Sonar So Far

Sonar So Far

Rob & Scott Naysmith

“The age of 360 thinking has arrived.”

In the beginning there was ‘drag your sinker until you hooked a reef’… followed by secret landmarks, and the rest is history.   So that we are all on the same page, I’m from the old school.  When I say ‘old’ I mean the first flashing echo sounders entered the market when I was already in my late teens, and I was proudly one of the early flasher guys.  Then came paper echo’s, followed by the early monochrome TV screens, colour TV screens, LCD screens, right up to today’s technologically advanced Touch Screens with every bell and whistle you haven’t even begun to think of yet.  All to stay one step ahead of the dwindling fish stocks.

Transponders, or as many of us refer to them as Transducers, went from two, one for sending and one for receiving the signal, … to one unit that does both. Transducers were first housed inboard, in tubes filled with oil … the secret of a good signal was the oil.  I’m not sure why I still hold on to that secret, but anyway …..   Recreational transducers went from a mere 50 Watts output, that’s the power of the pulse sent out, to today’s 3 kilowatt units.  Let’s put that into perspective, the more the output watts, the stronger the signal and the further away it can read, think definition like HD … don’t confuse it with the frequency or Hertz. 

Hertz, or Hz is the frequency of the sound pulse.  In water, lower sounds travel slower but further, so a 50Hz pulse, much like a bass drum, will show up better at a deeper depth than a 200Hz, which is like a snare drum. This CHiRP signal is still something I’m trying to convince myself about.

We all understand Echo sounders, whatever swims into the cone width we’ve chosen for our pulse, will be seen.  However, anything outside that cone will go undetected.  We know and accept that, well some do.  Not the young, new-age anglers, those with an inherent passion to catch fish, and here I talk predominantly of the commercial pelagic anglers, those who target Tuna, Marlin, Wahoo, Dorado and those other exciting sporting fish.  They have come to realise that the slow growing reef dwelling fish need to be protected if we are to preserve anything of our heritage.

And so it came to be …. about 50 years after I gazed with absolute amazement upon the first ‘fish finder’, I now stare with equal amazement at the latest of the new-age SONAR systems.  One must take a step back to absorb the technology, opportunities, cost implications and possible destruction these systems can bring.  Not to get bogged down in this almost endless plethora of technology, its multitude of applications and the myriad of new-age jargon, this article aims to give an extremely basic idea of how this system works.

What is SONAR (SOund Navigation And Ranging)

ASDIC, or as the Americans termed it SONAR, was developed, and used extensively during WW2 to find and track submarines.  A simple explanation would be that Sonar is a cross between a Radar and an Echo Sounder. The difference being that radar uses an electromagnetic signal that travels 360 degrees horizontally above the water, while a Fish Finder uses an acoustic signal that travels vertically downwards.   The Sonar unit sends out a multi-directional high-powered sound wave known as a “ping”, audible from the surface to the ground in a 365-degree sweep, like a big, inverted dome.  Acoustic signals are preferrable for use underwater as sound waves can travel for hundreds of miles while retaining an intensity of 140 decibels as far as 300 miles from their source.  That’s why sea mammals such as Whales and Dolphins use sound to communicate over such vast expanses of ocean.

Basically, how it works is a Sonar ‘ping’ of between 60 and 240-kHz is sent out from a transponder and only returns if it strikes something.  When it is returned, it shows up on the Sonar screen as a mark or target, exactly as RADAR functions.   We’ve all seen and heard Sonar being used in those submarine movies, that loud ping as the signal is sent from the boat above, that is the same loud ‘ping’ that emanates from the fishing Sonar unit while in use. 

The Sonar Transponder lives in a vertical tube built through the hull of the boat.  This allows the transponder to be raised and lowered to see through a full horizontal 360-degree circle and vertical 90-degree arc.  The transponder is retracted when not in use and only lowered for operation.

The onboard SONAR unit comprises a screen and a control board from which the mode of operation is determined.  The screen layout varies according to the mode being used.   If the vessel is carrying out a general search for fish, the screen will mostly be in the ‘all-round’ or Radar like mode, where the vessel is in the middle and the top of the screen the direction of boat travel.   The transponder is set by the operator, to view in a wedge-like beam, at a determined depth, over a set distance.   What one sees on the edge of the screen is a big red ring as the perimeter of the signal, any signal returned between the center of the screen and the edge of the perimeter, is fish.  This ‘target’ tells the distance and direction from the boat and the depth it is at.

Once a target is acquired the sonar screen is changed to a ‘searchlight’ mode, just like the beam from a torch, to get a more exact indication of the fish.  Then it’s as simple as staying on track and just riding down the beam until the fish are under the boat.   With absolute focus, the operator follows the shoal while giving the skipper constantly updated compass directions and distances, also indicating any changes in shoal depth or behavior.   Remember, this is a beam where the fish can swim in and out of by going up or down, and worst, you don’t always know which way they went.

Because of the relatively slow speed of the displacement hull Tuna boats used in the Cape, these boats tend to troll a few hand-lines on thick rubber tubing, more commonly known as ‘bungies”, while they move around.  If the fish are at a depth less than 20 to 30 meters below the boat, invariably one or more of the back lines will indicate the fish are on the surface and ready for catching.   If the troll lines do not hook a fish after a few passes, a drift and bait routine is implemented.  As the chum bait sinks into range of the targeted fish, they will hopefully, begin to swim up the chum-line all the way to the boat.

All this time while preparing for the arrival of the feeding fish, the Sonar operator will keep a sharp eye in staying with the shoal, keeping the crew informed and ready.  Sometimes while following a Longfin Tuna shoal, bigger fish, such as a Yellowfin, Bluefin or Big-Eye, will move into the area and the crew need to be advised as a different fishing technique may need to be employed.  The Sonar can tell you everything you need to know and like your fish-finder, experience rules.

But before you dash out and buy the very latest unit for your boat, there are a few considerations  …

Probably the first question on everyone’s tongue, “what does it cost”.  I suggest you now hide this magazine away from your partner or there is no Sonar for you. In the past year we have seen the first of the entry level products appearing on the local recreational market.  Here I speak of a full-on Sonar but limited in its functions, not unlike my Flashing sounder.  These units start at around R 150’000 …. oopsie,! up we get …  and yes, they do catch fish, but when compared to the price of the latest commercial unit, you’ll understand how much you are not getting.

The latest, technically advanced Sonar units will set you back above the region of R 1.2-million just for the equipment.  That may sound like a lot of money to a recreational angler, but a commercial Tuna boat can recover that in a few good outings.  Having seen the latest Sonar in operation on Sam and Scott’s boat ‘Easy Rider’, there is no doubt that every commercial Tuna boat needs one.

I think practicality is a major issue for the recreational angler.  For the moment Sonar units are big and they need a big tube to go through your hull for the transponder, although there is one with a side mount.  Sonar works best against a solid, dense target, just like radar.  When the target is small, like an individual fish, things become a little tricky and requires constant focus on the screen, something you don’t want to do in a little ski-boat. 

Sonar is the way of the future, but at what cost?

In my view Sonar is awesome as a concept, yet lethal from a future fishery perspective. In the past, what we didn’t see on our Fish-finders always remained for our future fishery.  With the ever-increasing numbers of anglers taking to the sea with this form of advanced method of detecting fish, time will eventually run out for what little stocks are left.  I know I may sound like a grumpy old man but think about it, in the face of rapidly diminishing fish stocks, we now push what is left into a corner with no escape.  Nowadays anglers don’t need to experience a lifetime of learning to become a good angler, just the latest technology … and a picture of a big fish on Facebook helps.   And just think, the best time to target our Reef dwelling fish, is when they congregate to mate or spawn.   I think you get my train of thought …

What the sales brochures don’t say ….

ASDIC or SONAR pulses can be deadly to a human who is close enough to the sound source. At 200 decibels, the vibrations can rupture your lungs, and above 210 Db, the sound can bore straight through your brain until the delicate tissues haemorrhage.

In the past, environmental groups have tried to halt underwater sonar use, claiming that the technology harms or even kills whales, dolphins and other forms of marine life.  However, recent studies indicate that SONAR does not pose a threat.  We read that gamefish are unable to hear high-frequency sound waves, including that of sonar however, they must feel the harmonics of the passing sonar waves through their lateral line.

The following assumption is personally concluded after experiencing this phenomenon many times.   The first boat to arrive on the Tuna shoals using Sonar will be good to find and catch fish.  The second and maybe third boat arrival will also do well but in dwindling numbers of fish.  There are ways around this in the early stages but that’s a long story.  By the second day of Sonar pings across the area the fish show a marked dislike for the sound.  Either they leave the area completely or go into sulk mode sitting way down below the 40-meter mark.  It was never the case during the 80’s and 90’s, where if you found the Tuna, they would invariably stay in the area for days if not weeks … but there was no Sonar then.

As Cape Snoek have only recently become victim to the smaller Sonar sets now installed on Ski-boats, their reaction is still less certain although it appears to follow close to form of the Tuna at this stage.

Is Sonar the Holy Grail of catching fish?  

At this moment in time, I would have to say yes however, that’s probably what I said when I saw my first Fish-finder.  When I look back on my earliest ‘Flashing Fish-finder’, I had paid an inordinate amount of money for what I actually got by way of features and ability.   Today the standard features and ability of a fish-finder are extremely cost effective and considered the absolute basics. 

The Sonar technology is brilliant, amazing in every way for those who need to make a living out of what fishery we have left.  For recreational anglers it is a ‘nice to have’, but entry level units currently come at a price beyond their capability.    My belief is that Sonar will follow on from the traditional fish-finder in that, as the technology continues to advance, so the features value will become greater amid declining prices.

We as anglers need to understand the tremendous power of Sonar to wipe out a fishery.  We must use it wisely and not succumb to greed or heroics for a day. 

For more information on this and other boating related topics, feel free to contact ROB NAYSMITH at DOWN SOUTH MARINE on 083 235 9550.