How much fuel will 2, 200HP, 4 cycle outboards use in one hour? Lets say at half throttle. A rough guesstimate is all I need.
It will depend on the size, weight and propeller size
to figure fuel burn. I am familar with the DFI 2 strokes
and they would probably burn 15-20 GPH @4,000.
The four stroke would probably be around 12-15GPH.
My previous boat was a 27' Blackfin powered by twin
225 Mercury Optimax. It burned about 19 GPH at 4,000 RPM.
What type of boat are you building or repowering?
Just for rough estimates, try 6 grams per horsepower per minute. Actual consumption will vary depending on level of tuning of the engine, octane rating of the fuel, and atmospheric conditions, but this will put you in the ballpark for figuring out tankage estimates.
((6xPxT)/1000)x0.264 = GPH in US gallons
P = horsepower
T = time (use 60 to convert to hours)
As the originator of that particular set of design details, it was from personal experience that I suggested the use of dfi outboard power for our project boat.
My parents run a heavy (4 ton) 26 foot deep vee dive boat with a pair of 225 Optimax Mercs on the back. Consumption generally runs at arund 2 litres per nautical mile @ 45 knots. (approx 2.5 nmpg) At displacement speeds - where traditional 2 strokes threw fuel straight out the exhaust at an alarming rate - the boat can better 6 nmpg.
My own boat, a 27 foot Searay with a 5.7L mercruiser sterndrive, can almost match the optimax's at cruise (though in my case that is around 22 K), but in order to attain anything like the 6nmpg you would have to look at a lightly powered diesel displacement cruiser.
I must confess that I have no experience with the larger 4-stroke outboards, but magazine tests would seem to indicate that their consumption is similar.
Imaginocean Yacht Design
Logic will get you from A to B... Imaginocean will take you everywhere else...
I'd say about
70 litres between the pair of them probably (or 15 - 16 US gallons roughly)...but heck thats a real rough guess based on what my twin 115 hp 4 stroke hoonda's on a 25 ft boat use.
It does vary a heck of a lot depending on wind, sea state, whether on plane ir not, prop pitch ahd so on...
Thing is - a fuel flow gauge will tell you the answers at all throttle settings real time - so rather than estimate / guess - jut=st figure what HP you need - and make te fuel tanks as big as you safely cab for best range - then trim everything else in after she's built and launched.
It will all need tweaking after the fact anyway...so why bust a boiler over it before hand?
Simplest "rule of thumb" each 10 hp will cost a gal/hr with a gasoline engine.
200hp engine at half power 10gph per engine.
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