Stowe Type Log

This is an update on my "walker" type log. http://www.thingiverse.com/thing:740651.
I was fortunate to be able to borrow a Stowe trailing log and so this is a more accurate copy. The main difference is that the fins are now straight. The curved fins on the previous version may have made the calibration speed dependent. A real Stowe log is (I think) 8600 turns per nautical mile, and has only one magnet.
This version has two to make it nearer the Raymarine / Airmar number of pulses per nautical