This is a very common question and it helps to know a bit about typical engines. A two-stroke outboard motor is the heaviest user of fuel and the figures in examples we give will always be the worst possible case. The new four stroke and EFI technologies will give you significant reductions in fuel consumption.
Divide the horsepower by 10. (This gives you the number of US gallons per hour at full load.)
Convert US gallons per hour to litres by multiplying by 4.
Example: A 100 horsepower engine will use approximately 10 US gallons or 40 litres per hour flow at maximum revs.
As a rough guide an inboard four-stroke engine will use about 60% of the typical outboard engine, for example, a 100 horsepower engine will use 6 US gallons or 24 litres per hour, once again at maximum revs, and this is a worst-case situation.
NB: These are typical values for a planing hull and a typical boat with almost any petrol outboard engine will be reaching a maximum speed of approximately 30 knots unless it has an exceptionally large engine for the size of the boat.
Navman's diesel system has been designed to be installed and operate on most diesel engines in the 100 to 400 horsepower range. However, the key specification is the fuel flow rate through the engine (note: this is not the consumption rate).
For the system to work accurately, the flow in the supply pipe to the engine must be less than 400 litres (105.7 gal(US)) per hour.
The flow in the return pipe back to the tank must be more than 25 litres (6.6 gal(US)) per hour.
Yes, if you have two FUEL3100 or DIESEL3200 instruments then fuel data is shared by these instruments over Navbus.
In choppy seas fuel can surge back and forwards through the flow transducer. This back and forth motion causes the flow transducer to measure flow readings, which affects the accuracy. The solution is normally to place a fuel resistant one-way valve between the flow transducer and the tank.
This problem can also be a symptom of inadequate baffles in the fuel tank allowing fuel to surge in the tank causing pressurised surge in the fuel lines. If you have this problem on an 2100 Series F41 then just wire the unit into the ignition so that when the engine is off the gauge is off.
Always wire your Fuel Computer into your boat's ignition so that when the engine is turned on, the Fuel Computer is recording the fuel used. If an accessory switch is used and you forget to turn the unit on then the Fuel Computer will not have recorded the fuel used and will be inaccurate. If you are unsure how to do this, contact a qualified marine electrician.
The current one-piece flow transducer is rated at a maximum flow rate of 130 litres per hour (32 US gallons per hour). In modern terms this is a relatively large amount of fuel especially with the advent of far more economical engines. In cases where users suspect the flow transducer of being the cause of a fuel supply problem then it is generally found that the design of the fuel delivery system is marginal to start with, in other words adding the flow transducer may be the straw that breaks the camels back but it is not the cause of the problem.
The critical measurement in any outboard engine fuel system is the total backpressure at full throttle. This is measured in 'Inches of Mercury'. The absolute maximum acceptable limit amongst most manufacturers is 7.0 inches of mercury and ideally should be far less (Always consult your outboard manufacturer for detailed recommendations). Our fuel transducer creates a maximum backpressure of 1.0 inch of mercury backpressure so even if your manufacturer specified a maximum of 4.0 inches backpressure then you have plenty of margin for the fuel delivery system components.