Chain Stopper Install

[Frankly]

I think the idea that you can connect a big anchor to a yacht in a storm with only chain is wildly misguided. Many years back a neighbor of a friend anchored his 30' +- cabin cruiser for one of our hurricanes with nothing but a Big A** storm anchor chained to the bow eye (like a put it on a trailer U bolt). After the storm the boat was on the hill. The bow eye, a large chunk of heavy layup fiberglass, the chain, and anchor were right where they started.

Got to have some compliance to take the shock loads. After about 50 or 60 knots the chain catenary no longer provides any give and shock loads go through the roof.

There is a reason all those tall skinny palm trees survive in South Florida (they flex).

[Terra Nova]

The guy should have put out more chain.

[Snowpetrel]

Originally Posted by Cheechako

The bolts are far lower strength in shear than tension aren't they?

Typically approx 60% or so of the tensile. Of course there is lots of different tensile grades of stainless bolt, to make life interesting..

[Adelie]

Try a drill guide to keep the holes aligned: http://m.homedepot.com/p/General-Too...Q&gclsrc=aw.ds


A house is but a boat so poorly built and so firmly run aground you would never try to refloat it.

[wsmurdoch]

Originally Posted by Cheechako

The bolts are far lower strength in shear than tension aren't they?

That is a hard one to figure. Think of a bolt passing through two plates. Sometimes the shear force between the plates is taken entirely by the friction of the two plates clamped solidly together by the bolts and the bolts never see the shear. Sometimes if the bolts are a little loose, the two plates are thin, are hard, and have sharp well formed holes, the plates act like sharp scissors and slice the bolt in half. Sometimes if the plates are soft, the holes oversized, and the bolts are a bit more slack, the holes deform, the bolts deform and things go more into tension.

The first case it the easiest to calculate. So, what is the maximum clamping force that can be achieved with the four blots and a backing plate the size of the hardware without breaking the bolts or crushing the interior wood or the external FRP? Given the coefficient of friction of stainless on FRP, will the resulting friction hold the chain stopper in place at the chain breaking strength?

[UNCIVILIZED]

Originally Posted by wsmurdoch

That is a hard one to figure. Think of a bolt passing through two plates. Sometimes the shear force between the plates is taken entirely by the friction of the two plates clamped solidly together by the bolts and the bolts never see the shear. Sometimes if the bolts are a little loose, the two plates are thin, are hard, and have sharp well formed holes, the plates act like sharp scissors and slice the bolt in half. Sometimes if the plates are soft, the holes oversized, and the bolts are a bit more slack, the holes deform, the bolts deform and things go more into tension.

The first case it the easiest to calculate. So, what is the maximum clamping force that can be achieved with the four blots and a backing plate the size of the hardware without breaking the bolts or crushing the interior wood or the external FRP? Given the coefficient of friction of stainless on FRP, will the resulting friction hold the chain stopper in place at the chain breaking strength?

I'd concur on most of this, & you did some great explaining of things BTW. Bravo!!! I'd though of doing such earlier, but the fuel gauge for my brain read "E".

Anyway, I would think that when calculating the required bolt strength for a chain stopper, such needs to be based on a worst case scenario. In addition to adding in a Large safety factor.

As in a storm, with the shock loads on the rode, even with the snubbers taking the load most of the time, there will be occasions where the snubbers are stretched past their limits. At which point the chain then yanks hard on the stopper. Which could & would, loosen the stopper's mounting bolts a bit. And probably elongate their holes by a small amount, as well as stretching the bolts somewhat, so that now everything is a tiny bit loose.

This would reducing the bolts clamping force by a small fraction. Enough so that the friction between the chain stopper & the deck/mounting block would fall off dramatically.
So that at that point, the only thing holding the chain stopper in place would be the bolts. Loaded partially in sheer, & partially in tenstion. Thus said fasteners need to be significantly oversized in order to deal with this, as well as to provide a safety factor.

A safety factor much like the bolts on a Mantus. Where each of them is more than strong enough to hold everything together. And yet there are a number of them doing so. The same is true of keel bolts.

[Three Sisters]

Originally Posted by a64pilot

OK, got it, stopper must be Hell for strong.
I'll have to get a good look at this thing, initial impression was the gate part would be weaker than the chain. Maybe not.


Sent from my iPad Pro using Cruisers Sailing Forum

Exactly what I concluded. The gate would appear to give way before tearing the deck off.

[Dockhead]

Originally Posted by Frankly

I think the idea that you can connect a big anchor to a yacht in a storm with only chain is wildly misguided. Many years back a neighbor of a friend anchored his 30' +- cabin cruiser for one of our hurricanes with nothing but a Big A** storm anchor chained to the bow eye (like a put it on a trailer U bolt). After the storm the boat was on the hill. The bow eye, a large chunk of heavy layup fiberglass, the chain, and anchor were right where they started.

Got to have some compliance to take the shock loads. After about 50 or 60 knots the chain catenary no longer provides any give and shock loads go through the roof.

There is a reason all those tall skinny palm trees survive in South Florida (they flex).

I completely agree with this, but did anyone suggest otherwise? Shock absorption is what you need snubbers for. In a really big storm, you will eat through nylon snubbers pretty fast, so you might better use very long pieces of polyester, with excellent chafe protection, and probably a couple of them.

Another serious problem of being anchored in a big storm is sheering back and forth due to the inherent instability of being anchored by the bow (center of aerodynamic pressure ahead of center of hydrodynamic pressure, which is why your bow blows off). I don't know the solution to this. Some people have suggested that you should actually anchor from the stern in a big storm. A riding sail might be another solution, although I have no idea how a riding sail would behave in a hurricane.

[UNCIVILIZED]

Originally Posted by Dockhead

I completely agree with this, but did anyone suggest otherwise? Shock absorption is what you need snubbers for. In a really big storm, you will eat through nylon snubbers pretty fast, so you might better use very long pieces of polyester, with excellent chafe protection, and probably a couple of them.

There are purpose made mooring pendants, & rope which may work for this. Both have a polyester cover, with a nylon core. So that you get the perks of both materials without their downfalls for the most part. And the recommended sizes are hell for stout. So hopefully they work. Which the evidence thus far suggests. And they've been in use for a good 2 decades+ so they're likely on to something.
Polydyne is one trade name for the mooring pendants, & there are others.

Another serious problem of being anchored in a big storm is sheering back and forth due to the inherent instability of being anchored by the bow (center of aerodynamic pressure ahead of center of hydrodynamic pressure, which is why your bow blows off). I don't know the solution to this. Some people have suggested that you should actually anchor from the stern in a big storm. A riding sail might be another solution, although I have no idea how a riding sail would behave in a hurricane.

I'd nix the idea of a riding sail in truly heavy weather, as you'd want as little windage as possible. So some suggest dropping an anchor under foot to aid in minimizing this veering back & forth. While others have mentioned bridles, in order to cant the boat ever so slightly to one side.

Tough calls.

[Dockhead]

Originally Posted by UNCIVILIZED

There are purpose made mooring pendants, & rope which may work for this. Both have a polyester cover, with a nylon core. So that you get the perks of both materials without their downfalls for the most part. And the recommended sizes are hell for stout. So hopefully they work. Which the evidence thus far suggests. And they've been in use for a good 2 decades+ so they're likely on to something.
Polydyne is one trade name for the mooring pendants, & there are others.



I'd nix the idea of a riding sail in truly heavy weather, as you'd want as little windage as possible. So some suggest dropping an anchor under foot to aid in minimizing this veering back & forth. While others have mentioned bridles, in order to cant the boat ever so slightly to one side.

Tough calls.

Nylon has two (or three) problems for being reliable in a big storm -- it loses strength when wet, if fails due to internal heating if it is stretching a lot, and it is very vulnerable to chafe. A nylon mooring pendant with a polyester cover would solve one of these problems. To solve the others with nylon, it would just have to be big enough and long enough. How much I don't know. I think I might just go with very long pieces of polyester instead. There are lots and lots of stories about nylon snubbers or rode failing in storm conditions, and I had a nylon snubber fail on me -- with a bang -- in a storm once. It just exploded. It was all melted inside. It was pretty stout, too, I think it was 20mm.


The problem of sheering is maybe the key one, which produces the really big loads. If a riding sail is out (and I believe you), then I don't know what to do about sheering. I use a spring line to the anchor chain in milder conditions, but that wouldn't work in a storm. Maybe really anchoring from the stern would be the best option.

I rode out hurricane force winds in Cowes Yacht Haven earlier this year. It was a scary night, with the boat heeling 20 degrees or more at times in her berth. I didn't get much sleep. The marina was almost empty so I was able to haul the boat off the pontoon by taking lines to the next pontoon, and that prevented bashing against the pontoon. I had enough warning that I was able to spend a whole day arranging chafe protection. In the event it was ok and no damage, although a couple of my dock lines were damaged by chafe. There was a lot of destruction of boats in the Solent that night.

[thinwater]

I think the reason nylon fails is not as simple as pointing a finger at heating or chafe. Everytime I have gone throught he math on a failure there are 2 problems:

Too small and too short.

Too small. Chain can work at a high % of WL, nylon cannot. Often as not the nylon snubber is the same strength or weaker than the chain and is working well above it's safe working load. Of course it heats.

Too short. A boat that is anchored on all-chain will have forces at least double that of all-rope. We add some rope (snubber) to absorb the force, but if the rope is only 6-8 feet long, it cannot actually reduce the force enough and is too small. The snubber needs to be >30 feet if it going to be similar in strength to the chain.

---

So if you want a short nylon snubber to be safe, it has to have the same WORKING LOAD as the chain, which because nylon requires a 12:1 safety factor, means it will be 2-3 times the strength of the chain. It is going to be fat, it is going to be long, or it is going to fail. Very basic, if you think in terms of working load rather than strength (which is irrelevant).

I like long, thin snubbers (twin 10M x 8mm), because generally I'm more concerned with the hook moving than line breaking. But if I were planning on a hurricane, I would stay with nylon, but I would go BIG. I would be using twin 30' x one inch on my 34' cat, larger than one poster broke on a 54' mono. That is what the engineering calculations actually call for (I've done load cell testing of anchoring loads). Go Big.

[deblen]

Nylon 3 strand for mooring/anchoring should be medium or hard lay.Not the nice soft lay sold for yachts.
Medium & hard lay are not as nice to handle-much more stiff-but you don't get near the internal or external chafe. Check with comm. fish.-they know what works.

Then,there is polysteel type -a much improved poly that is one of the most popular & long lasting comm. ropes. Again,not as nice to handle.

Polysteel - Specification Sheets

[ErBrown]

A64 - As is so often on your threads, we're have the exact same dilemma. Recently upsized anchor, chain and windlass and the last piece is a good quality chain stopper. As has been said many time here, a true snubber will always be primary (and secondary) but I like the chain stopper as a last resort backup or to help if having to recover by hand.

So I'd be very interested in what you end up doing for the mount. The suggestions I've gotten from folks locally has been to use massive lag bolts. I still haven't installed them because somewhere (likely CF) I read something along the lines of "there are two types of fasteners on boats, through bolted and temporary"...and that stuck with me.

Our plan was to go with the Maxwell stopper but since I haven't settled on the mounting option, this is still on the todo list.

The thing that concerns me about the Maxwell levered stopper (other than price) is that it appear to have the bolts permanently attached to the base of the stopper.

Maxwell

So if we go this route I'd have to work with our local stainless shop re-work it for our use. Maybe we'd be better off going with the Lewmar you linked to above...

[UNCIVILIZED]

Originally Posted by thinwater

I think the reason nylon fails is not as simple as pointing a finger at heating or chafe. Everytime I have gone throught he math on a failure there are 2 problems:

Too small and too short.

Too small. Chain can work at a high % of WL, nylon cannot. Often as not the nylon snubber is the same strength or weaker than the chain and is working well above it's safe working load. Of course it heats.

Too short. A boat that is anchored on all-chain will have forces at least double that of all-rope. We add some rope (snubber) to absorb the force, but if the rope is only 6-8 feet long, it cannot actually reduce the force enough and is too small. The snubber needs to be >30 feet if it going to be similar in strength to the chain.

---

So if you want a short nylon snubber to be safe, it has to have the same WORKING LOAD as the chain, which because nylon requires a 12:1 safety factor, means it will be 2-3 times the strength of the chain. It is going to be fat, it is going to be long, or it is going to fail. Very basic, if you think in terms of working load rather than strength (which is irrelevant).

I like long, thin snubbers (twin 10M x 8mm), because generally I'm more concerned with the hook moving than line breaking. But if I were planning on a hurricane, I would stay with nylon, but I would go BIG. I would be using twin 30' x one inch on my 34' cat, larger than one poster broke on a 54' mono. That is what the engineering calculations actually call for (I've done load cell testing of anchoring loads). Go Big.

I'm going from memory, & if my recall is correct, much of what you're saying is the same as has been concluded by some of the harbor masters in some New England ports. Where they at times get storms of F9 & above, which can wreak real havoc on the boats in their mooring fields.
The kicker being that dual 1"+ pendants were also what was said to be the only thing with a chance of surviving one of those storms. As anything less failed fairly quickly.

I wish that I had the article, but... one other thing which came out of their reports, was the creation of a new type of rope to be used for mooring pendants. Specifically one with a polyester cover, & nylon innards. The reasons being to enhance chafe resistance while retaining elasticity. And these are a couple of the items which came out of that idea:
::Â*Teufelberger:Â*Poly / Nylon Mooring Pendants
Polydyne / High Strength Double Braided Rope | Yale Cordage
Maxi-Moor II | Yale Cordage

I can't say that I've tested any of them, so (as always) the risk's entirely on the user. But there may be some information on the stuff in some back issues of Professional Boatbuilder, as it's fairly common for that magazine to do some in depth studies on marinas, moorings, & the technology which goes into modernizing docking & mooring systems. And odds are that it was in a back issue of said periodical where I read the article that's pointing me towards the above information.

Regardless, I'd definitely be up for trying out some of the new pendants/rope designed for these high load, heavily cycled applications. Or if not that, then finding some very stretchy polyester rope to use instead.
I wish that the old Regatta Braid was still being made. It was NICE & stretchy due to it's braiding style, despite being polyester. The new stuff has a lot less give to it as o last check.
Tine to hunt for a replacement.

[Dockhead]

Originally Posted by ErBrown

A64 - As is so often on your threads, we're have the exact same dilemma. Recently upsized anchor, chain and windlass and the last piece is a good quality chain stopper. As has been said many time here, a true snubber will always be primary (and secondary) but I like the chain stopper as a last resort backup or to help if having to recover by hand.

So I'd be very interested in what you end up doing for the mount. The suggestions I've gotten from folks locally has been to use massive lag bolts. I still haven't installed them because somewhere (likely CF) I read something along the lines of "there are two types of fasteners on boats, through bolted and temporary"...and that stuck with me.

Our plan was to go with the Maxwell stopper but since I haven't settled on the mounting option, this is still on the todo list.

The thing that concerns me about the Maxwell levered stopper (other than price) is that it appear to have the bolts permanently attached to the base of the stopper.

Maxwell

So if we go this route I'd have to work with our local stainless shop re-work it for our use. Maybe we'd be better off going with the Lewmar you linked to above...

Don't forget you can also use a strop, as an alternative to a stopper, in case you have a good place to anchor it.

It's terrible that modern boat builders don't provide samson posts (my next boat will have one, however), as this is the ideal place. I use a chain strop, but I will probably replace it with Dyneema over the winter. I anchor mine to the inner forestay chainplate, which is strong enough, and no drilling/mangling of the deck was required.