Cummins 6 bta 5.9 330hp

[Fishsail]

Curious question? Anyone have a pair of these that can give an approximate fuel burn at slow speeds 7-8 knots in a 40’ something vessel? Tnx

 

[Comodave]

Welcome aboard. Most likely in the range of 5 or 6GPH.

 

[Ken E.]

Agree with Dave

 

[Sababa]

I have a single that burns 2 gph at 1200 RPM to go 7.5 knots in my 40 LOA Nordic Tug 37. I’m guessing a pair would be running no more than 800 or 1000 to go the same speed in a similarly sized boat. So I’d expect 3-4 gph tops. But I’d be worried about carbon buildup running them so low for extended periods. 660 HP on a boat that size sounds like go-fast sizing to me, not a trawler setup.

 

[rslifkin]

In a 40 footer, I'd expect 2.5 - 3 gph total at 7 kts. Maybe a little better if you're lucky.

 

[PJHoffnet]

I have a 1999 Maxum 4100 SCA with twin 6BTA 5.9 M3s. I cruise in the 8-9kt range at ~1,900 RPM and burn (combined) about 1g/nm. This is a six year average over a lot of weather conditions/tides, etc.

 

[PJHoffnet]

Sorry, see that you're looking for GPH ... so doing the math, I'm getting about 8g/h for the pair.

 

[Sababa]

I have a 1999 Maxum 4100 SCA with twin 6BTA 5.9 M3s. I cruise in the 8-9kt range at ~1,900 RPM and burn (combined) about 1g/nm. This is a six year average over a lot of weather conditions/tides, etc.

These numbers don’t make sense to me. The M3 is the 370 hp version. At 1900 RPM you should be consuming 11-12 gph and generating about 500 hp between the two engines. Seems like you should be driving a 25,000 lb boat a lot faster with that much grunt. For comparison, my single 330 drives my 22,000 lb boat at 10 knots with 227hp at 1800 rpm burning 5.2 gph.

https://www.sbmar.com/docs/performance-curves/6BTA%20%5B370,3000,2208,HO,Dec%2000,M-90034%5D.pdf

https://www.sbmar.com/wp-content/uploads/2018/07/6BTA-33028001975HONov-00M-90208.pdf

 

[Fishsail]

Thanks guys, I was hoping for those low numbers, PH Hoffnet the boat we’re looking at is similar to yours. I’m guessing at idle she would do around 4-5 knots ? Bump up to 1200-1300 would put me around 7 knots. Coming from a sailboat we’re pretty happy. I understand I’ll have to run them up every few hours to keep the temps up and run the turbos,

 

[sunchaser]

Although 3-5 gph is in the ball park at theoretical hull speed, props move boats per Tony Athens the Cummins guru. Once a specific boat and props are known then some additional and real world data points will spring forth at various boat speeds.

BTW, calm waters vs offshore swells result in very different numbers. Throw in generators and diesel heat different numbers appear too. For longer distance cruising range becomes a watch point in addition to gph.

 

[rslifkin]

Thanks guys, I was hoping for those low numbers, PH Hoffnet the boat we’re looking at is similar to yours. I’m guessing at idle she would do around 4-5 knots ? Bump up to 1200-1300 would put me around 7 knots. Coming from a sailboat we’re pretty happy. I understand I’ll have to run them up every few hours to keep the temps up and run the turbos,

I ran the numbers for swapping the gassers to QSB 380s at one point in my boat (38'). With a 26 - 27 kt top speed (25 kts with the slightly lighter weight 340hp gassers), I estimated something like 4.5 - 4.8 kts at idle and a 7 kt slow cruise would be at or just below 1000 RPM. I remember someone on here mentioning that while Cummins warns about extended idling, they were fine with the idea of cruising a couple hundred RPM above idle for sustained periods. Periodic run-ups would be a good idea though.

 

[MV CELESTIA]

Curious question? Anyone have a pair of these that can give an approximate fuel burn at slow speeds 7-8 knots in a 40’ something vessel? Tnx

I have this exact set up. Cruising RPM 1350. 2.9 GPH for both engines. Speed 6.8 against strongest current and 10.2 going with the strongest current. Hope that helps. Great engines!!!

 

[Jorgeinseal]

I have exact engines on a 41 ft Maxum and this is what I copied from Cummins burn rate at varying rpm's, not knots per hour.

Fuel Consumption
RPM Gals/Hour/Eng Tot Fuel/Hour
3000 20 40
2800 15.8 31.6
2400 10 20
2000 6.5 13
1800 4.9 9.8
1600 3.6 7.2
1400 2.7 5.4
1000 1.4 2.8
800 0.9 1.8

 

[DDW]

These numbers don’t make sense to me. The M3 is the 370 hp version. At 1900 RPM you should be consuming 11-12 gph and generating about 500 hp between the two engines. Seems like you should be driving a 25,000 lb boat a lot faster with that much grunt. For comparison, my single 330 drives my 22,000 lb boat at 10 knots with 227hp at 1800 rpm burning 5.2 gph.

https://www.sbmar.com/docs/performance-curves/6BTA [370,3000,2208,HO,Dec 00,M-90034].pdf

https://www.sbmar.com/wp-content/uploads/2018/07/6BTA-33028001975HONov-00M-90208.pdf

You have to be a little careful reading those charts. While the engine CAN produce 227 hp at 1800 rpm, because of the prop absorption curve, it WILL only be producing about 100 hp, as shown on the prop chart. As a reality check, using a rule of thumb of 20 hp/gal/hr typical of a modern diesel, 5.2 g/h x 20 is 104 hp.

 

[Sababa]

You have to be a little careful reading those charts. While the engine CAN produce 227 hp at 1800 rpm, because of the prop absorption curve, it WILL only be producing about 100 hp, as shown on the prop chart. As a reality check, using a rule of thumb of 20 hp/gal/hr typical of a modern diesel, 5.2 g/h x 20 is 104 hp.

OK, but apples to apples the twins should be putting out more than double the prop horsepower at 1900 rpm than the single at 1800 rpm. So why are the twins not moving a boat of roughly the same size faster?

 

[Gdavid]

OK, but apples to apples the twins should be putting out more than double the prop horsepower at 1900 rpm than the single at 1800 rpm. So why are the twins not moving a boat of roughly the same size faster?

The answer is because the engine's are not putting out double the horsepower. Remember that the line you see on a horsepower/rpm is the maximum potential, it can operate under the curve. If the engine is not operating under a load, it can reach that rpm without the fuel consumption or the vessel speed that would correspond with the output along the power curve. It is kind of like running the engine to a higher rpm in neutral.

 

[ksanders]

In my Bayliner 4788 I get about 1.75 nmpg at 1250 RPM with a speed of around 7.5 knots.

That is real life fuel burn from my 330 cummins

That comes out to be abut 2.15 GPH from each engine.

 

[rslifkin]

In general, speed vs RPM with a given engine is going to depend on how the boat is propped. So the top speed of the boat matters a lot for that. A boat that does 12 kts at WOT will need more RPM to reach 7 kts than the same engine in a lighter boat that does 20 kts at WOT (assuming both are propped correctly).

 

[PJHoffnet]

You're correct

Thanks guys, I was hoping for those low numbers, PH Hoffnet the boat we’re looking at is similar to yours. I’m guessing at idle she would do around 4-5 knots ? Bump up to 1200-1300 would put me around 7 knots. Coming from a sailboat we’re pretty happy. I understand I’ll have to run them up every few hours to keep the temps up and run the turbos,

Idle (~600RPM) for in and out of slip/marina about 4kts and no/min wake (~1,000RPM) about 6kts.

We do just like you say ... normally cruise around that 8-9kts range, but bump it up onto plane and run in that 2,000-2,500RPM range for ~20 minutes every day (depending on area/navigation restraints). Push to WOT (~2,800RPM) for 3-5 minutes too.

We're prop'd with 24X26X4

 

[Comodave]

Thanks guys, I was hoping for those low numbers, PH Hoffnet the boat we’re looking at is similar to yours. I’m guessing at idle she would do around 4-5 knots ? Bump up to 1200-1300 would put me around 7 knots. Coming from a sailboat we’re pretty happy. I understand I’ll have to run them up every few hours to keep the temps up and run the turbos,

I run my boat up on plane for 15 to 20 minutes after we get out of the river or the marina to heat up the engines and then we slow down. If we run slow for the beginning of the cruise then the engines don’t really come up to temp. So rather than running them cold all day and then running them up at the end of the day, I like to heat them up first.

 

[PJHoffnet]

Agree to disagree

These numbers don’t make sense to me. The M3 is the 370 hp version.

My engine's data plate does not agree

At 1900 RPM you should be consuming 11-12 gph and generating about 500 hp between the two engines. Seems like you should be driving a 25,000 lb boat a lot faster with that much grunt. For comparison, my single 330 drives my 22,000 lb boat at 10 knots with 227hp at 1800 rpm burning 5.2 gph.

The 4100SCA is 30,000lb. Looks like we're looking at the same fuel curves, but not coming up with the same ball park numbers. I'm just providing a real world (average of six years of data) observation ... not a 'laboratory' curve number. So, we'll just agree to disagree. Too many real world variables those curves don't take into considerations.

 

[Sababa]

My engine's data plate does not agree

The 4100SCA is 30,000lb. Looks like we're looking at the same fuel curves, but not coming up with the same ball park numbers. I'm just providing a real world (average of six years of data) observation ... not a 'laboratory' curve number. So, we'll just agree to disagree. Too many real world variables those curves don't take into considerations.

I blame the Internet for any confusion on my part about engine models and boat weights, and I don’t doubt for a second your real-world experience. I was just curious to learn why it takes you roughly double the fuel and power to push your boat with two engines at the same speed as mine with one.

 

[PJHoffnet]

Don't konw.

I was just curious to learn why it takes you roughly double the fuel and power to push your boat with two engines at the same speed as mine with one.

That's a question I'm afraid I can't answer. If we were just a little different we could easily chalk it up to the countless variables in environment/cruising styles. You getting twice the milage (which is fantastic, good job) - that's something I can't figure out. As you say, tough to 'argue' with real world observations ... in the long run, it is what it is.

 

[Sababa]

That's a question I'm afraid I can't answer. If we were just a little different we could easily chalk it up to the countless variables in environment/cruising styles. You getting twice the milage (which is fantastic, good job) - that's something I can't figure out. As you say, tough to 'argue' with real world observations ... in the long run, it is what it is.

The most important thing is that we are getting on the water and living the dream!

 

[Captain Doug]

My 2003 37 Nordic Tug, Cummins 6BTA 5.9 M3 gets just over 3 nmpg at 1400rpm.

 

[North Baltic sea]

I ran the numbers for swapping the gassers to QSB 380s at one point in my boat (38'). With a 26 - 27 kt top speed (25 kts with the slightly lighter weight 340hp gassers), I estimated something like 4.5 - 4.8 kts at idle and a 7 kt slow cruise would be at or just below 1000 RPM. I remember someone on here mentioning that while Cummins warns about extended idling, they were fine with the idea of cruising a couple hundred RPM above idle for sustained periods. Periodic run-ups would be a good idea though.

yep, I asked the Cummins factory about it and they advised that the Cummins QSB can run without worry 24/7 min rmp 830. Idle max 5 minutes. Correctly dimensioned propeller by default. No coal. glazing or past blowing.

Note, only QSB!

NBs