Maximum Depth

Just like an audio system, the maximum range of a fish finder is primarily a function of its power output. The quality of the resulting signal depends on operating frequency and signal processing. Low frequency and a narrow cone angle are better in deep water too.

Manufacturers most likely specify max depth for freshwater conditions, especially when the fish finder description says something like “performance may be reduced in saltwater conditions”.

In deep water, split screen allows you to view full range of depth on one screen and zoom to bottom (assuming that’s where the fish are) on the on the other.

It is a juggling act to simultaneously optimize for depth and signal clarity, when buying a new unit. It really depends on water depth, and the skill of the user to optimize their fish finder device.

Instead of trying to optimize, sometimes it’s best to “think overkill” and purchase a unit you know will work for all your specific conditions.

Follow the instruction manual and experiment with settings to optimize for specific environments, whether it is deep salt water, shallow salt water, pelagic fish or bottom feeding fish.

It is unlikely that an electrically underpowered craft will require a high performing deep water fish finder, but it should be noted that deep water models consume more power than those designed for shallow water.

A fish finder with GPS and lights on could easily draw 1.3 Watts.

Usually, the greater the max depth, the more power is available, which also tends to drive up the price of the whole unit. Higher price usually means better display resolution, bigger display, and possibly better electronics.

According to Lowrance® LCX104C user manuals 80% of fishing needs can be meet by a 200 KHZ unit using a 12-degree cone angle (beam). The other 20% of usage is in saltwater from 300 – 500 feet or more, and by downrigger users who want to know where their baits are located. Presumably, because it is the Lowrance default angle, the optimal cone angle is 20 degrees on single frequency 200 KHZ units.