wire rope blocks and sheaves free sample

Primarily, we are an engineering firm.  We take your technical requirements for wire rope sheaves and translate them into cost effective solutions to meet or exceed the performance required of your application.

For years, Sheaves Inc. (Esheaves) has been the number one source for the wire rope industry, developing and providing custom engineered wire rope QSheaves™ that meet your specific needs and rigors of your application. We also supply a large inventory of stock sheaves from the best known brands in the industry.

Our expertise is based on decades of engineering and supplying leading manufacturers, from the simplest applications to the most demanding. We’ve supplied sheaves for a range of applications, from industrial machines, manufacturing equipment, and military applications, to recreational equipment, theater rigging, and large commercial boat lifts.

We pride ourselves on our quality products and excellent customer service, as well as our continual desire to look for innovative ways to meet your needs; achieved, for example, in our patented line of steel sheaves that allow us to provide an extensive range of 6” to 12” QSheaves™ to be shipped the same day.

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The calculator below can be used to calculate effort force in block, tackle or pulley construction. The calculator can be used for metric and imperial units as long as the use of units are consistent.

Bairstow Lifting Products supplies and distributes lift assistance products from some of the very best, quality manufacturers such as McKissick, Johnson, RopeBlock, Skookum, Harrington Hoists, Tractel, CM, Coffing, Lug-All, Little Mule, Caldwell, VersaBar, TandemLoc, Lettelier and more. Our pulley blocks and sheaves for wire rope are made from the highest quality materials.Browse our industrial pulley systems below and find the ideal product for your specifications.

About: My name is Alex Crease, and I"m an engineer, a musician, and an adventurer. I love building things and taking others apart to see how they work, because every creation is an adventure!

From tank treads to bike gears to fishing lines, pulleys are used all over the place when it comes to mechanical transmissions. All types of pulley mechanisms consist of some sort of flexible belt (chain, cable, rope, etc.) turning around the circumference of a wheel, and pulleys can be incredibly useful in a variety of situations. In this Instructable I"ll go over some basic pulley concepts and interesting mechanisms, and hopefully you"ll be able to design your own pulley systems and make stuff like this!

The pulley is one of the six simple machines. Basically, all that a pulley is is a wheel spinning around an axle to aid the motion of a belt. The sprockets on a bike, for example, are a type of pulley, because when they spin, they drive other sprockets on the bike, that in turn rotate the rear wheel. So to make a basic pulley, all you need to do is loop a rope over some sort of wheel and axle.

Two pulleys can be used to create a simple belt and pulley system, in which a belt is looped between the two pulleys. One pulley is the "driving pulley", and as it spins, it transmits power through the belt either via friction or teeth, thus spinning a "driven pulley". I"ll be showing how you can use pulleys to make some pretty insteresting mechanisms later on.

Pulleys are probably most commonly used for lifting heavy loads and transmitting power across axes. Elevators, cranes, and boats all use pulleys because a pulley changes the direction of the applied force on the belt. Because the rope or belt is looped around the circumference of the pulley, the force of the object on one end of the rope can loop around the pulley to the other end. Certain types of pulley systems, like the block and tackle (to be explained later), can actually lessen the applied force needed to lift an object via a system of moving pulleys and lines, which can be very useful in high-load situations.

Pulleys are also one of a few different methods of transmitting rotation from one axis to another. Belts and pulleys can be used to transmit power over larger distances and in constricted spaces, which is one advantage they have over gears. Because most pulleys are driven by the friction between the pulley and the belt, if a part of a mechanism jams, then the belt transmitting power will slip on its pulleys instead of stalling the motor.

The speed ratio is equivalent to the reference diameter of the output pulley over the reference diameter of the input pulley in a two pulley system. Calculating the speed ratio of a more complicated pulley system is fairly simple as long as you take it step by step. With multiple pulleys, the ratio for each segment of the mechanism has to be calculated to determine the overall ratio. In the image above, the lower, driving pulley has a reference diameter of 20 mm and the upper pulley has a radius of 40 mm, making the ratio 2:1. It takes 2 rotations of the lower wheel to rotate the upper wheel once. The speed ratio also tells us something about the torque of the system, as the ratio of the output torque over the input torque is equal to the speed ratio. The upper wheel thus exerts twice the torque, but half the speed.

Movable Pulley:A pulley that can both rotate and translate based on the motions of the pulley or belt. This is commonly used in block and tackle systems, which I"ll explain later.

A belt and pulley system is one of the simplest types of pulley systems. As I described before, it contains two pulleys, one driving the belt and one driven by a belt. Belt drives can take many different forms; in tank treads, band saws, and sewing machines. Below are the four most common types of belts.

Round Belt:Round belts have a round cross sectional profile. They are used for lighter loads and are usually made of rubber. All "sides" of the profile of the belt are the same, so you can make some fancy pulley systems that interface with different sides of the belt to transmit motion in interesting ways.

Flat Belt:Flat belts have a rectangular cross sectional profile. Usually they are elastic, so they reduce vibration of the belt and usually do not need tensioners as a result.

Timing Belt:Timing belts are like flat belts except they are toothed on their inside face. This allows for more precise control over the position of a mechanism, and it means that power is transmitted via the teeth instead of friction between the belt and pulley. As a result, timing belts don"t slip like other belts do, so the pulleys remain in sync. Some mechanisms, like XY gantries, use timing belts and mount parts to the belts to control their position.

Other types of belts are specific to certain situations but branch off from these four belt types. The blade on a band saw, for example, is a type of flat belt, while tank treads are a type of timing belt.

Although we often refer to the sprockets on a bike as gears, chains mechanisms, like the ones on your bike, are actually pulley systems. The sprockets are just toothed pulleys, and each tooth catches in the link of a chain to pull the chain along. Here are some of the important things to know about chains:

Link:A single unit of chain, consisting of a pin going through two symmetrical plates with one hole for the link"s pin and one to cover the pin on the next chain link.

Chains, unlike belts, cannot slip because the teeth mesh with the links in the chain. As a result, they are great for high torque situations, which is why chains are used for things like bikes, motorcycles, and heavy machinery.

A cable drive is a bit different than a belt or chain drive because the cable doesn"t have to be a continuous loop. The cable can be fixed at one end and free or attached to something else at the other. A fishing line is a great simple example of a cable system. The line is wrapped around a drum, and by spinning the pulley one way, you can let out the line, and spinning the pulley the other way, you can reel it in. Other things that use cable drive systems include cranes and some weightlifting machines.

Cable drives can be beneficial over belt or chain systems because they don"t need a continuous loop to operate, and the cable can be attached to things other than more pulleys. For example, a crane uses cable to pull in and let out the hook block it uses to lift loads. While belts and chain are usually the best for continuous rotational motion of two pulleys, cable drives can be useful because they can be used to manipulate the motion of mechanisms with smaller, slower movements, and these rotational motions can be easily translated to linear movements.

There are lots and lots of different types of pulley mechanisms out there, and this Instructable definitely doesn"t cover all of them. However, I hope this will give you a basic idea of some of the ways that you can use pulleys to improve your mechanical design techniques. I"ll be starting with some of the simplest mechanisms and design techniques and I"ll introduce some more complicated mechanisms, but not all of them. If you"re really interested in learning more, I would suggest you check out this book, 507 Mechanical Movements, as it comes with a lot of really neat mechanisms!

As I mentioned previously, the simple pulley is a wheel and axle with a rope or belt looped around it. As the rope is tugged, the pulley turns. The force on the rope travels around the pulley to the other end of the rope, so the pulley changes the direction of the force. If you were to attach a weight to one side of a rope, loop it around a pulley, and pull down on the other side of the pulley, the weight would lift up! It"s very simple. The direction of the force of your tug is changed from down to up.

A block and tackle is a cable system primarily found on cranes and boats that involves two pulleys and a cable or rope. The mechanism consists of one fixed pulley and one movable, usually hanging, pulley. A single rope is fixed to on or near the carriage of the fixed pulley, loops down and around the movable pulley, then back up and around the fixed pulley. A hook is attached to the underside of the movable pulley, and by tugging on the rope, the hook will lift or lower.

The beautiful thing about the block and tackle is that it decreases the force required to lift an object. As shown in the image above, the force of the object pulling down is split between the side of the rope with the fixed end and the free end. Thus when you pull on the free end, you only need to exert half the force that you would have had to exert with just a single pulley. The downside of the standard block and tackle is that the weight will only rise half as far as the distance you pull the rope, because the change in distance is split between the rope segment on the fixed end and the free end.

Block and tackle mechanisms can be stacked to incorporate multiple pulleys, which even further decreases the applied load required to lift a weight. Cable mechanisms in cranes frequently use this system to lift very heavy loads.

As I mentioned before, the belt and pulley system is a very simple one, composed of two pulleys and a belt connecting them. You can use a belt and pulley to trasmit rotation from one axis to another by simply spinning one of the shafts connected to a pulley.

A belt and pulley system can transmit rotation and power to other axes over long distances and tight spaces. To do this with something like a gear mechanism, you either need a lot of gears, or very large gears, and that can ramp up the cost of a product pretty quickly. Another advantage of a belt and pulley system over a gear system is that the direction of rotation is conserved on a standard belt and pulley drive (although it can be altered). If the drive pulley spins a certain direction, the driven pulley will too. This is a big difference from gear mechanisms, in which two adjacent gears will turn in opposite directions.

Most pulley systems are friction based, which means that if the one side of a belt and pulley system jams,the belt can slip against the pulley if it needs to. Although this may sound bad, it is actually beneficial because it prevents the system from stalling out the motor by taking on too much torque. Band saws are a great example of this. The blade of the band saw is a large loop that acts as the belt, and two large pulleys turn the band saw to make it cut. If the blade were to catch badly on something, the saw would simply jam while the motor would keep turning the drive pulley.

Winches are mechanisms that allow you to wind up or unwind cable. They provide the basis for many large cable drive systems, because they consist of a large drum that can spool up the cable and can be used to collect slack. Many winches come with a ratcheting system that stops the drum from spinning if the cable is tugged on, which can be very useful in heavy lifting machines like cranes. A simple example of a winch is a fishing rod. When you cast out a rod, the ratchet is released and the line can extend freely. Once the ratchet is locked in place, any tug on the line will not turn the drum, but you can reel the line in to shorten it. A winch is a very simple, yet powerful cable drive mechanism.

While most simple pulley systems usually just spin in one direction, you may need to reverse the direction of spin on one of your axes. These methods cannot be applied to all types of pulley systems as they depend on the flexibility and type of belt. Here are two of the most common ways to invert rotation:

Cross Belt Drive:The simplest method to invert rotation is by "flipping" one side of your belt so that the belt loop creates a figure 8. This is commonly seen in cable drive mechanisms. However, this technique cannot be applied to chain or belts with specific profiles, like V-belts or timing belts, because chains are not flexible enough, and the pulley would interface with the outside face of the belt. This technique may be tricky if the pulleys are close together.

One of the great things about pulley systems is that they can be very modular, and you can make very simple mechanisms to create variable speeds and torques in a system. Here are a few different ways you can do this:

Speed Pulleys: This is pretty common in drill presses and lathes. By stacking pulleys of different diameters on top of one another, you can create different speed options just by sliding the belt onto a different set of pulleys. Each set of pulleys is paired such that the belt length and the distance between the pulleys" pivots stay the same while the speed ratio changes. This is similar to how a bike chain mechanism works, except on a bike a tensioner (which I"ll talk about soon) compensates for the slack on the chain.

Cone Pulleys:Cone shaped pulleys can be used to manipulate the speed as well. This system gives the user much more fine control over the speed ratio of the system, and is commonly used on milling machines and some other rotary tools. While stacking the pulleys allows for set ratios that need to be changed while the machine is stopped, with conical pulleys the belt can and should be moved while the mechanism is running, as the belt makes use of the spinning pulleys to slide up or down the pulleys. Cone pulleys usually work best with flat or round belts.

Tensioning pulleys is a pretty important aspect of pulley design. Most belts, including chain, may not be a perfect fit on the system you design, and may stretch a little after repeated use. This is when tensioners come into play. Tensioners are usually idler pulleys or sprockets whose position can be adjusted. They can either be found on the outside of the belt pushing inward, or on the inside of the belt pushing out. Belts can be tensioned in one of two ways:

Note:You may not need or want to tension your belts all the time.If your mechanism isn"t going to spin at very high speeds, the pulleys are not very far apart, or your belt is elastic and thus self tensioning, you may not need to use a tensioning system on your mechanism. However, it"s never a bad idea.

To An Axis on the Same Plane:If you want to use a pulley system to transmit rotation from a driving axis to another axis on the same plane, you"ll need to feed the belt around two idler pulleys and onto the pulley you want to drive. The idler pulleys basically allow the belt to "bend" at a given angle to get to the driven pulley on the other side. This system can work with most belts and cable, although it will not work with timing belt pulleys because they aren"t very thick, and the idlers contact the side of the belt.

To An Axis on a different plane: To transmit rotation to an axis on a different plane, all you have to do is twist the belt! This requires wider pulleys, to give the belt space to wrap around, as the belt may come and leave contact with the pulley at an angle. This means that timing belts are unsuitable for use on this type of mechanism, because they require meshing with the teeth on timing belt pulleys.

Now its your turn to make something cool with pulleys! I made this simple 3D printed PulleyBot to go along with this Instructable, but there are many other directions to go in from here. Use what you"ve learned and don"t forget to share it!

Hi all, I"m having trouble sorting out how an electrical window blind system works. we have two blinds that work off a motorised roller with one cord. when operated to shut the blinds the top blind goes up and the bottom blind goes down off the one cord and the same for the blind to down to allow light in. The cord is first attached to the electrical roller and runs through the bottom blind then it goes up to a fixed point at the top of the window, goes through a little normal roller point and comes down to attach to the top blind. When activated to shut or open the blinds move in opposite direction. Can anyone send a diagram to help me determine the cord positioning to make this happen? I can send a rough diagram if required. Thank You billsmith49@me.com0

I went to a gym where 100% of the Lifetime Fitness machines used pulley systems that were Closed Loop and ... all the machines operated extremely quietly and smoothly. Can that, in any way, be attributed to the Closed Loop design, or simply to the quality of the machines" manufacturing and components (parts)? Thank you.

I have this setup and belt skips. In the picture motor turns counter clock wise. The motor needs to move a heavy load. Where should the tension pulley be positioned? Does it matter if its a belt or chain? Also thanks for your info. Any help is appreciated.

Idler pulley is used to keep tension on system, it is always used on the "slack" or take up side and prevents a high speed belt from "whipping" and flying off the pulley or coming in contact with something. The tensioner is also used to aid in replacing the belt :loosen tensioner and the belt will just slide off the pulleys. and usually was taught in school that the number of lines in a block and tackle minus 1 (the end line has same advantage going up or down) was the machanical advantage or ratio of force to lift. It kinda makes sense looking at a picture of it but am not sure if there are systems that break that rule. You can make a block and tackle system with a single rope, a "Truckers cinch": Tie one end to a stationary object (bed of a truck) and throw line over load. Tie an "8" knot (make a 2 foot loop and tie it in a half hitch so you end up with a knot and loop in the middle of the rope) then run the tail of the rope to other side of the load, loop it around a stationary tie down and then run the rope back up through the loop. Bring it back down now and pull on it. youll exert 2X the pulling force (there is that 3 line rule), with the same effort as a one rope tie down system. If you have enough rope, you can make more loop backs and really put some tension on it but friction will eventually start to play a factor. This method is used for tensioning makeshift rope bridges.0

I believe that the idler pulley in Step 4 is meant as an example only. It, indeed, does not seem to serve any practical purpose. I"m not sure what is going on in Step 5 (or what that object even is?), but that doesn"t mean that the pulley isn"t serving some sort of function that I"m unaware of. Generally an idler pulley is used when you need to route around some other mechanical device that would otherwise be in the way of the belt. One of the best examples I can think of is a car engine, where your radiator hoses or A/C refrigerant lines need a somewhat direct route from Point A to Point B and requires re-routing of the drive belts to accommodate.0

In step 5, this is actually the inside of a giant pair of robotic googly eyes! As I also explained above, the idler pulley is serving as a tensioner because the belt is a bit larger than the distance around the driving and driven pulleys.0

Great question! I guess I didn"t show it clearly enough. Guide pulleys and idlers are very similar: guide pulleys are mostly used to guide cable through specific points to make it easier to route them along specific paths. Guide pulleys also frequently come in pairs. An idler pulley is also an unpowered pulley, and can be used to get the belt around corners and stuff like that, as lfoss mentioned, but can also be used to keep the belt taut, which is what is happening in the image in Step 5. The belt itself is too large to just wrap around the large pulley and the drive pulley and still drive the pulley effectively, so the idler pulley acts as basically a fixed tensioner to keep the belt tight around the other two pulleys. Does that make sense?0

There are actually TWO under there, believe it or not. They Just don"t seem to travel far enough to do any good. From what I"ve read on various forums, its a common problem with my mower and replacing the tension springs with stiffer ones seems to generally be the best solution. I may look into it next summer. Its really not worth messing with this late into the mowing season. =P0

Very nice, I inherited a drill press about a year ago and didn"t know about the variable speed drive mechanism up until a week ago (I"ve used it once). I just popped open the cover but haven"t taken the time to teach myself the theory behind the pulley system in there. Now I don"t have to, thanks!

Yeah , that is fairly common on drill presses and milling machines . The speed depends on the type of material you are working with and the cutting tool you are using . When you are not sure , a slower speed is usually the best choice . Aluminum and stainless steel can be a little tricky at times .

Very informative ! I have been working with these things for a lot of years , and understand the principles of how they work . But you explained it very well , probably a lot better than I could ! Thanks !

6-1. INTRODUCTION. Section I of this chapter discusses blocks which are among the most important fittings used aboard ship on the deck, in the engine department, and in other operations. Section II covers elements of wire rope rigging which cargo handlers in a terminal service company must know. It details the care and use of wire rope, procedures for computing the safe working load and breaking strength, and inspection and handling. Section III covers marlinespike seamanship, which is a general term for handling and caring for fiber line and wire rope used aboard ship or in other marine operations.

6-2. COMPONENTS OF WOODEN BLOCKS. A wooden block, as shown in Figure 6-1, consists of one or more sheaves (pulleys). Each block has one or more steel straps which strengthen the block and support the sheave pin. Personnel may suspend the block or apply a load by means of a hook or shackle inserted in the top of the strap. The strap may continue through the block and form a projection, called the becket, to attach another line. The becket usually has a thimble to prevent chafing of the line. The front of the block is called its face and the sides of the shell are called cheeks. The opening between the top of the sheave and the block where the line is passed through the block is called the swallow. The breech is the opening between the bottom of the sheave and the block and serves no definite purpose. Line is never passed through the breech of a block except for a small tail line used to keep the block from bouncing on the deck. The entire wooden portion of a block is called the shell; it protects the sheave and line.

6-3. COMPONENTS OF METAL BLOCKS. Metal blocks have basically the same part as wooden blocks. The metal block has bolts to hold its cheeks together and a metal shell. The parts of a metal block are shown in Figure 6-2. This figure shows the diamond and roller bearing block.

6-4. TYPES OF BLOCKS. There are several different types of blocks, each with a particular use. Wooden and metal blocks are of the same design except for the head or heel block which is only metal. These blocks are explained below and illustrated in Figure 6-3.

The snatch block has a hinged cheek on one side and differs from all the other blocks. The advantage of a snatch block over the other types is that it can be opened and a bight of line placed over the sheave without passing the end of the line through the swallow. The snatch block also has a swivel hook. The primary function of the snatch block is to change the direction of the load or pull.

The head or heel block has a cast metal shell, roller bearings, and a grease fitting in the sheave pin. The cargo runner can pass over these blocks at the head and heel of the cargo boom. These high-speed blocks must be lubricated every time they are used. A good winch operator can pass the cargo runner over the sheaves of these blocks at a rate of 500 feet per minute.

a. Blocks are named according to the purpose for which they are used, the places they occupy, or from a particular shape or type of construction. According to the number of sheaves, blocks are designated as single, double, or triple. A traveling block is attached to the load being lifted and moves as lifting occurs. A standing block is fixed to a stationary object.

b. Every tackle system contains a fixed block attached to some solid support and may have a traveling block attached to the load (see Figure 6-4). The single rope leaving the tackle system is called the fall line. Personnel apply the pulling force to the fall line which may be led through a leading block.

6-5. SIZES OF BLOCKS. Users can determine the size of blocks by measuring the length of the cheek in inches. Blocks are designated for use with a specific line size. Bending line over a sheave that is too small causes distortion and strain, resulting in the line wearing on the shell. Personnel can use line smaller than that designated for a sheave with no damage, but should never use line of a larger size.a. To determine the size wooden block to use with line of a known size, personnel may follow these formulas:

b. The size metal block to use with wire rope depends on the diameter of the sheave. The sheave is never less than 20 times the diameter of the wire. For example, personnel can determine the size block to use with 3/4-inch wire rope as follows:

6-6. MAINTENANCE OF METAL BLOCKS. Personnel must frequently disassemble metal blocks in cargo-handling rigs and other blocks that are in continuous use and inspect them for wear. Blocks used only occasionally seldom need to be disassembled if they are kept well lubricated.a. To remove the sheave from a diamond or oval block, personnel take out the cotter pin, remove the hexagonal nut from the sheave pin, and drive out the sheave pin. For a diamond block, personnel must loosen all bolts holding the cheeks together and remove one before the sheave will slide out. With an oval block, it is necessary only to loosen the bolts.

b. To disassemble a roller bearing block, personnel loosen the set screws and remove the retaining nuts. Next, they take out the bolt holding the shell together and remove the shell, closure snap rings, adjusting nut, closure washer, and closure. The sheave pin and the bearings from the sheave are removed last.

6-7. TACKLE USES AND TYPES. A block with a line led over the sheave makes applying power by changing the direction of the pull easier. Used with line and another block, it becomes a tackle and increases the power applied on the hauling part. Tackles are designated according to their uses and the number of sheaves in the blocks that are used to make the tackle. The various types of tackle are rove with different size blocks and all have a limited lifting capacity depending on the number of sheaves, the size blocks and the size line used. The tackles are named for their use or from their makeup. The most commonly used tackles are explained below and illustrated in Figure 6-5.A single whip tackle consists of a single fixed block with a line passed over its sheave. This tackle has no mechanical advantage.

The gun tackle, named for its use on old sailing ships to haul the cannons back to their gun port after firing, consists of one single-sheave fixed block and one single-sheave movable block.

6-8. REEVING TACKLES. Personnel reeving tackles reeve each type differently. If a tackle is rove improperly, too much friction and possible binding of the falls can result when lifting or lowering a load, creating a safety hazard. It is important to use the proper method of reeving each type of tackle up to and including a threefold purchase.

b. The reeving of each type of tackle is explained in subparagraphs (1) through (5) and illustrated in Figure 6-6, with the exception of single whip and runner tackles. Single whip tackle offers no mechanical advantage and runner tackle has a 2 to 1 mechanical advantage.(1) Gun tackle. Place two single-sheave blocks about 3 feet apart with the hooks or straps facing outboard and both blocks in the same position, either on their face or cheek. Next, they should run the line through the first and second block, then splice it to the becket of the first block. Gun tackle has a 2 to 1 mechanical advantage.

(2) Luff tackle. Position one single- and one double-sheave block in the same manner as with the gun tackle. Run the line through one of the sheaves of the double-sheave block first and then to the sheave of the single-sheave block. Next, run the line through the other sheave of the double-sheave block and splice the line to the becket of the single-sheave block. This tackle offers a 3 to 1 mechanical advantage.

(3) Twofold purchase. Position two double-sheave blocks in the same manner as with the luff tackle. Reeve the line through the top or bottom block, stay in sequence, and never cross from one side to the other. After reeving the tackle, splice the standing line to the becket. Twofold tackle has a 4 to 1 mechanical advantage.

(4) Double luff tackle. Obtain a double- and a triple-sheave block. Place the blocks 3 feet apart with the hooks or straps facing outboard and position the blocks so that one is face down and the other cheek down. When reeving a tackle that has one block with more sheaves than the other, always start with the block with the most sheaves. In this instance, start reeving through the center sheave, keeping the line parallel. Never cross from one side to the other. Double luff tackle has a 5 to 1 mechanical advantage.

(5) Threefold purchase. Place two triple-sheave blocks 3 feet apart, with the hooks or straps facing outboard, positioning the blocks so one is face down and the other is cheek down. Start reeving in the center sheave of one block and finish in the center sheave on the other. Then splice the standing part to the becket. This tackle offers a 6 to 1 mechanical advantage.

6-9. MECHANICAL ADVANTAGE. The mechanical advantage of a tackle refers to the relationship between the load being lifted and the power required to lift it. In other words, if a load of 10 pounds requires 10 pounds to lift it, the mechanical advantage is one. If a load of 50 pounds requires only 10 pounds of power to lift it, the mechanical advantage is 6 to 1 or 5 units of weight lifted for each unit of power applied.a. The mechanical advantage of a tackle is determined by counting the number of parts of the falls at the movable block. The gun tackle in Figure 6-6 has a mechanical advantage of two. This tackle is rove to a disadvantage as are most vertical lifts. For a horizontal pull, the block with the cargo hook attached should be connected to the load, making it the movable block. This tackle would then be rove to an advantage which would be increased by one. Since most lifts in this test are vertical, the tackle is rove to a disadvantage unless otherwise stated.

b. To ascertain the amount of power required to lift a given load by means of a tackle, cargo handlers should determine the weight of the load to be lifted and divide this figure by the mechanical advantage. For example, lifting a 600-pound load by a single luff tackle, cargo handlers first determine the mechanical advantage gained with this type of tackle by counting the parts of the falls at the movable block. By dividing the weight to be lifted by the mechanical advantage it is possible to determine the pounds of power required to lift a certain amount of weight.

6-10. FRICTION. A certain amount of the force applied to a tackle is lost through friction. Friction occurs in a tackle when lines rub against each other or against the frame or shell of the block, and pass over the sheaves. This loss in efficiency of the block and tackle (roughly 10 percent of the load per sheave) must be added to the weight being lifted to determine the total weight. For example, to determine the total weight of a load when lifting a load of 500 pounds with a twofold purchase, personnel use the following formula and compute:TW = W x (1 + Friction) or (1 + F)

6-11. BREAKING STRESS AND SAFE WORKING LOAD. The following paragraphs explain the procedures used to determine breaking stress and safe working loads for blocks and tackle loads. The symbols used in the formula for computations are as follows:W = Weight

Step 5. Compare the BS to the figures shown in Table 6-1. It is desirable that the SWL of the line used be greater than the computed BS for the block and tackle.

* This table is computed in pounds for new line. For line that has been used these figures will decrease. Old line may have only 60 percent of the strength shown in pounds for a given size of line.b. To determine the SWL for a line of known size to be rove into a tackle, personnel should use one of the following formulas as appropriate, where "C" denotes circumference and "D" denotes diameter. The formulas for manila and nylon will give the SWL in pounds. The formulas for wire rope will be in tons.

c. If personnel are unsure which type of wire rope they are using, they must always use the formula for mild steel when figuring the SWL. This will ensure ultimate safety since the different strengths of wire rope cannot be identified visually.

6-12. CARE AND USE OF WIRE ROPE. Wire rope is made of steel except for its core which is likely to be fiber. The grades of wire rope in descending order of strength are: Extra improved plow, improved plow, plow, and mild plow steel. Of these four grades, the Army uses improved plow steel extensively and plow steel to a lesser extent. The manufacturer stamps the grade on the reel. Because the grade of wire rope is not visually apparent, it should always be considered as plow steel when in doubt.

6-13. MAKEUP OF WlRE ROPE. The basic unit of wire rope is the individual wire. Wires are laid together to form strands. The number of wires in a strand varies according to the purpose for which the rope is intended. Strands are laid around a core to form the wire rope itself. With preformed plow steel wire rope, the core may be hemp or polypropylene, a synthetic fiber. The core is a foundation to keep the wire rope round, to act as a shock absorber when the wire rope contracts under strain, and to serve as a reservoir for lubricant. Figure 6-7 shows a cross section of wire rope.

b. Strand Construction. In most wire rope used today, the wires and strands are preformed. Preforming means presetting wires in the strands into a permanent corkscrew form which they will have in the completed rope. As a result, preformed wire rope does not have the internal stresses found in nonpreformed wire rope, does not untwist as readily as nonpreformed wire rope, and is more flexible.

c. Types of Lay. Lay refers to the direction of winding of the wires in the strands and the strands in the rope. Both may be wound in the same direction or in opposite directions.(1) In regular lay, the strands and wires are wound in opposite directions. Most common is the right regular lay in which the strands are wound right and the wires wound left. This lay is used in marine operations.

6-15. MEASUREMENT. Whatever its grade, wire rope is usually measured by its diameter. Figure 6-8 shows the correct method of measuring the diameter of wire rope. To measure wire rope correctly, personnel should place it in the caliper so that the outermost points of the strands will be touching the jaws of the caliper.

6-16. SAFE WORKING LOAD AND BREAKING STRENGTH. The SWL and BS formulas are listed in the paragraphs below.a. Formulas for determining the SWL of several grades of wire rope have constants that are not to be confused with safety factors. For example, the formula for the SWL in STONs (2,000 pounds) for extra improved plow steel wire rope is diameter squared multiplied by 10, or SWL = D2 x 10. The formula to find the SWL of 1-inch, 6 x 19, extra improved plow steel wire rope is as follows: SWL = D2 x 10 = 1 x 1 x 10 = STONs.

b. A figure relatively constant in marine operations, especially for new wire rope, is the SF, which is 5. The SF is used with the SWL to find the BS.

6-17. INSPECTION OF WIRE ROPES. Wire ropes should be inspected frequently and replaced if frayed, kinked, worn, or corroded. The frequency of inspection depends on how often the rope is used. Wire rope used 1 or 2 hours a week requires less frequent inspection than one used 24 hours a day.a. Common causes of wire rope failures are as follows:Using rope of incorrect size, construction, or grade.

b. Carefully inspect weak points and points of greatest stress. Worn or weak spots show up as shiny, flat spots on the wires. If the outer wires have been reduced in diameter by one-half, the wire rope is unsafe.

c. Inspect broken wires, since they show where the greatest stress occurs. If individual wires are broken next to each other, unequal load distribution at this point will make the rope unsafe. Broken wires are called fishhooks. To determine the extent of damage to the wire rope, users can slide a finger along one strand of wire for one complete turn, equal to the length of one wire rope lay. Next, count the number of fishhooks. If six or more fishhooks are discovered, the wire rope is unsafe and should be replaced immediately.

6-18. HANDLING. There are different handling methods for wire rope. These methods are listed below.a. Kinking. When loose wire rope is handled, small loops frequently form in the slack portion of the rope. If personnel apply tension to the rope while these loops are in position, the loops will not straighten out but will form sharp kinks, resulting in unlaying of the rope. Personnel should straighten these loops out of the rope before applying a load. After a kink has formed in wire rope, it is impossible to remove it, and the strength of the rope is seriously damaged at the point where the kink occurs.

b. Unreeling. When removing wire rope from a reel or coil, personnel should be sure to rotate the reel or coil. If the reel is mounted, the wire rope may be unwound by holding the end and walking away from the reel. If a wire rope is in a small coil, personnel may stand the coil on end and roll it along the deck, barge, wharf, or ground. Remove any loops that may form, although rotating the reel or coil usually avoids causing loops to form.

c. Seizing. Personnel should seize (lash together) all wire rope before cutting it. If the ends of the rope are not properly secured, the original balance of tension is disturbed. Maximum use cannot be made on wire rope when some strands carry a greater load than others.

(2) There are three formulas for determining the number and length of seizings and the space between them. When a calculation results in a fraction, the next larger whole number is used. The following formulas are based on a 3/4-inch diameter wire rope.(a) The number of seizings required equals about three times the diameter of the rope. For example: 3 x 3/4 = 2 1/4 or 3 seizings. Because the rope will be cut, six seizings are required so that there will be three on each rope end after the cut.

d. Cutting. Wire rope may be cut with a wire rope cutter, a cold chisel, a hacksaw, bolt clippers, or an oxyacetylene cutting torch. When cutting wire rope, personnel should follow the procedures outlined below.(1) To seize the wire rope, insert it into the cutter with the blade between the two central seizings, close the locking device, then close the valve on the cutter. The handle should be pumped to build up enough pressure to force the blade through the rope.

(2) Use the bolt clippers on wire rope of fairly small diameter. Use the oxyacetylene torch on wire of any diameter. Cutting with the hacksaw and cold chisel is slower than cutting with the other tools and equipment.

e. Coiling. Personnel may need to take a length of wire rope from a reel and coil it down before using it. Small loops or twists will form if the wire rope is coiled in a direction opposite to the lay. To avoid loops, users should coil right lay wire rope clockwise and left lay wire rope counterclockwise. When a loop forms in the wire, they should put a back turn in as shown in Figure 6-10.

Figure 6-10. Putting a back turn in wire ropef. Size of Sheaves and Drums. When a wire is bent over a sheave or drum, two things happen: Each wire is bent to conform to the curvature, and the wires slide against each other lengthwise because the inside arc of the rope against the sheave or drum is shorter than the outside arc. The smaller the diameter of the sheave or drum, the greater the bending and sliding. Personnel should keep this bending and moving of wires to a minimum to reduce wear. The minimum recommended sheave and drum diameter is 20 times the diameter of the rope. For example, for 5/8-inch rope: 20 x 5/8 = 12 1/2-inch sheave. If a 12 1/2-inch sheave is not on hand, personnel should use the next larger size, never a smaller size.

g. Lubrication. Wire rope is lubricated as it is manufactured. The lubricant generally does not last throughout the life of the rope, which makes relubrication necessary. Crater "C" compound is recommended, but personnel may use oil on hand rather than delay lubrication. Crater "C" compound should be heated before it is put on the wire rope. Personnel should use a brush if possible to apply lubricant. If a brush is not available, they may use a sponge or cloth, but they should look out for fishhooks or broken wires.

h. Reversing Ends. It is sometimes advisable to reverse or cut back ends to get more service from wire rope. The wear and fatigue on a rope frequently is more severe at certain points than at others. Reversing distributes stronger parts of the rope to the points getting wear and fatigue. To reverse ends, personnel remove the drum end, put it in the attachment, and then fasten the end taken from the attachment to the drum. Cutting back the ends has a similar effect, but not as much change is involved. In reversing ends, personnel should cut off short lengths of both ends to remove the sections with the greatest local fatigue.

i. Storing. Wire rope should be coiled on a spool for storage. Its grade, size, and length are noted on a tag attached to the rope or spool. Wire rope should be stored in a dry place to reduce corrosion. Personnel should not store it with chemicals or where chemicals have been stored because chemicals and their fumes can attack the metal. Personnel should always clean and lubricate wire rope before storing it.

j. Cleaning. Personnel can remove most of the dirt or grit on a used wire rope by scraping or steaming. Rust should be removed at regular intervals by wire brushing. Personnel must clean the rope carefully before lubricating to remove foreign material and old lubricant from the valleys between the strands and from the spaces between the outer wires. This permits the newly applied lubricant to freely enter the rope.

6-19. CHARACTERISTICS AND FIBER LINE. To be able to work with fiber line, personnel must know its characteristics and properties. They must be able to handle and care for the line, and tie basic knots, bends, and hitches.a. Materials for Fiber Line. Fiber line is made of either vegetable or synthetic fibers. Vegetable fibers include manila, sisal, hemp, cotton, and flax. Synthetic fibers include nylon, Dacron, polyethylene, and polypropylene. The Army primarily uses nylon synthetic fiber line, so this manual covers only that synthetic fiber.(1) Manila is a strong fiber that comes from the leaf stems of the abaca plant, a part of the banana family. Varying in length from 4 to 15 feet in their natural state, the fibers have the length and quality which gives manila rope relatively high elasticity, strength, and resistance to wear and deterioration.

(2) Sisal is made from sisalana, a species of the agave plant. Although sisal is not used much in the Army, it is covered here because it is a good substitute for manila. Sisal withstands exposure to seawater very well.

(3) Hemp is a tall plant that has useful fibers for making rope and cloth. It was used extensively before manila was introduced. Now hemp"s principal use is in fittings such as ratline and marline. Because hemp is absorbent, the fittings are tarred to make them more water-resistant.

(4) Nylon made from mineral products is waterproof, absorbs shocks, stretches, and resumes its original length. It also resists abrasion, decay, and fungus growth.

b. Construction of Fiber. Figure 6-11 shows how fiber line is made by twisting fibers into yarns, yarns into strands, and strands into the finished line. The fibers are twisted from left to right to spin the yarn. The yarn is twisted from right to left to form the strands. The strands are then twisted from left to right to lay or form the line.

c. Size of Line. Fiber line is measured by its circumference in inches with the exception of "small stuff" which is fiber line 1 3/4 inches or less in circumference. It has three strands and the number of threads it contains determines its size. Small stuff will range in size from 6 to 21 threads. To determine the number of threads, personnel count the number in one strand and then multiply it by three. Small stuff is used for lashing material and heaving lines. Fiber line between 1 3/4 and 5 inches in circumference is referred to as line, and line over 5 inches in circumference is referred to as hawser. Hawsers are used for mooring and towing.

Figure 6-11. Fabrication of fiber lined. Strength of Fiber Line. Manila is the standard line against which all other types of fiber line are measured. The measurement implies that all the other lines have the same circumference as the manila line against which each is measured. The strengths of the lines are as follows:

Three-strand nylon line will stretch 30 to 35 percent under an average load or a load that does not exceed the safety factor for that size line. Three-strand nylon line will stretch 40 percent without being damaged and will draw back to its original length.e. Useful Formulas. To find the SWL and BS of the various lines, some useful formulas are listed below.(1) The manufacturer states the size and BS of its lines and if available, crew members should use the manufacturer"s figures for determining the strength of line. If this information is not available, personnel should use the following formula and constant for type line to compute the SWL and the BS: C2 x constant for type line = SWL (in pounds), where "C" denotes circumference in inches. Constants for type line are as follows:

For example, to find the SWL of a 3-inch sisal: 32 x 160 = 9 x 160 = 1,440 pounds SWL(2) In marine operations an SF of 5 is generally used for new line or line that is in good condition; old or worn line may have an SF of 3. As line ages and wears through use, the SF drops. If the SF is multiplied by the SW, the result is the BS of the fiber line. The BS is the amount of weight in pounds required to part the line. The BS of a line divided by the SF of 5 results in the SWL.

6-20. CORDAGE. In marine usage, cordage is a collective term that includes all cord, twine, line, and string made from twisted vegetable or synthetic fibers. Cord, string, and twine are loosely used to mean small line.a. Cotton twine is similar to the string found in homes. It is used for temporary whippings and should be run through beeswax before use.

6-21. INSPECTION OF LINES. The outside appearance of the line is not always a good indication of its internal condition. Therefore, it is necessary to inspect line inside as well as outside. Overloading a line may cause it to break with possible damage to materiel and injury to personnel. Before using unfamiliar line, or line that has been stored for a long period of time personnel should perform the following procedures.a. Inspect line carefully at regular intervals to determine its condition. Untwist the strands slightly to open the line to examine the inside. Mildewed line has a musty odor and inside fibers have a dark, stained appearance. It is easy to identify broken strands of yarn. Dirt and sawdust-like material inside the line means that it has been damaged. If the line has a core, it should not break away in small pieces. If it does, the line has been overstrained. If the line appears to be satisfactory in all respects, pull out two fibers and try to break them. Sound fibers should offer considerable resistance to breakage.

b. When any unsatisfactory conditions are found, destroy the line or cut it in short pieces. Make sure that none of these pieces is long enough to permit its use. This not only prevents the use of line for hoisting, but saves the short pieces for miscellaneous use such as lashings, whippings, and seizings.

6-22. UNCOILING NEW LINE. New Line is coiled, bound, and wrapped in burlap for protection. Since the burlap covering protects the line during storage and prevents tangling, it should not be removed until the line is to be used. To open, personnel strip back the burlap wrapping and look inside the coil for the end of the line. It should be at the bottom of the coil. If it is not, turn the coil over so that the end will be at the bottom. Pull the end of line up through the center. As line comes up through the coil it will unwind in a counterclockwise direction. Nylon is handled differently from natural fiber line. Nylon comes on reels and to uncoil it, personnel should place the reel on stands or jacks.

6-23. WHIPPING LINE. Personnel must never cut a line or leave the end of a line dangling loose without a whipping to prevent it from unlaying. A line without whipping will unlay of its own accord. Whenever a line or hawser has to be cut, whippings should be put on first, on each side of the cut. To prevent fraying, a temporary or plain whipping can be put on with any type cordage, even rope yarn. Figure 6-12 shows one of the several methods that can be used for putting a temporary whipping on a line.

Figure 6-12. Plain or temporary whippinga. To make a temporary whipping, personnel should-Lay the end of the whipping along the line and bind it down with three or four round turns.

b. A permanent whipping, as its name implies, is put on to stay. One way to fasten a permanent whipping is with a sewing palm and needle. Sewing palms are made for both right- and left-handed people. The width of the permanent whipping should equal the diameter of the line. Two whippings are recommended. The space between the two whippings should be six times the width of the first whipping. The needle is threaded with sail twine, doubled (Figure 6-13 shows a single strand for clearness). When putting on permanent whipping, personnel should-Put the needle through the middle of a strand so that it comes out between two strands on the other side.

Ensure the thread comes out through the middle of a strand the last time it is pushed through, so that the strand will hold the end of the twine after it is knotted and cut.

6-24. KNOTS, BENDS, AND HITCHES. Each of the three terms-knot, bend, and hitches-has a specific definition. The choice of the best knot, bend, or hitch to use depends largely on the job it has to do. In a knot, a line is usually bent or tied to itself, forming an eye or a knob or securing a cord or line around an object, such as a package. A good knot must be easy to tie, must hold without slipping, and must be easy to untie. In its noun form, a bend ordinarily is used to join the ends of two lines together. In its verb form, bend means the act of joining, bent is the past tense of bend. A hitch differs from a knot and a bend in that it ordinarily is tied to a ring, around a spar or stanchion, or around another line. It is not merely tied back on itself to form an eye or to bend two lines together. This portion of the manual explains why a given type is used and also gives the efficiency or strength of many of the knots, bends, and hitches.

WARNING: Tying a knot, bend, or hitch in a line weakens it because the fibers are bent sharply, causing the line to lose varying degrees of efficiency or strength. Never tie a knot on which you are not willing to stake your life. A general rule to follow, then, is to use a knot, bend, or hitch for temporary work and a splice for permanent work because it retains more of the line"s strength.a. Overhand Knot. The overhand knot shown in Figure 6-14 is the basis for all knots. It is the simplest and the most commonly used. Personnel may use this knot to prevent the end of a line from untwisting, to form a knot at the end of a line, or to be part of another knot. When tied to the end of a line, this knot will prevent the line from running through a block, hole, or other knot.

Figure 6-14. Overhand knotb. Figure Eight Knot. This knot shown in Figure 6-15 forms a larger knot at the end of a line than an overhand knot forms. It also prevents the end of the line from running through a block. Personnel can easily tie this knot by forming an overhand loop in the line and passing the running end under the standing part, up the other side, and through the loop. They can tighten the knot by pulling on the running end and the standing part.

Figure 6-15. Figure eight knotc. Square Knot. Personnel use the square knot to tie two lines of equal size together so that they will not slip. Figure 6-16, shows that in the square knot the end and standing part of one line comes out on the same side of the bight formed by the other line. This knot will not hold if the lines are wet or are of unequal sizes. It tightens under stain but can be untied by grasping the ends of the two bights and pulling the knot apart. Its strength is .45 percent. To avoid a "granny" or a "fool"s knot" which will slip, personnel should follow this procedure: Pass the end in your right hand over and under the part in your left hand as illustrated in Figure 6-16. With your right hand, take the end that was in your left hand and pass the end under and over the part in your left hand.

e. French Bowline. A French bowline is used as a sling for lifting an injured person. For this purpose one loop is used as a seat and the other loop is put around the body under the arms, with the knot drawn tight at the chest. Even an unconscious person can be hoisted safely in a properly secured French bowline, because the weight applied will keep the two loops tight so that the individual will not fall out. Personnel must not allow the loop under the person"s arms to catch on any projections. The French bowline may also be used if a person is working alone and needs both hands free. The two loops of the knot can be adjusted to the required size. Figure 6-18 shows the step-by-step procedure for tying the French bowline.

Figure 6-18. Tying a French bowlinef. Half Hitch. The half hitch is used to back up other knots, and is tied with the short end of the line. Personnel should not tie two half hitches by themselves; instead, they should take two round turns so that the strain will be on the line, not the hitches. Then they tie the hitches (see Figure 6-19).

Figure 6-19. Half hitchg. Clove Hitch. The clove hitch is the best knot for tying a line to a ring, a spar, or anything that is cylindrical. It will not jam or pull out and has a strength of 55 to 60 percent (see Figure 6-20).

Figure 6-20. Clove hitchh. Stopper Hitch. A slight defect of a clove hitch is that it can slide along the cylindrical object to which it is tied. To guard against this, personnel should use a stopper hitch (commonly called a rolling hitch) which is illustrated in Figure 6-21. This figure shows fiber rope; with wire rope, personnel would use a small chain.

Figure 6-21. Stopper hitch(1) When tying, personnel should take a turn around the line with the stopper as in the first view, pull tight, and take another turn. This turn must cross the first turn (first view) and then pass between the first turn and the stopper (second view). This completes the stopper hitch itself, but it must be stopped off in one of several ways.

(2) Personnel can take two or more turns with the lay of the line and then seize the stopper to the line with marline. Another method is to tie a half hitch directly above the stopper hitch. A third method is to tie a half hitch above the rolling hitch (third view), and then take a couple of turns against the lay, and seize the stopper to the line.

6-25. SPLICING THREE-STRAND FIBER LINE. Splicing is a method of permanently joining the ends of two lines or of bending a line back on itself to form a permanent loop or an eye. If two lines are to be spliced, strands on an end of each line are unlaid and interwoven with those of the standing part of the line. Small stuff can be spliced without a fid, which is a tapering length of hard wood used in splicing larger lines. A knife is used to cut off the ends of the strands.a. Short Splice. The short splice is as strong as the rope of which it is made. However, the short splice increases the diameter of the rope and can be used only where this increase in diameter will not affect operation. The splice is frequently used to repair damaged ropes or where two ropes of the same size are to be joined together permanently. Damaged parts of the rope are cut out and the sound sections are spliced. Personnel should follow these steps-(1) Untwist one end of each line five complete turns. Whip or tape each strand. Bring these strands tightly together as in Figure 6-22, view 1, so that each strand of one line alternates with a strand of the other line. Put a temporary whipping on the lines where they join to keep them from suddenly coming apart. Do this procedure with small lines until you are skilled enough to hold them together while you tuck.

Figure 6-22. Short splice(2) Starting with either line, tuck a round of strands in the other line. Then, using the strands of the other line, tuck a round in the first line. Make sure to tuck in one direction, the reverse and tuck in the other direction. When making a round of tucks, regardless of the direction, face where the lines are butted so you will always tuck from right to left. Pull each strand as required to tighten the center of the splice.

(3) Tuck two more rounds in each direction. After tucking in one direction and reversing and tucking in the other direction, pull the strands as required to strengthen the center of the splice. When finished with three rounds of tucks in each direction, cut off any excess length on the strands.

NOTE: To have a smoother splice, you may cut off one-third of the circumference of each strand before making the second round of tucks and another third before the third round.(4) When the splice is completed, cut off the excess strands as before. Lay the splice on the deck and roll it with your foot to smooth out and tighten the splice.

b. Eye Splice. When a permanent loop is to be put in the line, personnel should use an eye splice which has a strength of 90 to 95 percent. (Compare this with the strength of a bowline which is 60 percent.) Personnel should follow these steps:(1) Unlay (untwist) the strands in the end of the line four or five times and splice them into the standing part of the line by tucking the unlaid strands from the ends into the standing part. Whip or tape the ends of the strands. An original round of tucks, plus two more complete rounds, is enough. If the line parts, it will likely part in the eye rather than in the splice, so three rounds are as effective as a greater number.

(2) Always whip or tape the ends of the strands before starting, otherwise, they will unlay and be troublesome. Seize large lines at the point where unlaying stops to avoid trouble working with them. For lines with up to 21 threads, you can open the strands in the standing part with your fingers. Use the fid for larger lines.(a) Figure 6-23 shows how to make the first two tucks. Separate the strands in the end and hold them up as shown in the first step. Place the three unlaid strands against the standing part where they will be tucked, forming the desired eye. The middle strand facing you always tucks first. Put a reverse twist on the standing part so that you can raise the strand under which you will make the first tuck. Pick up the stand to be tucked, and tuck it under the strand raised. Always tuck from right to left or with the lay of the line.

Figure 6-23. Making eye splices(b) Be sure to keep the next strand, in step two, on the side of the line that is towards you. Tuck that strand next. Put it over the strand under which the first one is tucked, and tuck it under the next one.

(c) Now turn the incomplete eye over as shown. Check the third strand to be sure that it has not unlaid more. If it has, twist it back to where it should be. Take the last strand, put it across the standing part, turn its end back toward you, put it under the strand over which the first tuck was made, and tuck it in a direction toward you. This results in the third tuck going to where the second came out and coming out where the firs