fuel consumption DD 671 N's

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05-30-2004, 01:08 PM
wshelton

fuel consumption DD 671 N's

I have a 80 model 43'FBDC with DD671 N's, I think J&T rated at 310hp. WOT is a honest 2500 RPM which is what they are rated for under load. My question is at what RPM would this boat need to run to be the most efficient under the following circumstances? I will be going upstream on the Miss. R. here in Memphis about a total of 310 miles without a fuel stop. I carry 275 gallons in the aft tank and in a forward tank 90 gallons. I intend to carry two 55 gallon barrels as well. With the current here around 8 to 10 mph this boat seems to run better at around 2200 to 2300 upstream. I can back down to around 2000 which requires a lot more effort to steer against this strong current which I think due to the large keel these boats have. Whats the difference in fuel consumption at these deferent RPM"S and any other thoughts about a running speed. I think at 2000 I am making about 10MPH and at 2300 maybe 12MPH. There will be 4 adults on board with enough stuff for 4 days. tuned props and a clean bottom just painted. Thanks
05-30-2004, 04:02 PM
captjack43

fuel burn / hr.

I have twin J&T 310 6/71's in a 37 Hatteras. 2250 rpm is as fast as I run, burning 24 gals. per hour total for both engines
05-30-2004, 07:36 PM
Jaxfishgyd

fuel burn

I have a 1973 43'DC. I run 1100 rpm and burn 6 gph while getting 9kts. I can run 12 kts but then burn 18 gph and at 15kts burn 28 gph.
Since hull speed it the deciding factor (my 43's is 8.9 kts) it then takes four times the power for each kt you want to go after that
05-31-2004, 02:15 AM
Walter Pereira

fuel burn (6-71 JT's) 310 hp

Quite a few years ago I also had a 1973 43 DC with 310 JT's. My fuel burn was about the same as listed above, I liked to run at 1200 RPM's (9.2 K) average with about 6-7 gal per hr. When I sold the boat years later, the engine surveyer said that the engines were like new, however, he also noted that they should be run hard on occasion to keep temps etc ok. One of my present boats is also a 43 DC (1980) but it has 6-71's TI's and as such it is not a good idea to run slow because of possible "coking" of the turbo's. I love the trawler economy but it's nice to know that I have the juice to move if nec. Incidently, check with the river pilots and try to figure the best way to get upstream by staying closer to either shore. The currents swirl and can actually improve your performance over running the center. Walt
02-07-2020, 05:13 PM
Texsdream77

Re: fuel burn / hr.

Quote:

Originally Posted by captjack43

I have twin J&T 310 6/71's in a 37 Hatteras. 2250 rpm is as fast as I run, burning 24 gals. per hour total for both engines

Old Post I know. Maybe someone will see this. I have a '73 43' MYDC with DD 6-71s rated at 216 HP. How are people figuring out fuel burn? Gauges? (What setup?). Or just cruising and filling the tanks?
02-07-2020, 05:21 PM
madhatter1

Re: fuel consumption DD 671 N's

On both boats I cruise, fill, and figure. Get to know what it burns both on plane, off, and overall with a mix of both. Then use on plane numbers when budgeting and figuring for trips. That way it’s always less than figured and plenty in reserve just in case.
02-07-2020, 05:50 PM
Jammin'

Re: fuel burn / hr.

Quote:

Originally Posted by Texsdream77

Old Post I know. Maybe someone will see this. I have a '73 43' MYDC with DD 6-71s rated at 216 HP. How are people figuring out fuel burn? Gauges? (What setup?). Or just cruising and filling the tanks?

That seems like a low HP rating for those engine. Do you know what injectors you have?
02-07-2020, 07:23 PM
lisaann

Re: fuel consumption DD 671 N's

Mine burn .75 miles per gallon@2050rpm
1968 41c
02-11-2020, 08:43 PM
spartonboat1

Re: fuel burn / hr.

Quote:

Originally Posted by Texsdream77

Old Post I know. Maybe someone will see this. I have a '73 43' MYDC with DD 6-71s rated at 216 HP. How are people figuring out fuel burn? Gauges? (What setup?). Or just cruising and filling the tanks?

Never heard an hp rating that low. Most (all?) Naturals (non-turboed) 6-71's are J&T 310hp. (J&T= Johnson and Towers). Was that a typo?
02-11-2020, 08:57 PM
Texsdream77

Re: fuel burn / hr.

Quote:

Originally Posted by spartonboat1

Never heard an hp rating that low. Most (all?) Naturals (non-turboed) 6-71's are J&T 310hp. (J&T= Johnson and Towers). Was that a typo?

I can't find the injectors it has. But the surveyor checked twice. He says by the serial numbers these engines are 216 hp. He also said that the Detroit could be 165-225 for this vintage. Unless of course they were retuned. I looked at 3 of these boats before buying this one. This is the lowest HP rating of them all. The others were around 250 each.
02-14-2020, 02:28 PM
newinlet

Re: fuel consumption DD 671 N's

J & T 671n 310 HP n/80 Injectors
02-14-2020, 03:13 PM
Jammin'

Re: fuel consumption DD 671 N's

Mine are J & T 671n 260 HP n/70 Injectors.