Monday 4 February 2013

Fishfinders - understanding how they work

Last weekend I had a very nice couple from the East Coast buy a Furuno colour sounder from me. As I ran them through the features and options it became clear to me that even experienced fisherpeople, as these two were, still struggle with the terminology and methodology used in mid-range and above sounders. I guess I know it well and tend to rattle through the features; in fact my darling is always telling me to slow down when explaining things to people. So, with that in mind, this month I'll cover a few of the key buzz words that refer particularly to Furuno colour sounders, but are relevant to almost all types of fishfinder.
Frequency
We have covered this in detail before. Suffice to say here, the lower frequencies will give greater depth, but at the cost of definition and target separation. 5OkHz is the normal low frequency. Higher frequencies define better, are less subject to turbulence but give less depth. The normal here is 2OOkHz. Most Furuno units we sell are dual frequency; that is, switchable between either 50 or 200kHz, depending on conditions.

 
 Photo Credit: Google Images

Transducer
This is the piece attached through the hull or to the back of the boat that contains the elements that send and receive the sound signal. A transducer typically contains one or both frequencies. A triducer usually does depth plus speed and temperature. A quaducer is two frequencies plus speed and temp. These terms seem to get swapped around a bit. There are several types and materials used in conjunction with Furuno and other units.
Transom mount
This is constructed of plastic then filled with resin. It is made for mounting on the back of the transom with the face below the hull. It is suitable for use with outboards and stemdrives. Shaft drives generally have the prop mounted forward of the transom meaning it would run in turbulence. The transom mount is the first choice for all trailer boats. Sometimes we see them glued to the inside of GRP hulls. I don't recommend this practise, as there will be some loss through the hull, unless it's essential such as in glass trailer yachts. The speed and temperature component is often attached to the back or can he a separate unit.
Through-hull
This type can be constructed of either plastic or brass. Through-hull transducers are designed for external fitting in a suitably shaped fairing block with the threaded shaft and cable inside the hull. These are usually fitted to moored boats; obviously they are exposed to damage for trailer craft.
Rubber through-hull
These are the high performance models in the range. Designed to be fitted in a fairing block like the brass models, they are much bigger in size and typically add up to 50% more range. If you need maximum depth, this is what you fit. Expect to pay around $1500 for this extra depth. We have also transom-mounted these units. This isn't a simple issue to get the best out of it, but does work very well when done properly. It is suited to bigger trailer boats only as it can act as a trim tab! Call us to discuss this as an option - it needs to be carefully planned.
16 colour
This refers to the number of colours displayed on the screen, which relate to different signal strengths returned to the transducer. Dark red is usually the strongest return, through orange, yellow and green, and with blue indicating the weakest return. The key fish species, such as tarakihi and snapper, generally show as blue dots, groups or clusters. Baitfish, particularly if being worked by predators, can even show as a big red ball. Other situations range between the two extremes.
The movement in colour below the bottom shows the changes in bottom hardness. It soon becomes second nature to read these subtle variations. This is the real strength of a good colour unit. What needs interpretation on a monochrome display, sticks out like dog's bits in colour. It allows a person of relative inexperience to very quickly become an accomplished finder of fish. Unfortunately (or maybe it is fortunately for those of us that would like to believe they are in the so-called ten percent), it doesn't replace the need for fish catching ability, or even more importantly, the ability to accurately anchor a boat.
Gain
Perhaps best described as the volume control, increasing the gain amplifies the signal being returned. Too much gain and the weaker returns are lost in a mass of colour. Too little and the lighter returns, which are the most important, are not seen. Think of it like this - turn on your TV and set the volume. Walk to the end of the room (increase depth) and you need more volume (increase gain). Leave the volume where it is, then walk across and stand in front of the TV. It will be too loud and distorted (too much gain) and you won't hear all the subtle tones.
Auto mode
On the Furuno models there are generally two auto modes. The first of these, 'cruise mode' , is basically used when travelling between destinations and you're not interested in finding fish. The most important one is 'fish mode'. This does a remarkably good job of setting the gain to a position I would call 95% effective. It takes the guesswork out of knowing how the machine should he set. That's great when it's new technology to you. As much as I hate to admit it, I too use 'fish mode' most of the time. There are times when the machine needs to be set to manual. At speed, rough conditions and extreme depth, manual gain and ranging is the only way to go.
Shift
Shift is a bit like the range function. The difference is that instead of taking the view from the surface to the bottom, it takes a band and 'shifts' it down. For example, you are fishing in an area of 38 metres of depth that drops off to 45 metres. Instead of having the range change from 0 to 40 metres to 0 to 80 metres, its possible to move the 40 metre hand down, 10 to 50 metres, 20 to 60 metres, etc. This helps keep maximum expansion on the screen, especially when there is no interest in what is happening at the surface. We also use shift to target an area when there are baitfish mid-water. It's very effective at keeping the lures in the strike zone


Source:  http://www.fishing.net.nz/
More News:  http://gofishtalk.com

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