Fuel Systems & Consumption

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Original Post:

This post is part of a series describing some of our common boat systems and their operation. 

We refer to these often not only for our own use, but also when asked specific questions about systems on Denali Rose, and when participating in discussions on various forums.

Overview

We have a single 90 hp diesel propulsion engine [Ford Lehman SP90] and a 10kw diesel generator [3 cylinder Kubota]. [Both are naturally aspirated.]

Our SOP is to use 10µ filters in our twin Racor 500 filters, but keep 20µ & 30µ filters on hand in case of problems with contaminated fuel. [So theoretically we could motor for longer periods between filter changes if needed due to abnormal circumstances...]

Details

More details follow to provide context regarding fuel handling, storage and maintenance, fuel types, consumption, monitoring, etc. if you are interested in how busy our filters are.

Fuel flow management:
We have an a couple of 12VDC fuel pumps that perform several functions depending upon which valves we open: [I mention this because all of these functions pump through the Racor filters.]

• Help bleed the fuel circuits [propulsion engine and generator]
• Runs the fuel polishing loop [recirculate or fuel transfer to another tank]
• Transfers fuel between tanks or into external jug [through the Racor filters]
• Backs-up the fuel pumps on the engines [will provide fuel flow in the event an engine pump fails]

Fuel Storage:
Our two steel tanks each have 10 x 12 inch clean-out hatches above each baffled section of each tank [and were last mucked out and cleaned in 2009.]

Each tank also has sump drains which [to date] routinely yield pure fuel in the samples [no water or sediment... yet...]

We also installed H2Out air dryers on each fuel tank vent to help reduce moisture ingress via the vent lines.

Consequently- knock on wood- so far the fuel remains in great shape. [And local conditions in some of the straights we routinely transit make sure our fuel is well agitated several times each year...]

Capacity:
2 tanks; 216 US gallons total: 86 gallons #2 diesel for engine and generator: 130 gallons #1 for the heater. [For the curious: The 130 gallon tank is original. The 86 gallon tank was the max size the previous owner could reasonably fit when the other 130 gallon tank needed to be replaced...]

Both tanks have analog fuel gauges [and calibrated sight gauges with shut off valves...]

Design note about the sight gauges: The sight gauge is plumbed to a 3-way valve which is plumbed to the tank sump drain hole. Therefore the 3-way valve can be: off [normal position]; open to drain/sample fuel from the sump; or open to charge the clear sight gauge [and then closed after the gauge has equalized and is read.]

After fuel fills we let it settle overnight [when in a calm anchorage or at the dock...] before opening the sight gauge valve on each tank. Since the gauge is filling from the tank sump- and the fuel in the sight gauge is lower than the fuel in the tank after a fill- we get a visual inspection of the fuel from the sump when the sight gauge fills...] 

We can also see the fuel from the sump by pushing the fuel out of the sight gauge through it's top valve with a couple of strokes from a bicycle hand pump. When it refills we see what's in the bottom of the tank... [I call this non-invasive sampling...]

Future plans include replacing the factory analog fuel gauges with the CruzPro digital fuel gauge which also tracks consumption per hour once calibrated.

Fuel type considerations:
The Espar heater prefers #1 fuel oil with no additives [extends time between maintenance periods; it can also run on #2 without issues, just more frequent maintenance.]

Therefore we dedicated one of our two tanks to #1 diesel to accommodate the heater since we are dependent upon it year around in our current cruising grounds.

The engine and generator both prefer #2 diesel [with temperature dependent additives to prevent waxing. [They can both also operate on #1 without short-term issues per manufacturer's documentation.]

The other tank is full of #2 diesel.

There are times when we are 'out there' when we need to transfer #1 diesel to the #2 diesel tank for the engine. When we do this, we just add the appropriate amount of additive to the engine tank to up the lubricity rating of the fuel to keep the diesel engines happy. [Note: both engines can run on straight #1 without any short term issues (according to the manufacturer's documentation) so if needed, we can just switch tanks and keep motoring/generating...]

Consumption:

• Engine [Ford Lehman SP90; 4 cyl, 90 hp] 
• 1.3-1.8 gph @ 7-8 knot- depending upon conditions
• Generator [Kubota D 722; 3 cyl]
• 0.3-0.8 gph- depending upon load
• Forced Air Heater [Espar D5LC]
• 0.15 gph- on high [worse case]

In our current cruising grounds where we motor ~80% of the time, we typically top-up diesel fuel once or twice a year.
[Note: When buying fuel from a low volume source, we run it through our large Baja filter on its way to the tank...]

Annual consumption currently averages around 200 gallons in our current cruising grounds- with 30-40% of that being used by the Espar heater while at anchor...

Fuel filter plumbing and monitoring:

Design note: Our twin Racor 500 filters are plumbed so we can use one at a time [SOP] with the other as an instant fail-over, or run them in series. [e.g., Put a 30µ filter in the first Racor, and a 10µ filter in the second.]

Future change: Add a vacuum gauge per filter to facilitate use in series; not necessary when used individually. Additionally, as currently plumbed we can sample pressure on each filter by switching the 3 way valve the vacuum gauge is plumbed to. 

The Racors are mounted in the engine room and, while very accessible, are not visible from either helm station. Therefore, I installed a vacuum gauge that reads the active filter, and the gauge has a red tell-tale needle to show the highest reading on the gauge since the last reset. Very handy.

I intend to install a second gage (with tell-tale) in the overhead display with the other engine gauges at the lower help position in the near future.

We also installed water sensor alarms on both Racors to get an early warning that the active filter is at risk of shutting-down due to water in the bowl...

Related References:

• How to change fuel filters (video)
• How to repair/rebuild Racor 500 fuel filters