F36 Fuel Consumption Question

[zimmermanj]

One more question for all you friendly people on this web site. Assuming you are cruising at 20 knots in an F36, what is the typical gallons per hour (probably did not state it correctly) consumption assuming all things are fairly equal (weather, load, etc)? Does any one have a fuel consumption chart based on various speeds for an F36?

[LandVF36]

About a month ago, I finshed the installation of a pair of fuel flow guages and posted the following:

RPM /MPG /MPH /Port GPH /Starb GPH /Total GPH
750 /1.63 /4.74 /1.3 /1.6 /2.9
1000 /1.69 /5.75 /1.4 /2 /3.4
1250 /1.44 /7.78 /2.6 /2.8 /5.4
1500 /1.36 /8.7 /3.4 /3 /6.4
1750 /1.18 /10 /4.9 /3.6 /8.5
2000 /1.13 /10.8 /5.1 /4.5 /9.6
2250 /0.95 /11.3 /6.9 /5 /11.9
2500 /0.74 /12.8 /9.2 /8 /17.2
2750 /0.88 /17.6 /10 /10 /20
3000 /0.74 /21.3 /16 /12.9 /28.9
3250 /0.75 /26.5 /18.5 /17 /35.5
3500 /0.75 /30 /18.6 /21.4 /40

I learned two thinks for my trouble. One, that the engines were not both performing the same. Since thing I've fixed a couple of carb issues and they are closer now. Two, once up on plane, MPG stays around .75. It just depends how quick you want to get there.

Since boating is more about wasting time than anything else, I've tended to go slow fearing the amount of fuel burned is exponential. Now I know that to go 100 miles on river is going to burn about the same amount of fuel, regardless of how fast I push it. Just the same, I've favored the slow cruise unless the weather is bad and I just want t oget back to the marina.

[zimmermanj]

LV,

Thanks for the post and taking the time to provide the information. So I guess that unless you have deep pockets.................it is wise to run at or below 2,800 RPM's as the fuel consumption really jumps above that. Do you or have you used RPM syncronizers to ensure your engines are running at the same RPMs. I had them installed on an older Trojan and it made it much easier to sync the engines quickly with the digital read outs.

You Said in your post "Now I know that to go 100 miles on river is going to burn about the same amount of fuel, regardless of how fast I push it." I am not sure I understand that statement and maybe I am reading it wrong as it indicates that speed will have no bearing on the final fuel consumption after running 100 miles. Using your examples of 1,750 RPMs and 2,750 RPMs it seems that for the first scenerio that the Trip Durantion would be 10 hours, consume 85 gallons at a cost of $297 (assumes $3.50/gallon) with the second example being a trip of 5.68 hours, consume 113.6 gallons at a cost of $397. So if this is true, I guess the primary driver is what is your time worth and how deep are your pockets.

Again..............the chart is really helpful as I typically run 30 miles to fish and than troll at a slow speed for 4-6 hours and It makes the whole cost issue much easier to understand and also gives me a good idea of just how far I can go with full tanks.

By the way.................I came from Duluth Minnesota......where do you keep your boat.

Thanks,
Jim

[LandVF36]

I guess I should have been more specific. What I should have said is that over 2500 RPM, its really about .75 MPG. The faster you run, the faster you burn fuel but it costs about the same. When you are not up on plane, the incremental increase has a more drastic change on the pocket book.

We normally curise below hull speed, about 9 MPH.

I do not have a good syncronizer. I do it by ear. I installed a Lowrance electronics at the flybridge helm this summer with fuel flow guages. I'm hoping to pick up NMEA-2000 engine monitoring over the winter for tach, temp, and pressure and get rid of the analog guages.

We keep the boat in Red Wing, MN on the Mississippi and live about an hour away near Minneapolis.

Mitch

[Danny Bailey]

My 1980 F-36 did about the same performance with the 440 gas engines. No matter if I ran at 1600 RPM / 8 kts or 2700 RPM / 17 kts it was still all less than 1 mile per gallon. I'm getting considerably better mileage since I repowered with Cummins 250's. Not sure exactly how much better because I don't have Flowscans on the Cummins and I have not run it that much since the Arabs have decided to bleed us to death. It appears I'm getting between 2 - 2 1/2 MPG at 8 kts now but this is just a guess. These boats could be made fairly economical with two small diesels but you would never plane it out again.

[kboette1]

I know it is a really, really old post, but I was looking for exactly this information. I have an F36 and was wondering where the most economical cruising speed is other than hull speed. The only bit of information missing from the details were the prop sizes and engines. I assume that the engines were Crusader 454/350Hp. Thanks for any information you can add.

[Stripermann2]

Jim Zimmerman was the OP of this thread and a friend of mine. He died shortly after inquiring here, as he was thinking of purchasing an F36. He used to have a 32. He and I discussed it briefly and I don't recall for sure but think they had the 454s.

[prowlersfish]

I believe LandVF36 numbers are with 440s but should be close to what 454s do at the same speed

[bjanakos]

I have the 360's and I am not getting anywhere near 20mph on plane.

[kboette1]

I am very curious about the consumption at different speeds. I would love to find the sweet spot with out buying the flowscan, but I guess i need to get flowscans for the boat, and that is the only real way to find out. The key is running it just before the 4bbl kicks in, but it difficult to see that from the fly bridge I'm going to take her out for a spin this weekend a few times. Perhaps I'll wind her up a bit and get some speed/rpm info.

[prowlersfish]

I have the 360's and I am not getting anywhere near 20mph on plane.

What are your getting for top speed ?

[LandVF36]

The numbers from my F36 as shown in the table from Oct 2008 runs GM 454s w/ 330HP ea. I believe that there was about 400 hrs on rebuilt blocks at the time I took those measurements (if you believe the story the broker told me when I bought the boat a couple years prior ).

I'm pretty certain that the gears are 1.88:1 velvet drives. I will have to look again this weekend. The props are 3 blade 20x20.

It does make a lot of difference with the amount of gear on board. Empty in the spring, just after a fresh bottom paint, no water on board, and 1/4 tank of gas in each saddle tank (the aft tanks have been removed), and me as the only passenger, I pushed it up to 33 MPH at about 3900 RPM for 20 seconds once. The fuel rate was 57 GPH!!! I've not tried to run it that fast since , it is a 40+ yr old boat. Loaded down for a week long river trip with full water, fuel, supplies, and 5 adults, about 25 MPH is the max.

Another big factor is how clean the bottom is. I hate to admit it, but one summer my boat had to sit in the marina for 5 or 6 weeks with no activity. Here on the Mississippi you can literally grow a carpet on the bottom in that amount of time in late July / August. I could barely get the boat to plane with a full load until I stopped at a beach and cleaned up the bottom with a stiff brush.

[P-Dogg]

i need to get flowscans for the boat

If you have gas engines with no return line to the tank, I recommend Garmin GFS10s instead. Connect them to the fuel line and to a Garmin chartplotter (possibly any N2K compatible plotter) and you miles per gallon, miles to empty, etc. As an added bonus, you can connect a level sensor to each GFS10 and the tank level shows on the chartplotter. How many people have a fresh water level gauge on their boat? ME! Since I have twin engines, one level sensor is for the fuel tank, the other is for the water tank.

[mikeandanne]

I second the Garmin gfs 10's....I installed that stuff, great info and all on the chart plotter just like Pdogg said..makes it easy to run your boat as efficiently as you want.....Mike

[bjanakos]

I have the 360's and I am not getting anywhere near 20mph on plane.

What are your getting for top speed ?

I haven't taken her down that hard yet. But I get up on plane at about 3,000 rpms and i'm at about 13 knts.

I had the bottom completely refinished on my other boat and there was a noticeable difference in top speed. I may do that this this one over the winter.

Another future upgrade will be the Lowrance version of the fuel flow sensors and tank sensors.