The last big change in mooring rope technology was the introduction of synthetic rope. In the following case study, BW Shipping and Samson analysed the advantages of synthetic rope over traditional wire rope for a fleet of 11 tanker newbuildings
Typically, the shipyard specifies and supplies the mooring hardware for tanker newbuilds, including the winches and fairleads. Although synthetic rope has been available for many years, shipyards will default to specifying wire rope as it is cheaper, and in some cases, a more familiar option.
However, shipyards are not the final users of the newbuilds, and may be unfamiliar with some of the issues arising from using wire rope. Wire rope is constructed from steel, and so is naturally heavy and requires a large task crew compared to synthetic rope. Wire rope is also corroded by seawater and the rope must be constantly greased and protected from corrosion.
Special spooling trucks are required to maintain wire rope and to keep it sufficiently lubricated. These are inconveniences, but the biggest problem with wire rope is safety. Back injuries from handling heavy wire rope are not uncommon, as are cuts and abrasions from rough and corroded wire rope, of from broken strands of wire.
Further, the aggressive recoil properties of wire rope can result in fatalities, should the wire rope partially break or snap completely. Although wire rope is cheaper, taking into account maintenance, extra crew for handling and possible compensation or litigation in the event of an accident, the cost benefits are not so clear cut.
To compare the difference in costs, Samson prepared a cost benefit analysis for BW Shipping. BW Shipping general manager of the marine department Capt Paul S. Jones said: “We had doubts about the higher costs involved and the actual quality of the [synthetic rope], as we were not familiar with this type of rope. But the cost issues were covered by an in-depth analysis that looked at all the costs involved with mooring wires, that we had not previously considered in detail.”
The first comparison that was made was between the maintenance costs between wire rope and synthetic rope. According to Capt Jones: “There can be significant savings in maintenance, greasing and crew time as there is almost no work to be done in those areas.”
He stated that the company could expect to save between US$20,000 to US$50,000 every two years, since the synthetic line did not need to be refurbished like wire.
Next, mooring efficiency was examined. Since synthetic lines are lighter and easier to handle, it was estimated that the port deployment time of deckhands could be reduced by one hour in each port call. This was an estimated saving of around US$80,000 a year.
After the cost benefit analysis, Samson estimated that BW Shipping’s return of investment would be met in four years. This was significant, as the average life of wire ropes for mooring is between four to five years. At the time of the cost benefit analysis, the average life of available synthetic rope was 11 years.
Capt. Jones also visited an Italian-owned tanker in Singapore which had been equipped with Samson’s AmSteel Blue synthetic mooring for two years. He was able to speak to the crew, who were full of praise for the synthetic ropes.
AmSteel Blue is a premium non-jacketed mooring line made from Dyneema SK-75 fibre, which is a super-strong high molecular weight polyethylene fibre. It is a 12-strand braided rope that size-for-size, is as strong as a wire rope, but one-seventh the weight, according to Samson.
Finally, the analysis highlighted that specifying synthetic rope on a series of newbuildings effectively moves the deck mooring equipment away from the shipyard (with a loss of lucrative revenue) into the hands of the owner. However, when replacing wire rope with synthetic rope on existing tankers, owners must also consider the deck equipment.