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Originally Posted by tumbleweed35
At a little above idle speed my A4 pushes 13,000 disp at 3.5 kts and uses .5 gal per hour. Increase speed to 4.5 kts and use between .75 and 1 gal per hour. This is with a three blade 12x6 prop
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I've measured this closely and with a 33 foot, 10,000 lb. fin keeler pushed by a 12 x 6 fixed prop AND towing a Zodiac at 5 knots cruising speed (about 1,700 RPM at a guess), I used 0.73 Imperial gallons per hour, which is about 0.875 U.S./hour.
Had I dropped to 4.5 and took the Zodiac off the stern, I estimate I would have gained about 0.15 Imp gal/hour. I used these figures to determine that I could replace the original 15 Imp. gallon Monel tank with an 11 U.S. gallon Tempo tank and could gain needed locker stowage and shed weight. My range is cut by approximately 1/3, but if I am cruising, I can carry 5 gallons of jugged gas and solve that problem as needed. Frankly, if I only day-sail, I have difficulty using up a single tank in a season just motoring in and out of my basin...which is why an A4 makes a lot more sense than a small diesel when you motor two-three hours a month! Diesel HATES that kind of light duty use.