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Old 15-10-2017, 05:33   #1
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Breaking Docking Lines

I am currently with " Burnout " in Kapsali harbour on the Greek island of Kythera, sheltering from a front passing through with northerly winds 35 kts+. The harbour is open to the south, but a swell has worked itself in.

I came back from lunch to find that one of my 8 docking lines had snapped! This despite all my docking lines having the biggest mooring dampers Forsheda produces on them. The line itself which snapped was a 20mm polyester line.

It'samazing which forces a swell can put on a lightweight catamaran! But all is well again !

Happy sailing and and docking!
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Old 15-10-2017, 05:52   #2
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Re: Breaking Docking Lines

Chafe protection?

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Old 15-10-2017, 06:46   #3
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Re: Breaking Docking Lines

The Polyester part of that equation may be the cause of your troubles, given it's relatively small ability to stretch, thus absorbing & dissipating energy.
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Old 15-10-2017, 09:04   #4
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Re: Breaking Docking Lines

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Originally Posted by UNCIVILIZED View Post
The Polyester part of that equation may be the cause of your troubles, given it's relatively small ability to stretch, thus absorbing & dissipating energy.
This. Use Nylon.
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Old 15-10-2017, 09:32   #5
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Re: Breaking Docking Lines

Sorry to hear that. During months long flooding I think it was my partners awesome chafe gear that saved us and lots of lines too.

He came up with clear vinyl tubing (found at hardware stores), slit open (use a hair dryer to heat up first, makes cutting easier). Insert line then ziptie it acting as hose clamps. That probably was a key component in none of our 9 lines snapping that we used to keep 43' Hooked (19k lbs, very well built, offshore grade, really high end cleats and bedding helped) from being swept off a side tie lying broadside to the Sacramento river during the floods earlier this year (had up to 7 kts flow speed, avg 5/6 for three months - it was friggin insane, up to 80,000 cfs in a narrow river!). We had local armchair boaters saying they thought we would loose her, however we were diligent and checked and rechecked even more both lines and hardware they were attached to and she's built to a high, tough as nails standard which helped.

I might be able to find some pics, pm me if you want me to look.
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Old 15-10-2017, 12:38   #6
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Re: Breaking Docking Lines

Thanks for your comments and advice. There was no chafe, the mooring line broke approx. 1m after it exited the rubber damper being suspended between the dock and my boat. Whilst Nylon rope could be the answer I would have thought that the rubber dampers would have fulfilled that job.
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Old 15-10-2017, 14:11   #7
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Re: Breaking Docking Lines

Hmmmm I know what you mean, the rubber shock absorbers can take a good beating. Well how many lines do you have per side and how long is your boat?

I'm not trying to say you are a novice or anything like but having had a long term mooring in a constant wake zone (SF Bay Area) from both multi day ferries and tug boats for ships we know all about getting hammered broadside by big wakes. Those rubber shock absorbers are great, our neighbors swore by them however we swear we, who didn't use them, moved less than our neighbors who did use them. I truly think the more lines the better, particularly spring based and the zen of tweaking them just right.
Ps- this advise comes from nearby, in SW Turkey
Come visit us please, it's downwind, an awesome bohemian coastal town plus we desperately need to go sailing ! (enjoying by land at a lovely villa on the Med no less).
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Old 15-10-2017, 15:41   #8
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Re: Breaking Docking Lines

As Uncivilized and Terra Nova already said: use nylon for dock lines. For extra strength, you can buy nylon double braid.

For our boats we've always used nylon 3 strand, never with additional shock absorbers. Have had problems from chafe on dock cleats, should use pro-tek around the line where it intersects the cleats.

You might be interested in this thread: http://www.cruisersforum.com/forums/...ey-190275.html I was really impressed.

Ann
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Old 15-10-2017, 17:27   #9
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Re: Breaking Docking Lines

Were you against a seawall? In a big swell the forces can be enormous in those situations. Those big heavy spring dampers work well in those cases.

As I recall polyester is more likely to fail from heat from being dynamically stressed repeatedly.
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Old 15-10-2017, 18:10   #10
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Re: Breaking Docking Lines

If the dock cleat and the boat cleat are too close together, short scope often breaks in swells or big waves. I've seen yachts tied with the deck cleat almost directly over the dock cleat. Something has to give. If you look at ships docked the line length between the ship and bollard often is 1/4 of the vessel length.
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Old 16-10-2017, 02:02   #11
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Re: Breaking Docking Lines

Quote:
Originally Posted by JPA Cate View Post
As Uncivilized and Terra Nova already said: use nylon for dock lines. For extra strength, you can buy nylon double braid.

For our boats we've always used nylon 3 strand, never with additional shock absorbers. Have had problems from chafe on dock cleats, should use pro-tek around the line where it intersects the cleats.
<snip>
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+1

Rubber snubbers are a triumph of marketing hype over logic.

A spiralled line, wrapped around a rubber shaft, when straightened will increase it's reach by about 15% of the snubber's length - cos 30. For 18inch snubber, that's not more than 3 inches.

Dock lines will usually be at least half your LOA. Otherwise, up/down snatching becomes too violent. Let's say 21ft free play.

Nylon, depending on the lay, stretches up to 10% before deforming or weakening. That's 2ft of the free play. Polyester, about 3% - say 7.5 inches

Nylon = 24 inches of spring. Polyester + snubber = 10 inches of spring.

A triumph of marketing hype over logic.

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Old 16-10-2017, 04:38   #12
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Re: Breaking Docking Lines

Check the snubber itself. I noticed you said "where the line exited the snubber."

I was inspecting dock lines on my Hunter 420 this summer and found a 5/8" line mostly frayed through. The BIG snubber I purchased last year had a sharp internal plastic edge where the line exited the snubber. Over time it was eating through the line.

Just a thought- in a place you wouldn't expect...
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Old 16-10-2017, 05:11   #13
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Re: Breaking Docking Lines

I never had issue with the rubber snubbers that you snake docklines around & through, & for me they've been helpful in high motion areas.
One other thought though, is that the looser your lines, the higher the snatching force on them & the attachment points when they go taut.

Also often it's wise to use different size lines for different docklines, & even in conjunction with one another. Such as something thinner, with more gentle shock absorbtion capabilities for spring lines. Or as one of 2 mooring lines on the same cleat, with a larger diameter line secured with a bit more slack in it, as breast lines.

That way if you have say a 1/2" diameter line snugged up tightly, & a 5/8" or 3/4" line which isn't quite so tight as the thinner one, the thinner one will do the bulk of the work until it stretches enough for the thicker one to begin to take some of the load as well.

The idea is much the same as having 2 snubbers on your anchor chain, with the 1st one in line being longer & thinner than the 2nd one. Who's function is to absorb a portion of the load in gusts, or larger wave sets.

And not to sound like a broken record, but get some Maxi Jacket II & apply it to the high wear areas of your lines. Such as where they meet cleats. This along with tubular nylon webbing, or even purpose made chafe cover, or spare line jacket. Both of which are easy enough to splice into the eyes of docklines, & to replace when it gets too fuzzy. Especially given that all but the stiffest of 3-strand line is pretty easy to resplice several times throughout it's life. Plus it stretches more than most other line types, as a bonus.

Note that you can even go so far as to serve the eyes in some lines to assist with chafe protection. With or without extra chafing protection overtop of the serving. And you can even go so far as to splice PVC hose around the line which forms loops/eyes. Or for that matter, add some metal thimbles, shackled to short lengths of chain wrapped around highly abrasive dock fittings or pilings.
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Old 16-10-2017, 05:24   #14
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Re: Breaking Docking Lines

Quote:
Originally Posted by UNCIVILIZED View Post
I never had issue with the rubber snubbers that you snake docklines around & through, & for me they've been helpful in high motion areas.
One other thought though, is that the looser your lines, the higher the snatching force on them & the attachment points when they go taut.

Also often it's wise to use different size lines for different docklines, & even in conjunction with one another. Such as something thinner, with more gentle shock absorbtion capabilities for spring lines. Or as one of 2 mooring lines on the same cleat, with a larger diameter line secured with a bit more slack in it, as breast lines.

That way if you have say a 1/2" diameter line snugged up tightly, & a 5/8" or 3/4" line which isn't quite so tight as the thinner one, the thinner one will do the bulk of the work until it stretches enough for the thicker one to begin to take some of the load as well.

The idea is much the same as having 2 snubbers on your anchor chain, with the 1st one in line being longer & thinner than the 2nd one. Who's function is to absorb a portion of the load in gusts, or larger wave sets.


And not to sound like a broken record, but get some Maxi Jacket II & apply it to the high wear areas of your lines. Such as where they meet cleats. This along with tubular nylon webbing, or even purpose made chafe cover, or spare line jacket. Both of which are easy enough to splice into the eyes of docklines, & to replace when it gets too fuzzy. Especially given that all but the stiffest of 3-strand line is pretty easy to resplice several times throughout it's life. Plus it stretches more than most other line types, as a bonus.
I'm going to offer an alternative opinion to some expressed here, so that the OP has a lot of choice

I don't like nylon for docklines. In my experience, they are much more likely to break, than polyester. Nylon doesn't like being worked continuously, and is highly vulnerable to chafe.

I use polyester octoplait for all my docklines. The key is rigging them right. As Uncivilized said -- slack in the docklines enormously increases snatch loads, which is usually what breaks them, if it's not chafe. The key is to avoid rigging docklines so that they will snatch right up when the boat moves. So, they should be quite tight, and they should all be ANGLED, not straight between the boat and the dock. Polyester, especially octo, also stretches, not as much as nylon, but it is a more sustainable stretching with less internal heating. If you give your docklines a mechanical advantage by angling them, then polyester is quite ok.

Concerning rubber buffers -- in my experience, these are absolutely great, BUT they should be used correctly. If you put them on a line which is not tight enough, the snatch loads will break them. And they should be big enough. Also, don't mix them up with lines taking the same force vectors, but without buffers. I like to add a couple of lines with buffers at a steeper angle to the rest of the docklines -- I find that this really dampens the motion in a nice way.

Last point, and I'll shut up: if there is wave action in the marina which causes the boat to roll appreciably, or if there is enough wind to heel the boat over, then you're going to have problems no matter what. If the boat rolls and catches a fender under the pontoon, then you can rip out lifelines (happened to me). I sometimes use a big horizontal fender, and tie it to cleats, not life lines, with doubled lines. But best of all is to take lines to the other side to hold the boat off the pontoon -- if there is any chance of that.

Marina berths are not the best place to be in really strong weather, if there is not perfect shelter.
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Old 16-10-2017, 07:20   #15
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Re: Breaking Docking Lines

Nylon 3-strand dock lines outlast polyester braid at about 10:1.
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