Canadian hovercraft stand ready to go places other vessels cannot

Feb 28, 2007 12:00 AM
Hovercraft can go over water, mud flats and even flat land at relatively high speed. The Canadian Coast Guard believes those qualities make them ideal for many search-and-rescue operations.

Capt. Allan Taylor with Siyãy, one of two Canadian Coast Guard hovercraft stationed near Vancouver International Airport. In the event of a plane crash, the hovercraft would be able to operate on the shallow waters and mud flats around the airport.
   Image Credit: Alan Haig-Brown

The Coast Guard has two of the craft stationed at their Sea Island base in British Columbia near Vancouver International Airport. The airport's runways extend to the edge of the Fraser River delta. That means aircraft either land or take off over a marshy area that merges to mud banks. If a plane were to overshoot the runway, conventional land- or water-based rescue vehicles would be unable to reach it. The Coast Guard hovercraft would be invaluable in such an event, and they have simulated rescues with airport staff on occasion.

While sharing the same basic hovercraft technology, the two hovercraft based at Sea Island are distinctly different in configuration. CCGH Siyãy, named with the Salishan word for "friend," was built by Hike Metal Products in Wheatley, Ontario, in 1998 to a British design. The vessel is 93 feet 6 inches long with a beam of 39 feet 4 inches. The deckhouse is aft with a pilothouse located over a compact galley, first-aid, diver-rescue and communications area. Forward, a large 683.5-square-foot well deck capable of loads to 27.5 tons can be accessed through a ramp as on a landing barge.

Image Credit: Alan Haig-Brown

Penac is similar to Siyãy in concept, but has a larger house with controls set forward. The boat is 80 feet 4 inches long, or about 13 feet less than Siyãy.

Lift for Siyãy is provided by two Caterpillar 3412 TTA engines rated for 900 hp at 1,800 rpm. These turn sets of three fans on each side that pump air under the skirts, which are about 4 feet high and have attached sacrificial fingers. The area under the skirt is divided into fore and aft sections by a stability bag two-thirds of the length from the bow. A keel bag further divides the stern section longitudinally. These bags are inflated by the same two engines and fans that provide the lift. A second pair of Caterpillar 3412 TTA engines, but rated for 990 hp at 1,800 rpm is mounted aft of the deckhouse to turn the two 8.8-foot variable-pitch air propellers through a belt-drive system that increases prop speeds to 1,950 rpm.

A second hovercraft, CCGH Penac, meaning "fair winds" in the Saanich dialect, was added to the base in the fall of 2004. While the functionality of this craft is similar to Siyãy's, its configuration is quite different. Penac's hull is slightly smaller at 80.3 feet long with a 36.7-foot beam. Purchased by the Canadian government from a British owner, the vessel underwent a significant conversion and update from a passenger to a search-and-rescue craft. The retrofit was done at Hoverwork Ltd., Isle of Wight, England.

In addition to new paint and updated components, Penac received a new interior layout. The seats were removed from the large passenger cabin, and a pair of air-refilling stations was installed along with spaces for a hospital, first-aid area, diver-rescue area and galley.

Image Credit: Alan Haig-Brown

First Officer Bruce Wright at Siyãy's controls. The craft carries a crew of seven (two pilots and five rescue specialists/divers) and operates within a 56-mile radius of its base near the airport.

Power for the lift is provided by a pair of Deutz BF12L 513FC air-cooled, turbocharged diesels of 386 kw (525 hp) each. Propulsion power comes from a pair of MTU 12V 183TB32 water-cooled, turbo-charged diesels each delivering 613 kw (820 hp) to four-bladed Hoffman 9-foot variable-pitch propellers.

Operationally, the vessels are interchangeable and operate rather like fire trucks with crews spending time on standby and leaving the base station for drills and emergency calls in addition to some limited role in navigational-aid maintenance and lighthouse supply. Each vessel is crewed by two pilots and five rescue specialists/divers. The station is staffed 24 hours per day. The normal operations area for the hovercraft is within a 56-mile radius of the station, a distance that effectively covers the Gulf of Georgia as well as the lower reaches of the Fraser River.

On a sunny mid-July weekend, Capt. Allan Taylor, one of five available captains, and First Officer Bruce Wright made a routine run up Howe Sound from their base. The Gulf was rippled with a foot-and-a-half swell left over from a southwesterly wind. After the crew fired up the engines, the craft lifted off the ground and moved down a ramp into the water in a matter of minutes, with Wright at the starboard controls and one of the search-and-rescue crew as observer in the port-side seat.

Taylor was in the navigator's seat at the rear of the cabin. While the noise from the four engines, six fans and two propellers was not overwhelming, the people in the cabin seats wore aircraft-style headphones with boom microphones. This gear also kept them in voice contact with one or more of the dive/rescue crew in the lower accommodation area.

Image Credit: Courtesy The Hovercraft Museum Trust

Christopher Cockerell, the designer of the first working hovercraft, lies on the bow of SR.N1 to act, in his words, as "moveable ballast" during the pioneering crossing of the English Channel in 1959.

As Siyãy left the concrete ramp and moved out over the water, there was no change in the feel of the ride. Coming out from the short stretch of river in front of the bases to the open waters of the Gulf, the GPS showed a quick increase of speed over the rippled sea to 32.5 knots. As we moved across the eastern side of the Gulf, a foot-and-a-half ground swell left over from an earlier northwesterly wind began to roll the boat gently on her beam. This action brought the speed down to around 28 knots, but once we entered the waters of Howe Sound, where only the summer breeze broke the surface calm, the speed climbed quickly over 33 knots. The ride was remarkably smooth, with the movement somewhere between that of a light aircraft and a deep-V planing hull.

I sat in the second observer's chair on the starboard side behind the operator. Over my headphones I could hear the crew's comments. The observer sitting beside the captain pointed out the many pleasure craft, both sail and high-speed, that were ahead of us. It is often difficult for amateur boaters to ascertain the speed of a large fast vessel, so the constant lookout is essential. As we entered Howe Sound, the voice from the Coast Guard coordination center announced that a 30-foot pleasure craft was in trouble in the mouth of Horseshoe Bay, near a ferry terminal and marina, a few miles off our starboard bow. The initial report said both outboard engines were under water and that two people might be in the water. Siyãy was told to respond and immediately began to cover the couple of miles that separated us from the small boat's reported location.

Taylor asked the dive team to stand by, and they moved out into the forward deck well. At the same time, he exchanged the navigator's chair for the operator's chair. In minutes we were entering the bay behind one of the big car ferries. Ahead of us we saw the semisubmerged boat being towed back to the marina with its passengers still aboard. A check by radio phone revealed that they had forgotten to put the plug in the boat when they launched it from their trailer.

It takes some practice to get the feel for maneuvering a hovercraft. We were now bow-first into a tight place with a ferry terminal to port and a moored barge supporting pleasure boats to our starboard. Taylor was able to turn the craft in its own length using the controllable-pitch props assisted by a pair of "bow thrusters."

Image Credit: Alan Haig-Brown

Siyãy is propelled by two four-bladed variable-pitch propellers turning in nozzles. Each propeller works in combination with three rudders, making the craft maneuverable in close quarters.

These are large vents that project up from near the bow, allowing air from the skirt to escape upward to a 90° elbow that can be rotated 360° to provide light thrust in any direction. When set to thrust aft, they generally will hold the vessel stable in balance with the idling props. In the rare event that both props lose power, the thrusters can propel the craft at 3 knots. Controlled by a knob between the operator's knees, they are a handy adjunct to the triple rudders behind each prop that are controlled, aircraft-like, with foot petals. In the hands of an experienced operator like Taylor, the craft is extremely maneuverable. "We are getting all of our control from the air," he explained. "If it is whistling by, it can be difficult to control."

As with the other operators, Taylor has an extensive background and certification on conventional vessels. To gain the hovercraft endorsement, he served 500 hours as a first officer, as Wright is currently doing. He then did a written test and took an examiner out in the Gulf of Georgia to demonstrate his practical handling skills. The Coast Guard employs the only licensed operators in Canada, as most other hovercraft are small recreational vehicles.

While these craft are most important for their abilities in shallows and marshes, they can handle up to 5-foot seas and 30-knot winds. Taylor has had the vessel out in 40- to 45-knot winds and 10-foot seas in an emergency. The major limiting factor, he explained, is that "most ships or boats have a better water-shedding ability. If we get water through our props, we can be severely limited."

After the situation at Horseshoe Bay seemed under control, Taylor ran the craft over to a small island in the sound where a Vancouver yacht club has a mooring. The crew gave tours to the assembled yacht crews before heading back to the base. The swell had gone down a little, but the sea surface had the small waves of a freshening afternoon breeze, so the craft's speed peaked at 39.9 knots. It is capable of 50 knots in ideal conditions.

With a fuel consumption of 130 gallons per hour, the hovercraft doesn't do routine patrols, but given its good speed and central base, it acts as an emergency responder. The refurbished Penac burns a more modest 80 gallons per hour.

The presence of the two hovercraft is reassuring to commercial and pleasure boaters, because a few years ago the dive team was decommissioned in a cost-cutting drive. Shortly after that unpopular decision, a commercial fishing boat rolled over in the mouth of the Fraser River. People were trapped inside the hull and the skilled divers were not permitted to dive and enter the craft to enact a challenging rescue similar to others they had done before. A loud protest went up from the commercial marine community, and now these guys are back on the job. With the right craft for rapid response and the right people to perform the rescue, this is once again a strong force in search-and-rescue operations on the Canadian West Coast.

Crossing of English Channel tested early hovercraft concept

The concept of air-lubricating the passage of a vessel hull through the water has been around since at least 1716, when Swedish designer Emmanual Swedenborg proposed an oar-like apparatus to force air under the hull of a small boat. He abandoned the idea when he realized it would take much more than human power to generate enough pressure to gain any useful effect.

It wasn't until the 1950s that the first working model was developed. English designer Christopher Cockerell developed the concept from "air lubrication" forced under the hull to an actual cushion of air on which the vessel would float over a liquid or hard surface. The cushion would be created and contained by a curtain of air jets. Propulsion would derive from some of the air being ejected through ports at the rear of the vehicle.

Dubbed SR.N1, a prototype was built in 1959 by Saunders-Roe, a company based on the Isle of Wight. In July, the vessel was transported to France, where it began the first passage across the English Channel between Calais and Dover. While the passage was successful, some limitations of the design were identified immediately.

The difficulty hovercraft have in rough seas became evident in mid-Channel, when the vessel had to change speed and course to avoid colliding with a small boat. The log recorded the ensuing events:

"After this incident the SR.N1 took an appreciable time to get above the hump speed [the speed needed to lift the boat off the surface]: in all probability due to the variable wind and moderate swell. Both Mr Chaplin and Mr Cockerell tried moving their positions with little success. After proceeding for two miles below hump speed, the craft crossed the swell of a large ship proceeding north through the Straits of Dover. An appreciable amount of water was shipped on the port side from this swell and both observers moved to starboard to compensate the trim of the craft and avoid getting washed overboard.

"After refueling, the craft was clear of the swell in the lee of St Margaret's Bay, and it proceeded at the best speed it had obtained throughout the whole passage up and through the entrance to Dover Harbour. It was estimated that the craft probably achieved 30kt in the last mad dash." (www.

hovercraft-museum.org)

The limitations imposed by waves on the performance of the hovercraft were much reduced in 1962 when a flexible 4-foot skirt was fitted to the hard body of SR.N1. This innovation allowed it to traverse seas with wave heights of 6 or 7 feet. Development from this point was rapid. Sacrificial fingers were added around the skirt to cope with wear and tear. Modifications to improve efficiency and power of the fans to fill the hover skirt and the addition of one, two or more propellers followed.

By 1968 the big SR.N4 vessels were in service, carrying 254 passengers and 30 cars on scheduled runs across the English Channel. But the 28-mile runs, taking only 35 minutes in ideal conditions, continued to be weather permitting, which it often was not. Over the next three decades the craft were improved, along with their mechanical reliability and ability to operate in rougher weather. By the 1990s, the wave-piercing catamarans were taking a share of the high-speed traffic. With the opening of the Chunnel for railways, the end was clearly in sight for the hovercraft, with the last commercial passage coming with the new millennium.

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