THE MIXTURE OF POLYPROPYLENE ROPES

Further to our article in Weekly NEWS no. 27/2001 regarding the requirement by NAVION that vessels should comply with the OCIMF recommendation regarding NOT using 100% polypropylene mooring ropes and tails.

NAVION will not accept Polypropylene rope tails, that are composed of 100% Polypropylene - this is due to inherent problems with Polypropylene and its diminishing properties due to age, friction and U.V. and is in accordance with the OCIMF Mooring Equipment Guidelines, section 6.3.1.3 which states the following:

QUOTE:

Polypropylene rope has approximately the same elasticity as Polyester rope, but is significantly weaker than either Polyester or Nylon. Polypropylene has a low melting point and tends to fuse under high friction. It also has poor cyclic loading characteristics. Lastly, prolonged exposure to the suns ultra violet rays can cause Polypropylene fibres to disintegrate due to degradation. Polypropylene is lighter than water and can used for floating messenger lines. Otherwise, the use of Polypropylene for moorings is not recommended.

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NAVION will not accept mooring ropes that are composed 100% of Polypropylene.

NAVION have also stated that they cannot accept 100% Polypropylene rope tails that are U.V. Protected.

However, NAVION are allowing a "Grace Period" for the replacement of such 100% Polyprop rope mooring lines and are asking Owners to replace the 100% composition polyprop rope lines (as and when they are ready for replacement). The replacement must be an alternative that is acceptable to the OCIMF Mooring Equipment Guidelines. There will be no grace period with regards to 100% Polypropylene rope tails.

NAVION will however, accept Polypropylene mooring Ropes and Tails that are mixed with other materials such as Polyester and/or nylon  for example.

However - Members have raised questions regarding details of what "mix" is acceptable. i.e. it can be seen from the above that it is stated that some mixes would be acceptable such as Polyester and/or Nylon, but the specific question raised is "mix in what ratio". There would appear to be a lack of industry guidelines regarding this, which is creating some confusion both amongst members and the rope manufacturers. Accordingly, we have sought guidance from OCIMF on this matter who have advised us further as follows:

QUOTE

Your colleagues are quite correct in noting that the Mooring Equipment Guidelines (MEG) does not specify mixture proportions or fibre arrangements except to give general advice. This is deliberate.

The philosophy behind the guidelines is for the shipowner/master to firstly be aware of the mooring loads the ship is likely to experience; the number and strength of mooring lines required to remain securely moored; then consider the types of material and range of manufacturers to specify for purchase and fitment.

The final stage of the process (deciding on material and manufacturer) is very dependent upon the size of ship and its trading pattern. The MEG describes the properties associated with different materials and types of mooring line and makes both general and specific recommendations including some recommendations implied from the text content.

The properties of particular materials used on their own are fairly predictable although different fibre and construction techniques can alter strength/abrasion resistance/stretch when compared to basic ISO, BS, Cordage Institute and other standards. With mixtures of fibres, great variation in properties can exist depending on the proportion of materials, the form of the fibres themselves, the lay and the manufacturing processes.

Rope manufacturers continually update and improve their products. We cannot reasonably specify certain rope types or mixtures for use as a particular brand may be made "almost obsolete" shortly after publishing any guidelines.

Certain materials have properties that make them inherently unsuitable for use as moorings - the MEG is quite clear on this for Polypropylene (see 6.3.1.3) and by implication Polyethylene (see 6.3.1.4) where the material is noted as being even weaker and more easily damaged than polypropylene.

The composite materials where MEG does make reference and recommendation are Polyester and/or nylon mixed with polypropylene where compromises between strength, elasticity, resistance to damage and cost can create a range of good products from a wide selection of manufacturers which can be marketed/tailored for specific uses/purposes. A small breakbulk coaster may want hard wearing, light and easy to handle elastic ropes. A large tanker may want minimal elasticity and will not be so concerned over the weight or flexibility of the lines if they are drum mounted.

It may well be possible for a manufacturer to produce a rope with only nominal materials (other than polypropylene) in its construction. This may be considered by some users as a way of "legitimately" avoiding a comment within a SIRE VIQ report. However, the spirit of the recommendations will be ignored, which are there to enhance the safety of personnel and help to avoid material and environmental damage resulting from failure of mooring lines.

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Contact: Howard Snaith howard.snaith@intertanko.com for further information