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Old 11-24-2021, 05:56 PM   #21
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Thanks all. Very helpful. Now it's down to this particular vessel.
Love this forum! Guess I'll be spending time on Hatteras owners sites.
I may be two boat owner. My Albin 40 isn't going anywhere soon.
Our plan is keep a boat in RI and one in FL, and snowbird it. Funny cause we live oceanfront in RI. Gotta love the boating life!
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Old 11-24-2021, 06:07 PM   #22
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@Lepke, my old Gray Marines generated about 16.3 hp/gal-hr but the more recent 4 valve head models were about 18-ish. These are all naturals of course.

Iím wondering if itís possible to build an X-71 which is super efficient. Perhaps turbocharged for efficiency butwith tiny 45 injectors, to keep the power-rating down to 150-180 hp, and hopefully pushing 19+ hp/gal-hr.

What do you think?
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Old 11-24-2021, 06:45 PM   #23
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Have you founf a particular 53?
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Old 11-24-2021, 06:49 PM   #24
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Iíve owned a Hatt 58 LRC now for about 4 years with 4-71 naturals in it. Itís our 4th boat. I love these engines. Simple, super reliable, parts available, and yes - theyíre loud.

They push the 110000 lb (full fuel and water, clean bottom) boat at 9.66 knots at about 1950 RPM.

If you want to talk more send me a PM Iíll give you my cell number.
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Old 11-25-2021, 02:51 AM   #25
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Quote:
Originally Posted by Mako View Post
@Lepke, my old Gray Marines generated about 16.3 hp/gal-hr but the more recent 4 valve head models were about 18-ish. These are all naturals of course.

Iím wondering if itís possible to build an X-71 which is super efficient. Perhaps turbocharged for efficiency but with tiny 45 injectors, to keep the power-rating down to 150-180 hp, and hopefully pushing 19+ hp/gal-hr.

What do you think?

If I remember right, the blowers produce about 6psi at full rpm. Normally a turbo Detroit has a lower compression ratio. With turbos on a natural you'd get much higher temps and combustion would be much hotter, shortening the time between overhauls, maybe burning valves and injector tips. And with smaller injector, a much lower fuel/air ratio. Fuel is part of the cooling. Fuel is passing thru the injectors all the time, cooling the tips between firings. And even though the fuel is heated from passing thru the head, it's 1000į cooler than the piston tops. And with smaller injectors you get some lesser amount of cooling. My experience with smaller injectors is loss of higher rpm. The governor doesn't know what injector is installed, so it just opens the injector as far as it can until it's wide open. It still takes fuel to create hp.
The nice thing about naturals is long life, at least 3x longer than turbo models. It probably costs a lot more to rebuild the engine than buying more fuel.

I get better mileage out of my engines by adjusting each cylinder to have the same exhaust temp by how I adjust the rockers, and I use a fuel conditioner (archoil AR6200) that does the usual stuff, but also makes the fuel combust better and gives me 6-10% better fuel economy depending on how much conditioner I use. And I have self made hydrogen generators that break down water into 2 hydrogen, 1 oxygen molecules that is fed into the intake. The hydrogen is additional fuel and the oxygen improves the burn. That gives more than another 10% improvement. So while I should be burning 6 gallons/hour per engine at 1800, I burn a little less than 4.25 gallons/hour. If I did the math right, about 30% better mileage.
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Old 11-25-2021, 07:33 AM   #26
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The usual of Thumb on 71 series is 20-30 HP per cylinder for long life.

The best operating range is 1200-1800 RPM


If starting one that has been out of service for 6+months be SURE to remove the cover and observe that all cylinder injectors are free to move.

If not a "stuck rack" (from one injector) could cause very high RPM with only cutting off the fuel or air to stop it.


The WWII Grey Marine instruction book is the best tutorial for 71 series and worth the purchase price.
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Old 11-25-2021, 08:06 AM   #27
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If I remember right, the blowers produce about 6psi at full rpm. Normally a turbo Detroit has a lower compression ratio. With turbos on a natural you'd get much higher temps and combustion would be much hotter, shortening the time between overhauls, maybe burning valves and injector tips. And with smaller injector, a much lower fuel/air ratio.

The extra air should help keep combustion and exhaust temps down and avoid those issues. Adding turbos on the higher compression engine should be ok in that sense, you just can't fuel them as hard as the lower compression ones (so you'll get less power before starting to hurt durability). EGT gauges would probably be necessary to get the setup dialed in.
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Old 11-25-2021, 09:23 AM   #28
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The usual of Thumb on 71 series is 20-30 HP per cylinder for long life.

The best operating range is 1200-1800 RPM


If starting one that has been out of service for 6+months be SURE to remove the cover and observe that all cylinder injectors are free to move.

If not a "stuck rack" (from one injector) could cause very high RPM with only cutting off the fuel or air to stop it.


The WWII Grey Marine instruction book is the best tutorial for 71 series and worth the purchase price.
As close to 1200 as you can get would be my choice .Probably about 1400 if you get the power you need There
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Old 11-25-2021, 09:48 AM   #29
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Detroit Diesel 4-71 NA

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.
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Old 11-25-2021, 08:49 PM   #30
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Iíve owned a Hatt 58 LRC now for about 4 years with 4-71 naturals in it. Itís our 4th boat. I love these engines. Simple, super reliable, parts available, and yes - theyíre loud.

They push the 110000 lb (full fuel and water, clean bottom) boat at 9.66 knots at about 1950 RPM.
@Juliet, what is your fuel burn at 8 knots?
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Old 11-25-2021, 11:30 PM   #31
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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.
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Old 11-25-2021, 11:32 PM   #32
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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.
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Old Yesterday, 06:38 AM   #33
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"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.
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Old Yesterday, 07:15 AM   #34
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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
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Old Yesterday, 07:30 AM   #35
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FF thatís 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 ďrun at full power once a day to blow out the carbon?Ē
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Old Yesterday, 12:37 PM   #36
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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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Old Yesterday, 02:23 PM   #37
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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.
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 wouldíve 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
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