FloScan installation

We do a lot of cruising on our tug and I want to keep track of our fuel consumption as we travel. The fuel gauge on the Cummins instrument panel has not worked since we purchased the tug three years ago and dipping a stick in the tank can be inconvenient when underway, especially in rough weather and seas.

I purchased and installed a FloScan 950M-BOS-2 meter (right meter for my Cummins 6BT5.9M engine) which combines a digital LCD engine hour meter, tachometer, fuel flow meter, fuel totalizer, and nautical miles per gallon over the ground in a single 3-3/8" diameter instrument directly from FloScan (www.floscan.com). FloScan was running a special promotion that let me put 25% down and pay the balance interest-free over 12 months (always better to use somebody else's money over time).

There are two major parts of the installation: 1) installing the fuel flow sensors in the primary and return fuel lines, and; 2) installing the meter on the helm. The final part of the installation involves calibrating the meter.

Diesel engines create pulsations in the fuel lines because of how they pump the fuel, so the fuel flow sensors are combined with pulsation dampers (look like oil filters) to smooth out the pulsations so the sensors can accurately measure the fuel flow. There are two sensors: one to measure the fuel flow from the tank to the engine and a second sensor to measure the fuel flowing back to the tank from the engine. The high pressure fuel pump uses the fuel to cool and lubricate the pump, so some of the fuel is not burned in the cylinders and must be returned to the tank. The meter subtracts the fuel flowing in the return iine from the fuel flowing in the primary line to determine the fuel the engine is actually burning.

I installed my fuel sensors in the lazarette on the same white marine board that the primary Racor fuel filter is mounted on (see photo). FloScan recommends installing the sensors as far away from the engine as possible. There is a bit of plumbing required to connect the sensors to the pulsation dampers and install a couple of brass pipe fittings and hose barbs to connect the fuel hoses to. The entire assembly is then mounted on supplied aluminum plates and "L" brackets that make mounting the assemblies easy on the white marine board. One note: Use a good quality pipe dope that is compatible with diesel fuel on all threaded parts, NOT teflon tape. Particles of teflon tape will get into the plumbing during assembly and jam the tiny turbines that measure the fuel flow through the sensors. You will need a few feet of extra fuel hose to connect things up (remember, the primary- and return-fuel hose inside diameters are different; you will need a few extra feet of both hoses). The primary fuel line sensor is installed AFTER the primary Racor fuel filter.

I ran two 16 AWG 2-conductor shielded twisted pair wires (Ancor) from the lazarette through the conduit that runs on the starboard side of the shaft alley up to the wire channel that runs from the pilothouse sole to the roof and finally into the space below the horizontal instrument shelf forward of the helm (the surface the compass is mounted on). One wire carries the 12 VDC to the sensors, the other wire carries the signals from each sensor to the meter. I connected the shields to the ground/bonding systems of the boat. I ran a second 2-conductor wire from behind the helm down into the engine compartment and then through the same wire channel and, again, to the the space beneath the instrument shelf. One wire carries the tach signal from the Cummins tachometer and the other carries switched 12 VDC from the engine key switch to turn the meter on. You need to find out from your engine manufacturer what type of tach sensor they use and how many pulses/engine revolutions are generated to properly set up the FloScan digital tachometer.

I looked behind the Cummins instrument panel mounted on the helm and decided that replacing the existing tach/hour meter was more of a job than I wanted to tackle. There are a lot of wires and a printed circuit board that controls the engine alarms connected to the back of the Cummins tach that I didn't want to sort out so I opted to install the FloScan meter in its own little teak case (see photo). I sketched up what the teak case needed to look like and then built a mockup out of foamboard from the local office supply store. I made sure there were sufficient clearances for the switches and the cable assembly that comes out of the back of the meter, then copied down the final measurements. A local cabinet maker made the teak case for me out of teak stock that I already had, and he did a fine job. The panel that holds the meter can be removed from the case using four brass screws.

I removed the compass to get a look under the instrument shelf and make sure that I had sufficient room and access to run the wires and connect everything—I did. I placed the teak case where it needed to go and secured it to the shelf with a couple of small "L" brackets. I then drilled a 1-inch hole in the shelf to pass the wires through (and sanded the sharp edges around the top and bottom of the hole to protect the wires). The wire harness from the meter is long enough to hook up most of the wires through the hole the compass sits in. Everything was hooked up using Ancor butt connectors covered with heat-shrink tubing following the clear diagram in the FloScan instructions. I wired the meter light to the existing compass light power source. The NMEA data (SOG) required to calculate NMPG came from my Raymarine E120 chartplotter. I encased most of the FloScan wire harness in a flexible plastic tube to protect against chafing and tied up everything neatly before closing things up.

The meter worked exactly as advertised when I started up the engine. I calibrated the instrument using the FloScan instructions on our summer cruise (boat loaded with provisions, fuel, water, bikes and other stuff) and found that there was only a half gallon difference between what the instrument said I consumed and what the fuel pump read when I filled up the tank (same place on the dipstick as when I started). I measured fuel consumption (GPH) and the mileage (NMPG) on a calm day (best case scenario) in 500 RPM increments for 1 minute and constructed a fuel/speed/distance curve for the tug. I found that I could get 3.5 - 3.8 NMPG if I cruised at hull speed, or 7.5 kts, depending on wind and seas. Fuel economy went down dramatically as I increased RPM and speed as the tug tried to plane. I've been keeping an hourly log of RPM, SOG, GPH and NMPG as we cruise and plan to use the data to build a more accurate "average" set of values that reflect varying wind, sea, and weather conditions.

The entire project took about two full days to complete—one for the sensors and wiring, and a second for the meter and final wiring. Calibration requires you to start with a full tank (measured using a dipstick or some other accurate method), consume thirty or more gallons of fuel at your normal cruising speed, fill-up at the fuel dock to the tank level you started at, and compare the FloScan totalizer amount to the number of gallons you put back in the tank. A simple calculation and switch setting on the meter will account for any error. Including the meter, the small teak case, wire and other parts, I spent about $1,400 on the project.

Mark Laffin
Respite - NT 32-135
mark.laffin@gmail.com

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