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Old 12-20-2015, 10:51 PM   #21
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Just because its called a two stroke does not in any way make it even remotely similar to a simple 2 stroke lawn mower engine. How about 3 push rods per cylinder, 4 valves per cylinder, a variable injector per cylinder, operated by a pushrod from a roller lifter integral to the cylinder head, as are the 2 pushrods for the 4 valves, all built into the head. Then the blower, that is driven by the camshaft gear train thats behind the bellhousing adapter, and the govenor that is driven by the blower shaft, or a seperate gear off the cam train depending on how its configured. Then the mechanism for controlling all this, the rack, thats controlled by one of many types of govenors. The only similarity is that they do indeed produce power on every up and down of the piston, which means all those valves and pushrods are moving twice as fast as a fourstroke at the same rpm. Much, much more complicated, by far. Then add up the incredible number of different configurations available (starter, blower, exhaust, fuel pump, oil filter, all of which can be had on either side of the engine, which by the way on the inlines is completely reversible, and even laid on it side for busses) and it becomes very complicated.
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Old 12-20-2015, 10:57 PM   #22
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You have received some good advice. The engines may come through a survey just fine. If so you will have time to evaluate your replacement as well as rebuild options

Suggest you read the J&T 6-71 archives on boat diesel. You will be able to address questions to some very good DD people who frequent that site.
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Old 12-20-2015, 11:00 PM   #23
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Blindhog, thanks. Which model engines= did you have this done on?
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Old 12-20-2015, 11:08 PM   #24
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Guys, thanks for all the help and great suggestions. Much to think about. The boat is one I don't want to lose and have looked on the docks and YW ad nauseam. I like the idea of dropping the Turbo's and dropping the horse power so RPM's lower/higher? What does this do to fuel burn? Right now, captain states. boat burns 1.2 gallons/mile, so that's 10 gph if my math is correct? Does sound right guys?
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Old 12-21-2015, 06:52 AM   #25
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"Yes, DD's are simple low RPM engines. If you maintain them and run them at low RPM."

DD are rated and can operate at 2100 , but unless you are a sport fish you will not like the fuel bill.

Between 1600 and 1800 they have Very long service life , assuming 2 stroke not 4 stroke oil is used.

J&T do "hop up" the engines and running them for long hours at the higher 2400 J&T rating will shorten the service life.

The "sports" consider 1000 hour life a good deal.

Having the hop up goodies will not shorten the service life IF the engine is operated and loaded as a cruiser.

Basically the engine will burn a certain amount of fuel in its lifetime , the burn RATE is up to the opertator.

"The only similarity is that they do indeed produce power on every up and down of the piston, which means all those valves and pushrods are moving twice as fast as a fourstroke at the same rpm."


Yes the exhaust valves are moving 2x as often as is the injection the difference is each stroke is a POWER stroke , no wasted effort of an exhaust stroke .

The valves have a great service life as the scavenging blower cools them asa does their time seated.

But they have been doing this since 1936 with no effort.

"Then add up the incredible number of different configurations available (starter, blower, exhaust, fuel pump, oil filter, all of which can be had on either side of the engine, which by the way on the inlines is completely reversible, and even laid on it side for busses) and it becomes very complicated."

This is the VIRTUE of the motor for end users.

Almost any configuration can be arranged , twins with the service items on ship center line , but turning in opposite directions , just ask, no problem, no added expense.

While the configurations can run probably to 50 variants ,
after its assembled its just a Jimmy , simple and cheap to keep like 10,000,000 others.
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Old 12-21-2015, 08:09 AM   #26
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The Captain says "always run at 11 knots." For a 62 foot vessel that seems about 10 to 15 % faster than an efficient cruising speed thus putting the engines into a higher HP fuel burn zone and shortening their life. Heed Kulas's advice.
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Old 12-21-2015, 09:31 AM   #27
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Dont get me wrong, I love the old DDs. I also know there biggest weekness is being "jacked up" by J&T and Covington, and in the later years even by the DD boys themselves. Its my opinion, and that of most others that know DDs, that the 485 hp 6-71 is the shortest lived of all. Even if ran conservatively. And, no matter what the captain says there is no way you can really know how this boat was operated. Another thing to look at is that these engines are totally inappropriate for a 62 foot boat. 12v71 NAs would have been about right. A lot of folks here are going to say the hp rating makes no difference, its how they were operated that matters. To some extent, and on most engines they are correct. The 485 DD has a BIG turbo, BIG injectors, BIG aftercooler, overdriven blower, BIG raw water pump, LOW compression ratio, etc. At low power levels it is way overcooled, even when the temp gauge says 180 the cylinder temps are to low for good combustion. Hence the need to "blow them out" occasionally. These engines purpose in life was to go fast for a short time. 2500 hours is the max between rebuilds. Read Pasco's thoughts on marine diesel engines, particularly the DDs, you'll enjoy it.
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Old 12-21-2015, 10:21 AM   #28
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Phi, presently down in Texas and has been under a boat house cover all it's life. Teak decks and that is what scares me about Everett....rain, rain, rain. Will look forward to meeting you this spring. Thanks again.
We presently are at South Padre TX with the land yatch. We are heading north Dec 28th to fly out of Dallas Jan 7, so we have two weeks to kill. That's a hint.

The Eagle has teak decks, however every year they have to be maintained, sealed, and covered from October to June. The back and Portuguese bridge is canvas covered so both area are usable area all year. The back deck is varnished and heated. The front deck is covered with a thick heavy white tarp where we store some of the summer stuff. So make sure the teak decks are maintained, rain proof and covered.

So how do you plan on transporting the boat to Everett and why. We are thinking of moving South for the winter, and keep the boat in the PNW for the summer. There are many boats for sale in the PNW? The Seattle boat show is the last week in January.
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Old 12-21-2015, 10:45 AM   #29
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Have you considered the cost of getting this boat home.

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Phi, presently down in Texas and has been under a boat house cover all it's life. Teak decks and that is what scares me about Everett....rain, rain, rain. Will look forward to meeting you this spring. Thanks again.
The cost of getting this boat the west coast will be considerable. On the face of it the boat sounds overpowered, however once in a large sea state having reserve power for climbing large waves is an asset. On a boat of this size engines is just the begining of expensive systems, especially if you plan on a delivery on its bottom up the west coast. There are a number of Hatteras 58' lrcs on the west coast already that might suit your needs as well that have proven durability.
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Old 12-21-2015, 10:58 AM   #30
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Just because its called a two stroke does not in any way make it even remotely similar to a simple 2 stroke lawn mower engine. How about 3 push rods per cylinder, 4 valves per cylinder, a variable injector per cylinder, operated by a pushrod from a roller lifter integral to the cylinder head, as are the 2 pushrods for the 4 valves, all built into the head. Then the blower, that is driven by the camshaft gear train thats behind the bellhousing adapter, and the govenor that is driven by the blower shaft, or a seperate gear off the cam train depending on how its configured. Then the mechanism for controlling all this, the rack, thats controlled by one of many types of govenors. The only similarity is that they do indeed produce power on every up and down of the piston, which means all those valves and pushrods are moving twice as fast as a fourstroke at the same rpm. Much, much more complicated, by far. Then add up the incredible number of different configurations available (starter, blower, exhaust, fuel pump, oil filter, all of which can be had on either side of the engine, which by the way on the inlines is completely reversible, and even laid on it side for busses) and it becomes very complicated.
My comments were TIC. I know how the DD's work, and am well aware that the only thing it shares with a lawn mower is that every down stroke is a power stroke and that they have intake ports instead of valves. I know about the rack, the blower, the N30's etc etc. And yes, there are endless configurations. But, that's for the designers to worry about. When you buy a boat those decisions are made. And I still maintain that they are pretty straight forward mechanical engines. Yes, you have to learn how to adjust the rack, injection timing and the governor, but it's all straight forward. Everything, including a complete rebuild in situ, can be accomplished with simple hand tools. No ECM (until you get to the DDEC's) no sensors, no software, and thus no "bugs". In fact, once it's running you can rip every wire off the thing and it will keep on running as long as it gets air and fuel.

And yes, hopping them up shortens their life. Like someone said, HP is ideal when it(they) move the boat just under hull speed somewhere in the 1600-1800 RPM range, and the whole thing truly runs at about 170F
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Old 12-21-2015, 11:28 AM   #31
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We presently are at South Padre TX with the land yatch. We are heading north Dec 28th to fly out of Dallas Jan 7, so we have two weeks to kill. That's a hint.

The Eagle has teak decks, however every year they have to be maintained, sealed, and covered from October to June. The back and Portuguese bridge is canvas covered so both area are usable area all year. The back deck is varnished and heated. The front deck is covered with a thick heavy white tarp where we store some of the summer stuff. So make sure the teak decks are maintained, rain proof and covered.

So how do you plan on transporting the boat to Everett and why. We are thinking of moving South for the winter, and keep the boat in the PNW for the summer. There are many boats for sale in the PNW? The Seattle boat show is the last week in January.
Phil, thanks again. Will seek your counsel on how/what you do on the decks to preserve them. Getting the boat to the west, is something I am currently seeking out skippers and also boat transport bids, since it's a USA-USA transfer. If I can get down there to Tex soon, will hail you and see if we can meet up.
Folks, thanks again for all the input. I am learning a great deal here and will heed the suggestions.
As for the Hatteras, I just don't know that much about them, their reputations etc.
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Old 12-21-2015, 11:28 AM   #32
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The BSFC for a JT running at 1600 RPM can't be very good. One thing DD did right was size the 6-71s build specs to the application keeping a close eye on BSFC for each application. The sweet spot for fuel burn on these "hopped up" engines is in the 75-80% range.

Used to run a 6-71 off highway fleet and we did out of frame rebuilds on average at around 2500 hours or 18 months. Tear one out in two hours and back in same. This was the cheapest way to go in the 350 HP range until OPEX for higher fuel burn and increased rebuild costs got to us vs Cat engines that were going above 7,500 or so hours.

Great engines in their day.
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Old 12-21-2015, 11:33 AM   #33
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One more comment. Well maybe, probable not.

Make sure it has enough heat for the PNW winter months. Get down into the 20 and 30, freezing weather for weeks. Most larger PNW boats have stand alone dirsel heat that will cost 20+ grand. Since we are not on the boat the diesel heat can not be run, so we are heating with electric, using the full 240 volts 50 amps for heat. So make sure the eletrical is up to date. We had the AC electric check in preparation. When on the boat we use the diesel as it keeps the entire boat warm and dry. Even the bilge and engine room.
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Old 12-21-2015, 03:02 PM   #34
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I will have to admit, I've never seen an N30 injector in a DD.
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Old 12-21-2015, 03:14 PM   #35
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I will have to admit, I've never seen an N30 injector in a DD.
You are correct. 70's, 60's 55's..others.... no 30's... Senior moment.
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Old 12-21-2015, 05:55 PM   #36
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1) there are a lot of threads on this forum re: teak decks and a lot of us with them would disagree with Phil about spending time and money "preserving" them as such preservation typically means shortening their useful life.

2) yes, on the DDs pay attention to Kulas; he and I don't always agree on these matters, but do on the issues on this thread. Even so, you are getting mostly spurious "interesting to know" and not entirely relevant advice from us (and a ton of it from others) , only an experienced Detroit 2 stroke mechanic tell what is going on with those specific engines in that specific boat, and only by giving them a thorough physical and work out.
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Old 12-21-2015, 06:16 PM   #37
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1) there are a lot of threads on this forum re: teak decks and a lot of us with them would disagree with Phil about spending time and money "preserving" them as such preservation typically means shortening their useful life.
There's a lot of covered moorage in the Everett area, so I would pay any price, and prioritize it above all, although that might impact your liveaboard plans. You might want to look at rail freight to Seattle for transport.

Personally I'd look for something 40-50 ft in the PNW that has been extensively upgraded or was a quality boat under cover all its life, and keep it that way. They exist in surprising numbers behind all those curtains you idle past in these marinas.
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