— April 2003
By Ben Ellison
Mind the Vectors
|Airmar Ultrasonic Boat Speed|
Airmar is a little shy about calling this transducer “new” because it was originally introduced several years ago. It even won a prize for innovation, but full production had to be curtailed until some RF interference issues could be resolved to comply with strict European standards. Perhaps the CS4500, now encased in protective bronze and fully certified, is better termed “newly available.” At any rate, it has no moving parts to foul, claims an accurate range from 0.1 to 40 knots, and also manages to skip over the boundary-layer effect that can mess up a conventional paddle wheel’s precision.
The unit works by sending out twin beams of acoustic energy, much like a sounder, but at a very high 4.5-MHz frequency capable of generating super fast and microscopically narrow returns from passing air bubbles, plankton, etc. The signals are first “range-gated” to include only those three to five inches away (bye-bye boundary layer), then pattern-analyzed and timed to generate a speed value every half second (see inset). The ultrasonic insert includes a temperature sensor and can be had with a choice of housings. It can also be retrofitted into most two-inch paddle wheel housings, and its “pulsed” output format will work with many existing instrument systems. It sells for about $600.
Airmar Phone: (603) 673-9570. www.airmar.com.
This article originally appeared in the March 2003 issue of Power & Motoryacht magazine.