Thin or long power cables lose voltage, and fish finders and sonar can reboot, show noise or shut down when the voltage drops too low. Enter your system voltage, the current the device draws and the one-way length of the cable run to find the minimum wire size.
How to Measure the Run
Measure the one-way distance from the battery (or fuse block) to the device along the route the cable will actually take, not in a straight line. The calculator doubles it automatically, because current travels out on the positive wire and back on the negative.
Which Voltage Drop to Choose
A common marine wiring guideline is a maximum 3% drop for electronics and other critical loads, and up to 10% for less sensitive loads such as some lighting. Fish finders and sonar should use the 3% setting.
Important Limits
This calculator sizes wire for voltage drop only. It does not replace the fuse rating, wire type and installation instructions in your product manual. Always fit the fuse the manufacturer specifies, use marine-grade tinned copper wire, and if you are not confident with boat wiring, ask a qualified marine electrician.