OnBoard Magazine - Issue XII - 2020 Season

THE THEORY Much testing has been performed to research a streamlined, in-motor solution, but manufacturers have yet to find a silver bullet. This is where Selective Catalytic Reduction (SCR) systems for exhaust gas treatment come into play. An SCR system consists of several bulky components that inject chemical solutions into the exhaust system. These components require a great deal of plumbing, ventilation and additional space in the engine room, which can be the equivalent of adding another full engine footprint to a yacht’s belly. The exhaust catalyst comes in liquid form and is known as Diesel Exhaust Fluid (DEF) or by a more basic chemical name: urea. The urea must be stored onboard in a separate tank, and estimates are that a yacht would require 10% of their fuel load in urea storage capacity. The equipment required for a functioning SCR system adds several tons in weight, depleting performance and fuel efficiency of the yacht. The bulky components would cramp engine access which also leads to safety concerns. An engine room would need to be stretched in length and height to accommodate the system. Space within a yacht is always at a premium and this would completely change the proportions and layout of any given yacht model— decreasing livable space and requiring engineers to return to the drawing board to keep a model in production. Top these concerns off with an estimated purchase price increase (for a Viking 92C) of over $500,000 and heightened operating costs, and the fear is that most prospective buyers would steer clear of SCR-equipped models. IN PRACTICE For SCR to perform efficiently and provide the claimed reduction of NOx emissions, the diesel exhaust needs to be incredibly hot, exceeding 500° F (260° C). High heat is what activates the chemical reaction required between the urea and the noxious exhaust particles, to break them down into less harmful ammonia and water vapor. However, these high temperatures are only achieved when the engine load is high—over 80% load in the case of Viking’s models—a figure that is rarely sought after in operating large cruising yachts and sportfishing convertibles. Aside from current SCR and DEF equipment being inadequate at lower engine loads, there is also the concern of obtaining and maintaining urea. Executive Co-Chairman of the Viking Group, Bob Healey. Jr. explains, “There will be very few ports that have urea, certainly not your mom-and-popmarinas or remote locations. Only your major ports like Miami and Fort Lauderdale will have urea.” Boat owners and captains can face hefty fines for operating a vessel in current and future Tier III zones with a non-functioning SCR due to empty urea tanks. There is also a maintenance issue surrounding urea: it has a relatively short shelf life. Being concerned about fuel integrity and lifespan is nothing new for mariners. However, where gasoline has a whole market of conditioners and stabilizers, and diesel benefits from advancedfiltration and circulation systems, urea has no backup plan yet to prevent chemical degradation. The typical storage life for DEF (urea solution) is roughly 6 months. Beyond this time frame, the solution can crystallize leading to blocked DEF plumbing and other maintenance concerns. It could become quite a juggling act for Captains to determine the amount of DEF to maintain in their specialty tanks. Too much unused urea could lead to maintenance issues, while having too little onboard exposes them to citations and fines. The engine room of the Viking 93MY would be a much more complex and cramped space with additional SCR equipment. Viking may have to cease production of their 92C and 93MY due to Tier III emissions regulations. 37 2020 SEASON