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22-01-2017, 15:56
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#1
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Registered User
Join Date: Jul 2005
Location: Bellingham
Boat: Outbound 44
Posts: 9,319
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What's the right amount of chain loop with a snubber?
I was sitting at anchor in the Hauraki Gulf, NZ on inauguration Eve listening to the met service up their forecast from 35kts NE gusting 45kts, to 45kts gusting 55kts. The last time we anchored in one these it turned into a true Charlie Foxtrot. There were probably 200 boats in the area and a good 30 dragged. This time we are in a Bay with 3 other boats. Anchored in 25-30ft with 225ft of chain out and a 20-25ft snubber.
This got me thinking about what is the best length of chain loop to make the snubber affective. I see 3 options.
1. Set the chain so it is just short of the max stretch length of the snubber. The chain would take affect just before the snubber broke.
2. Set the chain just longer than #1. You'd get all the snubber could give you.
3. Set a large loop way longer than #2. No real need to estimate how much real stretch the snubber has. If the snubber breaks, the boat might get some serious acceleration before the chain snaps taunt- not a good thing.
I probably end up somewhere between 2 and 3 when anchoring for a serious blow. Measuring the right length for 1 or 2 could be tough.
( in the end the winds in the anchorage we overnighted in only made it into the 30's and there was no drama. Had to move in the morning as the winds clocked and stayed high).
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22-01-2017, 16:09
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#2
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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What's the right amount of chain loop with a snubber?
I leave about three ft of slack. My snubber is a bridle of 25' 5/8" three stand nylon, displacement of about 25,000 lbs.
I don't think I have even seen 1' of stretch, but I have only seen about 40 kts worst case and that would have been a gust.
I would want the chain to be tight and prevent the snubber from breaking, I see no reason to allow it to break?
However I believe in my case of a bridle of 5/8" that breaking strength is right at about my displacement, so it's not going to break I don't think, chafing is the enemy I believe
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22-01-2017, 16:14
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#3
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Registered User
Join Date: Sep 2015
Location: Sf Bay
Posts: 140
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Re: What's the right amount of chain loop with a snubber?
I would say number 1 is your ideal situation, if you can measure it correctly.
With that much chain in that kind of depth, you should have a decent catenary effect from the chain though anyway. That should be helping to even out the yanks on the chain as well.
Good scope with all chain, long snubber, I wouldn't overthink it, you're already doing the right things.
I would suggest instead making sure you have good chafe protection on the snubber and a good anchor selection for the ground you're in. Dive the anchor if practical (I know that is difficult outside the tropics).
Set an anchor alarm and hope for the best. In a protected bay, gusts to 45 should be very manageable with the right ground tackle. Sounds like you're already doing the right things.
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22-01-2017, 17:03
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#4
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Registered User
Join Date: Mar 2016
Location: New England. USA.
Boat: McCurdy & Rhodes Custom 46
Posts: 1,474
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Re: What's the right amount of chain loop with a snubber?
second snubber?
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22-01-2017, 17:14
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#5
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Re: What's the right amount of chain loop with a snubber?
I think three strand nylon is good for 12% stretch at 20% of breaking force, so I go for three ft of chain on 25 ft of line, the three ft is a guess, an approximation.
I use three stand as it seems to be very stretchy, and cheap.
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22-01-2017, 17:39
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#6
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: What's the right amount of chain loop with a snubber?
For Typhoon conditions here in the Philippines, I use a very heavy duty bridal snubber, made up of 1.5" braided nylon with stainless chain Clamp.
If eye is coming close, in Typhoon shelters like Looc Bay on Tablas Island, I select the southern end which has heavy mud and a gradual gradient towards a muddy beach..
I lay out and dig in about 90% of my chain the day before and then create a long bight with the balance of my chain, to act as a water brake to reduce veering.
With the red danger mark on deck, the bow is now much lighter and the bitter end is ready to let go if needed.
I have rode out a couple of Typhoons that way with winds recorded over 90 knots.
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23-01-2017, 08:38
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#7
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Registered User
Join Date: Jun 2013
Posts: 26
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Re: What's the right amount of chain loop with a snubber?
Paul L , you've just given me a name for my "hopefully" boat this spring "Charlie Foxtrot" kinda sums it up for me.
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23-01-2017, 08:49
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#8
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Registered User
Join Date: Jun 2014
Location: Up the mast, looking for clean wind.
Boat: Currently Shopping, & Heavily in LUST!
Posts: 5,629
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Re: What's the right amount of chain loop with a snubber?
Quote:
Originally Posted by Stemci
Paul L , you've just given me a name for my "hopefully" boat this spring "Charlie Foxtrot" kinda sums it up for me.
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Are you sure that you want to tempt fate like this? And if you're running around with the idea in your head that your boat is a Fuster Cluck, conscious of it or not, then it's fairly likely that such situations will happen more often than if she has another name. Non?
__________________
The Uncommon Thing, The Hard Thing, The Important Thing (in Life): Making Promises to Yourself, And Keeping Them.
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23-01-2017, 09:16
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#9
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Registered User
Join Date: Oct 2010
Location: Wandering the US Gulf Coast
Boat: 78 Pearson323 Four Winds
Posts: 2,212
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Re: What's the right amount of chain loop with a snubber?
Pelagic, the idea of a long bight from the remaining chain is new to me. Sounds good, to decrease sailing and to expedite a getaway.
Just last night I buoyed the chain end in anticipation of forcast gusts over 60 knots and a questionable neglected boat off my bow. Close off my bow.
As I ran through the process in my mind to dump and run, it was clear the time needed to get the extra chain overboard could be critical to success.
Thanks for the idea to help speed up this process. I have yet to have to dump the gear but set up for it several times.
Probably try this sometime soon to see how it affects my boats willingness to sail at anchor.
__________________
Life begins at the waters edge.
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23-01-2017, 09:42
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#10
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: What's the right amount of chain loop with a snubber?
Hi Four Winds
The excessive hunting(sailing) in storm force winds dampens the range of movement quite a bit when I deploy that large loop.
As I have a long steel bowspirit the snubber and loop is kept well away from the bow.
Another trick if you are storm anchoring in soft mud slurry, is to also deploy a second anchor that hangs down vertically with just a few feet dragging on the bottom
That resistance stops the sailing around dramatically which in that type of slurry often causes main anchor to drag.
Being able to let go quickly in Typhoon conditions is critical here in the Philippines when local ferries and cargo vessel's share the anchorage and often drag all over the place
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23-01-2017, 09:47
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#11
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Registered User
Join Date: Aug 2010
Posts: 3,074
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Re: What's the right amount of chain loop with a snubber?
I was always under the impression the large amount of slack in the chain is to keep a chain-hook from dropping the chain accidentally. A Mantus chain hook can prevent this issue from occurring.
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23-01-2017, 09:55
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#12
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Registered User
Join Date: Feb 2008
Location: GREEN COVE SPRINGS, Florida
Boat: Irwin 43 Mk111 CC, Sloop
Posts: 386
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Re: What's the right amount of chain loop with a snubber?
Quote:
Originally Posted by a64pilot
However I believe in my case of a bridle of 5/8" that breaking strength is right at about my displacement, so it's not going to break I don't think, chafing is the enemy I believe
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Force equals Mass x Acceleration so could be considerably more than displacement.
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23-01-2017, 10:36
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#13
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Moderator Emeritus
Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
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Re: What's the right amount of chain loop with a snubber?
Given slack chain and enough velocity you could pull the bow off the boat.
But I'm not understanding where the slack would come from? My little storm anchoring experience suggests things get tight and stay that way.
I do like the idea of the secondary anchor to control sailing though, sailing is an issue with my boat and I can see how if it got bad, that loads could go through the roof.
BTW, a 5/8" bridle of three strand nylon assuming both share the load, exceeds the breaking strength of my chain slightly, so I don't see the logic in going to larger line, except maybe chafing of course.
I have asked and asked, so far nobody can tell me about their chain parting, it seems as if that is a very rare event
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23-01-2017, 10:36
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#14
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Registered User
Join Date: Jun 2014
Location: Up the mast, looking for clean wind.
Boat: Currently Shopping, & Heavily in LUST!
Posts: 5,629
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Re: What's the right amount of chain loop with a snubber?
Rigging 2 snubbers of differing lengths, & sometimes line diameter, isn't all that uncommon. To even include that at certain levels of stretch, both snubbers begin to work together in order to disipate the energy of a gust or wave strike. Kind of like a progressive rate (mechanical) spring, in order to prevent one's loop of chain from becoming taut.
One other thing that comes to mind for me for anchoring in storm conditions is that it might be wise to keep one's bolt cutters handy. That way if some chain needs severing in a hurry, you have the capability at the ready. Since in such circumstances using a hacksaw will likely be pretty much impossible. Whether it's your anchor chain that needs cutting NOW in order to facilitate your egress, or that of someone that's blown down onto you. Given that there are times when allowing the rode to run out enough so that you can cut the pendant holding the chain's bitter end to the boat isn't possible. So that the chain needs to be cut in situ.
__________________
The Uncommon Thing, The Hard Thing, The Important Thing (in Life): Making Promises to Yourself, And Keeping Them.
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23-01-2017, 11:39
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#15
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always in motion is the future
Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 18,757
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Re: What's the right amount of chain loop with a snubber?
Quote:
Originally Posted by Shrew
I was always under the impression the large amount of slack in the chain is to keep a chain-hook from dropping the chain accidentally. A Mantus chain hook can prevent this issue from occurring.
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Indeed.
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“It’s a trap!” - Admiral Ackbar.
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