Talking gensets

33771 16

A reliable supply of commercial-line quality AC power has become a necessity of onboard life for many power voyagers. Fortunately, recent improvements in genset design are making it easier to meet this need. Computer-controlled engines are replacing the traditional mechanical speed control governors, ensuring accurate frequency control. Quiet and fuel-efficient common rail diesels are gaining popularity in higher-powered units. Engine speed control and alternator excitation supplied by microprocessors ensure precise maintenance of AC frequency and voltage and improve the genset’s ability to deal with load surges that accompany the starting of induction motors in air conditioning compressors.

The benefits of applying computer technology to genset design is also evident in the new, and substantially improved, supervisory monitoring and control systems such as Westerbeke’s D-NET. Operating with either Westerbeke’s proprietary Westerlink databus system and displays, or using the NMEA 2000 databus and compatible Westerbeke, or other comprehensive display modules, the system provides the boat owner with an enhanced level of assurance of genset operation and the ability to efficiently analyze and correct problems.

Today’s typical power cruiser is equipped with both a low voltage (usually 12 volt) DC electrical system and an onboard source of AC electrical power. The AC power may be supplied from the boat’s battery bank via a DC/AC inverter or an engine-driven AC power alternator (a genset). The choice of inverter or genset is usually determined by the magnitude of the peak AC power load and the length of time the AC loads must be powered; inverters can supply in excess of 7 kW of AC power. However, the cost and size of the battery bank necessary to provide this much power for more than a relatively short time will usually lead to the installation of a genset. Boats equipped with electric galleys and air conditioners larger than about 5,000 BTU will almost invariably carry a genset.

Matching needs

A successful genset installation requires matching power output to the vessel’s AC loads, selecting a model whose voltage and frequency stability will closely match the power supplied by a high-quality shore power connection and ensuring a proper installation. Most often the unit selected will burn the same fuel as the boat’s main engine, although some gasoline-propelled boat owners have elected to install diesel sets to gain the advantage of low to no carbon monoxide emissions. (All of the major genset manufacturers now offer gasoline-fueled gensets equipped with computer controlled engines and catalytic converters to produce exhaust that is virtually free of CO).

The next and critical step is to select the size or power rating of the genset. It may seem desirable to install a unit whose maximum power output is equal to the total rating of the shore power system, for example a 12 kW genset for a boat equipped with a 240V, 50-amp shore power system. However, unless you operate your boat in the tropics and run all of the air conditioning equipment continuously, a 12 kW genset will be seriously under-loaded much of the time. Genset engines perform best when powering loads equal to at least 25 percent of maximum capacity; long-term operation at very low load levels is fuel inefficient and can decrease engine life. Many boat owners install inverters to provide the AC power required to operate appliances such as microwave ovens for short periods of time, eliminating the need to run the genset at a minimal load for five to 10 minutes.

Proper installation of the genset is critical to its ability to provide the sought-after AC power equilibrium. Gensets, like children in Victorian homes, are most welcome when they are neither seen nor heard. For this reason they are usually installed in the engine room (which in all but a large vessel may be a cramped place, offering only limited access to the genset). All gensets require a flow of air sufficient for the combustion needs of the driving engine and to remove radiated heat from the engine and alternator. The manufacturer’s installation instructions will provide a guide to the minimum required air-flow.

Most gensets are housed in a sound shield, which is also a visibility shield. Once installed, the genset can become a prime example of out of sight, out of mind. Although today’s genset engines are very reliable, things can still go wrong, including faults such as a water or oil leak not bad enough to cause a shut-down, but if left unchecked can lead to a significant mess and possibly significant damage.

Monitoring inside the sound shield

Lack of easy access causes the captains (who are used to regularly inspecting their propulsion engines when underway) more than a little stress when they consider that their genset will accumulate more operating hours per year than the main engines. Short of installing a group of color video cameras within the genset’s sound shield (not a bad idea), the best assurance that all is well is furnished by the genset’s monitoring system. Most genset monitoring systems will create alarm signals for high coolant temperature, low oil pressure, low AC voltage and excessive alternator temperature. Some may also alarm if the level of the lubricating oil becomes too low. In some installations the alarms may be limited to illumination of annunciator lights and perhaps a sound alert. Other installations may include a comprehensive control/status indicator panel. In most installations there is only one monitor panel, located at a lower helm station and connected to the genset with a multi-conductor cable.

The genset’s fuel should be supplied from dedicated fuel lines and water separator/filters, not teed off the supply to the propulsion engine. Remember that in many installations, the genset will accumulate more operating time than the main engines. The worth of locating the fuel filter where it can be serviced easily will be particularly appreciated when the filter element has to be replaced when the engine room is at its hottest.

When underway, many boats will have the genset in operation while the boat is being operated from the flybridge. A genset fault announced at the lower station may go unnoticed. Fortunately, the use of digital bus communication technology can alleviate this problem by making it easy to monitor virtually every system on a boat using either dedicated system-specific or general purpose programmable display and alarm annunciator modules. An excellent example of databus use can be seen in the new Westerbeke electronic diesel gensets equipped with D-NET.

Available in two digital communication protocols: Westerlink (Westerbeke’s proprietary system) or NMEA 2000, the latest marine electronics industry standard for digital communications, either system makes it easy to provide a boat with multiple monitor stations. The Westerlink module provides LED annunciators that will indicate deviation from normal for oil and coolant temperature, exhaust temperature, battery voltage, generator AC voltage and AC frequency. The LCD panel provides direct readings for engine speed, oil pressure, coolant temperature, battery voltage, generator AC voltage and engine operating hours.

NMEA 2000 monitoring

Electing to use the NMEA 2000 version of the Westerbeke display operating on the NMEA 2000 network will provide the same comprehensive range of monitored functions and allow genset monitoring on other, multiple displays including the Maretron DSM200 Multi-function Graphic Display. Maretron’s PC interface package can be used to display a wide range of information from a NMEA 2000 bus on computers running the Windows operating system. Many of the latest multi-function chartplotters are capable of displaying data transmitted on a NMEA2000 bus, and with the use of appropriate software, will be able to monitor genset operation. The convenience of being able to instantly view the operating condition of propulsion engines and the genset on the same screen being used for navigation can have immense value.

The NMEA 2000 digital bus system can be much easier to install in an existing boat than the bulky, multi-wire cables required when connecting a traditional and usually much less comprehensive genset monitor. The bus cable contains only four wires, is flexible and small in diameter. It does require the use of NMEA-approved connectors which may be more costly than the ordinary connectors or direct splices often used when installing NMEA 0183 or analog wiring, however, they offer the very real advantage of reliability in the marine environment and will maintain the data throughout capacity of the bus system.

By Ocean Navigator