An acquaintance of mine recently bought a new-to-him boat. He was out in it for the first time when he discovered he couldn’t get it out of gear, so he called me to ask what the problem might be. It would make a better story to say I knew what it was right away, but it took me a while to figure this one out. Then, once I had, I wondered why I hadn’t thought of it sooner.
Clearly, his shift-interrupt switch had stopped working, which is why it was stuck in gear. Nearly all marine engine and drive packages that use “dog clutch” gears also use a shift-interrupt switch. That includes MerCruiser’s Alpha One drives, Yamaha outboards, and old OMC Cobra drives, among others.
A shift-interrupt switch system aids in shifting the drive into and out of gear. It’s mounted in different places depending on the manufacturer, but the interrupter is usually a microswitch attached to a floating mount, which senses a load on the cable housing when the drive is being shifted into and out of gear. The switch momentarily interrupts the ignition power, which allows the gears to mesh easier at lower speed. In the case of shifting out of gear, the load is relaxed on the meshed gears, enabling them to disengage. Listen closely, and you can actually hear the engine cut out for just a millisecond.
If you find yourself in the same boat (pun intended) don’t call a lemon law attorney. Call a mechanic. You’ll be back on the water in no time at all.