Choosing designs and materials based on the type of vessel, the traffic area and the equipment onboard is crucial for mooring ropes to have the longest possible service life. Three experts that SAN News has met say the same thing.
A smell of tar hangs over the rope-maker’s premises just outside central Norrköping. The company has produced hawsers since the end of the 19th century and is now the only manufacturer of twisted rope on a large scale. Tore Dahlström has been in the industry since the 1980s. His business colleagues from Certex Svenska AB in Gothenburg, Mikael Jonsson and Kenneth Johnsson, have been going since the 1970s. Over the years, they have acquired sound knowledge and experience of mooring ropes. Hawsers are available in a number of variants with different characteristics, depending on the design and the type of fibres.
”It is important to know what is wanted for the ship when ordering a new hawser,” says Kenneth. ”It must be durable, of course, but there are many other things to take into account. Should it be light? Must it float? Should it stretch or be inelastic? Will it be used on a mechanical winch? We need to know the priorities, but we often help out to make the result as good as possible for the customer.”
”Yes, but on the other hand many people choose hawsers only on the basis of their price,” interrupts Tore. ”But it can be more expensive in the long run.”
On the desktop in Westerberg’s office there are samples of hawsers in different materials. Some are heavy and rigid, others light and flexible. In Scandinavia the six-strand hawser in wear-resistant polyamide fibre (for example, the Atlas hawser) with a high breaking load and elasticity is popular on ships with automatic mooring gear. But the good elasticity also means the risk of a powerful recoil if the hawser breaks. Other disadvantages are its high density, that means it sinks in water, and its sensitivity to sunlight.
Two other common types are eight-strand polypropylene hawsers and eight and twelve-strand polyolefin hawsers. These materials can withstand sunlight relatively well, are relatively durable and they float.
Products which are becoming more and more common on the market are hawsers made from HMPE or UHMPE fibre. They are light, soft and smooth in the hand. They float and do not absorb water, and stretch significantly less than other hawsers (5 % compared with up to 25 %).
”This is as strong as a cable,” says Tore and lifts up an HMPE hawser. “Previously it was expensive, but now that more companies are producing it, the price has become more reasonable.”
It is also important to adapt the choice of hawser to its area of use, handling and the technical equipment. In roller hawseholes, six-strand or round-braided ropes work well. For braided designs, the Panama hawsehole is recommended (located in the mid-stem or the stern), while braided hawsers work best on winches with a split-barrel. Six-strand hawsers work best on automatic winches. A round hawser has less wear surface in the hawsehole and lies in closer coils on a winch-drum, which reduces friction.
”It is very important to make regular checks on the condition of the hawsehole. If steel hawsers were previously used for mooring, the surface of the hawsehole must be ground and polished, otherwise fibre hawsers can be ruined on the first mooring,” says Mikael.
The breaking strength of a hawser depends on the fibre strength and quantity of material per metre. The harder the braiding or twisting, the more compact and durable it becomes.
”The amount of material is decisive. This is the reason why hawsers are often sold at a price per kilo,” says Tore.