Raymarine ST800 Through-Hull Speed and Temperature Transducer, Low-Profile, Retractable

Overview

The Raymarine ST800 is a through-hull speed and water temperature transducer for boats that need analog speed and temperature data without adding a larger sonar transducer. It uses a retractable insert in a low-profile through-hull housing, with only 5 mm or 3/16 in extending outside the hull to help keep drag low.

This transducer is used when a vessel has an in-hull transducer setup but still needs paddlewheel speed and water temperature sent into the Raymarine system. It has a 9 m or 30 ft analog cable, works over a 2 to 45 knot speed range, and uses a 51 mm or 2 in hole size for installation.

The ST800 range is offered with plastic or bronze housing options, so the hull material and installation environment can be matched before cutting the hull. The insert is retractable, and the housing includes a water valve that helps reduce water entry into the bilge when the paddlewheel insert is removed for routine cleaning.

Key features

• Measures boat speed through the water and water temperature from a single through-hull sensor.
• Analog output for compatible Raymarine speed, temperature, and fishfinder installations.
• Retractable insert allows paddlewheel service without removing the through-hull housing.
• Low-profile housing extends only 5 mm or 3/16 in outside the hull to help reduce drag.
• Speed range of 2 to 45 knots supports common cruising, sailing, and fishing use.
• 9 m or 30 ft analog cable gives practical routing length for many helm and electronics layouts.
• 51 mm or 2 in hole size supports installation in compatible through-hull locations.
• Suitable for 0 to 8 degree deadrise angles when installed in the proper hull location.
• Included Y-cable is for CP300 and CP370 installations only.

Variants

The Raymarine ST800 is available in two material configurations. Both versions are speed and temperature through-hull transducers with analog output, a retractable insert, a low-profile housing, and the same 9 m or 30 ft cable length.

The material choice changes the housing and the hull materials it is suited for. Plastic is listed for fiberglass and metal hulls, while bronze is listed for fiberglass and wood hulls.

• E66071: Material Plastic. This version uses the plastic P120-style housing and is listed for fiberglass or metal hulls, making it the lighter housing option in the range.
• E66072: Material Bronze. This version uses the bronze B120-style housing and is listed for fiberglass or wood hulls, making it a common fit where a bronze through-hull is preferred.

Installation and setup

The ST800 should be installed where clean water flow passes the paddlewheel while the boat is underway. On sailboats and planing hulls, placement matters because turbulence, air bubbles, or heavy aeration can affect speed readings.

The retractable insert is useful for boats that operate in weed, silt, or fouling-prone water, since the paddlewheel can be removed for cleaning while the housing remains in place. The water valve helps reduce bilge water entry during that maintenance step, but normal care is still required whenever any through-hull insert is opened.

Compatibility and fit

This is an analog speed and temperature transducer, not an NMEA 2000 sensor by itself. It should be matched to compatible Raymarine displays, sonar modules, or instrument systems that accept this type of analog speed and temperature input.

The plastic and bronze versions have different hull-material listings, so the housing material should be checked against the boat before purchase. For cored hulls, steep deadrise, tight bilge areas, or metal hull installations, the final location and sealing method should be planned carefully before drilling.

Use cases on board

The ST800 is a practical fit for cruising sailboats, racing sailboats, leisure boats, and fishing boats that need through-water speed rather than relying only on GPS speed over ground. Through-water speed is especially useful for sail trim, current awareness, performance comparisons, and instrument calculations that depend on water movement past the hull.

It also suits refits where an in-hull depth or sonar transducer is already in use and the boat still needs a separate source for speed and water temperature data.

Maintenance and care

Paddlewheel sensors should be kept clean so marine growth, paint buildup, or debris does not slow the wheel or stop it from turning. During haul-out or regular service, inspect the wheel, pin, and housing area, and avoid antifouling coatings that are not approved for transducer faces or moving parts.