# How to size rope



## TSOJOURNER (Dec 16, 1999)

The broker who sold us our boat suggested that we buy a spool of 3/4" rope and cut it into the variety of lenghts needed for different docking/rafting/slip situations. We went to a marine store and looked at a spool of 3/4" rope that was sitting beside a spool of 5/8" rope. The 3/4" looked huge. I'm sure the 3/4measurement is when the rope is stretched with rated load, but man, it looked like it would be impossible to knot and/or attach to cleats. The 5/8" looked like it would be difficult to work with but not as bad as the larger size. I could use some advice about purchasing the 5/8" rope as opposed to the 3/4". My boat is a 30,000#, 47' cruiser and yes it is high and will catch a lot of wind. I know there is no definitive answer to this since conditions exist that will cause even the 3/4" to fail, but generally, will the 5/8" rope be adequate? Thanks in advance for your thoughts.
Alvin


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## btrayfors (Aug 25, 2006)

Alvin,

Buy the 3/4" rope. Your boat size, weight, and high freeboard can put a huge strain on docking and anchor lines. 

The 3/4" rope should work very well on the cleats on your boat, and on dockside cleats.

Bill


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## pigslo (Nov 22, 2004)

All of your rope manufacturers have info online as well as a chart at the West Marine store. As I recall 3/4 is perhaps the minimum your craft needs but you can look it up. I think you can be too small, but not too big. One of the considerations on docklines is that they be made of nylon for stretch.
Pigslo


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## Sailormon6 (May 9, 2002)

There are numerous charts that recommend the correct size of lines for various sizes of boats. Consult those charts and follow their recommendations. Size does matter. Docklines should stretch, so that they absorb some of the shock when the boat rolls and draws up short on the docklines. That isn't terribly important normally, but when that 30,000# boat is bucking and rolling in it's slip during a hurricane or other severe storm, docklines that don't stretch enough can rip the cleats out of the deck. Oversized lines don't stretch as much as lines of correct size.


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## camaraderie (May 22, 2002)

Mod...3/4 inch has 4500 lbs. higher breaking strength than 5/8 in 3 strand nylon. If you have trouble dealing with 3/4 inch 3 strand then I would suggest spending a bit more and getting 3/4 inch double-braid nylon which is MUCH softer and more supple and easier to tie AND even provides more breaking strength. 5/8" is just not enough for your boat. 
http://shop.sailnet.com/product_info.php/products_id/33579 ... I know you can do about .30 cents a foot bettr on the price but I think sailnet will match prices.


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## T34C (Sep 14, 2006)

I tried the West Marine on-line product advisor for dock lines. It came back with 3/4", for both 3-strand and braided line, for a boat your size. To me that means that is the min. line size I would recommend. While it may be larger than you are used to, go with the 3/4.


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## TSOJOURNER (Dec 16, 1999)

What about a 1972 Pearson 36 sailboat. It displaces 13,500lbs. My current lines range from 1/2'' to 3/4''. The last owers cut up most of the long dock lines so my longest line is about 25'. Ive been thinking of getting a spool of rope and cutting some nicer docklines(esp now since ive got whipping down).


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## T34C (Sep 14, 2006)

I use 3/4" 3 strand dock lines on my Tartan 34 that displaces 11,500. Slightly over sized, but haven't had one break yet.


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## hellosailor (Apr 11, 2006)

Max, as pigslo mentions all the rope makers have sizing charts. They'll also gladly work with you on the phone or by email.

The size of a rope isn't everything, a better quality fiber or different manufacture can make a thin rope stronger than a thick one. You need to figure out the loads you expect on your lines, and then pick lines that can safely carry that load. "Working" load and breaking load being two very different things, also.

Dock lines should have some stretch in them, so they can absorb the snaps and jerks of bouncing around at the dock. And in time, they will wear and need replacing, so buying a larger spool and putting half away may actually be cheaper in the long run. 

Don't be surprised if the lines you select dont' fit properly under some cleats and hardware--it is not uncommon for hardware to be sized smaller and cheaper than it should be. If you can't fit the proper lines under the hardware--replace the flimsy hardware, too.

Some folks secure a boat, really secure a boat, every time they dock, figuring you never an be sure what weather will come through before you get back to the boat. Others are more casual about everyday versus storm prep. That's a choice you can make too, there's no need to use docklines that will hold you in a major hurricane all the time. (You just need to be sure you can and will get back to the boat as needed.)

And of course, if you're out cruising and tying up in other places, it never hurts to have some extra lines stowed. Some old ones that you don't mind using on tarred pilings, some longer ones if you need to float in tidal ranges, etc.


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## sailingdog (Mar 19, 2006)

Generally, cleats should be 16x the diameter of the rope you're putting on them. So, 8" cleats are generally good for 1/2" line, and 12" cleats for 3/4" line. While this may sound excessive, this guideline generally leaves the cleats large enough to put two lines of that diameter on them without trouble... and the cleats can generally handle the load from the lines without breaking, provided they're mounted and backed properly.


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## TSOJOURNER (Dec 16, 1999)

Well, I asked the question and you answered it. 3/4 it is. I'll check the cleats for size. Did not know the 16 times the rope diameter cleat thing. Great info. I'll look close at the difference between the 3 strand and the double braid. In fact I should do some research on spicing both types since I intend to splice a loop into one end of each dock line. Thanks to all of you who took the time to teach me something. You guys are great. Thanks and thanks again.
Alvin


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## sailaway21 (Sep 4, 2006)

I'd like to correct what I believe to be a misconception on stretch in dock lines. Stretch is really only desirable as far as tidal change is concerned. If it were not for change of tide I'd recommend wire rope. I know it's not practical. The point is that, when tieing up your boat you do not want it to move at all. It is the movement which is going to cause damage. In adequate number of lines as well as inadequate cleating are going to hurt you before stretch is a factor. Regarding cleating; doubling up on one cleat, while very common, is asking for trouble. If a cleat pulls out and you lose your breast line, the stern line may keep you adequately alongside. If your spring line was doubled up with the breast line on the same cleat you have now lost two lines, and allowed the boat to have a lot more movement.
I recommend dacron over nylon for dock lines as it stretches less and is more abrasion resistant.
I cannot emphasize the point of movement enough. If you look at a merchant ship or cargo secured on deck, or below, you will readily notice that there is no way the lines/wire rope are capable of lifting the vessel or the cargo. They are there to stop movement. Once movement starts, be it a diesel locomotive loaded on deck, or the ship alongside, you're done and it's just a question of how much damage will result.
The same point applies to dock side fixtures. If you have multiple lines running to a single cleat you are only as strong as the cleat and it's securing. Bollards and pilings make much better choices also as they are stronger than a cleat.
A common mistake made is to lead a breast line at too sharp a downward/upward angle to it's dockside fixture. As you walk along the dock you'll see breast lines leading from a vessel at a forty five degree angle down to the dock. With an off dock wind, these lines will part in a vain attempt to keep you alongside. Sometimes that lead is all you have, and may be suitable for benign conditions, but if weather is coming up lead them to the opposite side of the dock, acheiving a more horizontal lead and thereby using their full strength to hold you alongside.
One last item. The time to double up is well before the wind comes up. If your vessel has any significant "sail" area to hull and superstructure you are not going to winch her back alongside. Double up before she's laying two feet off the dock.


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## btrayfors (Aug 25, 2006)

Thought I'd seen some wild stuff, but this is the most cockamamie idea I've seen in a long time. The idea that you want to tie up a yacht as tight as possible and with as low stretch material as possible is just plain nuts.

While I'm sure someone will come forward to "prove" this theory mathematically, anyone who's been around boats in a marina for awhile knows it's just plain nonsense.

In fact, when you tie up a boat in a slip in such way as to leave the lines a bit loose, you put much less stress on the boat's cleats and on the dock's cleats. Any boat in a slip will move about, due to the wind, current, and wave action. Sometimes, there's quite a bit of movement, particularly up-and-down movement. Loose lines, and stretchy ones, allow the boat to move up-and-down with very little tension on the lines.

If the same boat were tied tight to the dock with non-stretch steel lines, there would be tremendous pull on the cleats, and a passing boat might just cause enough wave action to do some real damage.

Bill


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## sailingdog (Mar 19, 2006)

BTW, three-strand is often a better choice than braided line if you're dealing with rough pilings and such. Rough pilings will pull the outer braid apart, but will not affect three-strand to the same degree.

I'd also agree with btrayfors about some slack in the lines... swell, boat wakes, etc... will make the boat move, and if it is tied up too rigidly...something is going to give... usually something you don't want...and if enough gives...the boat is going to take a beating.


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## sailaway21 (Sep 4, 2006)

Btrayfors,
I think that you missed my point. Most lines stretch too much for good mooring lines. Manila is probably the best mooring line ignoring it's lack of strength. Dacron, preferably laid not 2in1, is a much better choice. All of the above stretch. It is when the vessel starts coming off the dock that it's inertia upon coming back to the dock is going to cause damage. I doubt that you leave any slack lines with impending weather. Deck hardware is going to be ripped out not from too tight a line, but from the weight of the boat coming hard up against it and shocking it. The fact that the line stretches only mitigates the shock somewhat, the solution is to not let the shock occur in the first place.
If it's coming on to blow and your vessel is tied up where the rise and fall of tide is a factor then you simply must tend the lines. There often is no intermediate position that will allow for the tidal change. Of course, long leads as I alluded to above will alleviate much of this.


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## camaraderie (May 22, 2002)

Sailaway...I'm afraid I'm with Trayfors on this one. You need lots of give in your dock lines to reduce the shock loading. I would think that the dock line manufacturers would know about this and there is a reason New England ropes recommends nylon and ALL of the made up dock lines West carries are nylon etc. etc. 
If you think you are right about this as I'm sure you do...how about some links to credible sources supporting this approach?
Here's one for my point of view!
http://www.boatus.com/boattech/casey/21.htm


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## sailaway21 (Sep 4, 2006)

Cam,
I am not crusading against stretch per se. What I am referring to though is shock loading or dynamic loading. The American Merchant Seaman's Manual refers to this in chapter one in discussing line in general. The working load of line is not applicable when it is shock loaded. Think karate and cement blocks!<G> When a stretchy line such as nylon is parted the energy imparted to it in the stretching is instantly released in the opposite direction. A mooring line parting on a ship will leave the lines imprint in a quarter inch steel bulkhead, or cut a man in two. Dacron is superior to nylon in this regard as it stretches 60% as much as nylon and is 90% as strong. Chevron USA switched all mooring lines from nylon to dacron for this reason. Most ships use a combination of mooring lines and mooring wires. The synthetic makes for good spring lines and the wires, which stretch only 1%, are better breast lines, head and stern lines.
The point to having your lines tight is that you do not start the vessel moving. Any stretch that is employed in this goal is useful. The problem comes in once the vessel is moving. Now you have the weight of the vessel in play. I was tied up in Bayonne, New Jersey in high wind against a dock with rubber fenders. The vessel came a foot off the dock and, as the gust subsided, returned alongside the dock. The rubber fenders compressed, and a shackle on one of them, previously not in contact with the hull, punched a hole in the hull. Eventually, tugs were called in to keep her alongside. Anotherwords, the working in and out on the mooring lines was going to slowly beat the hull to death. The problem was that we were light (not laden) and there was no good lead available (horizontal) for some good breast lines. On a sailboat in that situation, when you leave the side of the dock your fenders may shift or even fly up and when the boat surges back along side damage will occur. As the oscilation continues you are going to start shock loading the lines and that is where you will start to lose deck cleats and part lines. Most boats are woefully under equipped with cleats for mooring and often have multiple lines to one cleat exponentially increasing the demand on one fixture. I haven't come across too many docking plans for sailboats, something the naval archetect does for all merchant vessels. The safest way to moor any vessel is snugly alongside with, in the case of sailboats, the use of good fenders and the often overlooked fender boards. Fortunately, for most sailboats, it's possible to get good leads on bow, stern and spring lines but those alone will not keep her alongside, hence those pesky breast lines with all their attendant adjusting. The original poster could probably get by with the 5/8" lines as long as he kept the boat alongside and doubled up for weather. He would have more "stretch" with those lines, right up to the point where he beat his hull to death on the dock or the line parted. And it would be the weight of his boat and it's inertia moving about that would cause the problem. In short, stretch is fine until the vessel starts moving relative to the dock and then it CAN become an enemy.
Regarding Casey et al, I find not too much to quibble with except that I have found double-braid, or 2 in 1, to be more subject to chafing, when used in mooring, than laid line. Dacron is significantly more expensive than nylon. And laid line, regardless of material, will stretch more than 2 in 1.
Another inadequacy is the average fender. Most are just filled with air and do a fine job of protecting your hull from scuff marks from aluminum row boats coming alongside. A celled fender, such as a Yokohama float, is much less compressible if not lighter or easier to handle. That's what is used when 'lightering' between tankers offshore. You bring the two ships alongside with the floats between the two and tie up securely. The crew adjust the lines as the smaller tanker sinks to her marks. The fenders don't blow out because of their closed cell construction. Other than collapsability, the average yacht fender is, in my opinion, over-priced junk. You could do as good a job with those foam tubes the kids play with in the pool.
On a somewhat related note: I was tied up in Dutch Harbor to an oil platform loading crude. 70,000 ton tanker deadweight with 18 parts out. It was in January and when the tide turns in the Cook Inlet all the ice comes flowing back to the south from what seems like all the way to Ancorage. The angle of the platform is such that it catches you on the stern quarter. Finally had to stop loading and disconnect the cargo hoses. Good thing too as we parted all 18 and that was with the engine going dead slow astern. Sounded sort of like 18 syncronized shot-gun blasts! Once the ship started moving it was over. No one on deck, or injured, but we junked about a hundred thou. in mooring lines in about 30 seconds!


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## hellosailor (Apr 11, 2006)

Cam, did you notice the NE Ropes doesn't *sell* any manila products? They're low tech and hard to compete with. I suspect the comparison at Boatus for nylon lines is also "versus other synthetics" and again, omitting manila. Manila line does stretch--greatly. Which is why it was the traditional dock line. It's cheap to replace as it ages or chafes or gets tarred. There is, from what I've been told, a lot of variation in the quality depending on the source. And no profit in it for US rope makers and others in developed nations. 

I wouldn't run halyards with it, but I'd gladly tie up with it. And maybe keep the more expensive synthetic lines for storm use only, so they stayed fresh.


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## sailaway21 (Sep 4, 2006)

Good manila is very hard to find. Most of what you see is sisal are far weaker material. Manila, which comes primarily from the Phillipines(duh!), was difficult to get in WW II for obvious reasons. The US government experimented with growing it in Missouri I believe with rather mixed results. They did, on the other hand, end up with a close relative that did quite well in the fertile fields of Missouri; marijuanna.


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## Sailormon6 (May 9, 2002)

I think we're talking about apples and oranges here. We're comparing the lines and procedures for tying up a massive 800' steel commercial freighter with those for a 36' fiberglass private yacht. There is no comparison.

It would make sense to tie up the freighter on short lines, so that it doesn't start to move. When a freighter is in port, the professional captain can assign a paid crew member to monitor the docklines regularly and adjust them as the tide rises and falls. The owner of a private yacht has to go to work 5 days a week, and doesn't have paid crew to monitor the docklines and readjust them in his absence. Adjusting them so that they allow no movement is completely impracticable. 

When I bought my first small cruising boat, I decided I'd save a few dollars and use polypropylene for docklines. The first night I slept on the boat, I listened to the sound when the non-stretching poly pro docklines drew taut. It was like trying to sleep inside a kettle drum.

While it's interesting to know how the big guys tie up their boats, we're talking about private yachts here.


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## Goodnewsboy (Nov 4, 2006)

It is good to have eye splices at the boat end to allow best utilization of the available cleats/bitts.

It is possible to use smaller lines if you adopt Navy practice and "triple up" when the boat will be moored for a while. I think that a single, adequately sized rope is easier to handle.


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## btrayfors (Aug 25, 2006)

Sailormon6,

Amen.

Bill


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## T34C (Sep 14, 2006)

Sailaway, first, appologies for not being able to read your last post in total. Even IF I conceed your tying tight point of reducig the load on lines, (I'm not) but if I did, you would still be over looking wave action. There will alway be wave action (tital area or not) if your boat cannot rise and fall with the waves you will be putting significant stress on all points of your mooring, line, cleats, chocks, etc... that I'm guessing will be roughly equivilent to the bouyance factor of your boat. (hopefully significant). This isn't even including the possiblity of boarding waves sinking your boat if she cannot rise and fall with the wave action.


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## sailaway21 (Sep 4, 2006)

Non-stretching polypropylene lines. I'm not familiar with those. All the polypro I've seen stretches only 20% less than nylon, although it has only 55% the strength of nylon.


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## sailingdog (Mar 19, 2006)

Sailaway-

Last I checked, Chevron doesn't have any sailboats in their fleet as a general rule. There is a significant difference in the practices of tying up a commercial freighter or oil tanker, from those used by non-commercial, significantly smaller sailboat owners. I wouldn't want any vessel massing over 100 tons to get any movement or inertia...

Also, the cleats on a large steel ship have significantly more strength than do the ones on most smaller sailboats, which are held largely in place by the strength of the laminate in which they are fastened. Shock loading large steel cleats that are welded in place is probably less of a problem than doing so on a GRP sailboat. Boat wakes are probably not an issue for a 10,000+ ton steel commercial ship, but are a significant factor for small sailboats. 

Polypropylene is a horrible material to use for docklines, as it is very weak, and extremely susceptible to UV damage.


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## Giulietta (Nov 14, 2006)

If you see most boats over here actually have springs and rubber things (sorry I don't know the name in english) on the mooring ropes, to help absorb shock due to winds and current.

Here tying a boat with the rope tensile is a NO NO.


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## camaraderie (May 22, 2002)

Giu...the rubber things are called snubbers here. I saw the spring things in the caribe for the first time with chain running from one end to the dock and then rope to the boat from the other end. Didn't understand the need or purpose of the chain. Is that how it is done where you are?


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## khbritten (Jan 14, 2006)

On Aquila, we call it snubbage. And we like it. We have one of the least protected slips in the Bay, when the wind kicks up out of the south on a high tide, like it might in the next couple of days. The concern isn't the cleats on the boat, but more those on the 20-year-old dock. Either end cutting loose is not a good thing. On a 31,000 lb boat, we use 5/8" braided for the bow and stern lines, with snubbage, and have a mix of spring lines: two 3/4" and one 5/8". I think the that snubbage is unnecessary of the line run is reasonaly long and the line has some stretch. And, to be obvious, don't forget the chafe protection - I bet that cuts more boats loose than pulled cleats. To get back to the last post.... is that what the chain is for? Totally makes sense!


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## yotphix (Aug 18, 2006)

Chain is good for chafe prevention, especially aroung pilings when you are expecting a good blow. In an ideal world you would splice and eye around a thimble to connect to chain with a shackle. Good sound storm tie.

On the 150ton yacht I work on we keep mooring lines pretty tight. No motion unchecked or undamped by the lines stretching. My little 6 ton boat is always tied with slack for all the above mentioned motions to be accomodated. The big boat uses nylon braidline for most tie ups and the storm lines are nylon three strand with eyes and thimble to attach to the chains. The little boat uses all 5/8 nylon braidline, doubled when it blows and snubbers on the primary set.

To answer the OP, if that's still necessary, use the 3/4". If you have trouble fitting that around the cleats on your boat, consider replacing them.


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## Giulietta (Nov 14, 2006)

camaraderie said:


> Giu...the rubber things are called snubbers here. I saw the spring things in the caribe for the first time with chain running from one end to the dock and then rope to the boat from the other end. Didn't understand the need or purpose of the chain. Is that how it is done where you are?


Cam, over here we don't use the chain, its all rope, and the snubber and/or spring. I have never seen the chain istallation. Could it be to keep it snug with the chain's wieght??

The snuber/chain is only used on the bow to finger rope, and on the stern to finger rope. The springs and other cross ropes are straight but not too tight.


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## camaraderie (May 22, 2002)

KH...Yeah...I think it may be used to prevent chafe on the dockside cleats for boats in long term storage. Makes sense...thanks.


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## labatt (Jul 31, 2006)

sailaway21 said:


> Cam,
> A mooring line parting on a ship will leave the lines imprint in a quarter inch steel bulkhead, or cut a man in two.


Just to get slightly off subject - a TV show - MythBusters - did a test to see if a heavy line or heavy steel cable could actually cut a person in half if it snapped (I'm assuming that this will also apply for nylon or dacron line, since it should be somewhat less lethal than steel cable).

From a summary of the episode:

A 5/8" cable at 30,000 lbs of tension was unable to cut a pig in two (or even cut into it). The MythBusters took the test even further by adding a smaller cable at the end of larger one to create a "whip" effect, and even pre-looped a cable around the pig itself. None of these methods could cut the pig by the pre-tensed cable's inertia alone. The pig was cut in half only when Adam tied a cable around it and then tightened the cable. Also, after making inquiries with almost every safety organization imaginable, the MythBusters were unable to find any concrete evidence of a person being cut in half by a snapped cable.

Just thought people may be interested  They did determine, however, that it could break bones or cause internal injuries.

Chris


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## btrayfors (Aug 25, 2006)

Too bad they didn't use one of the "Myth Busters" TV show producers instead of the pig!

Bill


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## Giulietta (Nov 14, 2006)

Ahhhh 

PIGSLO will be very very upset!!! Used one of his cousins, shame on them....


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## camaraderie (May 22, 2002)

Giu...that's the difference between the chicken and the pig in the traditional "bacon and eggs" breakfast here in the states. The chicken helps out but the pig has committment!


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## Giulietta (Nov 14, 2006)

One good thing about pigs, too..

In case (and I am saying in case) we ever get occupied by the Islamic, pigs will be safe!!!!!


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## sailaway21 (Sep 4, 2006)

I think we have apples and oranges again here. By cable it appears you are referring to wire rope and it has a stretch factor of 1%. Nylon, on the other hand, has a stretch factor of 40% at breaking strain. 5/8" dia nylon has a breaking strain of approx. 9600 lbs while 5/8" dia wire rope, depending on construction, has a breaking strain of 30,000 lbs or greater. When wire rope parts it basically just falls in the water as it's only stretched 1%. I don't know if I'd trust my pig to almost 5 tons of snap from a nylon line.
Regardless, the lines mentioned earlier are 8-10" mooring lines (2-5/8" to 3-1/4" dia.) with breaking strains from 146,000 - 226,000 lbs. That's over 70 tons, long tons or short, flying back at you and if it hits a pig I think we'll have a new definition of rag-out of pork.
The vessel in question was the SS Thomas Nelson, a Mariner-class freighter, long consigned to razor blades. If, by chance, she's moth-balled somewhere the indentation is in the lazarette aft, starboard side.

The most common line parted is the spring line and it happens when coming alongside and checking the vessel. The old adage is, "strain it but don't part it" as a parted line has no stopping power. Even on a 20,000 lb boat, if you part a spring line, you are going to have 10 tons of force coming back at you. When ships were converting from manila to synthetic it was a common source of death or dismemberment. Seaman today are well educated on this and never stand in the lead of a line. BTW, the most common injury seemed to be amputation of the leg at about knee height.


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## khbritten (Jan 14, 2006)

Giu - 

Have you seen the book, "A Cook's Tour", by Anthony Bourdain? It chronicles vividly the delicious demise of a Portuguese pig. A great read, but be ready to become hungry. 

Ken


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## pigslo (Nov 22, 2004)

I saw that episode of mythbusters. That pig was not harmed at all. He is a family member that is from the acting branch and was paid quite well for that show. He is such a ham though.
pigslo


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## yotphix (Aug 18, 2006)

Can't speak for the mythbusters but when I worked in film special effects, I saw a small dia. (I think 1/8") 7x19 wire rope break during a tow in car crash scene. The wire shot out faster than the eye could see and neatly severed a 1 1/2" sapling and several smaller branches 15 yards from where it snapped before balling itself all up. Be careful with any tensioned material approaching it's yield strength.


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## pigslo (Nov 22, 2004)

I was on aa Endeavour 42 about 20 years ago sitting in the wrong place when a jib sheet was let fly. I thought I was hit in the head with a tire tool. That taught me to always be aware of what was going on around me on a boat and don't sit next to the sheet winch.
pigslo


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## sailingdog (Mar 19, 2006)

pigslo said:


> I was on aa Endeavour 42 about 20 years ago sitting in the wrong place when a jib sheet was let fly. I thought I was hit in the head with a tire tool. That taught me to always be aware of what was going on around me on a boat and don't sit next to the sheet winch.
> pigslo


Fortunately, Pigslo's skull was thick enough to protect him from serious harm...and apparently he learned something.... the impact may have pushed the lesson in...


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