Cummins has been building diesel-electric marine power systems since 2004. Then at the end of 2014, Cummins advanced its game with variable-speed, diesel-electric power generation. Its first variable-speed, diesel-electric package is powered by the QSK50.
The QSK50 has been used in standard propulsion applications and for fixed-speed diesel-electric. For the new variable-speed, diesel-electric generator package, the QSK50 has a rating of 2,183 hp at 1,800 rpm. That was optimized specifically for variable-speed applications to give maximum fuel efficiency at all operating points.
The big advantage of a variable-speed diesel generator over fixed-speed diesel-electric is matching loads and reducing fuel consumption. “You don’t have an engine that’s constantly screaming at 1,800 rpm with less than 20 percent load on it,” said Cummins Scott Roth. “That’s the big deal.”
Being able to run more efficiently, especially in low-load applications such as with ferries and other passenger vessels and offshore support vessels, results in reduced fuel consumption, CO2 emissions and maintenance expenses, and longer-lasting engines.
From an operator’s standpoint, there really isn’t a learning curve with variable-speed diesel-electric. “It’s similar to today’s diesel-electric,” Roth said, though there is a learning curve in terms of the designing and installation. “It will require different switch gear and alternators.”
You can expect more variable-speed diesel-electric generator units from Cummins. “We will have an array of ratings that will be specifically designed to be used with variable-speed diesel generators for diesel-electric applications,” said Roth. “We are working on our Q60 and some of the 19-liter products.”
All the ratings will meet IMO Tier 2 emissions standards at the ISO E2 and E3 test cycles.
AUTO TRANSFER
Another way to reduce fuel costs for power generation is to parallel smaller fixed-speed generators as needed.
Kohler’s J Series generators rated from 50 kW to 150 kW can now be operated with an auto transfer option that can parallel up to eight generators together without costly switchgear. “The ability to auto transfer load and to parallel generators leads to immediate fuel cost savings,” said Kohler’s William Bussier. “This creates an opportunity for customers to install smaller-sized generators properly fitted for loads they are carrying 80 percent of the time, and then parallel them together when they are running peak loads.”
Kohler’s new load transferring system also features the ability to “auto transfer the load” to a second generator, said Kohler’s Patrick Kline. “If a generator shuts down by itself, the load switches over in less than 10 seconds to another generator. No one else on the market has it.”
The system is pretty simple. It’s basically a cable that connects one generator to another with a “motorized operator mounted on the circuit breaker on the genset. It’s simple for it to auto transfer a load,” Kline said.
That’s opposed to the traditional way of auto transferring a load that requires about $50,000 in switching gear or $15,000 for marine transfer switches and the dedicated space for the transfer switches. Kohler’s load transferring system runs about $2,500 per generator.
Kohler’s solution to a generator shutdown has been available for about a year. The impetus for its development came from a need in the megayacht market to parallel generators without paying for expensive switching gear.
Kline said that since Kohler was gaining more traction in the commercial workboat market and “we knew the auto transfer function was capable, we started talking to customers in the workboat market. Everyone had a lot of interest, because if you lose steering [powered by a genset], it could be a problem.”
The system can be incorporated into newbuilds as well as repowerings. By this time next year it will be available for 13- to 40-kW genets.
Isolating noise and vibration
Whether the genset in the engine room is a Cummins, Kohler or another brand, the noise and vibrations are essentially the same. Daily crew exposure is ultimately unhealthy. It can affect the amount of sleep you get, your general level of irritability and how aware you are of what’s going on around you, which could become a safety issue. Above a certain decibel level, the noise affects your hearing.
There are two types of machinery noise, airborne and structural. A well insulated engine room blocks out most of the airborne noise. Insulation, however, won’t work for structural noise and vibration, which is created by mounting an engine and generator directly to engine beds.
“You have vibration pouring out through the ship’s structure. It makes panels vibrate and makes pipes vibrate, and creates noise and long-term wear on the vessel,” said Matt Coombs with Christie & Grey, Kent, England, a manufacturer of rubber and spring mountings for the isolation of onboard equipment. The company has a U.S. facility in Fairhaven, Mass.
Coombs has a good understanding of the damage caused by structural noise. After 27 years in the U.S. Coast Guard he has fingers that tingle because of the vibration and he has lost about 80% to 90% of his hearing because of high frequency noise.
Christie & Grey’s isolation mounts are designed to reduce engine and generator noise and vibration in the marine environment. “It’s a spring and rubber isolator. We are the only ones in the world to have perfected it in the marine market,” said Coombs. The mounts feature spring and rubber components that are isolated from the surrounding casting, so vibration isn’t transmitted through the mount to the boat.
Because a boat rolls, Coombs said that springs, while they allow the isolator to have an extremely high load-carrying capacity, aren’t sufficient by themselves. They are good up and down, but “not sideways. They tend to wander.”
The rubber element, which Coombs describes as an engineered product working on a “compression in sheer” principle, keeps the isolator properly aligned. As the weight comes down on the mount, instead of bulging, the rubber moves sideways along the length of its grain.
How effective can Christie & Grey isolation mounts be? Coombs said that an engine on an inland pushboat that had been bolted down to its beds was put on Christie & Grey mounts and the noise level dropped from 126 dB to 82 dB. Hearing damage begins to occur at 90 dB to 95 dB. — M. Crowley
