Mississippi Lake Compass and Sonar Trials

Further trials were carried out over the July long weekend on Mississippi Lake.  Several talking compasses have now been tested and have provided similar results.  Both talking compasses trialed require that the user position the unit almost perfectly at the horizontal for them to work effectively.  This meant when encountering waves or if the compasses were slightly off the horizontal, they would stick and give incorrect readings.  The other issue worth noting, is that the time lag from when the button is pushed to when the voice announces the direction is significant.  Thus, if the boat is in the process of altering direction, the announced direction may differ from the actual course of the boat.  The strength of talking compasses is in their ability to give a cardinal reading, but they shouldn’t be depended on for real-time navigation. 

The Boat has had as many as three separate sonar devices mounted on the bow plate at one time, and I carry a fourth in my pocket.  Mounting the handheld sonar devices on the bow plate was intended to ensure that the devices were located as far forward as possible and pointed in the correct direction.  The automobile reverse sensor performed well in this position as it was designed to mount at around the height of a car bumper, which is about the same as the bow of the Porta-Bote.   For the two hand-held MiniGuide sonar devices, mounting them on the bow plate resulted in unwanted feedback generated from waves.  Hand-held sonar devices such as the MiniGuide were designed to be held at waist level or higher, and were designed to pick up on things like steps or curbs, as well as poles, people or doorways, etc.  Consequently, when these devices are mounted on the bow plate at 20″ or so inches above the water  they often pick up on wave action.  This however, does not present a false reporting problem as waves are sequencial and are therefore reported by the hand-held sensors as consistently spaced beep tones — rythmic in sound.  Actual hazards or obstacles such as other boats, rafts, canoes, docks, etc., result in the hand-held sonar omitting more continuous sound feedback that is quite distinguishable from the waves.  The down side is that one is being presented with continuous audible feedback which can be distracting or anoying after a period of time.  The hand-held MiniGuides have a reported range of up to 25 feet on land, but on the water I was detecting obstacles as far away as 60 feet.  I’m guessing that the signal transmitted by the sonar device andreflected back by the obstacle may be skipping on the water surface, and thus, extending their reach.  The reasons

MiniGuides and other hand-held sonar devices offer various range settings is that the guide is limited in the level of feedback it can transmit to the user therefore extending the zone of coverage more than it’s actual range.  The difference being that a range of 25 feet means the device will report using different beeping or vibration rates obstacles from 12 to 25 feet away,  Any closer than 12 feet, and one receives the same signal as one does at 12 feet, regardless.  Beyond 25 feet and there is no feedback.  Thus, on the Boat I was able to judge distance to obstacles from 25 to 50 feet, but any closer than that, and I only could tell that the obstacle was anywhere from zero to 25 feet away. 

The automobile sensor came in handy for close in work as it was able to provide three distinct feedback sounds when detecting obstacles in our path at 3, 6 and 10 feet.  It also gave a sound that was less shrill than the MiniGuides which meant it was less distracting.  However, both the automobile and MiniGuide sensors required considerable set-up time due to the wiring configurations. 

The MiniGuides were mounted  on the bow plate at 15degrees from centre – the port sensor pointing a little to the left, and the starboard sensor pointing a little to the right.  Both units were attached with Velcro and could be slid forward or back as required.  The bowe plate itself could also be angled upwards as it was attached to the Boat with a bunjy cord.  A split stereo computer speaker wiring harness led each units monorrell signal back to a 2-1 headphone splitter.  I plugged a second set of computer speakers into the headphone splitter which continued the circuit to reach just below the middle seat.  All connection were wrapped with electrical tape to keep them dry.  I mounted two computer speakers, which drew their electrical power from internal batteries, under the middle seat.  Once it was determined which sensor fired which speaker, the speakers were taped to the under-side of the middle seat on the port and starboard sides.  This gave me the ability to triangulate on an obstacle in my path. 

The triangulation process to determine the position of encountered obstacles commenced when both speakers began firing.   This told me that the obstacle was somewhere dead-ahead.  The frequency of the beeping gave me an idea of the distance; somewhere  between 25-50 feet in front of the boat.  By changing course heading I was able to reduce the feedback from both sonar devices to just one.  Once I had eliminated feedback from one of the sonar devices, I assumed that the Boat was no longer on a direct course with the identified obstacle.  Once both sonar devices stopped omitting a signal, I assumed that I could safely pass the obstacle, and could begin counting down from either ten or five, depending on my speed,  before resuming my original course heading. 

A fourth sonar device made by K-Sonar was kept with me at all times.  This device was used to detect the distance to, and position of, obstacles that I was passing.  Since I wasn’t bringing my guide dog with me in the boat due to space considerations, I also wanted to have the means to detect obstacles in my path when on shore.  The folding cane is useful for detecting obstacles such as dock edges, but the range of a cane is only as long as the cane plus the length of one’s arm.  The sonar device extended this range for up to 10 feet, and proved useful for detecting things in my general vicinity.  It also came in handy when docking or coming along side other boats since my other three sonar devices were all facing forward and fixed in place.  By having the K-sonar in my hand, I was able to determine distance to docks and other boats with excellent precision after I came within the K-sonar’’s 10-foot range.