Peak Efficiency
From barge hulls to diesel-electric power, go with what works.

12/1/2013

Mike Whalen often went out to dinner with his wife at a restaurant on the Lake Washington Ship Canal, which connects Lake Washington and Lake Union with Puget Sound. Whalen, a partner at Hockema & Whalen Associates, a Seattle marine engineering and design company, remembered looking out on the canal and when a certain type of barge came along, he would tell his wife, “Boy, that sure is a sexy-looking barge.” 

“That’s an oxymoron,” she would say.

These days, Whalen has dropped the descriptive term “sexy,” preferring “slinky” instead. 

With slinky, he’s referring specifically to a deck-cargo barge design from Hockema & Whalen for customers that seek high-speed operations. “We’ve gone to great lengths to try and improve the efficiencies of the hulls,” he said. 

In the past, a barge design would have been model tested, but lately computational fluid dynamics (CFD) has been sufficient for analyzing a barge’s hull resistance. In its design process, Hockema & Whalen gives fixed parameters to a German company, which, in turn, “computer checks a whole bunch of different configurations to find patterns we can use to lower the resistance. We’ve had pretty good luck doing that,” Whalen said. 

The last time Whalen had a hull model tested was six years ago when the CFD analysis “came up with a pretty radical looking hull form that to our eye didn’t look correct.” So two hull designs were model tested, “one that looked a little more like we thought it should look, and then the oddball-looking one.”

Everybody at the model testing facility thought the oddball wouldn’t be as good as the other hull form. But, said Whalen, “surprisingly it came out exactly as the CFD analysis predicted.” 

Whalen describes the bow of that barge as looking like it has a flat spot in the middle and where you’d expect nice rounded edges on the sides, “this one has a quicker turn,” he said. 

The 438' barge is currently working on the West Coast hauling general cargo. Capable of being towed at 12 knots, it is, said Whalen, “really pushing the envelope.” So far it’s the only one built to that design. It’s definitely in the “slinky” category.

Besides designing a barge hull with as little resistance as possible, Hockema & Whalen favors using two sets of HydraLift skegs from Nautican instead of what Whalen refers to as “a big barn door on the back of the barge” for steering.

Whalen describes the skegs as “high-aspect-ratio vertical foils, like high efficiency sailboat centerboards or rudders” that are tied together at the bottom with a horizontal foil. The skegs develop very little resistance going through the water but create plenty of lift when turned sideways. So if the barge starts to go off to the side, “the foils create the lift that pushes it back to the center. You get directional stability without an increase in drag.”

Whereas the traditional style rudder has a drag of 25 percent or more, the drag on the HydraLift skegs is just a small fraction of that, Whalen said.

This skeg system has been around since the early 1980s, and while a few other outfits are designing barges with them, Whalen is surprised that more people haven’t put the skegs on barges. He attributes that to a perception they are fragile and easy to damage. 

However, he said, “Over the course of time, we haven’t had much problem with them.” One barge did hit bottom at full speed and tore off one of the skegs, but it wasn’t difficult to repair.


 

DIESEL-ELECTRIC? 

A lot of people feel that diesel-electric is now the most efficient type of power package for propulsion. If this is so, you might think that when a diesel-electric system starts to get worn out, another diesel-electric package would be the logical choice to replace it.

But that wasn’t the case with the Governor, a 242' center-island, double-ended ferry operated by the Steamship Authority in Woods Hole, Mass. It was built in 1953 with diesel-electric power, including Westinghouse 1,000-hp motors at either end of the hull directly coupled to the propulsion shafts. 

Yet when Gilbert Associates in Hingham, Mass., was put in charge of the repowering, it wasn’t diesel-electric but conventional diesel/gearbox combinations that went in the Governor. A 1,560-hp MTU 12V 4000 M53 matched up with a ZF W7510 marine gear turning a 5-bladed prop was installed at each end of the ferry. 

“The boat ended up garnering better emission standards and better fuel economy,” said John Gilbert Jr. “It was able to meet speed requirements at reduced engine rpm, and if it needed to, the boat would do 17 knots with a full load.” With the old diesel-electric package, the top speed was 11 knots. 

Plus, the new system cuts fuel costs and reduces overall engine wear and tear “because you could pull the throttles back to maintain the same schedule,” he added.

Part of the problem with the original diesel-electric package was that it wasn’t very efficient. “The heat rejection of the electric motors was so large, there were a lot of problems maintaining a good environment with the ventilation system,” Gilbert said.

He felt it made more economic sense to go with a conventional diesel arrangement than a new diesel-electric package because the boat’s electrical system “probably wouldn’t have lent itself to a new electrical drive.” Plus, a conventional engine package was more readily available. 

While Gilbert acknowledged that diesel-electric is the best way to go with a lot of boats, especially oil service vessels, for a new boat “to keep the cost of construction down, I would probably go with a conventional diesel-gearbox arrangement.”

The question, especially for larger boats, is if diesel-electric is cost effective. The batteries that go with a diesel-electric package “are very expensive and have a limited life span,” Gilbert said. 

Most NiCad batteries last about seven years. Depending on the size of the system it could cost hundreds of thousands of dollars to replace them. 

“No one ever considers what the cost will be eight to 10 years down the road when you have to look at the stuff again,” Gilbert said.


 


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