How FLS Technology Works
OTHER SOUNDERS ARE HISTORY! Some of the most popular vertical sounders show depth with a delay of up to 16 seconds. At just 5 knots this means the indicated depth is the depth 80 metres behind the boat. (at 10 to 15 knots the delay does not bear thinking about!)
At EchoPilot we believed that most boat owners would prefer to see hazardous obstructions in front of them. Several years of intensive research at EchoPilot led to the technical breakthrough which became the FLS - Forward Looking Sonar.
This achievement brought forward looking capability within the reach of the leisure boat owner for the first time. The first model, the FLS I, was launched in 1992, and there are now thousands of FLSs in use worldwide.
Real time forward looking sonar is unique to EchoPilot, who hold patents on the design. "Real time" means that the FLS. does not gradually build up the picture like a phased array sonar, instead the FLS both scans the whole forward view and updates the screen several times a second. An obstruction ahead of the boat will show on the screen, if the boat turns to another heading with no target ahead then the FLS. screen will immediately show clear water ahead. Information displayed is not historical, as is the case with all digital sounders and fish finders, instead it is real time.
The FLS displays a two dimensional profile of the sea bed beneath and ahead of the vessel on a high resolution and daylight viewable LCD matrix. Digital depth and shallow alarm setting are also displayed. The addition of an optional log transducer leads to speed and log data being shown on the screen. Some models also act as GPS repeaters, and can drive a second station unit.
Mounted close to the helm the F.L.S. can provide all necessary information - forward depth, current depth, speed, distance and GPS position data.
FLS PERFORMANCE
An FLS can show the seabed three to five times the depth ahead when on a flat muddy bottom (e.g. river or estuary). This ratio increases to eight or nine times if the seabed shoals upward, and more than this for a large target. Rocky bottoms give especially strong reflections and hard vertical surfaces like quay walls or coral reefs will often be seen at 150m or more.
In the vertical plane the FLS scans through 90 degrees from straight ahead to straight down. A useful analogy is to think of the FLS as an underwater radar but on its side and scanning in the vertical plane rather than the horizontal. In the horizontal plane (port - starboard) the beam is 15 degrees to 3dB. In reality the polar diagram is like an elongated balloon.
The FLS is not designed to be a fish finder, it is a collision avoidance device. In reality it does pick up larger fish and sometimes shoals of smaller fish. Dolphins show up well and some owners use the FLS to tell the foredeck crew when the anchor is about to break the surface!
INSTALLATION
Ultrasonic signals travel well through solids and liquids but are greatly attenuated in air. This means that a stream of turbulence and air bubbles will limit performance of an FLS. However, if a place can be found on the hull where there is a clear flow of water then good results can be obtained even at speed.
The best place to fit the transducer depends on the boat. In a sailing boat alongside the keel, on a motor boat if it is shaft driven and twin screw then a position between the gear box and stern gland is appropriate, and on a stern drive vessel just in front of the engines will give good results. Keep inboard of the lower spray rail if possible and not down stream of other through hull fitttngs (e.g. intakes, log or toilet sea cocks). Some "heel" port or starboard is acceptable, to a maximum of 5 degrees. In the fore/aft plane the transducer must be vertical. The transducer protrudes through the hull so that the transmitting face has a clear view forward. It is designed to break off cleanly, flush with the hull if it hits anything. The remains of the transducer are still in the skin fitting and so there is no risk of water ingress.
There are two types of transducer, both available with any FLS model. The larger professional transducer has a narrower beam, which gives a more accurate representation of the seabed, although the standard transducer can appear better simply because it is collecting data from a larger area. A thick hull or one with a steep dead rise will usually require the professional transducer as the bronze skin fitting has 3" of usable thread whereas the plastic standard skin fitting has 1" thread.
There are a range of different FLS instruments to cover the needs of a range of boat owners. These range from the low cost FLS Bronze - where space or budget is limited - to the high end FLS Platinum with a sunlight viewable colour display and greatest performance.