Mantus Chain Hook

[JonJo]

Originally Posted by thinwater

(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]

Originally Posted by JonJo

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]

Originally Posted by Cotemar

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]

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]

Originally Posted by Cotemar

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'?

Originally Posted by Cotemar

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?

Originally Posted by Cotemar

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]

Originally Posted by Cotemar

... 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


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]

Originally Posted by Auspicious

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]

Originally Posted by thinwater

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]

Originally Posted by Cotemar

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]

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]

Originally Posted by Cotemar

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]

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]

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]

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]

JonJo,
I agree. I would not use Baggywrinkle's either