First, I was unaware that the Emags were used in sailboats. All the references in the FAQ refer to a "tack" signal!
I didn't find any technical specs on their tach output. However, they say they can drive a normal tach, so we will probably work without any problems. You won't need to condition it, but without seeing a real waveform coming out of the mag, we would suggest you start with the 39Kohm resistor in line (provided with the EMS) and remove it only if that doesn't work.