Invader -Class Tugs – Turning back the Clock

These are the most bad-assed, sweetest-handling, powerful tugs going,” said Larry Miles of Crowley’s Invader-class tugs.

One of Crowley’s Invader-class tugs in Valdez, Alaska, in March 1999. Designed by a predecessor of what is now Elliott Bay Design Group, 25 of the boats were built in the 1970s.
   Image Credit: photos by Alan Haig-Brown

Miles is a port engineer with Crowley Marine Services in Seattle. During his years with the company, he has spent time in both the wheelhouse and the engine room of vessels built to this class more than a quarter century ago. Between 1974 and 1977, Crowley Maritime had 25 of these powerful boats built at the J. Ray McDermott shipyard in Morgan City, La. In recent years, the company has carried out an extensive refit, assuring them an extended life. Such an undertaking is expensive, but the consensus from those who know these popular craft is that it will prove to be money well spent.

The Invader-class tugs show a distinct West Coast influence in their design by Philip F. Spaulding & Associates of Seattle. This firm later became Nickum & Spaulding, which in turn became Elliott Bay Design Group.

Image Credit: photos by Alan Haig-Brown

Ranger sits at Pier 17 in Seattle. The tugs have a classic West Coast look inspired by wooden tugs built for the U.S. Army during World War II.

Their classic profile follows in the design tradition of the 61 wooden 128-by-28-foot 1,200-hp Miki-class tugs built for the U.S. Army during World War II, using a 1929 design by an earlier Seattle architect, L.H. Coolidge. This is not surprising, since Crowley started in San Francisco, and the company purchased many of these tugs after the war and earned good money for Crowley well into the 1960s.

Like the Miki tugs, the Invader boats have a clean shear line that sweeps aft from a plumb bow stem to a graceful stern counter. Also like the Mikis, they have a rounded front on the wheelhouse and a well-proportioned relation between the wheelhouse, officers’ quarters and main deckhouse. Crowley’s classic black-hull, buff superstructure and trademark red stack complete a vessel that sits low in the water and high in the esteem of boat buffs on both coasts of America and in most of the world’s ports where these boats have taken tows at one time or another.

The Klondike gold rush in the 19th century pressed every available means of marine transportation into service between Seattle and Alaska. In the 1970s North Slope oil and the trans-Alaska pipeline put dozens of tugs to work towing prefabricated production modules and hundreds of miles of large-diameter steel pipe up the Inside Passage. The Invader-class tugs were central to this operation. They had deep, round-bilged 136-by-36.5-foot hulls with a 17-foot light draft and a 20-foot draft when loaded with their huge ocean-spanning 155,000-gallon fuel capacity. They also carry 15,000 gallons of potable water and 3,300 gallons of lube oil.

Back in the 1970s, a salmon sports fisherman who came to Vancouver Island from a prairie wheat farm was startled to hear what he thought was the sound of a freight train coming across the water toward him. Of course it turned out to be the deep-throated roar of one of the Invader tugs’ twin 20-cylinder EMD diesels.

Image Credit: photos by Alan Haig-Brown

The Markey double-drum winch.

A former Crowley engineer once explained that the genius of the company in the 1960s was to do only minimum maintenance on the aging wooden Miki tugs. The engineer explained that he complained to his employer that the competition was spending a lot of money to maintain its fleet of Mikis. But then he understood the strategy when Crowley took the money that the company had saved and built the first Invader-class boats. The competition was left with a fleet of well-maintained but underpowered wooden boats.

As the Invader-class tugs reached a similar age at the end of the 20th century, the situation and the reasoning were opposite. These steel tugs had been maintained well, and their 7,200-hp rating was still relatively high in the competitive ocean-towing market. The decision was made to refurbish the vessels in a program that included other vessels as well.

When the Invader-class tug Ranger won the hotly contested Seattle Tugboat Race in 1971, a company press release said, “The first place tug Ranger is among 25 Crowley Invader-Class tugs to be refurbished as part of the company’s $60 million tug refurbishment program. The project includes the rebuilding of the tugs’ main engines, effectively returning each engine to zero hours.”

The engines were replaced in what Miles called a like-and-kind rebuild program. A pair of the original 20-cylinder V-configuration EMD 20-645 main engines was taken out and sent to the factory for rebuilding. A newly rebuilt pair of the same engines rated for 3,600 hp each at 800 rpm was installed. The engines’ massive Falk gears with their 4.345:1 reduction were also rebuilt. These gears connect to 34.5-foot-long 12.5-inch shafts and massive five-blade 132-by-88-inch stainless-steel open propellers that enabled Ranger to average 14.6 knots in the 1.9-nm 2001 Seattle tugboat race. At that speed she was able to finish the race in just seven minutes and six seconds. It is likely that for the race the engineer was taking a few more rpm out of her than is normal, but Chief Engineer Lee Todd, of the Invader-class tug Warrior said of these engines, “They are bulletproof. They’ll always bring you home. If you’ve lost a bolt off a broken water pump, it might go around and around in there for a year and then come out all round and shiny.”

Image Credit: photos by Alan Haig-Brown

Crowley Port Engineer Larry Miles at the controls of Ranger. The tug is powered by a pair of rebuilt 20-cylinder EMD 20-645 engines, each generating 3,600 hp.

While the Invader class, with their fine hull forms and open wheels, is noted for speed, they have been known to handle some very large tows. In 1975 the first of the new vessels proved themselves as part of a flotilla of Crowley tugs and barges towing to Alaska’s North Slope oil fields. That year they encountered the worst Arctic ice conditions of the century. It was the largest fleet in the project’s history, with 47 vessels amassed to carry 154,420 tons of cargo. The fleet waited two months for the ice to retreat and open a passage to Prudhoe Bay on Alaska’s Arctic shore. When the ice closed in again, it took as many as four of the tugs to push the barges, one at a time, through the ice. But the delivery was a success that has been repeated numerous times in challenging tows from the tropics to the Arctic.

Most of these successes are not about speed but are credited to the tugs’ 150,000-pound forward bollard pull. The vessels’ equally impressive 120,000-pound bollard pull astern has earned them a role in ship-handling as well.

Each Invader-class tug carries a pair of spare cylinder packs. These are a unit that includes a piston and connecting-rod assembly in a cylinder sleeve complete with a head. The connecting rod on a damaged cylinder can be disconnected through a port in the engine base. Then the removal of four big crab bolts allows the whole assembly to be taken out and replaced.

“You could almost fix them with a hammer and screwdriver,” Miles said.

Under Crowley’s ISO quality-control program, he noted, the engines are scheduled for top-end rebuild at something like every 28,000 to 32,000 hours.

The refurbishment included the accommodation areas of the vessels as well. New furnishings were built into the two crew bunk rooms located in the forecastle, as well as in the engineer’s main-deck cabin and in the mate and captain’s upper-deck quarters. The interior upgrade included replacing the concrete-over-steel decking with a sound-dampening rubber coating on the interior decks and rubber tile in the rooms. The aft working deck also received an upgrade with the installation of a nonskid heavy rubber flooring similar to that on the flight deck of aircraft carriers.

Image Credit: photos by Alan Haig-Brown

Chief Engineer Lee Todd in the engine room. He describes the engines as “bulletproof.”

In the galley, stainless cabinets have replaced wood for greater fire protection and easier cleaning. Old appliances have been replaced with stainless as well. In fact, a great deal of stainless has been added throughout the vessel, including high-wear and difficult-to-maintain areas such as chain-locker hatches, railings, ladders and replacement doors.

The wheelhouse is a dramatic change from the original. With a pair of upright steel posts removed and the console reduced to about 24 inches, the operator can move closer to the windows and have a better view of the crew working on the forward deck. This modification resulted from the crew’s reactions to a plywood mockup created to help them evaluate the new design.

A lot has changed in the realm of navigation since the 1970s. While much gear had been added over the years, the new suite of electronics brings the boats right up to date while leaving more space on the console. The big, old autopilot has been replaced with a smaller and better Simrad Robertson AP45.

The pneumatic controls for the clutch have been maintained, but new wheelhouse ZF Mathers control heads have been added. The Falk gears on the Invader-class have a two-stage system with a sort of slipping clutch that allows for very slow rpm on the propellers to increase fine control in ship- or barge-handling. The boats also have three barn-door-size rudders with one behind each wheel and one on the centerline. This combination allows these 136-foot vessels to continue to hold their own in the world of modern cycloidal and z-drive tugs.

Navigation electronics vary slightly from boat to boat but include two radars, a gyro-azimuthed stabilized Furuno FR1510MK2 or MK3 with ARP15 target plotter with GPS and depth data interface. The second radar is a gyro-azimuthed stabilized Furuno FR8111 or FR8100D with GPS data interface. The GPS itself is a Trimble NT300D or NavTrac XL. The loran C is Furuno; the depth-sounder is a 200-kHz Furuno LS6000. Some of the vessels have been fitted with Nera WorldPhone Marine Inmarsat mini-M satellite systems. The gyrocompass with universal gyro pilot is a Sperry MK37.

The business end of an ocean towing tug is the winch. The Invader-class boats have kept their Markey TDSDW 36C double-drum towing winches. Loaded with up to 3,000 feet of 2.25-inch wire, they allow for tandem tows; or, when towing oil barges, both lines can be put out to the barge with one on the bridle and the other providing safety and taking a share of the load off the bow of the barge.

Image Credit: photos by Alan Haig-Brown

The mess area. The interior upgrades included installing noise-reduction materials.

Invader-class tugs have been involved in countless salvage operations. One of the most memorable occurred in January and February 2000, when the tug Crusader saved a floating dry dock, the ex-Sustain, off Cape Hatteras, N.C. Over the course of six weeks and 2,000 miles, the tug battled winds up to Force 11 in an operation that included helicopter support and a complex of other vessels. The 1974-built Crusader was parted from the tow repeatedly and managed to re-acquire the massive dry dock four times, using her Orville Hook to snag the tow’s dangling bridle. At one point the winds were so strong that the tow was actually dragging the tug at 7 knots. In spite of a stove-in bulwark and a side trip to Bermuda, Crusader eventually brought the rogue dry dock to tether at Atlantic Marine’s shipyard in Jacksonville, Fla.

Those who have worked the Invader-class tugs in such seas over the past quarter century say that they roll a lot and their aft deck is more often awash than not, but the crews never have any doubt that the deep-set hull will bring them home safely. Now it seems that crewmembers and clients alike will have another quarter century of good service from these good boats.

By Professional Mariner Staff