Cruisers & Sailing Forums (https://www.cruisersforum.com/forums/)
-   Anchoring & Mooring (https://www.cruisersforum.com/forums/f118/)
-   -   Mantus Chain Hook (https://www.cruisersforum.com/forums/f118/mantus-chain-hook-117902.html)

thinwater 31-12-2013 20:40

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428214)
My 5/8 inch diameter 3 strand nylon bridal has a tensile strength of 11,650 lbs.
The rubber snubber with three turns is rated for storm surge conditions....

Cool, numbers! I should have caught the snubber description in your earlier post, and I did not understand that you had one in each leg.

Your description above makes it sound as though the snubbers are 1/3 extended with motor, perhaps 800-1000 pounds, and probably fully extended at full load. Perfect. (tesing could establish this)

I'm estimating that they extend about 12-inches, based on basic dimensions and 3 wraps around a 1" core. That's how much line they consume in twists. Any additional stretch would occur anyway (nylon).

Assuming linear elasticity (probably not, but gotta start somewhere) they would absorb about 70% x 3000 pounds x 1-foot/2 = 1050 foot-pounds each, 2100 ft-pounds total, or about 2900 joules. The 70% is the per-leg load division; I'm guessing because I don't know the exact apex angle, but I bet it's close.

Climbing rope can absorb a max of about 1000 foot-pounds per foot on slow pull and about 400 ft-#/ft at the target load. Your line can prbably absorb about 1/2 that (fatter line is stronger but stretches less) or 200 ft-#/ft, or about 400 x 40 = 16000 ft-pounds on a bridle of your size. Put another way, depending on line size, the twist snubbers act like another 4-5 feet of rope.

A much simpler approach is to consider that the nylon will stretch about 20% at this load, so 4-5 feet of rope will stretch the same amount as the snubber under the same load. It's good when 2 unrelated calculations give the same answer.

Really interesting idea, better for a cat because you can run 2 of them. The trade off is a clunky bit of rubber vs. extra line on the side decks. Fewer chafe challenges but substantially less energy absorption capacity. Same cost, perhaps, unless the snubber line is free (often is retired anchor rode or other free line--I've never bought any).

Development continues.

(missed JonJo's last post; was calculating and typing)

NorthPacific 31-12-2013 20:45

Re: Mantus chain hook
 
As to the elasticity of nylon rope. I can attest to this from personal experience as a rock climber. After an initial brutal blow to the privates, it does stretch somewhat, the idea being that you are not cut in half. The old 3 strand stretched much better than the strand rope until they built in more elasticity, then on a long fall it would get thin in the middle:) Not that I ever fell that often:-) .Thought this may be of help next time you guys are anchoring up. Happy New Year folks. Nice (polite fireworks display)

Cotemar 31-12-2013 21:38

Re: Mantus chain hook
 
1 Attachment(s)
JonJo,

Here’s the deal, you and I know that 3 strand nylon bridles are used on 95% of boats anchoring around the world today and they work very well.

Now add two rubber snubbers to that same 3 strand nylon bridle to make a Cat Snubber Bridal. Now you’re going to have a winning combination in the same 20 foot package. The shock loads to the boat from strong wind and waves disappears.

This cat bridle snubber cost me $55 usd for the 3 strand nylon line and $60 usd for the rubber snubbers for a total of $115 usd. This is all new gear. Not used or hand me down crap.

Sid at SailAway 31-12-2013 21:56

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1427093)
WOW, Staniel Cay.
Mind If I drop in for a week and wax your boat for you.
Well it's a big cat, it may take me 10 days. :whistling:

Crewed on an A class sloop today, the Lady Muriel. We won overall beating Tida Wave. Got a nice jacket for winning. Come on down, but you may be hooked as we are. Gonna be tough to leave here..:)

Cotemar 31-12-2013 22:01

Re: Mantus chain hook
 
Quote:

Originally Posted by Sid at SailAway (Post 1428322)
Crewed on an A class sloop today, the Lady Muriel. We won overall beating Tida Wave. Got a nice jacket for winning. Come on down, but you may be hooked as we are. Gonna be tough to leave here..:)

I am hooked already. I love Staniel Cay

CarinaPDX 31-12-2013 22:33

Re: Mantus chain hook
 
I have to note that the discussion gives snubbers a pass in marina applications. In fact they have the potential to cause great damage. Some marinas (Marina Bay, Gibraltar is one example) there is a surge, where the water will suddenly flow inwards for 5-10 seconds, then reverse and flow out. If the boat is moored on the inside, the inrush moves the boat inshore and stretches the snubber (rubber or spring steel) thus storing energy. When the current reverses the boat is accelerated outward with the combined force of the snubber and flow and can stretch the mooring line holding the boat off the dock (in this case a cement construction). A lot of damage can result. I got rid of my snubbers in Gibraltar and never looked back. For anchoring I use braided nylon which works great.

Greg

thinwater 31-12-2013 22:46

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428318)
JonJo,

Here’s the deal, you and I know that 3 strand nylon bridles are used on 95% of boats anchoring around the world today and they work very well.

Now add two rubber snubbers to that same 3 strand nylon bridle to make a Cat Snubber Bridal. Now you’re going to have a winning combination in the same 20 foot package. The shock loads to the boat from strong wind and waves disappears.

This cat bridle snubber cost me $55 usd for the 3 strand nylon line and $60 usd for the rubber snubbers for a total of $115 usd. This is all new gear. Not used or hand me down crap.

Overhand loops? Huh.

JonJo 31-12-2013 23:08

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428318)
JonJo,

Here’s the deal, you and I know that 3 strand nylon bridles are used on 95% of boats anchoring around the world today and they work very well.

Now add two rubber snubbers to that same 3 strand nylon bridle to make a Cat Snubber Bridal. Now you’re going to have a winning combination in the same 20 foot package. The shock loads to the boat from strong wind and waves disappears.

This cat bridle snubber cost me $55 usd for the 3 strand nylon line and $60 usd for the rubber snubbers for a total of $115 usd. This is all new gear. Not used or hand me down crap.

Cotemar,

I've already said - if it works for you, great. In fact we used to have a set up identical to yours, a rubber snubber each side and braided nylon but our lines were shorter. Once I'd made all the calculations I realised that the rubber was not adding and that I could achieve a much better - and I think significant - effect, simply using climbing rope as it works fairly consistently through the complete wind range. You could use 'all' rubber snubbers - but to achieve what nylon offers you need 5 of them, each side (plus the nylon to carry it) which we did think of but balked at both price and weight. We are twitchy about weight (though not when stocking with wine, but then we carry it amidships).

Climbing rope simply will not work for many - their yachts are too big. It comes as a maximum of 11mm (someone correct me if this is wrong) and beyond about a 45' yacht climbing rope starts to look too small (certainly when conditions are arduous). Anyone with a bigger yacht, or not able to get climbing rope (cheaply) could use 3 strand or anchor plait - which comes in almost any size one could ever want.

Your solution is fine, though I think I'd rather longer lines of lower diameter - but if it works for you stick with it. I'd be twitchy about the snubbers on the seabed - but if you can live with the possible abrasion, again, stick with it. We actually tend to anchor in deeper water (maybe like you) too close to shore in an ocean anchorage and swells build or steepen - much better further out.

Jonathan

Cotemar 31-12-2013 23:10

Re: Mantus chain hook
 
1 Attachment(s)
Quote:

Originally Posted by thinwater (Post 1428337)
Overhand loops? Huh.

All Figure 8 knots

JonJo 31-12-2013 23:14

Re: Mantus chain hook
 
Quote:

Originally Posted by CarinaPDX (Post 1428334)
I have to note that the discussion gives snubbers a pass in marina applications. In fact they have the potential to cause great damage. Some marinas (Marina Bay, Gibraltar is one example) there is a surge, where the water will suddenly flow inwards for 5-10 seconds, then reverse and flow out. If the boat is moored on the inside, the inrush moves the boat inshore and stretches the snubber (rubber or spring steel) thus storing energy. When the current reverses the boat is accelerated outward with the combined force of the snubber and flow and can stretch the mooring line holding the boat off the dock (in this case a cement construction). A lot of damage can result. I got rid of my snubbers in Gibraltar and never looked back. For anchoring I use braided nylon which works great.

Greg

We live and learn:)

We keep 'Josepheline' on a swing mooring, we anchor whenever we can and restrict marinas to refueling - fear of paying money unnecessarily. I do see snubbers, stainless springs and rubber, in use on moored yachts (and have seen some commercial lines with rubber incorporated into the build of the cordage) - but our marinas, or the ones I know, sound a bit more comfortable than yours - another reason its called the Lucky Country?).

Jonathan

JonJo 31-12-2013 23:20

Re: Mantus chain hook
 
Quote:

Originally Posted by thinwater (Post 1428279)


(missed JonJo's last post; was calculating and typing)

I wish I could calculate at the speed you do - you must be very young.

Jonathan

Suddenly realised you are bright and cheerful - its not New Year yet.

Enjoy the evening, and all the best for 2014.

Cotemar 31-12-2013 23:22

Re: Mantus chain hook
 
Quote:

Originally Posted by JonJo (Post 1428344)
I'd be twitchy about the snubbers on the seabed - but if you can live with the possible abrasion, again, stick with it.

The rubber snubbers always stay at the bows. Never in the water.

The rubber hose you see on the end is the chaff guard for when we are in shallow water and the end of the bridle is on the bottom. The hose also protects the bridal as the chain and bridal come into the anchor locker.

Auspicious 01-01-2014 09:01

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428111)
WOW, JonJo,
Not a word you said here is valid.

I'd like to see calculations to support that statement. I haven't seen any indication that the rubber snubbers have any benefits over properly sized three-strand nylon snubbers. What do you know that I don't?

Cotemar 01-01-2014 09:18

Re: Mantus chain hook
 
Auspicious,

This Bridle Snubber design is all done to eliminate the shock loads to the boat from strong wind and waves. Where 3 strand nylon bridle on its own runs out of stretch, so in this compact 20 foot setup you can get twice the stretch.

My 5/8 inch diameter 3 strand nylon bridle snubber has a tensile strength of 11,650 lbs.
The rubber snubber with three turns is rated for storm surge conditions.
The proper rubber snubber not only stretch’s on the three turns, but also coils and compresses the rubber core in 3 dimension’s.

When I back down on this cat bridle snubber with two 30 hp diesel engines at 2800 rpm with 3 bladed props, These rubber snubbers are at 1/3 stretch.

Auspicious 01-01-2014 09:48

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428543)
This Bridle Snubber design is all done to eliminate the shock loads to the boat from strong wind and waves. Where 3 strand nylon bridle on its own runs out of stretch, so in this compact 20 foot setup you can get twice the stretch.

Numbers please? in/# or cm/kg or any other measure of k? How much longer bridle would you need for equivalent 'x'?

Quote:

Originally Posted by Cotemar (Post 1428543)
My 5/8 inch diameter 3 strand nylon bridle snubber has a tensile strength of 11,650 lbs.
The rubber snubber with three turns is rated for storm surge conditions.
The proper rubber snubber not only stretch’s on the three turns, but also coils and compresses the rubber core in 3 dimension’s.



Tensile strength isn't relevant to stretch or load absorption, only to ultimate failure.

Rated by whom and to what standard?

Quote:

Originally Posted by Cotemar (Post 1428543)
When I back down on this cat bridle snubber with two 30 hp diesel engines at 2800 rpm with 3 bladed props, These rubber snubbers are at 1/3 stretch.

I can say from personal experience that you can't duplicate the loads from weather with engines.

thinwater 01-01-2014 10:01

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428543)
... Where 3 strand nylon bridle on its own runs out of stretch, so in this compact 20 foot setup you can get twice the stretch....

No.

Assuming the storm load is about 3000 pounds (2250 pounds per leg), a 20-foot leg will stretch about 20% or 4 feet. The rubber snubber will allow 1 foot of extension, or about 20% of the total 5 feet of extension.

You also assert that nylon quits stretching at some load. That is plainly false, and no where near true in the working load range, as any data source will show.

% elongation, left, load in # bottom
https://2.bp.blogspot.com/-kS9N6U2ldD...nd+dyneema.jpg

The 3 dimensional moment is confusing you; the only energy calculation that matters is how far it extends under what load history (the line can't see or feel the 3 dimensional movement any more than a bathroom scale can tell if you are standing on one foot).

If my numbers are wrong, please show an alternative calculation.

---

I'm not saying the snubber doesn't help--I'm certain that it does--but only as much as another 4 feet of rope would help. It is a clever idea, worth further investigation, since it provides energy absorption for those that cannot or would rather not have a longer bridle. This could be vital in a dockside situation, where there is no room for that additional rope. There is a similar devise that rock climbers use called a Screamer. It provides consistant resistance for a certain extension distance (a bit further than the snubber). Smart folks have determined that these too are equivalent to having about 4 more feet of rope in the system. Some climbers use them, most feel the complication is not worth the trouble. Where they are used is tethers (OSHA and via feratta), also situations where adding rope to the system is not possible. It seems there is no free lunch, only niche applications.

Cotemar 01-01-2014 10:05

Re: Mantus chain hook
 
Quote:

Originally Posted by Auspicious (Post 1428560)
I can say from personal experience that you can't duplicate the loads from weather with engines.


Exactly, that is what I have been trying show for a long time.
You can throw numbers at this all day long. In the end your real world experience will be much different. Now take that same 3 strand nylon line that cruisers have been using forever as a bridal and in that same 20 foot compact package add two rubber snubbers to double the stretch. No Math needed.

Cruisers are a smart bunch, but when you through a page of rubber durometer calculations at them for which they could give a sheet about . Get the real deal and go out and test it in the real world.

Cotemar 01-01-2014 10:19

Re: Mantus chain hook
 
Quote:

Originally Posted by thinwater (Post 1428565)
I'm not saying the snubber doesn't help--I'm certain that it does--but only as much as another 4 feet of rope would help. It is a clever idea, worth further investigation, since it provides energy absorption for those that cannot or would rather not have a longer bridle. This could be vital in a dockside situation, where there is no room for that additional rope. There is a similar devise that rock climbers use called a Screamer. It provides consistant resistance for a certain extension distance (a bit further than the snubber). Smart folks have determined that these too are equivalent to having about 4 more feet of rope in the system. Some climbers use them, most feel the complication is not worth the trouble. Where they are used is tethers (OSHA and via feratta), also situations where adding rope to the system is not possible. It seems there is no free lunch, only niche applications.

The nice part of this Bridle Snubber design is that the rubber snubber allows it to stay at the 20 feet compact size, but also acts as a fail safe fuse that if broken would still have the 11, 650 lbs tensile strengh nylon line holding your boat in place. Its a win win for $60 usd upgrade.

thinwater 01-01-2014 10:59

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428568)

Exactly, that is what I have been trying show for a long time.
You can throw numbers at this all day long. In the end your real world experience will be much different. Now take that same 3 strand nylon line that cruisers have been using forever as a bridal and in that same 20 foot compact package add two rubber snubbers to double the stretch. No Math needed.

Cruisers are a smart bunch, but when you through a page of rubber durometer calculations at them for which they could give a sheet about . Get the real deal and go out and test it in the real world.

You confuse me. You bandy numbers about ("the facts are," "here's the deal," "the numbers are...") and then deny numbers. No one denied or criticized your experience.

And yes, I've anchored a few times. I didn't say "my way is" because I have tested many ways (some for articles), and because I have found that many ways work quite well; as a 32-year engineer and 30-year sailor, I like to understand how they work. Cruisers are an inquisitive bunch.

Cotemar 01-01-2014 11:13

Re: Mantus chain hook
 
I am an engineer also with 35years experience and another 40 years of sailing and powerboats. It's a fun club to be in

Auspicious 01-01-2014 12:29

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428568)
Now take that same 3 strand nylon line that cruisers have been using forever as a bridal and in that same 20 foot compact package add two rubber snubbers to double the stretch. No Math needed.

You're going to have to show me the numbers.

Elongation of the nylon, elongation of the snubber, and degradation of line strength due to the bending.

Cotemar 01-01-2014 15:16

Re: Mantus chain hook
 
Auspicious,

Unfortunately, Life testing a new Bridle Snubber design takes years and I am past year one right now.

JonJo’s calculations last year stated that I would be able to anchor two times before the rubber snubbers broke.

In about five years I can tell you if this Bridle Snubber design was worth the extra $60.

If you want to do the proper analysis of this Bridle Snubber, you will need a 3D CAD model of the rubber snubber and 3 strand 5/8” dia. nylon line. When you’re done with the 3D CAD model, then you can export out a .stp file and bring it over to your Ansys software for doing your simulation and analysis.

I will be out sailing when you’re doing simulation and analysis.

sabray 01-01-2014 15:28

Re: Mantus chain hook
 
I destroyed a rubber add on. I am using dyneema at connections and chafe points. Mostly 3 strand for overboard wet absorption mooring has a braided piece that goes to the eye/bouy which has 3 strand. Seems pretty good so far.

JonJo 01-01-2014 16:02

Re: Mantus chain hook
 
I did a quick search, I came up with this:

12-04-10, 23:16 #9 Baggywrinkle's
Default Perishables.
Make sure you check on it regularly. Seen so many broken and perished ones hanging off mooring lines in the med and when they go the rope unwinds and gets longer (depending how many turns you put in).

Great for a quiet night, not so great if left in the elements for extended periods.

end quote

This describes benign application in a mooring scenario, not under slightly more aggressive anchor conditions.

It is 'anecdotal' I have no personal experience of them breaking (nor have any desire to break one) but the comment in not isolated. I could quote more. I also note the author has no knowledge of whether they were used correctly or not. But it would make me think twice when the forecast was 40 knots for 3 days.

But when incorporated into a bridle with a break strength of 11,000 lb the loss of a rubber snubber will not alter the strength of the bridle - it will just get a bit longer on one side.

But your nylon will continue to stretch linearly, or nearly so, until it breaks. It would break at about 40% stretch, 11,000lb but would be markedly degraded beyond about 30%.

I note you have joined your bridle at about 5' from the point where it attaches to the chain. Based on the original length of 20' your bridle arms, or the sections capable of absorbing energy, are only 15' long. Whereas I appreciate you have set up your system, and find it satisfactory, to allow a 'short' bridle the reality is you are expecting that 15' length to do a lot of work and as such it will not last as long as if it had been a true 20'.

Long bridles share the load and will thus last longer. You have a 20' bridle that will have the lifespan and effectiveness of a 15' bridle. If you want short - you may as well cut off that doubled 5' section, it does nothing for elasticity (or very little), it effectively reduces life of the 15' arms and it adds 'unused' length to trail on the seabed.

Jonathan

Edit, I note the comment above, came in as I was crafting the above - sadly does not describe how the rubber was destroyed.

Cotemar 01-01-2014 16:08

Re: Mantus chain hook
 
JonJo,
I agree. I would not use Baggywrinkle's either

sabray 01-01-2014 16:18

Re: Mantus chain hook
 
My rubber snubber failed at the eye let broke/chafed on both ends.
Given its pricey value I chose not to replace. I went after the places of high failure. Chocks and attachment points. As as was said shock absorption can be done at better value. For low end stuff the rubber things are great but if it's honking I would go with dyneema at the chafe point and 3 strand at the wet area between.

Cotemar 01-01-2014 16:33

Re: Mantus chain hook
 
1 Attachment(s)
Rubber Snubbers in the Bridle Snubber just remove the shock load.
The snubber elements themselves possess a nonlinear stress-strain curve.
The Snubber reduces the expected peak shock load loads 50%

JonJo 01-01-2014 17:24

Re: Mantus chain hook
 
There is something fundamentally wrong with that plot?

Without the snubber, and ignoring the peaks, the loads without the rubber snubber are half those with the rubber snubber. Maybe I made a mistake as I would expect the results to be the opposite, lower troughs with the rubber snubbers?

On both plots peak loads are huge - much higher than anything I would dare test and much higher than anything anyone is likely to experience on a 36' cat.

The troughs are at 1t (with the rubber snubber) and at 1t all the stretch will have already, long ago - see below, been taken up in the rubber snubber - consequently anything beyond 1t is all about the nylon (in fact beyond 270kg its all about the nylon) - so why the 2 plots are so different is something of a mystery. I tested one of these rubber snubbers and the load at maximum stretch (64%), 3 turns of supporting rope, is around 270kg. I used a chain winch to develop load and measured using a 2t load cell. I was testing in the horizontal with each end supported by 36 inch diameter reinforced concrete pillars. I was not using nylon but an old double braid halyard (I was measuring stretch of the rubber). Beyond a 270kg load - manufacturers seem to imply they expect their rubber snubbers to fail (270kg is beyond their idea of a safe working load).

Hopefully someone will explain it as it looks to me as if the rubber snubbers are having a catalytic or synergistic effect - which merits detailed evaluation.

Jonathan

sabray 01-01-2014 17:35

Re: Mantus chain hook
 
I guess that my experience with these is they work well at everyday stress. When heavily loaded at 45 to 55 and up they are not offering much. With all respect to cotemar we have a different experience. Like adding a weight like a killet the effect is best under low load.
I guess if it works for you that's good. Sure isn't hurting things like a killet wrapped around a line. This from a once killet fan.
I use the killet now for stapling the rhode of a second anchor down.

Delfin 01-01-2014 18:06

Re: Mantus chain hook
 
Quote:

Originally Posted by thinwater (Post 1425785)
3/16" Amsteel has a breaking strength of 5400 pounds. This is about 1/2 the strength of the chain. The working load is perhaps 4-7 times less than this. The size Amsteel loop that would fit through the G4 links is limitied.

Not sayin' this won't work, just sayin it might as well be matched with a lighter snubber.

5/16" G43 chain has a breaking strength of 11,600#, with an inside dimension of 1/2". You can easily fit a 7mm Dyneema Dux soft shackle through that, and it has a minimum breaking strength of 15,000#, which I believe would be a great deal stronger than a chain hook of any make I know of. With the 15% or so strength reduction from forming the shackle, this should match the final strength of the shackle pretty well to the chain. I use a 9mm Dyneema Dux soft shackle on 1/2" G4 and it is a good combination.

Delfin 01-01-2014 18:24

Re: Mantus chain hook
 
Quote:

Originally Posted by JonJo (Post 1428904)
There is something fundamentally wrong with that plot?

Without the snubber, and ignoring the peaks, the loads without the rubber snubber are half those with the rubber snubber. Maybe I made a mistake as I would expect the results to be the opposite, lower troughs with the rubber snubbers?

On both plots peak loads are huge - much higher than anything I would dare test and much higher than anything anyone is likely to experience on a 36' cat.

The troughs are at 1t (with the rubber snubber) and at 1t all the stretch will have already, long ago - see below, been taken up in the rubber snubber - consequently anything beyond 1t is all about the nylon (in fact beyond 270kg its all about the nylon) - so why the 2 plots are so different is something of a mystery. I tested one of these rubber snubbers and the load at maximum stretch (64%), 3 turns of supporting rope, is around 270kg. I used a chain winch to develop load and measured using a 2t load cell. I was testing in the horizontal with each end supported by 36 inch diameter reinforced concrete pillars. I was not using nylon but an old double braid halyard (I was measuring stretch of the rubber). Beyond a 270kg load - manufacturers seem to imply they expect their rubber snubbers to fail (270kg is beyond their idea of a safe working load).

Hopefully someone will explain it as it looks to me as if the rubber snubbers are having a catalytic or synergistic effect - which merits detailed evaluation.

Jonathan

It does seem to possess some miraculous properties - increasing tension at low loads and decreasing it at high loads. I wonder if you made rubber bullets out of this material whether their impact force would increase the slower the velocity?

Delfin 01-01-2014 18:39

Re: Mantus chain hook
 
Quote:

Originally Posted by JonJo (Post 1428106)
Rubber snubbers are a bit of a waste of time or money anyway in an anchor bridle/snubber combination , whether you (the yacht) are heavy or not.

If you use a small one they use up all their elasticity at low loads, you would need 5 x 1 inch rubber snubbers (from memory they are standard length around 15 inches) to absorb the same energy of a 12mm x 10m long piece of nylon cordage. If you simply use one small one they will become ineffective at higher loads - all the stretch will have gone - and its at higher loads you need the elasticity.

(To put another way - if you consider 'catenary' to be overrated then rubber snubbers (unless you use 5 of them!) fall into the same category - all the usefulness disappears at winds over, say 30 knots, probably lower.)

Bigger rubber snubbers are obviously better, have not worked out (nor intend to) energy absorption capabilities.

Rubber snubbers, even small ones, are heavy and very expensive, compared to 12mm nylon.

They are excellent when used in marina mooring environment as their elasticity is contained in such a short length and the loads when attached to a pontoon should not be great. But as part of an anchor snubber system - there are infinitely better options.

Jonathan

Jonathan, you are probably correct on the rubber snubber being essential useless since they aren't likely to do much that a bit more 3 strand will do. As you know, I'm experimenting with an Ultra rubber snubber, which is quite robust, on the Dyneema Dux pennant that leads to the plait nylon that forms my snubber. I'm curious to see how this works in terms of longevity, and have rigged it so it is inboard and easy to watch. Probably not going to add much, but it will be interesting to see if I can detect any value.

Cotemar 01-01-2014 18:41

Re: Mantus chain hook
 
2 Attachment(s)
Quote:

Originally Posted by Delfin (Post 1428926)
5/16" G43 chain has a breaking strength of 11,600#, with an inside dimension of 1/2". You can easily fit a 7mm Dyneema Dux soft shackle through that, and it has a minimum breaking strength of 15,000#, which I believe would be a great deal stronger than a chain hook of any make I know of. With the 15% or so strength reduction from forming the shackle, this should match the final strength of the shackle pretty well to the chain. I use a 9mm Dyneema Dux soft shackle on 1/2" G4 and it is a good combination.

I used to make this same mistake, so I just want to point it out to everyone.

When you look at the spec. on a 5/16 G4 or G43 chain you see an Inside Dim. Width.
It is not the dimension you would use to judge what diameter will fit through a link of chain.

You have to use the Inside Dim. Length – wire diameter x 2 = space between the links

So as an example on a 5/6 G43 chain you have an Inside Dim. Length (1.030”) – wire diameter (.329”) x 2 = .372 space between the links for your soft shackle.

Delfin 01-01-2014 21:11

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428946)
I used to make this same mistake, so I just want to point it out to everyone.

When you look at the spec. on a 5/16 G4 or G43 chain you see an Inside Dim. Width.
It is not the dimension you would use to judge what diameter will fit through a link of chain.

You have to use the Inside Dim. Length – wire diameter x 2 = space between the links

So as an example on a 5/6 G43 chain you have an Inside Dim. Length (1.030”) – wire diameter (.329”) x 2 = .372 space between the links for your soft shackle.

Quite true. And that is why a 1/4" soft shackle with a breaking strength equal to the chain can fit quite nicely on 5/16" G4 chain. If you want to shove it a bit you can fit a 5/16" soft shackle with about 25% greater breaking strength than the chain. If you think about it for a moment, you will understand why.

Cotemar 01-01-2014 21:35

Re: Mantus chain hook
 
2 Attachment(s)
Quote:

Originally Posted by Delfin (Post 1429066)
Quite true. And that is why a 1/4" soft shackle with a breaking strength equal to the chain can fit quite nicely on 5/16" G4 chain. If you want to shove it a bit you can fit a 5/16" soft shackle with about 25% greater breaking strength than the chain. If you think about it for a moment, you will understand why.

A Soft Shackle made of 3/16" (.187) Amsteel blue line with 5,400 lbs tensile strength will work well also.

Even though the Amsteel line is 3/16" (.187) diameter.

When you finish the Soft Shackle it will be .340 inch finish diameter, which will allow you to slide it through the 5/6 G43 chain link, which has a .372” diameter hole space.

Delfin 01-01-2014 21:54

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1429084)
A Soft Shackle made of 3/16" (.187) Amsteel blue line with 5,400 lbs tensile strength will work well also.

Even though the Amsteel line is 3/16" (.187) diameter.

When you finish the Soft Shackle it will be .340 inch finish diameter, which will allow you to slide it through the 5/6 G43 chain link, which has a .372” diameter hole space.

Starting to understand why you post what you post.

I am listening to the Baylor game so don't take the time to draw a picture, but.....

In a right triangle, if a = .5, b = .372, than c must necessarily = .62. So, a soft shackle made of line that is 50% of .62 inches, a.k.a. 5/16", will fit just fine between the links of 5/16" chain, and have a breaking strength greater than the chain.

thinwater 01-01-2014 22:29

Re: Mantus chain hook
 
Quote:

Originally Posted by Cotemar (Post 1428877)
Rubber Snubbers in the Bridle Snubber just remove the shock load.
The snubber elements themselves possess a nonlinear stress-strain curve.
The Snubber reduces the expected peak shock load loads 50%

Without more information the graph cannot be interpreted or discussed. The first 5 items are mandatory. We could be comparing a snubber bridle to no bridle, which tells us very little.
  • Which model snubber, 1 or 2.
  • Bridle angle
  • How much nylon line
  • What diameter line
  • Boat mass
  • How much chain
  • What boat
  • How much wind
  • How deep water
The wave period is suspicious. At about 15 seconds, NOAA tells me I would need a 50 kt gale with a 1600 mile fetch. The average wind load also suggests 60 kt winds. The range of no-snubber data strong suggests all-chain, short at that. So the boat was exposed to sustained (not squall) storm conditions in an open harbor, and someone was taking data? They switched from snubber to no snubber during the storm? Studly. I would have led with this data.



For this to be meaningful I would have to know that the no-bridle case is the same bridle with the rubber removed. Then, we would need to compare it to a longer bridle, which would be more apples-to-apples.



Is this your data, or some other source? Is there more?

boom23 02-01-2014 00:11

Re: Mantus Chain Hook
 
The rubber snubber application on the bridle seems interesting and I may try it when I make a new bridle.

Just FYI, I've used the 1" rubber snubbers for my ex-powerboat (55ft) dock lines while in Hotel/Marina Coral in Ensenada, which has very strong tidal surges, and 3 out of 4 snubbers broke. What broke was the metal reinforced holes where the lines go through.

For the first couple of snubbers, I contacted the company and they sent me replacements. I did not feel right asking for a third one. I do not know if they changed the design since 2009.

I think the 1" rubber snubber can be a useful product for some situations but it could be more durable. I do not know about the other sizes.

Just personal experience...

savoir 02-01-2014 02:37

Re: Mantus Chain Hook
 
It sounds like you are taking the snubbers beyond their elastic limit too often. Try one less turn of rope which will reduce the maximum stretch. That should extend the life of the snubber.

Dockhead 02-01-2014 03:03

Quote:

Originally Posted by Celestialsailor
I almost never back down on my chain around the gypsy. I always use the snubber to do so. Why stress it?

This has been discussed before. You need more than just the snubber to take load off the gypsy! The snubber is designed for shock absorption, not UTS! The chain should be belayed in some manner (chain lock, belaying strop) first, then back down. Only then, attach the snubber for shock absorption.

The chain belaying system should be designed to match or exceed SWL and UTS of the chain. The snubber should be tuned for the right stretch - a different design value. Both these systems are essential - shock loads can break the other parts of your ground tackle without the stretch of the snubber built in. But without a separate belaying system, the snubber will (if it is tuned right, unless it is extremely long) be a weak link in the ground tackle.


All times are GMT -7. The time now is 12:29.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.


ShowCase vBulletin Plugins by Drive Thru Online, Inc.