Alternative use of Thordon bearings in tanker mooring system

In 2014, Monobuoy’s innovative 400-tonne turntable Calm Buoys was specified for a tanker offshore mooring system off the coast of Libya.

The system is designed to allow oil tankers to load and offload cargoes offshore, but the situation in Libya has been politically and militarily fluid for some years.

The Calm Buoys incorporate an alternative use of award-winning Thordon bearings and seals, more familiar in shipping for propeller shaft applications.

A total of 48 bearings and bushings were supplied in 2014 for installing on the chain stoppers of the Calm Buoy that went into service at the end of 2017.

“Despite the delay, construction and commissioning went very well,” said Monobuoy procurement officer Andrew Charlton.

“We have used Thordon bearings on two or three projects in the past. There are not many suppliers of these types of bearings, but we find Thordon offers a more simplified design and is easier to work with. When we have projects like this we tend to give Wenex a call to help during the design phase and assist with the calculations.”

Thordon’s authorised distributor in France, Wenex, calculated the load on each bearing, a crucial element in optimising the design of the Calm Buoys in line with the customer’s requirement.

Having a 12-m diameter hull, the Calm Buoy can accommodate four, six or eight chain legs.

An innovative and compact 40-tonne chain pulling winch is fitted, making the buoys easy and quick to install.

Single or multi-path swivel stacks can also be fitted with utility swivels to power and control subsea valves.

For each of the buoy’s chain stoppers, Wenex recommended 32 abrasion-resistant ThorPlas-Blue bearings, due to their ability to pivot with the anchor chain.

Thordon also supplied 16 SXL entry chafe bushings that were installed to provide a greater level of wear resistance to the anchor chain, while 32 SXL thrust washers were supplied to help reduce the side-to-side motion of the Calm Buoy during inclement operating conditions.

“There is a willingness with Thordon Bearings to work with companies and come up with specific solutions for applications outside of the norm,” said Mr Charlton. “We are very pleased with the technical support Thordon and Wenex provide.”

Wenex managing director, Benoit d’Alançon said “This was an important project for us. Calm Buoy projects like this are relatively rare in France, where Thordon bearings tend to be specified for use in the renewable energy sector, subsea turbines and river dams. We are delighted that Monobuoy’s system is now successfully operating offshore Libya.”

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