Rope bears much the same relation to the life of a mariner that water does to the life of a fish—he cannot be without it. To fill this need man has made rope from steel, grass, cloth, hemp, cotton, flax, sisal, and many other materials. In the long quest for the perfect material, manila has been found to be the most suitable fiber for the construction of an all purpose rope. Rival substitutes have been tried and found suitable for certain jobs, but manila still remains the king of rope fibers.
The main requirement for any rope is that it must have strength commensurate with its thickness and weight. Other desirable qualities are ease in handling and working, wear resistance, dependability, etc. Manila has been found to have most of the desired qualities and is therefore the yardstick used to gauge and evaluate the suitability of other rope fiber. For a given thickness of rope, manila is rated as 100 for breaking strength and other ropes are rated as a percentage of 100, since other fiber ropes of same size will break before the manila.
Steel-wire rope is not included in this comparison; however, it is perhaps well to mention in passing that although wire rope has more strength ratio to its thickness, it has failed to rival manila seriously because of certain undesirable qualities, such as weight, difficulty to work, a tendency to snap without warning, and the fact that one kink can render the whole rope useless.
The chief rival of manila fiber today is sisal. Sisal compares favorably with manila in most qualities, and when made into a rope it looks very much like manila. The true test is found in the strength of the two ropes of the same dimensions. Besides the fact that there is a considerable difference in money value, it is imperative that a mariner know the difference for safety of life and property. In many cases the substitution of sisal for manila requires expensive replacements of blocks, sheaves, and other rigging, if the same working load is to be maintained. If sisal is used, a larger rope is required to give the same breaking strength.
Considering the length of time that manila has been the king of ropes and has been the choice of experienced seamen, it seems incredible that few mariners can positively identify a pure manila rope when several samples of various ropes are placed side by side. Ropes made of hemp, sisal, manila, and similar materials, including mixtures, bear a striking resemblance once the fibers have been processed and made into rope. The similarity is deceiving, and the risk involved demands caution which is too often ignored.
To mistake the breaking strength of a rope would be a grave error, or, depending upon the circumstances, perhaps even tragic. Take the example of lowering away a lifeboat. During the war years sisal was substituted and supplied to ships without prior warning. Ignorant of the substitution, boat falls were renewed with sisal which had only 60-80% of the strength of manila. The substituted sisal operated safely when new and when loaded under its rated strength; however, the sisal in many cases parted when the lifeboats were loaded well under the boat’s normal capacity. The capacity was of course that specified for manila boat falls.
Floundering men in the water and a dangling lifeboat do not make a pleasant sight. The scene becomes more grim when it is repeated and multiplied by other unsuspecting seamen who “thought” they could positively identify pure manila rope from other fibers.
Most seamen with experience would definitely assure anyone that they could positively identify a rope made of manila fiber simply by the sight, feel, color, etc. It is far more complicated than that. A recent effort at this type of judgment was tried by several seamen with twenty years in the rigging business. Only 50% of the time could they determine which of two samples of rope was genuine manila. Positive identification only 50% of the time falls in the category of guess work and is not satisfactory. These self- styled experts also used the words hemp, manila, and sisal hemp, etc., interchangeably and loosely, so that it was often difficult to understand just what was meant. At this point a little explanation is needed so that that there can be agreement and understanding of exactly what is meant when one says, hemp, manila, sisal, etc.
Manila is the name given to the fiber taken from the abaca, a type of banana plant which grows only in the Philippine Islands. Similar plants grow elsewhere, but the fiber differs much the same as wood texture differs between short and long leaf pine. The fiber of the Philippine abaca is extremely tough and long. It sometimes measures as much as twenty feet.
Abaca plants are felled and cut into slabs or “tuxies.” The tuxies are stripped with a knife or machine which removes the soft pulp, leaving the raw fiber, which is dried in the sun and air. The fiber left after the stripping is known as manila, not hemp.
Hemp is fiber taken from the hemp plant (cannabis saliva, family cannabinaceae), a tall Asiatic herb bearing a slight resemblance in height and foliage to the bamboo (without the joints). Hemp fiber is shorter and not so tough as manila. Hemp is cultivated in the United States, Italy, and Russia.
Sisal, another widely used rope fiber, comes from the West Indian agave (agave sisalina) and grows in India, Africa, the British West Indies, and many other parts of the world. Unlike its aristocratic competitor manila, sisal was readily accessible during World War II and was widely used as a substitute, sometimes disastrously. Even since World War II sisal has been widely used because of the scarcity of manila. The scarcity is likely to continue; during Japanese occupation of the Philippines, the stock pile was exhausted without replacement. Since the war the demand has created such a great market that the plants have been over-cut and many plantations were destroyed. The life cycle of the plant is three years. With the introduction of more and more sisal, it becomes increasingly important to be sure that one can tell the difference and rest assured that the rope purchased is made of the expected fiber.
By the process of elimination many of the sensory tests long used by self-styled experts can be set aside. Rope manufacturers in an effort to improve their product treat the fiber with anti-molding compound and other chemicals which alter or destroy any taste, smell, or feel characteristics which the original fiber possessed. The color too is influenced and sometimes completely changed.
A strength test will definitely determine the fiber of the rope, but this test is seldom convenient since it requires machinery and equipment capable of producing tons of pull.
Pre-war, it was possible to determine the fiber content of rope manufactured under government contract by markings inserted in each rope throughout its entire length. During the war the demand for cordage was so great that much rope was purchased on the open market without the exactitude of inspection, so that in many cases this can not be used as a criterion. The identification by marking was accomplished by the insertion in each rope of a kraft paper strip in one strand. On this kraft paper strip there was certain information printed, and the manner and color of printing constituted a code so that at a glance an inspector could determine the fiber content. Printed on this strip of kraft paper was the type and name of the material used, and it was stated specifically whether pure manila, pure hemp, pure sisal, or a mixture. This printing was, in addition, done in a particular color ink which provided a further check. Between successive markings the name of the manufacturer was printed on the tape.
The following extract from the Navy Standard, Stock Catalogue (Section 21—Cordage) will serve to illustrate:
Type-Marker Designations and Strength Rating
|
Inc. Cir. Size Range Inches |
Type Desig. |
Consecutive Print on Tape |
Color of Printing |
Strength Rating in % |
|
2 ½ - 5 |
M |
Type M: Manila |
Red |
100 |
|
4 ½ -10 |
CMS |
Type CMS: Composite |
Maroon |
90 |
|
¾ - 1 ¼ |
S |
Type S: Sisal |
Purple |
80 |
|
¾ - 12 |
SX |
Type SX: Sisal Mixed |
Blue |
75 |
|
¾ - 12 |
SH |
Type SH: Sisal Hemp |
Green |
70 |
|
¾ - 1 ¼ |
J |
Type J: Jute |
Orange |
60 |
|
¾ - 1 ¼ |
A |
Type A: Agave |
Yellow |
60 |
When it is necessary to determine whether a rope is made of manila or sisal fiber, it is important enough for the responsible person to take the time and effort to use a method which eliminates guesswork and which will give conclusive proof. Other than the strength test no other method gives such positive and quick results as the chemical test known as the SWETT test. This method is government approved and can be found in Federal Standard Stock Catalogue section IV (Part 5) Federal Specifications for Rope; Manila. (T-R-601a Nov 26 1935).
Unfortunately the SWETT test does not identify hemp and sisal but only distinguishes between manila and non-manila fiber. However, the important information needed is whether a particular rope can be depended upon to take a “manila load” or whether the line is of doubtful strength and must be used with caution. The test proves satisfactory for the average seaman to use with confidence and safety and at the same time produce convincing results. The practicability of the test lies in the fact that it can be performed by the amateur who has reasonable color perception, with material readily obtainable aboard ship or at the local grocery store.
Solutions Required:
Ether or alcohol
Bleach (Solution or powder)
Acetic Acid, or white vinegar water
Ammonia (C.P. or household)
Procedure:
1. Wash test fiber thoroughly in ether or alcohol to remove oil or foreign chemicals.
2. Fan the sample in air until excess solvent has evaporated.
3. Make one teacup of bleach acid by adding one tablespoon of white vinegar or acetic acid.
4. Place test sample in acid bleach for thirty seconds.
5. Rinse in water, then dip into alcohol.
6. Fan sample until nearly dry.
7. Hold sample over open ammonia bottle, allowing fumes to rise through fiber. (Do not immerse.)
8. When color shows, remove sample.
Result:
1. Manila fiber will turn brown.
2. Non-manila fiber will turn cherry red.
Since the success of the test depends upon the chlorination of the fibers by an excess of chlorine, the bleach should be reasonably fresh and strong. Commercial bleach, such as Chlorox, from a new bottle is satisfactory. In the absence of commercial bleach, bleaching powder such as that used in the shipboard laundry can be worked into a paste with water. Add six parts of water to one part of paste for solution. If undissolved particles or impurities are suspended in the solution, allow the solution to stand for 12 hours, then draw off clear liquid. If future tests are to be made, keep bleach solution in a dark bottle.
Once color is produced, the fiber should be removed from the ammonia fumes. If the fiber showing “cherry red” color is kept in the fumes too long, the color will intensify and become maroon, which may be mistaken for brown by a person with poor color discrimination.
Identifying color appears within a few seconds after fiber has been exposed to the ammonia fumes. The color fades after a few hours, becoming indistinguishable after a few days.