ST800-P120 Speed/Temperature Sensor

This sensor is a dual-function model. It measures both:

The boat's speed through the water (surface speed) using a paddlewheel.
The water temperature.

No, this sensor is not directly compatible with modern instruments operating on an NMEA 2000 or SeaTalkNG network such as i70s displays or Axiom chartplotters. It is designed for older Raymarine instrument generations.

Yes, this sensor is a through-hull (transducer) type. The boat must be hauled out of the water to drill the hull and install it safely.

The ST800-P120 sensor housing is made of plastic. This makes it suitable for installation on fiberglass or metal hulls.

This sensor is specifically designed to be compatible with older generations of Raymarine instruments, including the ST series such as the ST40, ST50, ST60, ST60+, and ST290 displays.

The sensor is supplied with a 13.8-metre cable attached, providing sufficient flexibility for connection to your onboard instruments.

Installation of the P120 through-hull requires drilling a 51 mm (2 inch) hole in the hull. It is critical to respect this diameter to ensure a correct and watertight installation.

Yes, absolutely. The plastic body of this sensor is ideal for metal hulls (aluminum or steel) as it prevents any risk of galvanic corrosion that could occur with a bronze sensor.

The sensor uses a small paddlewheel that spins as the boat moves through the water. The rotation speed of the wheel is converted into speed data and sent to the display.

Yes, the sensor’s design allows you to remove the insert (the part with the impeller) from its through-hull fitting while the boat is in the water. The through-hull fitting is equipped with a self-sealing valve that limits water ingress, allowing you to clean the impeller or replace the insert with a blanking plug.

This product is classified as "obsolete" because it is designed for older navigation systems and does not use modern communication protocols (such as NMEA 2000 / SeaTalkNG). It primarily serves as a spare part to maintain existing installations.

Yes, electronically it is compatible and can replace a bronze model. However, the through-hull fitting is different. If you are replacing an existing bronze sensor, you will also need to replace the bronze through-hull fitting with the plastic one provided. Ensure the drilling diameter is compatible.

Yes, orientation is crucial. The sensor has an arrow that must point toward the front of the boat (the bow). Incorrect orientation will completely distort speed measurements.

Yes, the sensor body is made of robust plastic, a material perfectly suited and resistant to the marine environment, including prolonged use in saltwater.

Yes, this sensor with its plastic through-hull fitting is perfectly suited for installation on fiberglass hulls, which is one of the most common applications.

Yes, sensors of this type are generally supplied with a blanking plug. This plug can replace the sensor insert when the boat remains in the water for extended periods of inactivity, to prevent marine organisms from colonizing the impeller.

To ensure perfect watertightness, it is essential to use a marine-grade polyurethane sealant or adhesive, such as Sikaflex-291i or an equivalent product. Apply it generously around the through-hull fitting, under the collar, and on the threads before tightening the nut.

No, this sensor is neither NMEA 2000 nor SeaTalkNG. It uses a proprietary connection designed for specific Raymarine instrument inputs in the ST series (ST40, ST60, etc.).

The reference "P120" refers to the type of through-hull fitting used. It is a low-profile model made of plastic (the letter 'P' stands for 'Plastic') designed by Airmar, the manufacturer of many sensors for Raymarine.

Yes, it can replace an old speed-only sensor. If your Raymarine ST instrument has an input for temperature, you will benefit from this new data. If it does not, the temperature function of the sensor will simply be ignored and the speed function will work normally.