My Roberts 45' cut-away full keel cutter has a Perkins 4-236 85hp diesel and I'm trying to determine fuel consumption.
The boat weight is around 30000 lb. Unfortunately my generator runs from the same tanks which makes it difficult
for me to get some actual real life consumption data, even just ball-park values. I suspect the published values are
far removed from the actual ones and would appreciate some real data. Particularly, I'm interested in what rpm's
have been found most economical to get the best mileage and at what level one would expect to double consumption
per mile run. A plotted curve of consumption vs boat speed or rpm would be just dandy.
A second question is how to monitor consumption on an ongoing basis, keeping in mind there is a constant flow of excess
fuel back to the tank. Using a day-tank, accurately calibrated? Some gizmo? Monitoring the tank under way is not that easy
due to access and the fact that some of the tank walls are actually the hull and very much sloped. A dip stick or depth gauge
is not that feasible, though I may need to calibrate one during the next refill.
What have you done to solve this on your boat?
BTW: I have identical dual tanks on opposite sides of the engine, of about 115gals each. The return flow goes to one side only but I can draw off either side. Yes, a legacy PO design but it does allow for some load balancing. It also allows for diesel running out of the overfill escape if you forget to switch tanks at the right time. ( the EPA, Coast Guard and manatees all get their knickers wadded up and twisted into a knot when that happens! )
Thank you for your suggestions. They will be most beneficacious and welcome, no matter how squirrel-brained they may be