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After reading through a bunch of posts I see a 31 fitted with 454s will do approx 1 mpg at best. What is a typical cruise speed to get this and at what RPMs? How many gph is this burning?

In the real world offshore facing 2-3 footers and even 4's how much does that change the fuel economy or what is a more realistic fuel burn in these conditions? I will be mostly fishing offshore with a 50 mile round trip. How many gallons of gas would I burn just to make this trip not including trolling? Which brings me to my next question. What is the burn rate for trolling with just the engine put into gear, lowest speed possible? What is the burn rate for say a 6 knot troll speed?

What is the the max RPMs for these motors? What seems to be the best HP rating for economy and longevity?

I know threre a bunch of questions but I figured I would ask them all in one thread. This information will really help me figure out what it will cost ME to run this boat. Thanks again guys!

I had 454s ,in those seas I would cruise at 18-19 kts probably burning 24 or 25 gal/hr. mayt have to slow depending. at troll its hard to say, 5or 6 kts at idle, probably 6gal/hr just guessing there. a 50 mile rountrip run and 4 hr. troll I'd put in a min of 75 gal. now w 6btas same profile maybe 40 gals. Find a diesel boat. Oh and if you have little rudders, forget single engine trolling,except if your pattern is a circle

Max rpm is 4200-4400 on older 454s. My '69 FBC cruises at 3000 rpm at 22 knts., or 2800 rpm at 20 knts. For a 50 mile round trip, I'd stick with gassers. Gassers 31s are alot cheaper, and are easily maintained. If you ever need a mechanic, gasser mechanics are alot easier to find and bill at a much lower rate. They'll also slow troll down to 2 knots or so on one motor--no trouble steering if you get Capt. Pat's rudders (a must have). I don't have accurate numbers on fuel burn, but I'd guess 1 mpg is about right. I slow trolled last Friday for 6 or 7 hours on one motor at idle--fuel gauge never moved.

If you need the range (70 mile canyon runs, etc.), or are going to put alot of hours on the boat, go diesel.

When I had the 454's in mine at 3000 I was pushing around 19 knots. I am running light also, no tower and not loaded to the gills, only full fuel. So John does pretty good at over 20 knots. Our burn rate was around 25 gallons an hour. An trip to the tip of the Hudson from Barnegat Inlet, leave early morning/ troll all day, lay up for the night and troll half day next day and work our way insure would use between 160 and 175gallons.

For a 50 mile run I would not worry about fuel too much unless you do it a lot.

I had Chrysler 440's before I went to Cummins. Fuel numbers sound right with one difference that I found. If I ran to my usual offshore sharking spot with my son only, and did the same trip the following week with a crew of 4-5, the fuel consumption on our returns was considerably different. With the Cummins, whether I go alone or with 6 gorillas, the fuel consumption is exactly the same. I cruise at 20-21 kts @ 16 gph vs 28 gph, and presently gasoline and diesel prices are about the same where we are.

I have 440's and the numbers given I can ditto.

If you have an older boat, the tank was 160-170 gallons so a 50-60 mile trip is about the max (following the 1/3 rule), unless you stop early and troll out further.

The again if you have a fiberglass tank you may have already changed that or will and a bit extra fuel can be a nice thing.

I have Mercruiser 454 EFI MPs on my 31 Bahia Mar. In smooth water, I cruise 20 kts typically turning 2400 to 2600 rpm depending on how heavy it is. I don't have fuel flow guages, but if I zero out my GPS trip odometer when I top it off, it will usually take about the same number of gallons as the trip odometer says the next time I fill it, equating to 1 mpg. My boat might even be on the heavy side with a stainless steel marlin tower and hard top.