Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 25-03-2016, 16:35   #46
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,948
Re: Help me flesh out my ground tackle

Sorry but this horse falls at the first hurdle....We obviously have diffferent fundemental beliefs...
Quote:
Originally Posted by Dockhead View Post
Well, look . . .

* The snubber is made to stretch and absorb shock, right? My snubber is there to take the load off the windlass

* Therefore it can't possibly be as strong as the rest of the rode, else it wouldn't be stretchy enough. I have never compared the strength of the nylon v my chain

* The snubber is nylon, which as we know breaks down after repeated cycling. I replace mine quite frequently. After repeated cyclings with the frequent 'Bravezas' in Antofagasta I have had my nylon shore lines actually go 'solid' due to heating up under repeated shock loading but that was where the bight led around the shore cleats and was very localised..also extreme loads... nylon still didn't fail.

* The snubber is absorbing all the shock for the whole rode. No my catenary absorbs the load and I don't get shock loadings.

THEREFORE, the snubber is a serious weak point in the system, if it's used like this. A chain is only as strong as its weakest link.

In fact, the snubber is a break waiting to happen, something we accept in order to get the required stretch. You've never broken one?? I've broken at least three or four, and that's despite changing them every two years. You need heavier chain and more of it

If it breaks in strong weather and you haven't belayed your chain, your ground tackle will run out and be gone before you can even get up on deck. That could put you on the bricks depending on where you're lying. True enough.... if I was in conditions that bad I would put a very short and strong snubber between capstan and roller belayed to a frd cleat, which is what I do when backing down on anchor when setting it.


Now considering all of this, don't you think it would be reasonable to belay your chain in a manner as strong as the rest of the rode? And leave the snubber to do what it's intended for, without asking it to do something which it's not suited for? My snubber does everything I ask of it
And yes I have had my entire 70 meters leading straight ahead with no catenary in 60 knots mas o minos and haven't broken anything. Mind you I avoid anchoring in surf....

Q? where do you lead your snubber over the side? I take mine straight from cleat to fairlead and away.. not over the bow roller. 6 inches between cleat and fairlead so minimum stretch at that point... and I freshen the nip frequently.
__________________

El Pinguino is offline   Reply With Quote
Old 25-03-2016, 16:39   #47
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,447
Re: Help me flesh out my ground tackle

Quote:
Well, look . . .

* The snubber is made to stretch and absorb shock, right?

* Therefore it can't possibly be as strong as the rest of the rode, else it wouldn't be stretchy enough.

* The snubber is nylon, which as we know breaks down after repeated cycling.

* The snubber is absorbing all the shock for the whole rode.

THEREFORE, the snubber is a serious weak point in the system, if it's used like this. A chain is only as strong as its weakest link.
DH, your second premise seems faulty to me. Why can't the snubber be as strong as the rest of the (all chain) rode? Chain, of course, is not at all stretchy, hence any nylon or other common textile snubber will be more stretchy. If a large diameter nylon snubber is used, and of enough length, it seems to me that it can be essentially as strong as the chain and still provide adequate shock absorption.

Case in point: our rode is 10 mm G30, with a breaking strength of ~11,000 pounds. Our snubber is 16mm (5/8") double braid nylon with a breaking strength of ~13,500 lbs, and we typically deploy around 10 metres of snubber. Thus, to a first approximation, they are of equal strength; the snubber is not a serious weak point in the system. You may quibble that our snubber is not adequately elastic to absorb shock loads, but we, who live full time at anchor, have found it to be fine. IMO, large amounts of stretch do more harm than good in that it allows too much sag back in the puffs, with attendant "slingshotting" of our fairly light boat as the puff fades. This in turn leads to greater yawing, with all the well known issues that follow.

Final point: I certainly agree that there is no harm in a chain stopper or equivalent strop. But the one time we had a snubber failure (14 mm octoplait nylon) when we fouled the chain on a big boulder in a violent windshift and came up hard at ~1:1 scope, the chain did not all run out. It slowly ran the windlass backward (and that with a 56:1 worm drive!) for a few feet and then stopped. I'm sure that it wasn't good for the gears, but did not destroy anything! So, in harsh conditions we now do fit a second, short snubber just in case, but don't feel it necessary in routine conditions. I'd prefer a stopper, but it isn't practical with our foredeck layout.

Jim
__________________

__________________
Jim and Ann s/v Insatiable II , lying Port Cygnet, Tasmania once again
Jim Cate is offline   Reply With Quote
Old 25-03-2016, 16:48   #48
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by Jim Cate View Post
DH, your second premise seems faulty to me. Why can't the snubber be as strong as the rest of the (all chain) rode? Chain, of course, is not at all stretchy, hence any nylon or other common textile snubber will be more stretchy. If a large diameter nylon snubber is used, and of enough length, it seems to me that it can be essentially as strong as the chain and still provide adequate shock absorption.

Case in point: our rode is 10 mm G30, with a breaking strength of ~11,000 pounds. Our snubber is 16mm (5/8") double braid nylon with a breaking strength of ~13,500 lbs, and we typically deploy around 10 metres of snubber. Thus, to a first approximation, they are of equal strength; the snubber is not a serious weak point in the system. You may quibble that our snubber is not adequately elastic to absorb shock loads, but we, who live full time at anchor, have found it to be fine. IMO, large amounts of stretch do more harm than good in that it allows too much sag back in the puffs, with attendant "slingshotting" of our fairly light boat as the puff fades. This in turn leads to greater yawing, with all the well known issues that follow.

Final point: I certainly agree that there is no harm in a chain stopper or equivalent strop. But the one time we had a snubber failure (14 mm octoplait nylon) when we fouled the chain on a big boulder in a violent windshift and came up hard at ~1:1 scope, the chain did not all run out. It slowly ran the windlass backward (and that with a 56:1 worm drive!) for a few feet and then stopped. I'm sure that it wasn't good for the gears, but did not destroy anything! So, in harsh conditions we now do fit a second, short snubber just in case, but don't feel it necessary in routine conditions. I'd prefer a stopper, but it isn't practical with our foredeck layout.

Jim
A very long and large snubber might be as strong as the chain, and in that case the problem is lessened. If you are satisfied with the shock absorption. Most cruisers, however, use much lighter and shorter snubbers than yours, in order to get the stretchiness they want.


But also, you might think your nylon snubber has 13 500 lbs breaking strength, but that is only the rope, in dry and new form and without knots. The snubber is not the same as the raw rope.

First of all, any knot in it reduces the strength.

And if you read this:

http://www.bethandevans.com/pdf/dashew-right-rode.pdf

You know that nylon loses about 20% of its strength right off the bat, just by getting wet. Then, it is subject to internal heating as it "works", and is subject to sudden failure.

Then yet further on top of all the foregoing, nylon is very susceptible to chafing.

You were lucky not to lose your ground tackle that time your snubber broke. Was your windlass ruined? Why would you take such risks, just to avoid connecting the chain strongly to the boat?


Edit: You make a good point about snubbers which are TOO elastic, and I have also gone to thicker and less elastic snubbers with time. Less elasticity also means less chafe and internal heating, so less risk of breaking.

As I mentioned earlier, I'm actually not using a snubber at all any more in settled weather, as long as I have at least a shot or two of chain out. It took me a few years to get used to the different behavior of heavy 12mm chain, compared to what I had on my old boat. The catenary of the heavy chain has a remarkable effect.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 25-03-2016, 16:56   #49
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by El Pinguino View Post
Sorry but this horse falls at the first hurdle....We obviously have diffferent fundemental beliefs...


And yes I have had my entire 70 meters leading straight ahead with no catenary in 60 knots mas o minos and haven't broken anything. Mind you I avoid anchoring in surf....

Q? where do you lead your snubber over the side? I take mine straight from cleat to fairlead and away.. not over the bow roller. 6 inches between cleat and fairlead so minimum stretch at that point... and I freshen the nip frequently.
A: I lead my snubber over the second bow roller. There's no chafe at the roller, but there will be chafe at the roller cheeks if there is much yawing going on. If the boat is sailing at anchor, something I hate, I usually spring the chain with a second snubber taken to a midships cleat. I do freshen the nip, and my broken snubbers have all broken near the middle, not at chafe points.


"And yes I have had my entire 70 meters leading straight ahead with no catenary in 60 knots mas o minos and haven't broken anything. Mind you I avoid anchoring in surf..." And you were happy to be held by nothing other than a piece of nylon with a nip which may or may not have been freshened enough for the conditions? Or may or may not have been changed recently enough? You are a far bolder fellow than I; I recommend casinos.


"My snubber is there to take the load off the windlas"

Well, that's not a snubber then. If that's its purpose, then ditch the nylon, use dyneema, make it as strong as the chain, protect it from chafe, and you're golden
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 25-03-2016, 17:21   #50
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: Help me flesh out my ground tackle

Dockhead,

I don't think anyone except you is suggesting that the snubber is the last line of connection between the anchor and the boat. In our case the snubber was intended as the primary, but if it did fail there was always the last link of chain that was attached to a strong point inside the anchor locker. No single point failure would have been catastrophic.

Now these days I might attach it differently, but I certainly don't think anyone is suggesting all you need to hold the boat is the snubber.
__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 25-03-2016, 17:31   #51
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by Stumble View Post
Dockhead,

I don't think anyone except you is suggesting that the snubber is the last line of connection between the anchor and the boat. In our case the snubber was intended as the primary, but if it did fail there was always the last link of chain that was attached to a strong point inside the anchor locker. No single point failure would have been catastrophic.

Now these days I might attach it differently, but I certainly don't think anyone is suggesting all you need to hold the boat is the snubber.
Well, every sailboat I've ever been on has the bitter end of the chain attached with a bit of light line connected to a light eye bolt. With a knife hung next to it in case you need to cut it loose. I've never seen one with the bitter end attached strongly, certainly not as strong as the chain.

Besides that, this connection is only at the end. So if you only have half the chain out when the snubber breaks, the other half will run out and then bang when the bitter end is reached, most likely ripping it out in any case, no matter how strongly you've attached it.

So, I really don't think this counts as the ultimate connection of the chain to the boat.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 25-03-2016, 17:51   #52
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,447
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by Dockhead View Post
A very long and large snubber might be as strong as the chain, and in that case the problem is lessened. If you are satisfied with the shock absorption. Most cruisers, however, use much lighter and shorter snubbers than yours, in order to get the stretchiness they want.


But also, you might think your nylon snubber has 13 500 lbs breaking strength, but that is only the rope, in dry and new form and without knots. The snubber is not the same as the raw rope.

First of all, any knot in it reduces the strength.

And if you read this:

http://www.bethandevans.com/pdf/dashew-right-rode.pdf

You know that nylon loses about 20% of its strength right off the bat, just by getting wet. Then, it is subject to internal heating as it "works", and is subject to sudden failure.

Then yet further on top of all the foregoing, nylon is very susceptible to chafing.

You were lucky not to lose your ground tackle that time your snubber broke. Was your windlass ruined? Why would you take such risks, just to avoid connecting the chain strongly to the boat?


Edit: You make a good point about snubbers which are TOO elastic, and I have also gone to thicker and less elastic snubbers with time. Less elasticity also means less chafe and internal heating, so less risk of breaking.

As I mentioned earlier, I'm actually not using a snubber at all any more in settled weather, as long as I have at least a shot or two of chain out. It took me a few years to get used to the different behavior of heavy 12mm chain, compared to what I had on my old boat. The catenary of the heavy chain has a remarkable effect.
DH, a few iterations:

Yes, I realize that our snubber is not as strong as new, virgin line, and that knots would weaken it. So, as noted, the line's virgin strength is actually around 20% stronger than the chain, which also suffers from wear during its life and thus is weaker than the rated strength. Oh... no knots in our snubber, only splices.

But really! We don't generally plan on stressing things anywhere near the breaking strength. The working load limits on both chain and snubber are much less than ultimate strength and any sensible plan works within those limits. My point is that the snubber IS NOT necessarily a weak link in the system, one that you must expect to fail unexpectedly on a regular basis.

And re loss of rode due to snubber failure: As noted, our windlass did not fail. I suspect that the gears were abused by being forced to run backwards, but we continued to use that windlass until it fell apart from corrosion years later. Further, as others have noted, our chain is terminated with a length of strong line (12 mm dacron double braid, doubled) going to a big eye bolt in the chain locker. There is a very good chance that that would prevent loss even if it did all run out. And why should it all run out anyway? In most cases a rupture of the snubber would be from a surge load, not a steady state load, and I see no reason that the windlass should not retain the chain at least for a while.

Again, I'm not against having a backup snubber or stopper, I just think that you overstate the risks involved in not having such.

Jim
__________________
Jim and Ann s/v Insatiable II , lying Port Cygnet, Tasmania once again
Jim Cate is offline   Reply With Quote
Old 25-03-2016, 20:23   #53
Registered User
 
stillbuilding's Avatar

Join Date: Jan 2008
Location: Hong Kong
Boat: Custom Freya 20m
Posts: 961
Re: Help me flesh out my ground tackle

Well, I admit to having a different view of snubbers. I have always used nylon for its elasticity and lighter stuff at that to provide the absorption to "soften the blow" of relatively rigid chain.

I held to the chain caternary notion until recent years when more scientific analysis (forgot the reference but quoted here recently) indicated that caternary of chain disappeared in really hard weather. This more detailed analysis notes the desirability of elasticity in the rode as its corollary.

So I use suitably heavy full chain, chain stopper and about 10 m of 10-12mm nylon attached to the chain by hook or hitch. Purely sacrificial, easily replaced and stops the noise of chain.

If that nylon snubber breaks, the change in movement and noise is very different and gets me on deck fast. Either to replace the snubber with another or more likely to get the hell outta there.

Seems to me the drift towards heavy snubbers is inappropriate.



Sent from my iPhone using Cruisers Sailing Forums lily hhrn
__________________
stillbuilding is online now   Reply With Quote
Old 26-03-2016, 05:34   #54
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by stillbuilding View Post
Well, I admit to having a different view of snubbers. I have always used nylon for its elasticity and lighter stuff at that to provide the absorption to "soften the blow" of relatively rigid chain.

I held to the chain caternary notion until recent years when more scientific analysis (forgot the reference but quoted here recently) indicated that caternary of chain disappeared in really hard weather. This more detailed analysis notes the desirability of elasticity in the rode as its corollary.

So I use suitably heavy full chain, chain stopper and about 10 m of 10-12mm nylon attached to the chain by hook or hitch. Purely sacrificial, easily replaced and stops the noise of chain.

If that nylon snubber breaks, the change in movement and noise is very different and gets me on deck fast. Either to replace the snubber with another or more likely to get the hell outta there.

Seems to me the drift towards heavy snubbers is inappropriate.



Sent from my iPhone using Cruisers Sailing Forums lily hhrn
I think there's no controversy, and it's pretty obvious, that catenary only works until the chain is pulled tight. Then you're in trouble if you don't have a snubber. Chain catenary will work over a certain range only.


Light or heavy snubbers don't matter that much -- everyone should experiment with different lengths and sizes. You will find that some combination will be "tuned" right for you boat, will dampen the motion, and won't "rubber band". The longer the snubber, the thicker it can be, for the same amount of elasticity. That makes it stronger (in Jim's case, close to the strength of his chain) and capable of absorbing a greater quantum of energy. In light weather, it's ok to use a light and short snubber, which is easier to handle.



Just don't use that as the only means of attaching the chain to the boat which -- it's an elementary principle of systems design, people -- should be as strong as the rest of the system.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 26-03-2016, 05:53   #55
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,737
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by Jim Cate View Post
DH, a few iterations:

Yes, I realize that our snubber is not as strong as new, virgin line, and that knots would weaken it. So, as noted, the line's virgin strength is actually around 20% stronger than the chain, which also suffers from wear during its life and thus is weaker than the rated strength. Oh... no knots in our snubber, only splices.

But really! We don't generally plan on stressing things anywhere near the breaking strength. The working load limits on both chain and snubber are much less than ultimate strength and any sensible plan works within those limits. My point is that the snubber IS NOT necessarily a weak link in the system, one that you must expect to fail unexpectedly on a regular basis.

And re loss of rode due to snubber failure: As noted, our windlass did not fail. I suspect that the gears were abused by being forced to run backwards, but we continued to use that windlass until it fell apart from corrosion years later. Further, as others have noted, our chain is terminated with a length of strong line (12 mm dacron double braid, doubled) going to a big eye bolt in the chain locker. There is a very good chance that that would prevent loss even if it did all run out. And why should it all run out anyway? In most cases a rupture of the snubber would be from a surge load, not a steady state load, and I see no reason that the windlass should not retain the chain at least for a while.

Again, I'm not against having a backup snubber or stopper, I just think that you overstate the risks involved in not having such.

Jim
Well, everyone will decide for himself, of course.

But if you are so undemanding of the strength of this part of your anchor rode, then why bother with strong chain? You could downgrade it one or two sizes and gain a lot of weight off the bow and handling ease. As a matter of systems design, why would you route all of the possible forces of the ground tackle through one link which is vulnerable to chafe and -- read Dashew's paper -- subject to failure at 40% or less than its rated breaking strength? In a storm, a nylon rope can chafe through in an hour without your noticing it.

Like this, you degrade the strength of the whole system to the strength of this one element -- it's poor engineering. Objectively speaking, in engineering terms, it's just a crappy design. You have taken the trouble to use chain, which is chafe-proof, and strong chain, but these qualities are lost to your system, because you have chosen to attach it to your boat with a chafe-prone and much weaker (considering the degradation from internal heating and being wet discussed in Dashew's paper) piece of rope, and in fact, you are using that chafe-prone element of the system at the very place where chafe is most likely to occur.


If you would make a strong connection between the chain and the boat, then your snubber ceases to be the life and death link, and it can do its real job flexing and absorbing energy and, inevitably, chafing, and if it breaks, even in severe conditions, it's no big deal -- tie on another one.


The windlass doesn't count -- depending on the forces involved, it might slow down or stop the chain running out, with or without being destroyed itself, but more likely it will not. It's not designed to do that. You can be sure that it will not resist a force close to the breaking strength of the chain.


Whether I "overstate the risks" or not is actually not relevant. Again, it's a systems design question. If you are right on this particular point, and if in fact the risks are vanishingly low that you will ever exceed the strength or chafe resistance of your snubber, then the rest of your system is overbuilt and you should downsize it. That's because the difference in strength and chafe resistance between your chain and your snubber is lost and doing nothing for you, and you have paid for it in vain, and carry the weight of it in your bow for nothing.


But I seriously doubt that chain of whatever size you use is so grossly overspecified. There are conceivable situations where you will need all of its strength or nearly all of it, and even more, its chafe resistance. But you have castrated your anchor chain by inserting this weak, chafe prone link into the system. You have invalidated its whole existence. You might get away with it for decades, but the strength and chafe resistance of your chain might be specified for the once in 30 years event -- when it might save your life. In order to use these qualities of your chain, it must be attached to your boat in a manner which is as strong, and as chafe-resistant as the chain itself. Otherwise, these qualities are lost to your anchoring system.


And you, Jim, with your extra large and extra long snubber, are an exceptional case. I see cruisers in 12-15 ton 45 foot boats using 12mm three strand nylon snubbers and no chain stopper I've chartered boats set up like that. That's just a disaster waiting to happen.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 26-03-2016, 10:11   #56
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by Dockhead View Post


If you would make a strong connection between the chain and the boat, then your snubber ceases to be the life and death link, and it can do its real job flexing and absorbing energy and, inevitably, chafing, and if it breaks, even in severe conditions, it's no big deal -- tie on another one.


The windlass doesn't count -- depending on the forces involved, it might slow down or stop the chain running out, with or without being destroyed itself, but more likely it will not. It's not designed to do that. You can be sure that it will not resist a force close to the breaking strength of the chain.


Whether I "overstate the risks" or not is actually not relevant. Again, it's a systems design question. If you are right on this particular point, and if in fact the risks are vanishingly low that you will ever exceed the strength or chafe resistance of your snubber, then the rest of your system is overbuilt and you should downsize it. That's because the difference in strength and chafe resistance between your chain and your snubber is lost and doing nothing for you, and you have paid for it in vain, and carry the weight of it in your bow for nothing.


But I seriously doubt that chain of whatever size you use is so grossly overspecified. There are conceivable situations where you will need all of its strength or nearly all of it, and even more, its chafe resistance. But you have castrated your anchor chain by inserting this weak, chafe prone link into the system. You have invalidated its whole existence. You might get away with it for decades, but the strength and chafe resistance of your chain might be specified for the once in 30 years event -- when it might save your life. In order to use these qualities of your chain, it must be attached to your boat in a manner which is as strong, and as chafe-resistant as the chain itself. Otherwise, these qualities are lost to your anchoring system.


And you, Jim, with your extra large and extra long snubber, are an exceptional case. I see cruisers in 12-15 ton 45 foot boats using 12mm three strand nylon snubbers and no chain stopper I've chartered boats set up like that. That's just a disaster waiting to happen.
This I can agree with. I don't trust snubbers as a strength element of the anchoring system. They are for shock absorbing only. After the snubber we have a chain stop, then a windless with a mechanical stop rated to the stent th of the chain, then finally a massive backing plate shackled to the last link of chain.
__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 26-03-2016, 17:00   #57
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,447
Re: Help me flesh out my ground tackle

Quote:
Whether I "overstate the risks" or not is actually not relevant. Again, it's a systems design question. If you are right on this particular point, and if in fact the risks are vanishingly low that you will ever exceed the strength or chafe resistance of your snubber, then the rest of your system is overbuilt and you should downsize it. That's because the difference in strength and chafe resistance between your chain and your snubber is lost and doing nothing for you, and you have paid for it in vain, and carry the weight of it in your bow for nothing.
DH, there are a number of elements of your argument where the logic fails, but in particular, the above paragraph is flawed IMO. First, in my system, the strengths of all three elements are roughly balanced, ie, they have similar breaking strengths. Second, even if, as you contend, my chain is "overbuilt" in terms of strength (which I do not believe) there are benefits from heavier chain. We've discussed this before, but to reiterate, while the catenary will eventually be lost at high loads, the act of straightening it out absorbs lots of energy, and this energy absorption does not add to the loads on the snubber or cause chafe... it's a good thing, and heavier chain does it better. And of course, there are the advantages of better wear tolerance and ability to regalvanize that accrue with heavier low-test chain... but that's outside the scope of this discussion.

Finally, do remember that many cruisers do attach the bitter end of their chain in a robust manner, so that loss risk is small. And if one troubles to engage the pawl on the gypsy of the windlass, it will absorb a great deal of load ( I don't know just how much, for that is not addressed in the specifications that I have seen). There is risk of bending the drive shaft, and I certainly don't think that this usage is a good one, but again, it would very likely keep the chain from running out if the snubber broke.

I'm not an engineer by trade, so don't feel competent to comment on your judgement of "bad engineering". I'll leave it to the many engineers on board to discuss. But remember, I'm not advocating NOT using an additional chain stopper. I'm saying that failing to use one does not mean conclusively that the system is badly engineered.

Jim
__________________
Jim and Ann s/v Insatiable II , lying Port Cygnet, Tasmania once again
Jim Cate is offline   Reply With Quote
Old 26-03-2016, 17:13   #58
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,948
Re: Help me flesh out my ground tackle

Quote:
Originally Posted by Stumble View Post
This I can agree with. I don't trust snubbers as a strength element of the anchoring system. They are for shock absorbing only. After the snubber we have a chain stop, then a windless with a mechanical stop rated to the stent th of the chain, then finally a massive backing plate shackled to the last link of chain.
I don't think I really like that idea...may come the day when you want to slip your chain.... the 'bitter end' of the chain on big ships is secured in place by a pin so that it can be slipped quickly ..(edit) from outside the chain locker.. if needs be.
El Pinguino is offline   Reply With Quote
Old 26-03-2016, 17:16   #59
Registered User

Join Date: Apr 2011
Location: Edmonds, WA
Boat: Wauquiez Amphitrite - 43' Ketch
Posts: 159
Re: Help me flesh out my ground tackle

Regarding snubber thickness, is there an advantage to having a thin snubber for low winds, and a thicker for high? I'm thinking of the case where the anchor holding is crap (the anchor is good, just the bottom is poor), and you need all of the elasticity of a thin snubber to smooth the peak loads from waves. In that case, a thicker snubber, not stretching as much, may put a higher peak load on an anchor that is on a bad bottom, and pull it out.

But... Does this happen in reality?


Sent from my iPhone using Cruisers Sailing Forum
__________________
ScottMeilicke is offline   Reply With Quote
Old 26-03-2016, 17:16   #60
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: Punta Arenas ahorra
Boat: 39' Westerly Sealord
Posts: 3,948
Re: Help me flesh out my ground tackle

What more can I say.... except that my system works, I don't have frequent 'snubber' ( for want of a better name) failures..in fact I don't have 'snubber' failures .. and I sleep well at night.
__________________

El Pinguino is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Alberg 30 Ground Tackle Upgrade Help ! Nomdaica Anchoring & Mooring 32 09-01-2012 15:16
Ground Tackle Inventory Dockhead Anchoring & Mooring 11 11-03-2011 09:17
For Sale: Ground Tackle Randyonr3 Classifieds Archive 0 03-10-2010 09:45
Islander 29 - Ground Tackle Recommendations dissent Anchoring & Mooring 7 13-06-2010 13:06
Assess My Ground Tackle b-rad Anchoring & Mooring 13 15-04-2010 20:47



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 05:05.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.