The Navy calls them Range Testing Support Craft. Modutech Marine, the Tacoma, Wash., boatyard that is building three of the new aluminum 97-footers, calls them multimission boats.
Both are correct.
The Navy will use the new boats in Hawaiian waters where crews of eight sailors will retrieve training torpedoes fired by Navy submarines. The boats will also deploy various other weapons training devices including the MK 30, an anti-submarine warfare (ASW) training target that will be launched from the aft deck.
And then there’s the “threat emitter device,” which, according to naval architect John Myers, “has two space-age looking antennas attached to the top of the pilothouse that fire some kind of electronic signal that simulates surface-to-air missiles for the Navy aircraft flying overhead to practice defensive maneuvers.”
The 97'×28' semi-displacement vessels also have small (13.5"-dia.) moon pools installed on the working deck for deploying acoustic devices.
“The Navy has had torpedo retrievers for years,” said Myers, who works for Hockema & Whalen Associates in Seattle, “but the capabilities of these boats has certainly become more enhanced, and more and more things are being asked of them.”
To facilitate the retrieval of the training torpedoes, towed targets and other equipment, the new boats have a large stern ramp with rollers right at the waterline. Ballast tanks in both stern corners and one in the bow help balance the vessel’s trim with a variety of loads.
“After the torpedoes run through their programmed maneuvers, they run out of fuel and float vertically in the water,” said Myers. With two large, knuckle-boom, telescoping cranes, one on each side of the ramp, and small winches on the back of the deckhouse, the torpedoes are positioned on rollers, pulled up the ramp and secured.
“The torpedoes themselves weight about 3,500 pounds apiece,” said Myers. “The ramp can carry six, and they can carry another six up on the deck.”
The ramp can also be covered with removable deck platforms to create a larger, flat cargo deck that’s flush with the fixed cargo deck forward of the ramp.
GYRO STABILIZERS
Because the three new support craft will spend a lot of time at low speeds or idling in the same ocean waters beloved by surfers, the boats are all being equipped with large Seakeeper gyros to help stabilize them. “The Navy was an advocate right from the beginning for the gyros,” said Myers. “These boats do a lot of stationkeeping offshore, which demanded as comfortable and stable a ride as possible for the crew sitting out in the seaway.”
Each of the new support boats has three Seakeeper 26000 gyros, which are hard-mounted to the framing of the boats. One is low on the centerline, and the other two are slightly aft and sit a little higher on each side of the centerline. Each unit measures 50"×56"×37" and weighs about 3,000 lbs.
“The downside of gyros is the space they take up inside the vessel,” said Myers, “but if you’re adding them from the start of the design, you can find someplace to put them.”
The upside is the roll dampening.
The three testing support vessels under construction at Modutech are being called Mark IIs. Modutech built a prototype Mark I support vessel for the Navy in 2012 and it is currently stationed in Guam. The hull and the power are the same as the Mark IIs, and it also has three Seakeeper gyros. “The feedback I’ve gotten from the operators is that the gyros have worked really well,” said Myers.
Brian Swindahl, Modutech’s CEO, said the purchase and testing of the Mark I support vessel was a typical Navy pattern. “They like to evaluate newbuild boats like this before committing to additional vessels,” he said. “The Navy tested this boat for about a year here in Puget Sound and in the Strait of Juan de Fuca before sending it to Guam.”
Changes from the Mark I prototype to the Mark IIs include a slightly longer pilothouse and knuckle-boom cranes. The telescoping cranes on the Mark I are smaller with fixed booms.
“The Navy wanted the cranes to be personnel rated,” said Myers. “The idea being that they can get people out of the water or launch a small vessel with the crane with someone already in the boat. In order to make a crane personnel rated, it significantly increases the safety factors used in the engineering of the crane and its foundations.”
The model 40.000EX4 knuckle-boom marine cranes are designed and manufactured by DMW Marine Group, Philadelphia. Each is powered by individual hydraulic power packs that can be used with either crane.
The small vessel likely to be launched by the crane is a 27'×9' aluminum RIB built by Silver Ships, Theodore, Ala. Called a High Speed Maneuverable Seaborne Target (HSMST), the outboard-powered RIB can also be pulled up the stern ramp on rollers.
HULL DESIGN
The power on the three support craft for Hawaii is the same as the Mark I prototype in Guam: pairs of Caterpiller C-32 main engines, each rated at 1,450 hp. ZF Marine supplied the model 3050 marine gears with 2.952:1 ratios. The combination produces a full-load top speed of 17 knots and a cruising speed of about 13 knots.
The hull shape includes shallow tunnels and a 16° deadrise at the transom.
A flat chine plate transitions to a spray flat at the bow. “As the bow creates a bow wave, you get surface tension on that water in the bow that essentially wants to ride all the way up the hull surface,” said Myers. “If you don't have a solid break, that water is going to come right up to the top of the bulwark and you’ll end up with spray on the pilothouse windows. It effectively cuts that sheeting of water off the hull and makes for a clean and dry ride.”
The Navy wants the range support vessels to have a mission duration of up to 10 days and enough fuel for a range of 1,200 nautical miles. The boats also must be capable of conducting missions in Sea State 3 and transit/survive Sea State 5.
Accommodations include four small staterooms, each with two bunks, and two unisex heads with showers. Four additional fold-down bunks are available in the electrical equipment compartment (EEC) on the main deck. The 150-sq.-ft. EEC is also equipped with two workstations and a variety of racks for command/control and mission equipment.
Electric power is provided by a pair of Cat C6.6 gensets, each 125 kW, 480 VAC.
Swindahl said the boats are being built under a GSA contract with a small business set-aside.
A few years ago, Modutech built a 64'×18' aluminum workboat for the Marine Corps and five 80'×23' fiberglass ferries for the Navy. The ferries shuttle passengers to and from the USS Arizona Memorial in Pearl Harbor, Hawaii. Modutech is also building a series of 30'×15' steel micro tugs for the Navy.
“Yes, we like the Navy,” said Swindahl. “They’re a good customer.”
The next step for Modutech is international. “We’re looking to expand into foreign military sales, too.”
