Tech Hub

Please read our paper on Maintenance of Shut off Valves and Sensors

Please read our paper on Maintenance of Shut off Valves and Sensors

This can be caused by water ingress on the speed sensor or its connecting cable. Try temporarily disconnecting it from the processor to see if the alarm stops. If it does then the offending sensor/cable is determined and can be replaced.

The most likely cause is a damaged cable or faulty transducer. Replace with a known working one to check this. Also check for being painted over or marine growth on the transducer.

Firstly ascertain if there is a single paddle wheel or two selected with a gravity change-over switch. a)   Single paddle wheel. Remove from the hull housing and spin manually to check the sensor both electronically and mechanically. Measure the voltage with the black probe of a multimeter on the black wire and the red probe on the red. If this is not between 5 and 12 Volts (system dependant), the control unit is faulty. Now put the red probe on the green wire and turn the paddle very slowly. As the magnet passes the sensor the voltage reading should change from 5 Volts (+/- 1.5V) to 0 Volts (+/- 1.5V) and back again. If not, the paddle sensor is faulty. b)   Dual paddle wheel. In our experience a good proportion of twin paddle wheel issues are caused by faulty switches. These can be checked by manual selection or direct wiring until the issue is found. We can supply replacement gravity change-over switches which can be found here. In either case, the wiring and instrument system can be checked  (with the sensor disconnected) by tapping quickly the green wire to the black wire. This simulates the paddle wheel turning and so should show as speed on the instrument system. If it does not then the wiring or instrument system is faulty.

MHU Tests

First determine if the apparent wind angle is working properly. Check this ties up with the Windex at a good variety of relative headings to the wind and all around the clock. If there is one wire broken in the mast cable then the wind angle changes, but does not follow all around the clock, but ‘doubles back’ as the relative heading changes. This can also be caused by faulty wind sensor or wind board (in the processor). If the apparent wind angle is working properly then the culprits must be either the compass or speed log. Check these are working properly.

Calibration, calibration, calibration. It is not that difficult if you follow the procedures set out in the system manuals. Even getting some rough estimates or corrections in the True Wind Angle table will start to improve this quickly. Don’t be afraid to put in corrections up to 10 degrees into these tables in some circumstances. We are often at regattas and will help with this if time allows.

Apart from large yachts that take the compass heading from a north seeking gyro, most systems use a magnetic sensor for heading including (confusingly) the B&G Halcyon Gyro Stabilised Compass. Before looking anywhere else, locate the compass mounting and ensure that no magnetic or magnetically susceptible material has been placed close to it (typically tins of beans, spanners, tools, spare parts, hand bearing compass).

Having checked this, ensure that the calibration ‘turns’ have been done recently in the yachts current broad geographical location. The methods for doing this are different in different systems, see individual handbooks for this, also available here.

Finally set in the heading offset needed to get the electronic compass to agree with a recently swung traditional compass or hand-bearer or by taking bearing to a distance point.