Flexible and durable surface coatings for inflatables

During the past couple of decades, a range of rigid-hulled inflatable boats (RHIBs) have been built and refined by companies to meet the demands and stresses of maritime rescue services.

During the past couple of decades, a range of rigid-hulled inflatable boats (RHIBs) have been built and refined by companies to meet the demands and stresses of maritime rescue services.

The combination of rigid hull and large inflatable buoyancy tubes was first developed in the 1960s. The early inflatable sections were not very robust and were prone to deflating. Research showed that the strength and durability of the inflatable sections, often referred to as fenders, could be dramatically improved by using spray-applied surface coatings to cover the tubes. To be successful, coatings must be strong, flexible and resistant to the ravages of continual exposure to salt water and UV light.

Polyurethane coatings produced by Gold Coast-based Rhino Linings Australasia (RLA) are used by some RHIB manufacturers to protect and strengthen the inflatable sections, in addition to providing non-slip walkways on deck sections when required.

One versatile surface coating in particular, Rhino Tuff Stuff, provides maximum slip resistance with enhanced protection against impact, abrasion and corrosion. Spray-on application creates a single, seamless coating, that conforms to any shape and size and bonds to virtually any substrates.

Polyurethane coatings made by the company have a patented mix ratio that have been developed over many years. “We have dedicated staff who understand the chemistry of the product,” said Denis Baker, special projects engineer at RLA. “They have a great depth of knowledge and experience for which products can be used and in what situations.”

The elastomeric properties of the Rhino Linings coating systems allow for application to surfaces that are subject to vibration, expansion, contraction, movement, flexing, abrasion and impact. The selected coating in this case is extremely flexible while maintaining its integrity under repeated flexing, regardless of film thickness. “The polyurethane material used in Tuff Stuff has been tested by Australia’s premier research organisation, CSIRO, and has been certified as a Class III ‘Wet Area Membrane’,” Baker added

RHIBs range in size from 4 to 9 metres, although they can be as long as 18 metres. Their shallow draught, high manoeuvrability, speed and relative immunity to damage in low-speed collisions are advantages in the situations in which they operate. Constructed with a solid, shaped hull and flexible tubes at the gunwale, the design of a RHIB is stable and seaworthy.

The inflatable sections allow the vessel to stay afloat, even if large volumes of water get aboard in rough seas and act as a cushion between a boat and other surfaces with which it might come in contact, such as docks, pilings and other boats. Additionally, the coated sections help to reduce potential damage to the hull or superstructure from impacts and stress.

A RHIB is usually propelled by one or more outboard motors or an inboard hydrojet or stern drive, with the power ranging from 5 to 300 horsepower. The maximum speed of a RHIB depends on its gross weight, power, length and profile of hull, and sea conditions. A 6-metre RHIB carrying six passengers, powered by 110 horsepower engines, in heavy seas, can achieve a top speed of around 30 knots. High-performance RHIBs may operate speeds up to 70 knots depending on the size and weight.

One manufacturer of RHIBs that uses the Rhino Tuff Stuff coated fender sections, Naiad Design Ltd here in New Zealand, supplies harbour pilot boats as well as pursuit boats to the UAE, Singapore, Malaysia and New Zealand. With more than 25 years experience building boats for commercial operators, Naiad Design produces a tough, dependable, yet attractive and functional vessel.

Nearly every port throughout the world offers a harbour pilotage service and operators are licensed by the government of a country and usually employed by the local port authority. The services must be available in all weather conditions, so the harbour pilot boat must be manoeuvrable enough to get alongside container ships and tankers and strong enough to withstand continual battering against a ship in heavy seas. It must also be stable enough for the pilot himself to safely transfer to or from the ship.

A harbour pilot is responsible for the safe conduct and navigation of a ship from the time he assumes control from the master—after boarding at sea—until the vessel is safely moored at its allocated wharf, or vice versa. The work of the pilot includes all steering and engine orders, in addition to the placement and direct radio control of any tugs involved in manoeuvring a vessel. A pilot must have extensive local knowledge of the channels, depths of water, currents and dangers within and around the port for which he is licensed.

Safety is a vital aspect of all activities taking place in a maritime environment. A key component of this is effective and safe operation of life rafts. A variety of companies provide training in life raft handling for offshore rig and platform personnel, helicopter pilots and the crews of ocean-going vessels.

One common training scenario is that of a helicopter ditching at sea. A mock-up of a helicopter cabin is suspended above a diving pool and dropped sideways into the water. Trainees have to get out of the helicopter and into a deployed life raft. These courses often run several times a week, throughout the year.

Life rafts are designed to be deployed only in an emergency, so deployment dozens of times a year for training purposes means conventional canvas-lined rafts have a limited life span. To reduce the cost of continually replacing training rafts, Dreamboats WA (part of DSBC Pty Ltd) designed and constructed a non-inflatable alternative called ‘Hewey’. This training raft comprises cylindrical, closed-cell foam sections coated in 2mm thick spray-applied Rhino Tuff Stuff.

Hewey training rafts have an expected lifespan of at least five years. Being solid foam there can be no leaks which virtually eliminates most maintenance requirements and allows continual use in the training environment: a huge cost saving for those organisations that run survival training courses in the oil, gas and aviation industries. The solid life rafts have been approved by OPITO (Offshore Petroleum Industry Training Organisation UK) for practical use providing the organisation has a conventional aviation life raft for viewing purposes.

“Hewey” training rafts are similar in appearance to a traditional reversible aviation life raft and can be customised to match any life raft used in existing training courses. Sized to fit into a standard 20ft shipping container, “Hewey” training rafts are now shipped worldwide from the manufacturer’s Fremantle factory.

RLA has been working with polyurethanes since the early 1990s and now manufactures a range of consistent formulations in Australia which are suitable for a variety applications. “Many people do not know that spray-applied coatings are a very versatile and adaptable method for protecting a range of flexible structures,” Baker added.

Whereas epoxies and paints form a solid shell, the flexibility of polyurethane coatings allows them to move with the expansion and contraction of the underlying structure and as temperatures change.

Rhino Linings Australasia Pty Ltd (RLA) was formed in 2000 and established manufacturing and distribution capabilities for the region. RLA manufacturers its spray applied coatings in Australia and can draw on the more than 30 years experience of its American parent. The company sources all its materials from local suppliers except for some very specialised chemicals which are imported from America.