Autopilots also assist anglers looking to find new bottom structure. For simplicity's sake, you can set up a basic grid with the patterns already programmed into your unit. But if you want to get fancy, and you're not afraid of a little trigonometry, your search pattern can become as precise as a Coast Guard rescue scenario.
Furuno's Kunz explains it this way: "If the boater knows his transducer beam widths for both high and low frequencies [information should be available through the transducer manufacturer], he can calculate the rough footprint for each frequency [at a given depth - the footprint enlarges as the water deepens] to allow him to cover a given area."
Use this trigonometric function to determine that footprint:
?Take the tangent of the beam-width angle divided by two. (Hint: The easiest way to find the tangent is to use a scientific calculator that offers that function.)
?Multiply that figure by two times the water depth. That will give you the footprint diameter.
For instance: A 200 kHz transducer with a 10-degree beam width in 100 feet of water provides a 171/2-foot footprint. That's the tangent of 5 times 200. (For a quick shortcut, go to this utility on Furuno's website. Enter your beam angle and water depth and it will calculate the coverage for you. Also note: Raymarine depth finders automatically provide a readout of this footprint in A-scope mode.)
"I would then create a grid route [in the plotter] with parallel legs that extend over and slightly past the area of interest," Kunz says. "Once this gridded route is created, press the NAV key on the Navpilot to follow the route and perform the search automatically. Then simply watch the sounder and push the 'save' button to store the interesting locations."
This highly adaptable autopilot tech- nology comes at a price usually in the $2,000 to $5,000 range. That includes a head unit, computer, drive unit for hydraulic steering and flux-gate compass.
"It's kind of like having a plotter/navigator in your car," says Chemi. "Before you ever tried it, you didn't know what you were missing."
Merrimack, New Hampshire