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Old 12-05-2017, 10:22 AM   #21
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Thanks for all the help and guidance. With the information you all have shared I can at last make a well informed choice on whether or not to buy a boat with Dad's. Just want to know what I'm getting into with whatever engines a boat has.
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Old 12-05-2017, 10:56 AM   #22
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Thanks for all the help and guidance. With the information you all have shared I can at last make a well informed choice on whether or not to buy a boat with Dad's. Just want to know what I'm getting into with whatever engines a boat has.
Not so quick, you just asked from the owner's of DDs. Long before emission regs came out the heavy, fuel loving, oil burning DDs stopped going into boats and other applications.
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Old 12-05-2017, 11:33 AM   #23
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My Dream Boat would have a pair of DD with the std Navy gearbox to operate a single protected center line shaft.

I have seen these in Boats and Harbors with a US Navy rebuild for $6,000 for the package.

I would remove one 6-71 and swop it or purchase a 3-71.

Inshore with fuel easily available , the 6 would push or the 6+the 3 if I really wanted to defuel rapidly.

The 3- 71 would be the cross ocean unit with the lowest fuel burn at displacement speeds .

20-30HP per 71 cylinder is normal , and good for many thousands of hours ,

30-70 hp would push any boat I could afford around the world.

As there is so much in common, either engine could be used for spare parts.
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Old 12-05-2017, 12:12 PM   #24
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Not so quick, you just asked from the owner's of DDs. Long before emission regs came out the heavy, fuel loving, oil burning DDs stopped going into boats and other applications.

Seems that much of the DD love here is based on sentiment rather than sensibility.
It’s hard to turn away from something that has been such a large part of boating all these years, but emissions, fuel burn, noise and of course tier 3 regs say no to the venerable DDs.
With all the great engines available today, I would not spend good money to step back in time.
I worked on a charter boat with DDs that required oil about every three hours, and the motors had to be stopped to add it. If the oil filler was opened while running, it would spew it clear to the cabin ceiling! The bilgewater would have been perfectly acceptable to pour back into the sump, but the motors just kept on going.
One of the BIG pluses of an ER that used to have DDs in it is all the space!
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Old 12-05-2017, 12:23 PM   #25
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Seems that much of the DD love here is based on sentiment rather than sensibility.
It’s hard to turn away from something that has been such a large part of boating all these years, but emissions, fuel burn, noise and of course tier 3 regs say no to the venerable DDs.
With all the great engines available today, I would not spend good money to step back in time.

I doubt many here would strongly advocate for an older 2-stroke DD in a new build boat. Except for maybe FF.

But I think the point many have made is just that a good boat that happens to be powered with 2-stroke DDs doesn't need to be dismissed from consideration just because of the "era" of the engines.

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Old 12-05-2017, 12:38 PM   #26
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Last spring I did a mechanical survey on an old Chriscraft with 8V71N's. Built in 1967. Engines never overhauled and checked out perfect. A touch of cold start smoke then clean. No smoke under way. Various owners could not help themselves from "improving" electical and other systems, so engine room was a hash. But engines were just fine. Amazing.

Fifty years of service. Ready for more.
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Old 12-05-2017, 12:42 PM   #27
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I had a pair of 6-71's in my LCM 6. Best running engines I've ever had.


Yep.
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Old 12-05-2017, 12:53 PM   #28
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Tozz above presents a dismal view of service intervals (I suspect he means doing cylinder kit overhauls) for the DDs. I suspect he is referring to sport fishermen who can go through cylinder kits every 1,000 hours if they run them near the pins.

If you run them moderately, they will go lots of hours, probably more than 10,000 hours before requiring a kit overhaul. Any trawler run at displacement speed with one or more DDs will certainly be moderate use.

David
You are correct. I was talking about cylinder kits and you stated my point much better than I with regards to the impact to running them hard versus moderately at more reasonable speeds. Sorry for the brevity and confusion!

As stated, more data and opinions on boatdiesel.com and even over at yachtforums too.
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Old 12-05-2017, 04:59 PM   #29
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In addition to boatdiesel.com, which is excellent, the Hatteras Owners Forum has a ton of good threads by knowledgeable owners, as virtually all vintage Hatts were DD powered til the 2 strokes went out of production. I loved my 8v92 tti's.
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Old 12-05-2017, 07:00 PM   #30
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Lepke, what type of craft were you on in Vietnam that had Detroits?
The USN up to that time was a heavy user of DDs, especially the 71s. Many ships from WWII had DD emergency generators. I ran PBR - 2 6v53 running jets, Mike boat - 2 671s, ASPB - 2 12v71s, also generators w/671, 471 8v71, 12v71. Swift 2-12v71s, too. And another late war jet (can't remember designation -flat bottom, small bow ramp, carried about 30 troops @ 35kts) - 2 8v71s. Also YTM w/2 671 generators.
At the time I was told the 53 series was just military and was surprised to run into various 53 models later. I learned how to overhaul DDs in VN while passing the slow times. I've run many other engine types. Cats and Cummings are great engines but I guess I like DDs because I know them so well, hate injector pumps, never had a DD failure even with damage. PBR jets had a removable top and a hose for water removable. You could have a hell of a hole and still float if the jets were running.

In my current boat I can have a normal conversation in my "living room/bar" directly over 2 671s @ 1800 rpm. Proper sound proofing makes all the difference.
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Old 12-05-2017, 07:06 PM   #31
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FF:
When I was a fisherman I had a buddy with a 40' salmon boat with a 371. We fished together and cruising did 7-8kts. He used more fuel in his diesel stove than the engine. He fueled about every 3 weeks, I refueled every week.
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Old 12-07-2017, 07:02 AM   #32
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"With all the great engines available today, I would not spend good money to step back in time."

Depends on where you are and where you are going.

Some folks might prefer an engine that does nor rely on massive electronics to simply function.

A properly rebuilt DD with new style gaskets and sealants might be preferred , if it could be installed in a new boat .

The Air Police might be unhappy , but they sit ashore at desks , and have not weathered electrical storms afloat.

One question that is frequently chatter is an engine overhaul.

Auto and light duty engines (throwaways) have to be removed to be overhauled , which is labor intensive.

An industrial duty engine can usually stand a couple of in-frames , new bearings, cylinders, pistons before removal for a proper rebuild is required.

I read the eng folks are hard at work creating a pure mechanical engine that will please the Air Police worldwide.
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Old 12-07-2017, 10:06 AM   #33
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I had twin 6V53s in a previous boat. Ran like tops. Leaked oil. Burned about 1 gallon every 24 hours or so underway. Never had any breakdowns or really any problems with them. They misted oil from the air boxes, had a mechanic that made a Rube Goldberg collector that worked great to collect the oil mist so the engine room became clean after lots of scrubbing. Overall not bad engines, just have to keep a lot of oil diapers on board and carry extra oil.


Sounds like my old MG :-)
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Old 12-07-2017, 10:33 AM   #34
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The fact that all these DD two strokes are still running and serviceable really says it all with respect to reliability and service.

But for some of us, other things matter too. Personally, I would never even consider a boat with DD two strokes. Not because of reliability, but because noise level, a clean engine room, and minimal exhaust smell are very important to me too. Newer engines deliver on all the above, not just reliability. If electronics had a negative effect on engine reliability, we would see cars, trucks, and boats broken down everywhere we turn. But we don’t. In fact, all the above are far more reliable today than back in the 60s and 70s when everything was mechanical. It’s just fear of the dark.
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Old 12-07-2017, 10:50 AM   #35
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tree, I would agree with you about modern (say, year 2010+/-) engines. Given the choice I too would take one over an old DD without another thought.

But my engine rooms were clean and didn't smell. In fact we left the doors open in the winter so the block heaters could warm the lower level of the boat (the old Hatteras MY's had split engine rooms with a companion way between them from the galley to the aft MSR). We lived and cruised aboard full time for several years. I am very sensitive to exhaust smell, virtually allergic, and this was never an issue either; and our transom stayed clean. We could carry on normal conversation at the lower helm and in the salon which were directly above the ER's, so boat design, build quality and sound proofing come into play.
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Old 12-07-2017, 02:37 PM   #36
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My Dream Boat would have a pair of DD with the std Navy gearbox to operate a single protected center line shaft.

I have seen these in Boats and Harbors with a US Navy rebuild for $6,000 for the package.

I would remove one 6-71 and swop it or purchase a 3-71.

Inshore with fuel easily available , the 6 would push or the 6+the 3 if I really wanted to defuel rapidly.

The 3- 71 would be the cross ocean unit with the lowest fuel burn at displacement speeds .

20-30HP per 71 cylinder is normal , and good for many thousands of hours ,

30-70 hp would push any boat I could afford around the world.

As there is so much in common, either engine could be used for spare parts.
FF,

I am interested in hearing you flesh out this idea of a 6-71/3-71 combo driving a single shaft. Perhaps it deserves it's own thread.

I too love the 71 series Detroit. I love your idea.

How would you determine the appropriate size prop to work with the three possible power applications? It seems that the options would be 3-71 only for minimum fuel use at slow speeds, 6-71 only in most applications, or both in certain circumstances that require more power. If this is what you're thinking, how do you account for any concern of over or under propping? Or am I over-thinking it?

Thanks
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Old 12-07-2017, 04:09 PM   #37
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Great thing about DDs is that they leak so much lube oil that you can get home running on bilge oil if the fuel runs out.
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Old 12-07-2017, 04:59 PM   #38
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Great thing about DDs is that they leak so much lube oil that you can get home running on bilge oil if the fuel runs out.


See, just like my old MG. If you could pour the garage floor into the engine, you would have a full oil change -
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Old 12-07-2017, 05:07 PM   #39
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My newer rebuilt jimmy doesn’t leak a drop of oil after the rebild
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Old 12-07-2017, 05:46 PM   #40
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T4Liberty,
Yes I agree.
You could prop it for the 6-71 and 3-71. 9-71?
Then w the 6-71 only it would be overproped and when adding the 3-71 it would be way overpropped.
A good stout truck transmission w close to ideal ratios may permit any compination of engines on line to be propped right. That may be a nightmare of gears, shafts and perhaps clutches. May be worth some thinking.
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