Vanguard will have twin hybrid diesel-electric drive systems. New technology, is it simply fashion or do they have a practical use? Their facility on yachts is not the often quoted but incorrect assumption of operation over long distances on electric power. We are not going to save any puffins this time. For the true answer, read on.
Illustration - an early engine room layout showing position of John Deere 4045, step down drive from Esco Power, drive motor/generator and Power battery from Praxis Automation. Note battery positions later moved forward of the engines to improve trim (they weigh 1300kg each!).
Hybrid Marine Propulsion System Design Criteria
In the case of Vanguard, XPM-078, what we needed was three fold:
substantial power storage capacity to limit engine hours under light load. This also allows us to remove two dedicated diesel generators, relying instead on the hybrid motors and 6.5kW of solar panels.
easy and quiet implementation of dynamic positioning with flexibility to drive two propellers from a single diesel engine or no engine at all.
access to environmentally sensitive areas that intend to ban operation under diesel power (think Scandanavia).
In sympathy with our readers, we will divide the design considerations over several blogs as it's quite an involved topic. For this blog, let us consider issues of redundant system design, flexible shore power capability, and system resiliance. In this discussion, we will refer to the system drawing attached, N21.4051-F01, provided by Praxis Automation, our partner in this project.
Read also: Visiting Praxis Automation - Part 1
Visiting Praxis Automation - Part 2
To engineers or those who cannot sleep, the full installation file is here:
Hybrid Marine System Redundancy
Commercial systems lean heavily on redundant system design to improve overall system availability. This consideration goes hand in hand with an understanding of MTBF or Mean Time Between Failures. Thus, there are no point in onboarding two mutually redundant but intrinsically unreliable critical systems. Essential components in both systems need a high MTBF, typically above 25-50,000 hours for each assembly. The effects are cumulative, reducing the overall system MTBF. So, referring to the drawing, we have a system split port and starboard, wholly duplicated and able to run independently. To increase overall availability further, we can connect the power batteries or generator on either side to the motor on the opposite shaft. We can also link either power battery to the vessel's 3-phase AC Grid.
Hybrid Marine System Shore Power
Onboard Solar power is converted to 24VDC and fed to the house batteries.
Shore power at 230V 50Hz and 120V 60 Hz single phase is converted to 24VDC and fed to the house batteries.