Summary

A walker log replica/replacement. designed to give approximately 20,000 pulses per nautical mile.
Must be calibrated by user before any navigational use!

Instructions

Model needs 3mm dia by 2mm long Nd magnets fitted in each of the three holes, to give 3 pulses per revolution. I fitted two in each each hole, held with epoxy.
The Hall effect sensor is fitted in the head, the sensor is a A3144 Hall Effect Sensor. depending on your example, you may need to elarge the hole in the head to fit the rectangular transistor correctly. Be careful when fitting as it only detects one magnetic polarity. Make sure all the magnets are the same way around and that the sensor correctly detects them all.

A thermistor (10k) can also be fitted if required, to sense temperature.

Your wiring may be different, but Raymarine log wiring can be found on the Airmar sensor website. The head has a hole with room to fit 6 core telephone cable, which seems to work nicely. My Autohelm St50 uses 5 cores.

The fins are held to the head by a 50 mm long Stainless Steel M8 cheese head screw with a washer to help smooth running,but anything similar should do provided i does not affect the magnetics. You should tap the head with the correct thread before fitting the screw or fitting the wiring. The main purpose of the screw is to weigh the log down in the water.

I epoxied the transistor in place after making sure it was the right way around, and then painted the whole lot black. A drop of epoxy was used to lock the crew in the head.

I made a number of early versions with different twists on the fins. This one is supposed to have the closest to 20,000 pulses per nautical mile. However this has only been tested by walking a few meters on a slipway, so it may well vary in actual use. 20,000 pulses per NM was selected to be close to the standard Raymarine/Autohelm sensor output. I will try to get some calibration data and update this thing data later.

One last bit of advice: Apparently it is best to print or paint in black to avoid the log being mistaken by fish for a lure or food!

Walker Type Nautical Log