System Design

With government regulations now affecting system designers’ thinking, fuel systems will become more complex. The Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have both imposed requirements that directly impact design. They begin to affect boats built for the 2012 model year. It has become even more important now for boat builders to consider fuel system design early in their overall boat design process.

When it comes to diurnal emissions, the EPA has taken the lead on regulations. At this time, CARB rule making is not finalized and CARB is viewing the EPA regulations as being acceptable for California. The American Boat and Yacht Council (ABYC) and the National Marine Manufacturers’ Association (NMMA) have worked together with industry volunteers to develop industry standards covering the installation and performance of these new fuel systems. The EPA is on record as stating that a boat that meets ABYC H-24 meets the EPA’s objectives in diurnal emissions and in controlling fuel spill during refueling.

In the automotive world the primary difference between CARB and the EPA versions involves whether or not to capture vapors generated during refueling through the pump nozzle or on-board. CARB has implemented Stage II vapor recover (at the pump nozzle) for automotive and if implemented for marine would impact the fuel fill and cap designs. As a precautionary measure, ABYC is recommending that fuel cap tethers not interfere with a CARB style fuel pump nozzle. A CARB system involves two independent vent lines. A high volume vent line is directed to a vented fill where refueling vapors are delivered to the pump nozzle. After refueling, a cap on the fill seals both the vent line and the fill pipe from the atmosphere. A second low volume line then channels vapor and make up air through a canister. Pressure relief systems can work the same way but without the canister. For automobiles the EPA requires 100% of the cars to provide on-board vapor recovery and active purge. These systems vent through the canister during refueling.

Working together, the NMMA and the ABYC have proposed an industry specification for installing carbon canisters and pressure relief systems, which the EPA and CARB have accepted. The actual, detailed ABYC specification is in development. Builders will be asked to demonstrate that their products are built in accordance with these specifications in order to obtain NMMA certification. This will demonstrate to the EPA & CARB that a boat is in compliance. Representatives from boat & engine builders, tank, fill, valve and canister manufacturers, test labs and the U.S. Coast Guard are among the authors of the new specifications.

The specification calls for compliance with the EPA rules and automatic shut off at the pumps. There is also a regulation to demonstrate that the boat can be refueled at rates of 4 gallons per minute to either 10 gallons per minute or 18 gallons per minute, depending on the size of the boat. Most marine fuel systems will require rework to do this as well as to comply with the other components of the new rules. There are numerous additional issues designers may want to address with solutions possibly differing with each system.

In systems using canisters, regulations require that steps be taken to assure that water and liquid fuel do not enter the canister. Options include a means of preventing tanks from overfilling (i.e. maintaining 5% to 10% empty space), which reduces (but may not eliminate) the chances of raw fuel entering canisters and/or forcing its way back up fill tubes.

Designers can consider several new components and/or design features into these new systems to aid in addressing these issues:

  • Carbon Canisters
  • Tank Vent Valves (TVV) (also called grade valves or rollover valves)
  • Fill Limit Valves (FLV)
  • Inverted Loops
  • Inlet (i.e. Fill Pipe) Check Valves (ICV)
  • Ullage Tanks
  • OPR (over pressure relief valve)