[TG] [TG11] New Raymarine user - E165 Chirp

[Tom - Raymarine - Moderator]

Hello Mick,

The CP450C is a good sounder, but needs to be well set-up in order to get the most from it. One key advantage of our current CP470 over the CP450C is that it's essentially a hands-free operation: it can produce as good results in Auto as the CP450C can with an experienced operator at the helm.

The CP450C was designed to be used in Chirp mode, the non-Chirp 50/200kHz channels were really only there to help new users transition across. Chirp channels will produce much finer targets than non-Chirp at the same frequency range (High Chirp compared to 200kHz for example), but this is by design and is a consequence of the much higher resolution you get from Chirp signal processing. This is how a Chirp sounder can separate the individual fish in a school, where a non-Chirp sounder will just show a blobby mass.

Users coming from non-Chirp to Chirp tend to still use high frequencies in shallower water, but because of the much higher resolution of a Chirp sounder in fact that's generally not required. Most of the transducers that were available when CP450C was shipping had a very narrow beam at High/200kHz frequency, which means that they're good for imaging the finer details of structure but don't see many fish in the water column (spotlight instead of floodlight.) If you're looking in the mid-to-upper water layers then I'd recommend using Medium or Low Chirp instead of High, even in shallow water (as shallow as 10m) because these have a much wider beam and will show you more fish.

As far as manual setup goes, my recommendation is to:

1. use A-scope, Mode 2 (Right, on current systems) to measure the effects of your changes. Look at the signal levels down near the bottom, not at the surface.
2. start with Gain very high (e.g. 100%), Colour Gain very low (e.g. 15%) and TVG very low (software version dependent, see the attached document)
3. Looking at the A-scope, go through a cycle of Gain-down until most of the clutter is removed, then Colour Gain up until the strongest returns are just showing in red, then repeat until you have just a little clutter left down near the bottom.
4. Finally, use TVG (if required) to fade out excessive near-surface clutter. From the low starting point, make the smallest change to TVG that you can because large TVG changes can suppress wanted targets in the water column.
   

I would suggest not aiming for just blue-water, red targets. This is a high performance sounder with a wide dynamic range, and the full spread of colours gives very useful information about target signal strength or returns that are on the fringes of the conical sounder beam.
Finally, I recommend not using the Classic White colour palette. It makes even a small amount of clutter very obvious and obtrusive. My recommendation for use in bright sunlight is the Sunburst colour palette, where clutter is pale yellow and hardly shows up against the white background but strong returns are dark red and stand out with high contrast. See the attached image for an example of why not to use Classic White: the two images use the same Gain, but the white one shows really annoying levels of clutter which would cause you to reduce Gain and lose wanted targets.

Regards,
Tom