Enhance your boating adventures with a speed and temperature sensor that delivers pinpoint accuracy right from your boat's transom. Designed specifically for Raymarine ST40 instruments, this plastic transom mount unit combines speed-through-water measurement with water temperature readings, giving you the data you need for smarter navigation and peak performance on the water.

Precision Speed and Temperature Detection

At the heart of this sensor is a responsive paddlewheel mechanism that spins freely as your boat cuts through the water, translating motion into reliable speed data. Paired with a sensitive thermistor, it captures real-time water temperatures to help you monitor conditions for fishing hotspots or engine cooling efficiency. Unlike bulkier alternatives, its compact plastic housing slips easily onto most hulls without adding unnecessary drag or weight.

• Speed range: Handles everything from idle drifts to high-speed runs with consistent accuracy.
• Temperature sensing: Quick-response probe for immediate environmental updates.
• Durable construction: Impact-resistant plastic withstands constant submersion and trailering stresses.
• Low-profile design: Minimizes turbulence for smoother data and less hull interference.

Seamless Integration with Your ST40 Setup

Boat owners rave about how effortlessly this sensor syncs with ST40 displays and multifunction setups. It plugs into your existing NMEA 0183 network, feeding clean, calibrated signals without the need for extra converters or fuss. Whether you're upgrading from an older paddlewheel or starting fresh, it ensures your instrument panel shows speed in knots or MPH—your choice—for intuitive at-a-glance monitoring during races, cruises, or fishing trips.

Think of it as the reliable co-pilot that logs your vessel's performance over long hauls, helping you optimize fuel use or spot currents that could affect your course.

Installation Made Straightforward for DIY Enthusiasts

Setting it up doesn't require a marine yard—most skippers handle it in under an hour. Clean the transom area, drill precise mounting holes, bed it in with marine sealant, and route the cable through existing conduits to keep things tidy. Pro tip: Align the paddlewheel dead-level with the waterline for the most accurate low-speed readings, and always flush it post-saltwater use to prevent growth buildup.

1. Select a spot 1-2 feet off the keel line, away from strakes or prop wash.
2. Secure with stainless hardware for rock-solid hold.
3. Calibrate via your ST40 menu for hull-specific speed offsets.
4. Test in shallow water before heading offshore.

Built to Thrive in Real-World Marine Demands

Marine environments are unforgiving—salt, sand, and constant vibration test every component. This sensor's robust plastic body shrugs off UV exposure and corrosion, while the paddlewheel's self-cleaning design reduces fouling from algae or barnacles. Seasoned anglers and racers appreciate how it maintains calibration season after season, delivering trustworthy data when precision matters most, like trimming sails or timing lure deployments.

Compared to thru-hull options, the transom mount shines for trailered boats, as it's quick to inspect and service without hauling the vessel.

Maintenance Secrets for Peak Performance

Keep it running like new with simple habits: After every outing, remove and rinse the paddlewheel under fresh water, then spin it by hand to clear debris. Inspect the O-rings annually and lubricate with marine grease. If readings falter, a quick re-calibration or wheel swap often solves it—no shop visit needed. These steps extend its life, saving you headaches on your next voyage.

Frequently Asked Questions