Fuel Flow spread sheet for 300 da

[Iprof]

I've wanted to do this for a a long time but I just never got around to building a spread sheet for fuel flow. I have a Lowrance Chartplotter with the fuel flow meters and I have the the tank capacity gauge for one of my fuel tanks but I was not happy with the data it provided. Yes it gave me my speed over land and my fuel flow but I wanted to know my range and my best gph vrs speed and distance. Here are my calculations from 800 to 1600 rpm.

RPM's	Speed MPH	Stb Fuel Flow	Prt Fuel Flow	Combined GPH	MPG	Fuel in Tank	Range Miles
600				0.00	#DIV/0!		#DIV/0!	#DIV/0!
700				0.00	#DIV/0!		#DIV/0!	#DIV/0!
800	4.1	1.10	1.10	2.20	1.8636	100	186.36	45.45455
900	4.8	1.20	1.20	2.40	2.0000	100	200.00	41.66667
1000	5.4	1.50	1.50	3.00	1.8000	100	180.00	33.33333
1100	6.1	1.80	2.00	3.80	1.6053	100	160.53	26.31579
1200	6.5	2.10	2.20	4.30	1.5116	100	151.16	23.25581
1300	7.1	2.20	2.30	4.50	1.5778	100	157.78	22.22222
1400	7.5	2.60	2.80	5.40	1.3889	100	138.89	18.51852
1500	7.7	2.60	3.10	5.70	1.3509	100	135.09	17.54386
1600	8.1	3.20	3.20	6.40	1.2656	100	126.56	15.625

This shows so far that 900 rpm is my best economy 4.8 miles in an hour and 2.4 gallons consumed and 2 miles to a gallon of gas not bad for a very heavy carbed boat. I know my starboard carb needs to be rebuilt and the numbers are really going to get high once we start getting it on plan. I will do the chart all the way up to wot. I find it interesting that from 1300 to 1400 rpm there is such a big difference.
I have 100 gallons of fuel and 40 gallons of water and the holding tank is half full and there is very little food on board. The lake was alm not dead flat and I did the runs going out and coming back in over the same distance.

Ken

 

[jorge]

Hellow there, Great inf. thanks for your time looking foward to see the other chart as it go up:thumbsup: . this way we can safe fuel goin at lower speed.we are at $4.19 per gallon this weekend. i been goin at 2000 rpm to safe fuel and enjoy the ride to the beach. i just did the allure floor. will post later.:smt038
Jorge

 

[JVM225]

Great info!
My wife likes to cruise leisurely so I spend a good amount of time at about 1200 RPM when she is out with me. It's amazing how fuel efficient the boat is at that speed. I don't rely on my fuel gauges, so last year I installed fuel flow meters to work with my Garmin 4210. They work really well and seem to be off by about 6 or 8% overall. Part of that could be that I don't turn the Garmin on until I am ready to pull away from the dock so it isn't registering the gas between when I first start the engines and when I pull away.
They were a great investment.

 

[Ka1oxd]

I would like to see what you are getting around 3k rpm. I wish I had the money to through the fuel flow gauges in my boat. I also have 7.4 L so I am sure it is a little different.

 

[JVM225]

I would like to see what you are getting around 3k rpm. I wish I had the money to through the fuel flow gauges in my boat. I also have 7.4 L so I am sure it is a little different.

Mine is actually not bad at 3000 - 3150 or so. That's just before the secondaries open up.
Believe it or not those Qudrajets are pretty fuel efficient when just using the primaries. My replacement motors have the Holley replacements that are based on the Quadrajets.
Once the secondaries open up the motors get real thirsty. The trick is to keep them closed while on plane. The fuel flow meters really help you to see when you are crossing that point, but you can usually hear it anyway.

 

[Ka1oxd]

I also heard that you can tighten up the secondaries so they do not open as fast. Oh yes! I know what it is like to open them up. On the 4th fireworks, I was watching the sync gauge and not paying attention to the tach. The sync gauge is off a little. The port was running at 3500rpm and the starboard was running 3000 rpm. I did not catch it until an hour under way was over. I burned double on the port over the starboard engine.

 

[rondds]

I did not catch it until an hour under way was over

Wow...how did you not hear that difference? Stereo cranked?? ;-)

3000RPM = ~12gph
3500RPM = ~17gph

 

[SCORPIO]

This weekend I was troubleshooting a heating problem and ran for about an hour at 2800 rpm each and my flow meters showed 8.1gph port, 7.9gph starboard. Port is a bit fresher engine maybe that is the difference. BTW speed was 25.3mph. I had full fuel tanks, half waste and 1/4 or less water, all my tools, gear etc plus a friend with me.

 

[Iprof]

Here are some more results. I have done all the runs so far with the trim tabs up. Once I get a full set of numbers I will play with the tabs and the RPM to show the best economy, funny using that word with a boat, economy.

RPM's

Speed

Stb

Prt

Combined GPH

MPG

Fuel in Tank

Range Miles

​

1700	8.3	4.40	4.20	8.60	0.9651	100	96.51
1800	8.9	4.80	5.00	9.80	0.9082	100	90.82
1900	9	5.30	5.20	10.50	0.8571	100	85.71
2000	9.1	5.30	5.80	11.10	0.8198	100	81.98
2100	9.4	6.40	6.00	12.40	0.7581	100	75.81
2200	9.6	6.40	6.30	12.70	0.7559	100	75.59
2300	10	6.80	6.40	13.20	0.7576	100	75.76
2400	10.6	6.90	7.90	14.80	0.7162	100	71.62
2500	10.6	8.40	8.80	17.20	0.6163	100	61.63

I pulled my port carb off on Monday and sent it in to be rebuilt, it's the original carb never rebuilt. The fellow that rebuilt it said it looked like nothing was wrong with it. When we installed it I turned the key pumped the gas and within 2 seconds if started. I pulled the throttle back to neutral and the boat kept running at 850 rpm, once it warmed up we set the idle to 600 rpm and it sounds so nice. We have been having rain and high winds the past few days and it will continue over the weekend, I hope to get back out on the water compare my first and second set of numbers and finish the fuel flow to WOT by next week end.

Ken

 

[rondds]

You're going to burn all your gas money on trial runs!

 

[Iprof]

You're going to burn all your gas money on trial runs!

It has been a dollar or two. After the carb rebuild if and I did say if the fuel flow is equal on each engine and not how it has been when on plan. I will recover the 300.00 for the rebuild in 15 hours of boating now the trial runs are just fun to do and it gets me out on the water.


Ken

 

[Iprof]

Well the carb rebuild has been great for starting, pump the gas twice it fires up and I can pull it back to neutral and the boat idles fine.
The bad news I still have a difference in fuel consumption but not as bad but at 3600 rpm I am doing 27 mph and burning 8.8 starboard and 12.2 port. We went on a 50 mile run and the 3600 was the best economy. I need to figure this out and soon an extra 4 gallons an hour while on plan will start to add up next summer on our 7 week cruise.

Ken

 

[Iprof]

This weekend I was troubleshooting a heating problem and ran for about an hour at 2800 rpm each and my flow meters showed 8.1gph port, 7.9gph starboard. Port is a bit fresher engine maybe that is the difference. BTW speed was 25.3mph. I had full fuel tanks, half waste and 1/4 or less water, all my tools, gear etc plus a friend with me.

This is great economy, I wish I could get this but at 2800 rpm I am barely on plan.

Ken

 

[rondds]

Ken...I'm too lazy to read back through everything and I'm sure this was addressed...did you tune both engines? Plugs, dist cap, wires, rotor, points (if you have), ignition sensors. Last fall I had a pretty large discrepancy btwn the engines (port burning about 20% more). Discovered three plugs had (I guess) vibrated out and were barely finger tight on the port engine. Replaced all plugs and torqued properly and now the two motors run at the the exact same GPH at all RPMs (according to the Floscans). I had also replaced wires and both ignition sensors (that other thing inside the dist cap).

 

[Pack66Dad]

The 300DA's must be a lot lighter than the 300DB's I don't get those numbers. I carry 70 gallons of water and 140 gallons of fuel too. I'm sure the dinghy sitting on the swim step doesn't help much either.

I have almost stopped looking at GPH, now I look at the GPM readout on my fuel flow to judge economy. On our trip to Canada (loaded to the gills) I noticed that my GPM was almost the same at 8 knots as it is at 20 knots about 1 GPM total (both engines combined). The middle ground around 10-15 knots is abysmal, getting a bad as 3 GPM total.

 

[JVM225]

Well the carb rebuild has been great for starting, pump the gas twice it fires up and I can pull it back to neutral and the boat idles fine.
The bad news I still have a difference in fuel consumption but not as bad but at 3600 rpm I am doing 27 mph and burning 8.8 starboard and 12.2 port. We went on a 50 mile run and the 3600 was the best economy. I need to figure this out and soon an extra 4 gallons an hour while on plan will start to add up next summer on our 7 week cruise.


Ken

What kind of props are you running, and how many hours on the motors? I'm doing 30 MPH by GPS in normal conditions at 3100-3200 RPM with two new motors, the CR drive on the port side, and 15.5 x 17 stainless props with my wife and two kids on the boat and close to 100 gallons of gas and an alomost full fresh water tank. The props made a huge difference for me.

 

[SCORPIO]

Iprof, check the timing on the engine with the high burn rate in addition to the tune up suggestion.

JVM, did you go to four blade props when you did the counter rotating conversion? Are those prop specs three or four blade?

I'm going to do the conversion this winter and want to go to four blade props but don't know where to start on the pitch/dia issue. Hoping to find somebody thats done it already. Could you post the procedure you used on the shifter cable swap?

Thanks

 

[JVM225]

Iprof, check the timing on the engine with the high burn rate in addition to the tune up suggestion.

JVM, did you go to four blade props when you did the counter rotating conversion? Are those prop specs three or four blade?

I'm going to do the conversion this winter and want to go to four blade props but don't know where to start on the pitch/dia issue. Hoping to find somebody thats done it already. Could you post the procedure you used on the shifter cable swap?

Thanks

I stayed with 3 blade props. Mainly because I had swapped the props a year or so before I put the CR drive on and wanted to be able to re-use at least one of them. If I went with 4 blade props I would have needed to buy 2. Instead I just bought a matching CR prop.
The way the boat is performing, I am going to stick with what I have. I'm really happy with it.
As far as the CR swap is concerned there are no changes in the back of the boat other than getiing a CR prop. The only other thing that needed to be done was changing the position of the cable for that side up at the helm control.
I had a hack of a time finding a good used CR drive, but it was worth the wait.

 

[Iprof]

Lots of good questions and input.

The boat was tuned in the spring and the timing check again after the carb rebuild. I do have a CR drive with a 4 blade aluminum props, both re manufactured last winter. There are no points with my ignition. I will check the spark plugs, that is a possibility. I have just over 1100 hours on each engine, oil pressure is good on both 40 to 45 on port when warmed up and 45 to 55 on the starboard. I read through a thread on engine sync and I am wondering about my sync gauge and tac. I can switch the wires on the tac and try and sync by sound rather than the gauge.

I scanned the manual into a pdf file on how to change the shifter on the CR drive if you need it give me an email address that allows attachments and I will send it.

JVM225 I am not getting close to your economy, I do have a factory generator, running with 100 gallons in each tank 40 gallons of water and 3/4 full holding tank and 1 fridge and a portable 12V 47L freezer and 4 days of food. I do have a line on a pair of 383 strokes and if the price is right I just might change both engines 1100 hrs on gas is a lot even if most have been done at 1100 rpms.

She weighs just under 10,000lb dry, I figure it is about 13,000.

Ken

 

[SCORPIO]

Ken, what dia and pitch props did you go with? I'm trying to figure out the conversion from three blade to four and I figure if somebody has already done this, it would save me a few headaches. I'll PM you my email for the pdf on the cable swap, thanks.