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 Research 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.
The EPA and CARB rules are not identical. In general, a boat meeting CARB requirements meets EPA requirements. But the reverse is not necessarily true. To avoid the limitations on where a boat can be sold, most builders will build in accordance with CARB rules. 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. These standards are based on CARB rules.
From the component standpoint, the primary difference between the CARB and the EPA versions involves whether or not to capture vapors generated during refueling through the pump nozzle. CARB (at least until 2020) requires it. EPA doesn’t, but accepts certain CARB systems as meeting EPA requirements. Vented fills (with sealed caps) offer builders a way to comply with both. Such systems involve two independent vent lines. A high volume vent line is directed to a vented fill where refueling vapors are delivered to the pump. After refueling, a cap on the fill seals both the 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 work the same way but without the canister.
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 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 CARB 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)
- Fill Limit Valves (FLV)
- Inverted Loops
- Inlet (i.e. Fill Pipe) Check Valves (ICV)
