Detroit Diesel 4-71 NA

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With the caveats that

- I don't have fuel flow meters, and

- without genset fuel used, and

- understanding that with 2390 gal of fuel and 500 gal of water my burn rate changes as I reduce power to maintain the same speed (8 kts) as fuel burns/water is used:


My burn rates seem to average about 2.5 gal/hr per engine.


Hope that helps.
 
Also, I run at 1300 RPM most of the time. That puts me at 7.6 kts unless I haven't cleaned the running gear/bottom for a while...
1400 RPM is about 8.2 kts. At 1400 RPM I burn right at 3 gph per engine.
 
"At what rpm is that big blower cooling down the block in an unhealthy way? I always felt my engines were happier at 1400rpm or higher."

The blower on a DD is to push the exhaust gasses out while the exhaust is uncovered, and push clean air into the cylinder.

There is no loss of efficiency like a 2 stroke outboard or chain saw as the fuel is not injected yet.
 
As far as I know they run great lookup MV Flipflop on Facebook they have them and have been extensively cruising and I have yet to hear they have had any issues on their trip
 
FF that’s not what I was asking about. Let me reword.

What would be the minimum continuous rpm recommended to run a Jimmie where you would NOT need to “run at full power once a day to blow out the carbon?”
 
There are (were) MANY 71's in generator service that were equipped with small injectors and governed for 1200rpm. They would run for decades and gazzilions of hours.

Nothing wrong with running a 71 at 1200rpm in propulsion service. In propulsion work, I'd still kick it up to like 16-1800 every day or two to clean things up. Not really an option in generator service.

If a 4-71N is rated at 175hp, its got pretty big injectors in it. Probably N70 or N80. Hatt did this with their vendor Covington. They did a 671N rated at 300hp and I think it came with N80's. That would be 200hp in a 4-71. Most 71N's straight from DD had max inj size of N70.

Good engines. But beware of the noise out the exhaust. Most Hatt LRC's I've been on had an annoying exhaust drone noise at hull speed. Hatt did not do a good job setting up the proper mufflers.
 
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Ski in NC said:
There are (were) MANY 71's in generator service that were equipped with small injectors and governed for 1200rpm. They would run for decades and gazzilions of hours.

Nothing wrong with running a 71 at 1200rpm in propulsion service. In propulsion work, I'd still kick it up to like 16-1800 every day or two to clean things up. Not really an option in generator service.

If a 4-71N is rated at 175hp, its got pretty big injectors in it. Probably N70 or N80. Hatt did this with their vendor Covington. They did a 671N rated at 300hp and I think it came with N80's. That would be 200hp in a 4-71. Most 71N's straight from DD had max inj size of N70.

Good engines. But beware of the noise out the exhaust. Most Hatt LRC's I've been on had an annoying exhaust drone noise at hull speed. Hatt did not do a good job setting up the proper mufflers.
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Exhaust noise aside Hatteras does a pretty good job of powering there boats .Not many people would argue the quality of a Detroit .I wish they would’ve use these engines instead of the Ford Lehman which I have grown to dislike immensely .Great thread should be mandatory reading for the coastal trawler crowd
 
What would be the minimum continuous rpm recommended to run a Jimmie where you would NOT need to “run at full power once a day to blow out the carbon?”

Its the "run at full power" that is tricky.

An engine set up to operate at say 1200 RPM will have a "full power" HP that is very different from an engine set to operate at 1500-1800 or Sport fish/ fire truck.

If the 1200 RPM engine is correctly put together , there is no need to "blow it out",
it is the engines built for high RPM operation that may be over fueled at low speed use and might carbon up.

Full Load , at low RPM, is still that engines Full Load , although it might be 1/2 or less the HP a sport fish would hope for.

The art on a cruising boat is to prop and gear the drive set to stay in the center circle of a BMEP or fuel map for as much of the vessels ability as possible.

The difference can be 1,000 hours to rebuild for the sport fish ,
20,000 to 30,000 hours for the gen set or displacement cruiser.
 
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FF said:
An engine set up to operate at say 1200 RPM will have a "full power" HP that is very different from an engine set to operate at 1500-1800 or Sport fish/ fire truck.

If the 1200 RPM engine is correctly put together , there is no need to "blow it out",
it is the engines built for high RPM operation that may be over fueled at low speed use and might carbon up.
Click to expand...


Makes sense @FF. However bear in mind that a 2 stroke’s big blower is moving a large volume of air through the case and cooling off the block. At low rpm’s the block does not get up to proper operating temperature.

So based on the thread above, and your and @Ski’s comments, it’s starting to sound like 1200 rpm might be that point where continuous operation below that point (with the associated low load from a prop at that rpm) would be not recommended. The engine and the oil would not be able to reach a healthy operating temp.
 
Don't overthink this. There is nothing sacred about 1200rpm. You can run your DD at any power setting that makes sense for the boat as conditions dictate.

But if you do run low rpm/light load, it does help to power up for like a half hour to "let her eat". No need to go to full power, 1800 will get it done.

We ran a pair of 12-71TI at 950 rpm for a few days continuous as we were towing another boat offshore. Once we got to the coast and broke tow, I powered up to like 1900 and put boat on plane. It smoked pretty heavy for a minute or two, then cleaned right up. Those engines ran just fine for the next several years, and perhaps longer, as I lost track of the boat.
 
Had a 4-71 on a 23 ton Willard 40 it would reach hull speed at 1200 RPM and was quiet however developed a "wet stacking" condition (raw un-burned fuel in the exhaust) The solution was to run at 1500 RPM and at least run at max RPM for 5 min (1800 RPM in my case} to get max heat in the exhaust for a "burn out" this solved the wet stacking problem.
 
For me a 471 Jimmie is about as dependable as they get. Ran one for 27 years in a commercial freezer troller/longliner. When salmon trolling the engine would run 24/7 at low rpm and would idle at night keeping the hydraulic driven freezer operating. Longlining it would be operated hard between sets and to deliver in town, as these where ice trips, and time was of the essence.
It wasn't very noisy, the engine was set on super heavy duty mounts that kept vibration transfer to a minimum, and a short run drystack exhaust with very large muffler.
Normal conversation could be carried on in the wheelhouse, didn't require earmuffs or earplugs unless one ventured into the engine room.
Very common engine in Westcoast commercial boats.
Kit
 
My Willard was a conversion from an Albacore tuna boat and probably over powered for a cruising boat.....burned clean and was a 5000 HR rebuild, no smoke at all and ran like a top
 
CaptBud said:
My Willard was a conversion from an Albacore tuna boat and probably over powered for a cruising boat.....burned clean and was a 5000 HR rebuild, no smoke at all and ran like a top
Click to expand...

A lot of people on this forum no offense wouldn’t No a good engine if they tripped over it .How do you think your boat would be doing with a Ford Lehman in it . Moving on I recently read an article where a marine engine expert ,I don’t remember who he was but they were talking about Gardiner engines cat Detroit Cummings all a good commercial engines ,and was asked if he was going to power a recreational boat to do ocean crossings what would he use.To everybody surprise he recommended yanmar Said the Japanese really know how to build a small diesel engine . I like Kabota’s I know of one in a rental excavator keeping in mind it was a rental so not always treated well 38,000 hours and still going ,four-cylinder Kubota
 
453

Im coming into my 2nd year with a 453,oil changes at 200 hrs and gulf coast fuel filter itz in a 36 Willard sedan and think its a great setup,easy to work on,parts are everywhere,and it has been very reliable
 
Lostsailor13 said:
Im coming into my 2nd year with a 453,oil changes at 200 hrs and gulf coast fuel filter itz in a 36 Willard sedan and think its a great setup,easy to work on,parts are everywhere,and it has been very reliable
Click to expand...

Brain is a little foggy at my age but I think it was a 53 series they called the engine That powered or won World War II They put them in everything another wonderful engine
 
"At low rpm’s the block does not get up to proper operating temperature."

The 71 series has thermostats and will operate at low RPM at 180F , if that is the thermostat installed.

The hassle at low load , regardless of chosen RPM is slobbering, wet stacking.

This happens when the cylinder pressure is too low (from low power use) and the rings fail to seat/seal properly.

The cylinder pressure on each power stroke behind the rings , forces the rings against the cylinder wall , if the force is not high enough the rings will burnish the cylinder and the hone scratches will depart.

Hard and heavy operation can l burn some of the carbon out from behind the rings , hopefully un sticking them so they can work properly.

The big owner hassle is the drive package should have been decided by the NA , the boats designer.

A so called "cruising prop" is one cure (along with smaller injectors) can shift the load to a lower RPM , where a higher percentage of the power at low RPM will be used.

Yes, a cruising prop needs an informed operator , and an EGT gauge would be a help.

Folks that have slow speed (displacement) cruising in mind should sample oil more often , as more frequent oil changes might be required.
 
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FF said:
"At low rpm’s the block does not get up to proper operating temperature."

The 71 series has thermostats and will operate at low RPM at 180F , if that is the thermostat installed.

The hassle at low load , regardless of chosen RPM is slobbering, wet stacking.

This happens when the cylinder pressure is too low (from low power use) and the rings fail to seat/seal properly.

The cylinder pressure on each power stroke behind the rings , forces the rings against the cylinder wall , if the force is not high enough the rings will burnish the cylinder and the hone scratches will depart.

Hard and heavy operation can l burn some of the carbon out from behind the rings , hopefully un sticking them so they can work properly.

The big owner hassle is the drive package should have been decided by the NA , the boats designer.

A so called "cruising prop" is one cure (along with smaller injectors) can shift the load to a lower RPM , where a higher percentage of the power at low RPM will be used.

Yes, a cruising prop needs an informed operator , and an EGT gauge would be a help.

Folks that have slow speed (displacement) cruising in mind should sample oil more often , as more frequent oil changes might be required.
Click to expand...



I have a pair of 6v92ta in my boat and the slobber like crazy if I run them under 1300 rpm. My hull is efficient at around 7.5 knots and we like to go at that speed. Unfortunately that requires to run the Detroits at around 1000rpm. We tried it a couple of days of cruising and we just couldn't keep doing it. I'm removing my injectors this winter to have them rebuilt as Some of them are probably leaking and providing low atomization. I can see slobbering on certain cylinders when it leaks at the manifold gasket. We'll see if it improves next summer but I also suspect low compression. Not out of specs but in the lower portion of spectrum.

There are 2 thermostats on those engine (on on each bank of cylinders) and we can't get a good operating temperature (175-180F) if we don't run them over 2000rpm. At 1300, they are around 165F and it's the bare minimum according to Detroits. I personally think it's too low.

I think the boat is just over powered for how we want to use it.
 
To add to FF's points, on any engine with an oil cooler in the raw water loop instead of the coolant loop, consider either moving it to the coolant loop (and adding a bigger cooler), or adding a thermostat to the oil cooler. A full flow raw water oil cooler will cause the oil temps to be way too low under light load.

For engines that don't burn well at low rpm / light load, feeding them warmer intake air may also help get a better burn. It won't help if the engine design has ring seal issues under light load, but if it just doesn't atomize and burn fuel well, it should provide some benefit.
 
Another problem with Detroit engines starting to appear on the horizon is the lack of old school mechanics that have the skill to "adjust the fuel rack" properly after changing injectors. The same issues appear in aviation when it comes to mechanics with the skills needed to work on radial engines. Newer diesel engines require a mechanic with computer skills when it comes to fine tuning an engine. If the new engine electronics are out of wack it takes computer adjustments to repair not a wrench mechanic.
 
RichardM said:
I have a pair of 6v92ta in my boat and the slobber like crazy if I run them under 1300 rpm. My hull is efficient at around 7.5 knots and we like to go at that speed. Unfortunately that requires to run the Detroits at around 1000rpm.

I think the boat is just over powered for how we want to use it.
Click to expand...

Rich it sounds like you hit it on the head... for how you want to use it. Tough to have both ways in life (slow speed and high planing speed). Instead of putting all that money into the maintenance, you should think about either selling the boat for something more appropriate, or repowering accordingly.

The Hatt motor yachts are plentiful and popular, but not everyone wants to expend huge sums of money each hour to push them on plane. I bet if you powered just to hull speed 9.0 knots, that it would actually help your resale as well.
 
FF said:
"At low rpm’s the block does not get up to proper operating temperature."

The 71 series has thermostats and will operate at low RPM at 180F , if that is the thermostat installed.

The hassle at low load , regardless of chosen RPM is slobbering, wet stacking.

This happens when the cylinder pressure is too low (from low power use) and the rings fail to seat/seal properly.

The cylinder pressure on each power stroke behind the rings , forces the rings against the cylinder wall , if the force is not high enough the rings will burnish the cylinder and the hone scratches will depart.

Hard and heavy operation can l burn some of the carbon out from behind the rings , hopefully un sticking them so they can work properly.

The big owner hassle is the drive package should have been decided by the NA , the boats designer.

A so called "cruising prop" is one cure (along with smaller injectors) can shift the load to a lower RPM , where a higher percentage of the power at low RPM will be used.

Yes, a cruising prop needs an informed operator , and an EGT gauge would be a help.

Folks that have slow speed (displacement) cruising in mind should sample oil more often , as more frequent oil changes might be required.
Click to expand...

You guys can run yours however you want my boat will run at 1200 RPMs most of the time, just like my over the road trucks and excavating equipment. million plus miles on my cat in a freightliner ,excavators in excess of 30,000 hours Run just above idle .Better run down to the truckstop and tell those guys they shouldn’t be idling their trucks Or Loping down the road at 1300 RPMs
 
Particulate filters changed all that that’s why I won’t own one they need to be run hotter so they don’t plug up a ridiculous expensive filter caterpillar quit making over the road truck engines for that reason and others leave it to the government
 
When I was a commercial fisherman, too far at sea to come in at night, I would run at 700 rpm for as long as 9 days in a row before coming in at a higher rpm. At night, I shut down and drift. If the swell was high, I ran at idle on autopilot all night. No engine problems, keel coolers with a manually adjustable thermostat, ran at 175° - 180°. 671 naturals.
If you have a problem getting to operating temp, a restricter valve can be added to the cooling circuit. Engines with heat exchangers can divert some of the raw water over the side before it goes thru the exchanger. With some effort the valves can be controlled by engine rpm.



About 6,000 671s were made per month at it's peak in WWII. I think somewhere around 3 million were eventually built. They also made 1, 2, 3, and 4 cylinder 71 series engines. Generators run by these engines usually run at 1200 rpm and last forever.
 
Mako said:
The Hatt motor yachts are plentiful and popular, but not everyone wants to expend huge sums of money each hour to push them on plane. I bet if you powered just to hull speed 9.0 knots, that it would actually help your resale as well.
Click to expand...

Yeah, every once in a while I think through how nice it would be to take a 53 or 58 & repower at 100hp/side or so. The LRC's had that setup with the 4-71 or 6-71 we're discussing here (and displacement hulls) and seem to command a premium - even so, probably better just to get one of them rather than re-powering.
 
RichardM said:
I have a pair of 6v92ta in my boat and the slobber like crazy if I run them under 1300 rpm. My hull is efficient at around 7.5 knots and we like to go at that speed. Unfortunately that requires to run the Detroits at around 1000rpm. We tried it a couple of days of cruising and we just couldn't keep doing it. I'm removing my injectors this winter to have them rebuilt as Some of them are probably leaking and providing low atomization. I can see slobbering on certain cylinders when it leaks at the manifold gasket. We'll see if it improves next summer but I also suspect low compression. Not out of specs but in the lower portion of spectrum.

There are 2 thermostats on those engine (on on each bank of cylinders) and we can't get a good operating temperature (175-180F) if we don't run them over 2000rpm. At 1300, they are around 165F and it's the bare minimum according to Detroits. I personally think it's too low.

I think the boat is just over powered for how we want to use it.
Click to expand...


Your engines have a "boost cooler" that chills the water going to the aftercooler. At low rpm that cooler will sub-cool the whole engine as the coolant flow there meshes with the rest of the engine, thermostats closed.
 
mike66 said:
Any general knowledge about these engines in general and suitability for pushing a Hatteras 58 at displacement speeds? I believe they are 175hp each. Not much extra in reserve I'd think, but maybe adequate for ICW/inshore cruising? Hours unknown at this point.

Thanks.
Click to expand...
A very knowledgeable guy on Detroits is on Youtube channel "Bus Grease Monkey". I am aware of him working on at least 1 boat with Detroit's. He loves talking about Detroit's.
 
FF said:
"At low rpm’s the block does not get up to proper operating temperature."

The 71 series has thermostats and will operate at low RPM at 180F , if that is the thermostat installed.

The hassle at low load , regardless of chosen RPM is slobbering, wet stacking.

This happens when the cylinder pressure is too low (from low power use) and the rings fail to seat/seal properly.

The cylinder pressure on each power stroke behind the rings , forces the rings against the cylinder wall , if the force is not high enough the rings will burnish the cylinder and the hone scratches will depart.

Hard and heavy operation can l burn some of the carbon out from behind the rings , hopefully un sticking them so they can work properly.

The big owner hassle is the drive package should have been decided by the NA , the boats designer.

A so called "cruising prop" is one cure (along with smaller injectors) can shift the load to a lower RPM , where a higher percentage of the power at low RPM will be used.

Yes, a cruising prop needs an informed operator , and an EGT gauge would be a help.

Folks that have slow speed (displacement) cruising in mind should sample oil more often , as more frequent oil changes might be required.
Click to expand...


Cylinder pressure/temp is a good reason to run at full throttle for 5 minutes for every day after running at low cruising RPM. This applies to all diesels, but some makes more than others. Diesels LOVE to work and they are not happy if you don't work them.
 
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