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Advances in motorized vehicle vibration control have increased consumer expectations to feel minimal vibration when operating vehicles in any environment; on and off road. Small outboard marine engines have a heightened need for vibration isolation, since the user often steers using a tiller arm connected to the outboard. Traditional engine mount systems allow the mount reaction loads to create a periodic torque about the steering axis and result in significant tiller arm shaking forces. This paper presents a novel mount arrangement that minimizes the shaking couple about the steering axis and isolates the tiller from engine vibration. The concept was first modeled using rigid body dynamics software to predict vibration of the tiller arm. Testing confirmed the simulation, and demonstrated a significant reduction of vibration transmitted to the tiller arm and boat seat compared with a traditional focused mount system.

Isobutanol-extended fuel was tested in two recreational marine vessels placed in Annapolis, MD and operated for fifty hours on the Chesapeake Bay and surrounding tributaries. Field emissions testing was conducted using a unique portable marine bag sampling system (MPSS) which collected a weighted five mode composite emissions sample consisting of total hydrocarbons (THC), oxides of nitrogen (NOx) and carbon monoxide (CO) while operating recreational boats on both a non-oxygenated baseline indolene certification fuel and a 16.1% isobutanol-extended gasoline. Engine and boat runability was also observed throughout the six month operational period. In addition, back-to-back sampling yielded excellent repeatability from the portable bag sampling equipment. Based on the results of this preliminary study, isobutanol-extended fuels look to be very promising for marine engine applications.

This study evaluates iso-butanol as a pathway to introduce higher levels of alternative fuels for recreational marine engine applications compared to ethanol. Butanol, a 4-carbon alcohol, has an energy density closer to gasoline than ethanol. Isobutanol at 16 vol% blend level in gasoline (iB16) exhibits energy content as well as oxygen content identical to E10. Tests with these two blends, as well as indolene as a reference fuel, were conducted on a Mercury 90 HP, 4-stroke outboard engine featuring computer controlled sequential multi-port Electronic Fuel Injection (EFI). The test matrix included full load curves as well as the 5-mode steady-state marine engine test cycle. Analysis of the full load tests suggests that equal full load performance is achieved across the engine speed band regardless of fuel at a 15-20°C increase in exhaust gas temperatures for the alcohol blends compared to indolene.