The Voyage
In mid March 2020 Voyager 2.0 completed its first voyage in salt water. Voyage of 40 hours across Port Phillip in Victoria. A distance of around 30 miles. Completing a voyage of this distance was a good result, despite not sailing very well. But at least it made it, despite the problems.
This was about one or two weeks prior to isolation rules being stepped up in Victoria, where this would not have been permitted.
This article covers observations about the voyage. Subsequent articles will discuss the design adjustments to overcome the problems observed.
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| Stepping through the pre-launch checklist |
I've learnt from my mistakes that a pre-launch checklist is important. There's nothing more frustrating than launching the boat and then realising that you've forgotten something (like installing the SD Card).
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| Voyager heads off into the evening at 8pm Saturday March 14, 2020. |
The launch took place at dusk to ensure the boat would be well clear of the coast in daylight, to reduce the chance of passing by pleasure craft.
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| The actual course and the waypoints |
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| The typical winds for the majority of the voyage were 10 to 20 knots south easterly. |
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| Plot of positions from the Satellite Tracking. |
The satellite position transmitter was programmed to send a position every 15 minutes. These positions are shown in the image above. The spacing gives a sense of the speed variations.
The boat didn't quite make it to its intended destination. Mid-morning on the second day, travelling slowly with light winds, and about three miles from the finish, the boat was picked up by some passing fishermen in a half-cabin power boat. They phoned me and we arranged or a hand over at their boat ramp.
I thanked them for assisting with picking up the boat, but it was a pity that it wasn't allowed to complete the journey by itself. They were not to know that the boat did not need rescuing.
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| Voyager 2.0 just prior to being picked up |
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| The hand-over. |
A lot of data was recorded on to the SD card during this voyage. The recorded data is useful for analysing the performance of the boat and working out areas to be improved. Some of the interesting date plots are shown below.
The voyage was about 40 hours in duration or about 2400 minutes.
Cross Track Error
Unfortunately the boat went off course early in voyage, but did eventually recover. The plot below show the Cross Track Error (CTE) in metres.
The plot highlights an error in the CTE calculation. The CTE calculation is based on the SIN of the angle between the rhumb line bearing and the current Bearing to Waypoint (BTW). The angle is stored as an integer which means that the calculated CTE can be seen "stepping", rather than changing continuously.
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| Cross Track Error (metres) |
Steering Servo Signal
The steering servo is standard RC servo, with a neutral of 1500us, with a full range from about 1100us to 1900us.
There are clear periods of the voyage when steering was easy and when steering was difficult. The periods with lots of large steering movements correspond to the periods when the boat was not on course.
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| Steering Servo Signal - microseconds |
Rudder Servo Movements
The Rudder Servo made approximately 100,000 movements over the 40 hours of the voyage. This is corresponds to about 2500 movements per hour.
The number of movements per hour remains fairly constant over the whole voyage as shown in the plot below. But the amplitude of the movements does vary greatly depending on conditions, as shown by the image above.
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| Accumulated Rudder Servo Movements |
Rudder and Wingsail Trim Tab Servo Movements per Hour
The next plot shows the quantity of movements in each hour for both the rudder servo and the wingsail trim tab servo, rather than accumulated movements.
If the vessel is sailing well and holding course on one tack, then there should no movement in the wingsail trimtab. This was the case for a few hours. This can be seen in the blue line plot below.
The wingsail trim tab movements at other times are related to waves rolling of the vessel when reaching, or due to rolling while running downwind.
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| Rudder and Wingsail Trim Tab Servo Movements per Hour |
Power Consumption - Battery Voltage and Current
The battery is 2S LiPo battery made up of twenty 18650 cells.
Fully charged the battery voltage is 8.4V and it may discharge down to about 6.0V
The rate of discharge appears to be fairly constant, and actually seems consistent with tests performed on land.
Speed Over Ground
SOG is measured in metres per second. One metre per second is approximately 2 knots.
The first few hours shows the boat averaging around 0.5m/s (1 knot) in reaching conditions with wind of about 15 knots.
An increase in wind speed to about 20 knots lifted the average speed toward 1m/s, almost 2 knots. Then as the wind faded in the later part of the voyage the average speed dropped to well under 0.25m/s, less than 0.5 knots.
Temperature within the Electronic Housing
The plot of temperature clearly shows the diurnal cycle, with overnight lows of around 17°C and daytime highs of over 35°C inside the equipment housing.
The overnight lows are very close the published water temperature for Port Phillip at this time.
The daily highs are well above the outside air temperature. The equipment housing is clear plastic and the interior clearly heats up in the direct sunlight.
COG, BTW and CDA
Course Over Ground, Bearing to Waypoint and Course Deviation Angle.
The yellow plot of COG highlights the poor course keeping during the voyage. It clearly shows long periods of time spent off course. It does eventually recover and get back on course.
The blue plot of BTW clearly shows the passage past three waypoints, with the third waypoint involving a more noticeable course change from about 230°T to about 285°T.
As each waypoint is approached and closely passed, the BTW goes to extreme values until it goes behind the beam of the boat, and mission steps to the next waypoint.
Note: This is part of the ongoing development of a low cost autonomous oceangoing sailing drones, utilising a self-trimming wingsail. This is the Voyager series of sailing drones.
