Best yak depthfinder/gps with 500' depth capability?

I have a Humminbird Helix 5 DF-GPS but I cant get it to give me a depth reading beyond 200 feet.
Can anyone recommend a unit that has the power to go 500' that's a good fit for a yak?

You want a wider band of frequency...so, a lower number of kHz. All these fancy new fishfinders that feature “downscan” etc are using 455/800 kHz which sucks in saltwater and/or deep water. Look for something that operates on 50 or 83 kHz.