On Aug. 8, a Canadian Coast Guard hovercraft rescued two American fishermen when their vessel became stuck on the mud flats of Washington State’s Boundary Bay. On the same day, a little over 100 miles to the south, another hovercraft was being loaded onto a barge for delivery from the builders to the owners in Alaska.
As with the Canadian Coast Guard craft, the new vessel will soon be working in a very specific set of circumstances that could only be met by a vessel with the unique capabilities of a hovercraft. The people in the village of King Cove, at 55° north latitude in the Aleutians East Borough on the Pacific side of the Alaskan Peninsula, need a way to reach the airport at Cold Bay, 18 miles away by road and water.
While the population is less than 1,000 people and the distances involved are relatively short, the land to be crossed is environmentally sensitive and experiences significant climatic variables. Shallows and ice conditions preclude a conventional boat for the short crossing of Cold Bay. After years of planning and examinations of alternatives, a hovercraft was found to be the most suitable for the water crossing section of the route.
|The craft demonstrates its ability to perform as a landing craft that can come right up on shore.|
Working with the British firm Hoverwork Ltd., borough officials selected Seattle’s Kvichak to build a vessel that would meet the required specifications. The Hoverwork firm has 38 years experience in building hovercraft (www.hoverwork.com). Kvichak was a natural choice for builder, as the firm has worked with numerous American, Australian and European designers to build one-off aluminum vessels including catamarans, pilot and patrol boats, and a smaller hovercraft for Crowley Maritime.
Kvichak’s latest hovercraft, designated BHT130 by the designer but named Suna-X, has some impressive statistics. As with one of the Canadian Coast Guard craft (See PM #91), the new boat will have a forward well deck. This vessel also has an 11.15-foot-wide landing-craft-style ramp that can be lowered to allow a vehicle to be rolled aboard.
|One of the five-bladed propellers that turns in a 14-foot-9-inch nozzle. The vessel’s top speed it 60 knots.|
The hovercraft is designed to carry a payload of 49 passengers, a Super Duty F-550 truck laden to a gross weight of 17,600 pounds and 14,100 pounds of unspecified freight.
The 49 passengers can be seated in a heated enclosed cabin space just aft of and entered from a door off the open well deck or cargo space. This area is surrounded with Garibaldi Glass windows of a type most often seen in yachts but useful here as their frameless, glue-on design eliminates leaks and rattles while providing temperature and sound insulation (www.garibaldiglass.com/marine.html). The sound insulation is important for passenger comfort inside as well as for environmental considerations that were a major factor in the design.
Particular consideration was given to noise and disturbance of the surface over which the craft may operate. The use of large-diameter, slow-speed propellers will ensure low noise levels while the low cushion pressure of approximately 50 pounds per square foot will allow the craft to operate over low load bearing surfaces such as mud flats, marshland in tidal areas and near a wildlife refuge. Extensive work has been done to reduce the sound over earlier versions of the hovercraft, such as the Canadian Coast Guard vessel, which is recognizable by its sound before it is even in sight.
A pair of 12-cylinder MTU 2000 engines provides lift for the boat, turning horizontal propellers to force air under the hull where it is contained by a rubberized skirt that encircles the craft. The skirt, which is 5 feet deep at the stern and increases to almost 7 feet at the bow, provides good seakeeping characteristics over rough water. Transverse and longitudinal cushion dividers allow air pressure to be varied fore and aft. These cushion dividers provide the required pitch and roll stability when the craft is hovering. A pair of thrusters project up through the side decks from the skirted area. These are topped with large 90° elbows that can be rotated 360° from the pilothouse to provide reverse and sideways thrust for maneuvering.
Propulsive thrust is provided by a pair of 16-cylinder MTU diesels each turning an 11.5-foot, five-blade aircraft-type propeller in a 14.75-foot duct or nozzle. Mounted high on the craft near the stern these props are capable of driving the hovercraft at 45 knots in flat sea conditions. The hovercraft is designed to operate in inshore waters with sea states having significant wave heights up to 6.5 feet.
|The controls are different from those of a conventional boat. The rudders, for example, are moved by pedals.|
The designer’s notes explain that: “The speed achievable in rough water depends on both the wave height and the nature of the sea state with particular reference to wave length.”
In a passenger vessel, comfort is of particular importance, and this boat certainly delivers in that area. In the passenger area it is possible to carry on a conversation in a normal voice as the hovercraft speeds across a flat sea at over 40 knots. While seat belts are provided, they are not required. However, passengers are not allowed on deck when the boat is moving, but this is primarily to protect people from the spray that comes over the skirts in some turning maneuvers.
And these maneuvers are quite remarkable; the boat can turn and travel at an angle with seemingly no more effort than tracking straight ahead. On trials with the builder in Puget Sound, the boat rode on its skirt up the gentle slope of a sandy beach. Passengers loaded over the bow ramp. After filling the skirts, the thrusters gently pushed the boat back down the beach and out over the water. Turning, the captain moved the boat at speed along the shallow waters of the foreshore while children standing in ankle deep water looked on in awe. For the passenger, there was no difference in the feel of the vessel moving over land, shallows or deeper waters.
The craft can carry 49 passengers in a heated cabin. To ensure their comfort, the windows provide both sound and temperature insulation.
Salmon fishermen in small boats looked bemused as the big craft swept past them leaving virtually no wake to disturb their relaxation. With a noise level of less than 65 decibels at 1,000 feet, the fishermen had no need to adjust the volume of the ball game on their portable radios.
From the pilothouse the captain has good visibility forward and can see aft to the big air propellers. A pair of seats similar to aircraft seats are set well forward in the smallish area. With the port side seat primarily equipped for a navigator, the starboard seat is surrounded by an impressive array of digital monitors, with screens for each of the four engines flanking a radar screen.
Steering with the rudders that are mounted aft of the two propulsion propellers is managed with foot petals. The operation of a hovercraft is not something that a skipper accustomed to a conventional vessel can move to directly, as the control surfaces are working against air rather than water.
With the foot petals controlling the rudders behind the controllable pitch props, the captain can, when maneuvering or holding position while hovering, turn a small knob between his knees to rotate the bow thrusters. Once an operator has developed a “feel” for the hovercraft, the amount of control available is equal to most displacement-hulled craft.
The hovercraft is expensive technology to build and to operate. The boat’s four engines will burn 185 gallons per hour operating at their maximum continuous power rating. In-operation consumption is expected to be between approximately 130 to 170 gallons per craft “engines running” hour.
However, a great deal of thought went into the decision that, in the case of King Cove, this is the best available technology. To meet these particular needs it seems that Suna-X will serve the community well.