Designing a Modern Fuel Delivery System

I want to pass on a discussion from fuel expert Alex Marcus, president of ESI Total Fuel Management, to an audience of boat builders on modern fuel system design and installation. I thought it interesting and relevant to understand how things have changed. But let me begin by saying that if you have an older trawler, I am not suggesting you need to do anything to change what you have regarding your existing fuel system.

But before I dismiss any owner from taking a look at possibly upgrading or replacing parts in their engine room, let me mention that I know a good number of owners with older boats that still have the original fuel and exhaust hoses, and even engine hoses and belts that still do their job. Check out a Grand Banks built in the '70s or '80s. They were considered as finely built as any yacht of that time, but it will be no surprise that some things need some attention, and perhaps replacement. The standards of boat building have come a long way since then, and almost everything on a boat is done quite different today. Construction practices have matured considerably in recent years. And things just wear out.

Back to the lecture, Alex began by explaining the importance of reducing the number of fittings in a fuel delivery system. Sometimes workers get carried away and the system includes a tangle of pipe fitting going in all directions, rather than someone spending quality time on the drawing board to design a simple, complete system.

He recommends boat builders move away from using copper tubing for fuel systems, even though this has been the standard practice for many years. Copper tubing still works, but is not as good as a modern, Parker or Aeroquip USCG-approved Type A flexible fuel hose that is fire-rated and universally used in commercial marine fuel systems. He pointed out that copper can get brittle over time, can be inadvertently bent which can reduce fuel flow, and copper contributed to the oxidation of diesel fuel. (Again, If you have an older boat with copper fuel lines, that's fine. Just be aware that it is no longer the best way to go, as there are better alternatives.)

The value of designing the complete fuel supply system provides many benefits. The system will meet the highest current standards of boat building. It will use a minimal number of fittings to eliminate leaks in the future. It will standardize the use of hydraulic, high pressure connections instead of simple plumbing fittings, using standard thread O-ring and JIC flare fittings. These leak-proof fittings are the modern alternative to hose clamps and hose barbs for all aspects of marine fuel systems.

He also urged the audience to avoid using low-quality unreinforced hose not designed for marine propulsion systems. Such hose is easy to cut if using the wrong hose clamps (the ones with open slots), and he stressed that unreinforced construction of this hose is not good for suction.

In terms of location, he pointed out how important it is to centralize fuel management plumbing for ease of access and use by the owner operator, including all manifolds, filters (engine and genset), and polishing system if one is installed. No component of the fuel system should be installed in a hard to reach location. It is important to look at it from the perspective of the owner needing good access. Having to move around a hot running engine under way to inspect a fuel filter vacuum gauge is usually avoidable.

Design the fuel tanks for optimum performance for both delivery and management (polishing), and eliminate areas that can trap contaminants behind baffles and corners. Tank bottoms should be smooth, with a sump in the lowest point of the tank's physical location and actual orientation once installed. 

Getting back to the connections of the various components, he stressed the importance of training technicians in the proper methods of making professional connections on site, whether they be for sight gauges, crossover lines, and supply and return lines. Modern hydraulic fittings seal by O-ring or metal-to-metal contact, and leave no doubt when they are done right. Pipe fittings, as Alex pointed out, are tapered and seal by thread deformation, are not reusable, and very critically, are not positionable (when a fitting is properly tight but pointing in the wrong direction, so the worker unscrews it to face the right direction). How many times have you've seen a row of pipe fittings all lined up nice and neat. Guess what...most if not all are not tight, and rely on whatever pipe thread sealant the installer used.

Alex summed it up. "The question of 'How tight is tight enough?' goes away with hydraulic fittings, either JIC or threaded O-ring fittings."