I took a sampling of sound readings measured at the helm during our Certified Boat Tests, averaging the numbers from 25' to 30' center consoles, 20' to 24' runabouts, 30' cruisers, and 40' to 50' motoryachts. At 3500 rpm, the low end of the cruising range, an average for center consoles is 87 dB-A. Throttle to 4500 rpm and the average jumps to 90. On a runabout, the average at cruising rpm is 88; for a cruiser, it's 85. A motoryacht with an enclosed helm sees a more comfortable cruising dB-A of 73.
So how does this affect you as you zip around for the day, take an extended cruise, or fish for a few hours? You can lose your concentration while navigating, entering an inlet, dealing with traffic, or doing a complex task such as docking. That loss of focus may cause something minor such as scuffing your rubrail at the fuel dock or something major such as missing a marker and running aground.
What can you do about noise? Create a system to prevent or reduce fatigue while onboard. If you're going to cruise for any length of time, take turns behind the helm. Common practice for standing watch on commercial and military vessels calls for four-hour shifts. But this system is intended for people with a lot of time at sea. You're better off limiting time at the helm to two to three hours at a crack. If no one else aboard can handle the boat, include breaks in your cruise plan. Earplugs can help, from 50-cent foam plugs to more expensive custom-molded ones, but they aren't a cure-all. The best can cut noise by 30 dB-A while allowing you to hear your crew, radio transmissions, and warning alarms. Whatever you do, try to keep it quiet-and don't space out in the inlet.