Mercury - Speedometer 45 MPH Boat Speed Monitoring White Face Chrome Bezel 79-8M6020015. OverviewThis 45-MPH speedometer gives you a clear, steady look at your pace without jumping around when the boat shifts. The needle moves with a slow, predictable sweep, so it's easy to read with just a quick glance. Out on the water, the number you see usually matches the feel of the hull, which makes cruising or trimming out a little more comfortable. It's a clean, simple gauge that fits right in on any da