As a young deckhand, I can remember doing engine-room inspections to make sure everything down below was in good working order as we steamed to or from the grounds. Back then, most engine-room entrances were located in the salon floor between the engines, and you lifted a hatch to drop down into the space. I distinctly remember the suction imparted on those hatches while we were running; it made it very difficult to lift the hatch. Once we were back at the dock, the same hatch lifted out easily.
The reason it was hard to remove the hatch while under way was because of the negative pressure in the engine room due to undersize air-intake vents on the side of the boat. Back in the mid-1970s, the power increases in diesel engines made huge jumps, requiring larger turbos and more of them, with some engines carrying twin turbo packages. Companies like Johnson & Towers in New Jersey worked diligently to marinize the popular Detroit Diesel 71 series and then the 92 series of engines, addressing the saltwater impact on the fuel and air systems and the raw-water cooling systems of those engines with great success. It was hard to find a sport-fishing boat back then that didn't come with JT power.
Unfortunately, it took the boatbuilders some time to move their engineering forward to handle the larger horsepower and understand the requirements needed to generate the intended horsepower. When Jack Leek introduced his first Ocean Yachts model, the 40SS, it sported a pair of 6-71 JT turbos, making it the first production boat to achieve 30 knots consistently. That speed meant a quicker trip to and from the canyons and played an integral role in expanding the recreational sport-fishing boat market.
The evolution of the sport-fishing boat has been a treat to witness over the past 30 years. The introduction of advanced composites to lighten the boats, along with the continued refinement of marine power, produced a substantial increase in the power options available for the owner. In addition to these core advancements, the refinement, simplification and improvement in engine-room layout, as well as the physical support systems such as fuel transfers, air-conditioning systems, electrical systems, and engine-room and machinery space ventilation, has helped keep the equipment clean and in better working order. This translates to an increased engine life and a reduction in the required maintenance.
Most sport-fishing boats use one of two setups to ventilate the engine room. Back in the day, all boats used natural draft ventilation for both combustion air and cooling, meaning that the engines took in air from the outside air vents and used it to run and cool the engine at the same time. This system didn't cool the engine fast enough and really wasn't as good for the equipment.
Today, almost 99 percent of all boats use a combination of natural draft and fans to cool and ventilate the engine space. To keep up with the significant demands of higher-horsepower engines, boatbuilders made their hull-side vents larger to allow for more natural draft and installed fans to cool and exchange the air in the engine space at slower speeds. Typically, a thermostat controls these electric exhaust fans and regulates the engine-room temperature.
On larger vessels, the machinery spaces can be ventilated to control both the air pressure and temperature. The trick lies in engineering an intake that provides enough air for combustion and an exhaust system that doesn't create negative pressure at speed or positive pressure at idle. This requires controlling the air relative to the intake/exhaust needs while in use. Negative pressure stresses the engines, while positive pressure forces fumes into the vessel.
Two companies specialize in machinery space ventilation, especially for sport fishing: Livos Technologies and Delta "T" Systems. Both provide excellent solutions for proper engine-room ventilation. Livos president Michael Murray says, "The key to design is airspeed - salon carpet makes an excellent filter." We've all seen the soot that accumulates over time on the carpet or the soft goods in the salon, and Murray attributes this to the speed of the air coming through the hull-side vents. Too much air coming in can push engine-room soot up through the salon floor. But smaller vents create greater velocity and more noise as the engine works harder to draw air for its combustion.