Cargo Handling and Stability II

Synthetic fibre ropes

Student: Belehuzi AndreiIn maritime industry, we use mostly 5 types of ropes and they are: nylon (polyamide) ropes, polyester (PET) ropes, polypropylene ropes, polyethylene (PE) ropes and aramid ropes. Each one has advantages and disadvantages.

Nylon ropesThese type of ropes have been widely used in marine mooring and towing lines and they have medium price. Nylon ropes usualy contain green yarns, to differentiate from other synthetic ropes. Nylon ropes have the lowest stiffness modulus, and thus it is favored where high extension is very important. It is the strongest of the common fibers when it is dry. However, wet nylon ropes can lose up to 20% of their strength. The result it is that they have short service life and generally this thing makes them unsuitable for permanent deep water moorings. Also nylon ropes have good elasticity, they are stretching up to 30% and returning to its original length. Generally these kind of ropes are used for such functions as shock-absorbing required. The melting point is 215C and the UV resistance is acceptable. Another advantage of rope is that they are easy to handle. Their disadvantage is that they do not float and in cold climates they tend to stiffen up and become difficult to handle. We use this kind of rope at anchor lines, some tow lines, mooring lines and safety lines. Nylon rope

Polyester ropes Polyester ropes are very durable in cyclic tensile fatigue loading. Polyester have mechanical properties quite close to those of nylon. They can be as strong as nylon when they are dry. Polyester ropes do not lose strength when they are wet and are generally stronger than nylon in wet condition. Since the cost of both fibres is quite similar polyester should generally be preferred. The melting point of polyester is around 260C and the UV resistance is good. The advantages of polyester ropes are that they have: a good resistance to chemicals, moderate stretch, a good resistance to abrasion, moderate price and they are not unpleasant to handle. The disadvantages of polyester ropes are that they are sinking and they are quite stiff. Polyester rope

Polypropylene ropesPolypropylene fiber is lighter than water so that mean that polypropylene ropes are floating. Polypropylene ropes are sometimes favored for this reason and for lower cost. However, polypropylene is weaker than either nylon or polyester. Polypropylene rope can heat up and lose strength during high-speed cyclic loading and may creep under high loads. Thus polypropylene is not generally suitable for deep water moorings. Polypropylene and polyester yarns are sometimes combined in ropes. These hybrid ropes can have strength and stiffness properties similar to those of all polyester ropes but with lower weight and cost, and they can have greater resistance to surface abrasion and heat than all polypropylene ropes. The melting point of polypropylene is around 160C. Those ropes are not sensitive to chemical atack and they dont lose strength in water. The disadvantages of these ropes are that they have: a very low resistance to UV, a low melting point and the knots come undone after braids are made. We can use that type of ropes for rescue lines, tow lines and water ski lines. Polypropylene rope

Polyethylene ropesPolyethylene is uncommon in large ropes. It used water-ski ropes and other small ropes used for utilitarian purposes. It is used extensively in the fishing industry. Polyethylene is not damaged by ultraviolet effects, need not be dryed, and is usually natural white. Thus it is difficult to distinguish polyethylene from monofilament polypropylene by appearance. High Modulus Polyethylene (HMPE) is a special form of the conventional polyethylene discussed above and it is much stronger and stiffer than conventional polyethylene. Polyethylene and HMPE will float. Another advantages of that type of rope is: very chemically resistant and good flex fatigue resistance. Disadvantages of polyethylene ropes: slippery, low melting point, they tend to distort under load unless coated, knots tend to undo and they are expensive. Polyethylene rope HMPE rope

Aramid ropesAramid fibres such as Kevlar and Twaron are substantially stronger than nylon. Aramid ropes will not melt but start to carbonize at temperatures above 425C. Kevlar is successfully used in mooring systems for instrumentation buoys. Advantages of aramid ropes: very strong, low stretch, low creep, fire resistant, good chemical resistance, cut resistance, not electrically conductive. Disadvantages of aramid ropes are: UV sensitivity, sensitive to shock loads, sensitivity to Chlorine, poor fatigue resistance, weakened by knots, sensitive to internal friction and they are very expensive. we can use these ropes in the following tasks: winch lines, sometimes as steel rope replacement where weight saving is important, lifting straps and on large ships where we having a nonconductive cable with no electromagnetic interference.

Aramid ropeDirect piping system

In this picture is shown the direct system of pipeline system of a crude oil carrier. This type of pipeline system is the simplest. He just take oil directly from the cargotank, this cause it is reducing very much the friction which occurs durring flow of crude oil through the pipeline system. From that thing result a higher rate of loading/discharging. The direct system it is cheap and easily to install and mantain, because of the less pipeline length. Advantages of direct pipeline system: good operationality easy to handle low risk of pollution

Disadvantages of direct pipeline system: inflexible for multiport discharge difficult because of the trim control5