For thousands of years, boaters relied on wind to get around. Fortunately, steam and later diesel power freed us from this dependency upon fickle air currents. Or did it? A pair of 1,000-horsepower engines draws 4,000 cubic feet of air per minute through their cylinders, necessary both to burn fuel and dissipate engine heat. Without a clean, cool breeze coming in through the hullsides, performance and fuel economy suffer, and, over the long term, choked engines develop issues that could leave today's yachts as immobile as becalmed sailors of yore.
Problems arise when inadequate vents restrict air flowing into the engineroom. In extreme examples, engines starving for air won't create enough horsepower to reach their full-throttle rpm, overworking the engines. "If engineroom depression is high enough that you're not turning rated rpm then you're increasing turbo temperature, which will drastically reduce turbo life," says Dale Boggus, applications manager for Cummins Power South (www.powersouth.cummins.com). Conditions that prevent engines from reaching maximum rated rpm require immediate attention, but some problems aren't as obvious. Newer, electronically governed engines protect themselves by limiting fuel and rpm. But older, mechanically governed engines running without enough air can be damaged just as quickly as when turning oversized propellers.
In many boats, there is enough air for engines to burn their fuel, but not enough to cool the engineroom. Since warm air doesn't hold as much oxygen, engines end up with less power-and less efficiency. "The air gets heat-soaked before it reaches the engines, so you lose performance from air temperature long before losing it from engineroom depression," says Ryan Kamphuis, a marine applications engineer with MTU (www.mtu-online.com). Ideal intake air is 77 degrees Fahrenheit, but Kamphuis says raising it to 113 degrees causes an electronically governed MTU 16V2000 to make roughly 96 percent of its horsepower, and burn two percent more fuel to reach it. That's six percent less bang for your fuel buck. Even more sophisticated engines are susceptible to inadequate air flow-the common rail version of that same MTU engine retains its horsepower, but burns 3 percent more fuel with the same 113-degree air, literally sucking money out of your wallet.
Engineroom heat doesn't just affect engines, it also damages generators, cooling, and electrical systems. But solutions are simple. "If you're not getting enough air in, you won't get enough out, and temperatures are going higher," says Michael Murray, owner of Livos Technologies (www.livostech.com). His company, named for the Greek god of the favorable southwest wind, first looks for places to draw in more air-typically cockpit bulkheads, cabin sides, or even flying bridges. But more often than not, Murray relies on high-capacity axial fans, typically four per boat. "Two intake fans insert both combustion air and cooling air, while smaller exhaust fans pull out cooling air only," Murray says. "We control intake fans automatically, by sensing engineroom depression, and we control exhaust fans by temperature. As the engineroom heats up, the exhaust fans ramp up, and the resulting depression ramps up the intake fans."
In many cases engineroom heat is most pronounced when engines slow to idle speed, still hot from running but not drawing as much air through the engines. To reduce noise in those situations, Livos installs variable-speed AC- or DC-powered fans. "At half the flow, the fans make one-fifth the noise," Murray says.
Sea air is also rough on diesels. Salty mist becomes steam in the 300- to 400-degree air inside turbochargers, instantly vaporizing water and crystallizing salt, depositing minerals on turbo blades and clogging intake air coolers. The resulting salt grit acts like sandpaper on the inside piston liners and valves, and moisture rusts iron parts inside cylinders. If engines actually ingest seawater, not just mist, things go downhill quickly. "When that water hits a hot turbocharger, I've seen turbos get shredded," Boggus says. "It looks like someone took a paring knife to the turbo blades."
Livos and competitor Delta T Systems(www.deltatsystems.com) market mist eliminators designed to extract mist and seawater from intake air. "The cross-sectional profile is an "S" shape. The air can make those turns but water particles are heavier so they splatter against the sides, and hooks collect that water film," says Michael Gabriel, marketing manager for Delta T. "It's 97 percent effective, with no moving parts. If you're getting water in your engineroom you'll see the results right away."
In most cases, Livos or Delta T can retrofit mist eliminators and blower systems within an engineroom, avoiding hullside alterations. Often simply changing older salt eliminators that use synthetic media (similar to air conditioning filters) will significantly improve air flow and decrease moisture.
Many boats were built without adequate engineroom ventilation, passing initial sea trials by drawing air from the salon-and also pulling exhaust soot into the salon. Telltale black stains in the carpet and upholstery near the salon door or around engineroom hatches show your engines are getting air from the wrong place. Better engineroom ventilation will keep soot out, but enginerooms shouldn't be pressurized, which forces engine odors into the cabin. This is why automated blowers are favored by both Livos and Delta T. "It's a set-it-and-forget-it system," says Gabriel. "The ventilation system takes care of itself so the engineroom is always at optimum conditions."
Delta T and Livos include automatic dampers to close all air intakes in a fire, another reason to upgrade older ventilation systems. Considering the long-term consequences, there's no reason to let an engine gasp for air and take the wind out of your sails.