Nasa EML-2 Electromagnetic NMEA Speed Log

The EML-2 Nasa electromagnetic log measures the boat speed through the water with no moving parts. Robust and accurate, the sensor generates an alternative magnetic field below the boat and measures the resulting electric field which is produced by the boat as it moves through the water. 

The field is detected by small electrodes made of stainless steel on the underside of the sensor. Excellent linearity and a resolution of 0.1 Knot, over the range 0.2 to 40 Knots the interface box supplied with the system will amplify the signal and will convert it into speed trip and total distance reading and send it to any compatible NMEA-0183 display. The LED located on the interface box will flash each time NMEA data is sent out. 

The EML-2 system consists of a through-hull sensor, an interface box and optional clipper or target display units.

Technical Specifications

• NMEA 0183 output sentences VLW + VHW

• Supply voltage 12V

• Supply Current 8mA

• Speed Range 0.2 - 40 knots

• Transducer cable length of 5.0 metres

EML-2 Electromagnetic Sensor Installation Instructions:

Before installing the sensor please make sure you always wear safety glasses and a dust mask to avoid injury. 

Once a suitable location is found when the boat is out of the water, drill a 3mm pilot hole from inside the hull. Using a 51mm (2.0 inch) hole saw, cut a hole perpendicular to ht hull from the outside the boat. 

Please note:

The sensor must be mounted in such a way so that it remains in non-turbulent water flow at all times. This must be positioned as close as possible to the centre line where the water flow is unrestricted and can be easily accessible for cleaning. 

Is vital to avoid areas around devices which could create electrical or magnetic interference. 

Make a small chamfer around the hole. Just enough to fit the 2mm skin fitting flange. Sand and clean the hole in and outside so that the sealant will properly bond to the hull.

Using a well proper marine silicone sealant (CT-1 Sealants will be perfect for this bonding job) apply about 2mm of sealant around the skin fitting flange where it contacts the hull and also up the sidewall to a distance of 3mm higher than the combined thickness of the hull and to hold the nut securely in place. 

From outside the hull gently push the house into the mounting hole slowly with a twisting movement so that the excess of sealant is being pushed out. 

From inside the hull apply a 2mm thick layer of sealant around the hole which is equal to the diameter of the rubber washer. Place the rubber washer over the skin fitting and bend down onto the sealant. Apply more sealant to the upper face of the rubber washer so that you create an even coat and tighten down the nut - make sure you do not overtighten it.

When this is done please remove all surplus sealant from the inside and outside of the hull and leave until the sealant has cured. It is recommended that the area around the skin fitting is cleaned and the whole assembly is fibre glassed into the hull. Ensure that 20mm of the top thread remains free of resin or sealant.

For information about installing the interface box and the display unit refer to the installation manual available for download on the downloads tab on this page.