Read also: Visiting Praxis Automation - Part 1
A Scottish poet once opined, "The best-laid schemes o' mice an' men / Gang aft a-gley." or for us lesser mortals, "despite careful planning, something may still go wrong." We started this project with good intentions but an unsolidified plan. Now the end is in sight, and it is time to review and adjust in light of the experience gained. Or, in the words of a different bard, "ain't education a bitch".
Praxis are top of their game for supply of monitoring, control, power management and hybrid propulsion systems to commercial marine applications and a substantial number of Navies. Our visit to Praxis was an opportunity to review and refine their equipment as it applies to our own explorer yacht project. The project has experienced scope creep since first proposed. Four examples are:
The addition of two CAN-Bus gateways to convert J1939 engine signals to Ethernet that the control systems require.
An additional controller so we can operate rudders independently in support of more practical dynamic positioning.
An independent fire alarm system split it into discrete loops and identifies individual alarm heads.
Integration of a Mil Spec FLIR with IR illumination laser for spotting ice and objects in our path.
A range of screens that will be located at helm and engine room were connected to test functionality. Note engine & joystick controls are reinforced composite for operation in low air temperatures.
Now is when software is compiled to bind all the disparate components into one cohesive, logical system. Vanguard is built to be simple (we hope); with that in mind, we have limited control functions relying primarily on reporting as and when necessary. Reporting is via dedicated MIMIC displays covering the various systems and alarms. Product development does not happen in a vacuum but builds on the past. Our task was to distill that into a system understandable by a small crew under some pressure. So where we could combine screens we did, Navigation lights, weathertight access, and bilge alarms were combined on the same screen. Tanks, range, remaining liquid levels, and usage rates were combined similarly. Information can be transmitted textually but also graphically or by position and color. A complex screen may contain information needed but try reading it when you are cold, tired, and just broke your glasses. So we tried using precise color, shape, and position to simplify the layout for a quicker understanding. The acid test is my wife, Sebrina; unlike my nerdy self, she has no fundamental preconceptions, if Sebrina gets it, we are good to go. Time will tell.
Example MFD display setup at Praxis offices, I quite liked the way the screens were mounted.
We also spent time understanding the equipment beyond reading the brochures. For example, I (& the UK Marine Coastguard Agency) are nervous about the uncontrolled thermal runaway of LiPO battery packs. 120 kW.h is a lot of energy to contain.
Examining the design revealed that each battery rack consists of 16 isolated cells (blue in photo, exhaust is the light blue bursting disc). Each cell is cooled and monitored, having a dedicated exhaust (aluminium Chanel on green PCB) and thermal isolation in the event of a runaway. Each of the 12 battery racks is also independently contained and exhausted outside the engine room environment. So one single failure will not cause a runaway of the entire bank. The outer casing creates a practical battery room independent of the leading machinery space, thus satisfying Classification requirements.
We took time to examine the E-motors; there is nothing like a practical trial to stress test marketing speak. Our two E-motors were connected to a battery pack as a single motor and generator setup. They were run under full load, and the battery charge depletion was monitored. This tested the combined efficiencies of the battery cycle, two inverters, two line filters, and the motors. Something like 90-95% overall. We were pleased with that, so it's a pass.
Photo shows battery management operating at 598VDC, 2Amps (10kW) at 28% charged (LiPO can discharge more deeply than Lead acid ).
The scope of supply and equipment location was next. Our initial scope for signal Input/Output (I/O) could be reducing the number of modules needed as we focused on reporting rather than control. Other logic controllers (PLC) and I/O modules could be sensibly combined, reducing the engine room cabinet count. Dynamic positioning configuration was also amended to a single machine with simple repeaters at valid locations rather than everything in triplicate.
Finally, we asked for the drawings to be updated to reflect the "as supplied" system scope. Even with a push for simplicity, motor yachts are complex machines that change in gestation. Lucky is the final crew with drawings that reflect the reality in front of their eyes.