snubbers, the boat surges backwards a longish way in gusts. When the gust dissipates, the boat surges forwards, generating a lot of slack in the chain. When the next gust comes along, the bow is able to blow off a long way before the chain and snubber come tight again. In our boat, which has a fair amount of windage forward, getting a bit sideways like that means that greater loads are imparted to the ground tackle - a counter productive situation!

My solution is to use a snubber made of 5/8 inch double braid nylon, using lengths from 15 to 30 feet depending on conditions. This offers enough stretch to eliminate any shock loading, is strong enough for any reasonable conditions (we broke a 14 mm octoplait snubber once) and has excellent chafe resistance. Has worked in anger now for some years. Oh... it is terminated in a simple chain hook. I never veer enough snubber for it to reach the bottom, so it has yet to fall off accidentally; we seldom anchor in water shallow enough for that to be a worry. If at some point a shallow anchorage is needed in strong conditions, I'd use a soft shackle for connection.

For scaling, our boat is 46 feet long, medium windage for length, about 12 tons fully loaded for cruising/live aboard.

Jim

[darylat8750]

Originally Posted by Jim Cate

A point not often raised in these discussions:

Snubbers with extreme stretch do reduce instantaneous loads more than less stretchy ones, this is certainly true. What is not clear is whether this additional stretch makes very much difference in reality.

What I have observed is with very stretchy snubbers, the boat surges backwards a longish way in gusts. When the gust dissipates, the boat surges forwards, generating a lot of slack in the chain. When the next gust comes along, the bow is able to blow off a long way before the chain and snubber come tight again. In our boat, which has a fair amount of windage forward, getting a bit sideways like that means that greater loads are imparted to the ground tackle - a counter productive situation!

My solution is to use a snubber made of 5/8 inch double braid nylon, using lengths from 15 to 30 feet depending on conditions. This offers enough stretch to eliminate any shock loading, is strong enough for any reasonable conditions (we broke a 14 mm octoplait snubber once) and has excellent chafe resistance. Has worked in anger now for some years. Oh... it is terminated in a simple chain hook. I never veer enough snubber for it to reach the bottom, so it has yet to fall off accidentally; we seldom anchor in water shallow enough for that to be a worry. If at some point a shallow anchorage is needed in strong conditions, I'd use a soft shackle for connection.

For scaling, our boat is 46 feet long, medium windage for length, about 12 tons fully loaded for cruising/live aboard.

Jim

Jim, Do you use a single line or a bridle?