Fuel Watchdog - Money in the Tank A fuel computer is the only instrument that determines your engine’s optimum running speed and mechanical condition, fuel range, ideal trim and load distribution. Install one and you can save as much as 20% in fuel costs.Accurately measuring and monitoring fuel consumption can tell you a lot about your boat’s efficiency and condition of mechanical systems, and definitely save money in fuel and maintenance costs. Adding fuel consumption flow meters on our 37' (11.2m) Egg Harbor Double Cabin was based on my desire to know, as precisely as possible, what is happening at any given time with the fuel and propulsion systems. Fuel management instruments measure the movement of fuel through the fuel line, and through the magic of computer technology, provide the amount of fuel consumed by your engine(s) in U.S. gallons per hour (gph) and total gallons consumed. (Metric readouts are also available.) Linking to a GPS or Loran unit with NMEA 0183 output gives a readout in miles per gallon (mpg). The driver, by monitoring fuel consumption, can adjust throttle settings for the optimum speed-fuel consumption ratio. We installed a FloScan TwinScan Fuel Flow and Tachometer. Both are analog gauges that combine port and starboard engine readings with an LCD window on the bottom that provides a digital readout of the total gallons consumed on the Fuel Flow unit, and fuel consumption per hour on the other gauge. Fuel flow is measured by a special sensor, mounted near each engine, that calculates the amount of fuel passing through the line, and then transmits this information to a gauge at the helm. “Wiking,” our 1968-vintage semi-displacement “trawler” weighs in at a heavy 10 tons (9,072kg). Power comes from twin 427 Crusaders and, like all power plants of that era, were designed for leaded gasoline. We have since rebuilt the engines to handle unleaded gas, upgrading the distributors, carbs; intake manifolds and added a Multiple Spark Discharge (MSD). But for all new or old engines, some fine tuning, continuous maintenance and adding a few modern conveniences, such as flow meters, can spell better performance, less gasoline consumption and significant dollars saved on fuel costs, and ultimately a cleaner environment.
Installation and Testing
FloScan Instrument Company (Tel: 800/522-3610, Web: www.floscan.com) offers fuel consumption computers and fuel flow instruments for most gasoline outboards, stern drives and inboards and diesel engines. When ordering, you’ll need to provide the boat make and model, and engine make, model number and horsepower rating. Our boat required a TwinScan Fuel Flow Meter, from 1 to 32 gph, and tachometer from 1 to 6,000 rpm. Installation is relatively simple and required a very careful review of the instruction manual, help from my mechanic and about 8 hours time. While one could install this system without a marine mechanic, I would advise you at least get advice from a competent tradesperson or, even better, get them involved. I don’t think it can be said too often that the marine environment is much different from the automotive arena because of dampness and the enclosed spaces found on a boat. After selecting the best location for the fuel flow sensors, we ran the fuel hose and wiring neatly to their respective locations. While my mechanic installed the sensors in the engine room, I worked out the gauge setup on the instrument panel on the bridge and routing of the wires. Color-coded wires and a comprehensive wiring diagram made the job go very smoothly. Leaving extra long wire leads, wires were pulled out through the instrument holes, allowing me to take my time on the hook-ups and avoid trying to make sense of a maze of wiring behind the panel while working from underneath lying on my back. FloScan supplies all fuses, butt connectors and heat-shrink tubing for the job. Also mounted on the dash is a momentary On switch to reset the totalizer and a simple On/Off switch to change the tach digital readout between the synchronizer and miles per gallon. This switch is not included with the system but instructions are clear on its installation.
When I started the engines, both the gph meter and tach came up to power, performed their diagnostics as described in the instructions and worked perfectly. I did find that while I could adjust the tachs to read very closely for each engine, there is no individual tach adjustment. When my ear tells me the motors are in synch, the tachs are 50 to 100 rpm different from each other. It’s not my hearing for I’ve tuned guitars for most of my life and have a pretty good ear for this sort of thing.
Performance Data Before this installation, I always ran the engines at 1,800 rpm and traveled at about 8 knots per hour (kph). I cannot come up with any particular reason for this other than it seemed a decent speed and, without any scientific proof, not overly hard on the engines. I have read and believe it to be so, that while marine engines like to run long and strong, they also last much longer if they run at moderate speeds and are, of course, serviced regularly. Carefully observing the tachs, we ran the boat at 1,800 rpm, and then throttled up to 2,000, and then 2,200 rpm, and then backed off to 1,600, finishing up at 1,400 rpm. At each increment, we let the boat settle, rechecked the rpm, and then recorded the speed and gph (Figure 2). Results were surprising! Obviously the more rpm turned, the more gas used. At 1,600 rpm, “Wiking” traveled at 7.5 kp-h and engines burned 4 gph and 4.5 gph respectively for a total of 8.5 gph. This is more than one gph less than at my “ideal” 8 kp-h cruising speed, and a drop to 7 kp-h burns a full gallon less! With gas costing CDN$3.38 per U.S. gallon at the marina pump, at 50 hours of use per year, for example, I’m saving about CDN$186 and cruising tolerably slower.
Added Insurance It’s conceivable that some might consider the addition of FloScan equipment to be a touch extravagant. This twin-engine installation cost US$550 for one TwinScan Fuel Flow Meter, US$350 for the TwinScan Tachometer and add another US$100 for miscellaneous wire and connectors, for a total outlay of US$1,000 (in 2002). This very high-quality fuel management system might seem a bit pricey at first glance, but the benefits soon add up. About the author: In the two years since purchasing “Wiking,” Dwight Powell has rebuilt the engines, upgraded the wiring, reworked the interior, had the hull and deck professionally painted and new canvas fabricated. More work is planned for next season, including a new instrument console and dash, and articles documenting his progress will appear in future issues. |
During our tests, the FloScan Fuel Flow meter noted
that the starboard engine burned 1 to 1.5 gallons more per hour than
the port. I haven’t
determined the cause of the malfunction, likely a result of a carb
set too rich or perhaps off-spec engine timing, fouled spark plugs,
new and therefore stiffer valve springs on the cylinder heads, even
the high-output alternator robbing horsepower as it charges the house
battery bank. More importantly, is discovering that this engine needs
work to bring it to optimum performance, which could add life and therefore
fewer maintenance bills in the long run. Running both engines at the
same rpm will pay for those TwinScans even sooner! 
With these meters, I have a visual “watchdog” of problems
that appears instantly before the engine overheats or worse, breaks
down and leaves you stranded. If fuel consumption increases from normal
operating levels with no noticeable change in engine operation, you’ll
know to check for engine and drivetrain problems or a dirty hull bottom,
perhaps fish net or line around the prop, trim tabs set improperly,
even a potentially dangerous fuel leak. With FloScan providing accurate
fuel consumption and knowing the tank capacities, fwe can easily determine
our range, giving us added assurance that we'd likely never run out
of gas. We won't pay for the system in one year, but I'm convinced
that long after our original autlay is covered by fuel cost savings,
we'll still be enjoying the peace of mind these instruments provide. ©2009, Boat Owners Association of The United States. All Rights Reserved.
