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Old 08-01-2014, 06:15 PM   #21
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[QUOTE=psneeld;254319][QUOTE=sunchaser;254316]
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Originally Posted by Mule View Post
You might check e bay. 6BT Cummins brand new $ 10.5k. do

While a lot of that makes sense...what's the lowest HP the block puts out?

The 6BT remans are rated at 220HP, with the same block built at 115 HP years ago. The 6BT will operate all day quite happily at 1400 to 1600 RPM drawing whatever the throttle setting calls for, say 50 to 60 HP. Many 6s do the same. My Perkins Sabre225 TIs/Cat 3056 operate quite nicely at 40 to 60 HP each day in and day out with the odd time going to 150 HP each as sea conditions or passage making needs dictate.
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Old 08-01-2014, 07:20 PM   #22
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My engine mechanic says he rarely sees 4-cylinder JDs as compared to the 6-cylinders. But do I care as long as he looks/cares after mine? Do trawlers need so much horsepower?



No doubt, it depends.
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Old 08-01-2014, 08:08 PM   #23
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The JD 4's are now supposed to be smoother than the 6's due to the wonders of CAD, modern manufacturing and balance shafts. Certainly the old rule of 'always choose the 6 for smoothness' is no longer a given.

When repowering I decided that I did not need to travel at 16 kn (more to the point I did not want to pay for the fuel...) so I downsized from the total installed 540HP. At WOT it was kinda planing but needed help from the trim tabs. So, struggling a bit. I now believe that something like 800HP in total would be the right option for high teens travel in a Mk1.

Probably a bit under half of the Mk 1's were delivered with twin Lehman's. A lot of people felt the boat was underpowered with just 240HP in total. So I picked the middle ground, ending up with 402HP in total. Was that a good decision? Well, it was good in that I did not need to replace gearbox or props. I think Larry's high quote for his KK42 desktop study did include a gearbox, and it is not an insignificant cost.

Reality is that with 402Hp I can't get over the hump: I top out at 11kn now. I'm OK with that as I generally dont want to pay for the high fuel burn. But, I can achieve 10kn with 215HP. And 9kn is only using about 125HP. So, I would think the Lehman's are actually a good fit for displacement speeds in a Mk1.

Were I doing it again I would probably choose the JD 4's. My middle ground is not a problem, but I could be traveling the same speed for a lower purchase price.
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Old 08-01-2014, 08:14 PM   #24
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Repowering is a great place to be .......

Choices Choices Choices

Everything you want.
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Old 08-01-2014, 08:31 PM   #25
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The JD 4's are now supposed to be smoother than the 6's due to the wonders of CAD, modern manufacturing and balance shafts. Certainly the old rule of 'always choose the 6 for smoothness' is no longer a given.
CAD and modern manufacturing is not going to improve the roughness of a four. Sounds like marketing fluff.

There are two vibration modes on a four: Dead idle where there are only two fires per rev. Makes engine try to shake the boat at low revs. Usually an idle issue only.

Second is a high rpm "buzz". Technically described as a second order vibration, makes engine shake directly up and down twice per rev. This vibration is only noticeable at high revs (maybe 1600 or so, up) and can be canceled by the balance shafts the JD apparently has. So this mode should be a non-issue for those contemplating the JD 4045.

For trawler service, the idle shake is probably the biggest reason the four is avoided. It can be moderated with very good mounting design, but it cannot be isolated completely. Even my best design efforts with a four mounting have been only moderately successful isolating idle shake. Most just opt for a six. A six also has an idle shake, but since it hits three times per rev, you can idle it down lower and still be smooth. Sixes can idle down to around 600, a four even mounted well is lucky to go down below 750 before the shake gets too bad.

Fours can do the job, certainly. But the smoothness of a six to me is worth the extra cost.

There are good reasons most trawlers use a six of some flavor...
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Old 08-01-2014, 10:16 PM   #26
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I think that's basically not true Ski. But it is true relative to what we have at our disposal.

Three and 4 cylinder engines on motorcycles and cars can be made with almost no vibration at all.

I had a BMW triple that was so smooth I occasionally found myself riding for 5 or10 miles at 60-70mph not in top gear. No vibration at idle either or anywhere else. They employed a flywheel running off a gear and of course slightly offset and interestingly counter rotating. The counter rotating has a very significant effect on torsional vibration.
In a boat engine an offset flywheel would be much closer to the center of rotation and the output shaft location would be lower ... another advantage.

My new 4cyl VW Jetta is also smooth. Much smoother than any 4cyl car I've ever driven before. I need to look at the tach to see if the engine is running while idling. I could go down the highway in a low gear turning several thousand rpm and it would be smooth enough to go miles in that mode.

Diesels have considerably more torsional vibration but the principals of vibration control applies equally to gasoline and Diesel engines .. as far as I know.

My new (9 years ago) Mitsubishi engine is smoother than the Perkins engine it replaced. But not much. There's no design features that I'm aware of that should make the Mitsubishi smoother. Same pre-combustion chamber that Perkins has had since the 60s. Same type of fuel injection.

The inclusion of balancers in the 4cyl Deere indicates balancers are effective in diesels. Other technology probably is too. So Ski I believe 3 and 4cyl engines can be as smooth as 6cyl engines. The manufacturers need to employ the technology before it will become a reality. Also I think engines that are used for small boats are far down the technology road. So it will be a time yet till smooth boat engines are offered. And when that happens perhaps rubber engine mounts won't be necessary. Nice thought.

But for now you're probably right ... 6cyl engines are smoother than fours. My engine could be made smoother than it is though w a heavier flywheel. Probably isn't available as many applications of the Mitsubishi 4SL2 are weight sensitive. In a FD trawler a light engine has little value. Wish a heavier flywheel was an option. I did choose a marineizer that included a steel exhaust manifold. Nice to be able to make options such as that.
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Old 08-02-2014, 12:15 AM   #27
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MB- we probably agree more than not. A few bits: A three actually has a less "harsh" vibration than a four, and in smaller engines the vibes are much easier to deal with. On the BMW bike, the counter rotating flywheel is part of the vibe cancellation strategy. Threes have a first order "waddle" or orbiting force, but being first order is usually not that objectionable, and is fixable with balancing shafts or the flywheel.

I too drive a tdi jetta (2001) and it does not have balance shafts. The new ones (2009+????) do have balance shafts, and are quieter at higher revs. Mine has a drone (not bad, but as an engine engineer I detect it) around 2100rpm. The new ones with balance shafts, that vibe is gone. Also, the smoothness at idle is in part due to rpm being higher (800 for new tdi, 900 for my old one), and due to an excellent job by the Germans designing the mounts. I think I can design decent boat engine mounts, but I don't have the resources those crafty Germans have!!

But the bottom line is the 4cyl large displacement engine has a low rpm shake that is not easy to isolate from the boat.

Diesels also have more idle shake than gassers, as the higher compression ratio makes more of a "bump" as piston comes up to tdc to fire. Not only has the diesel a higher CR, but a gasser when throttled the effective CR is much less than that calculated. On a gasser, compression at idle does not begin until piston is past half way up, as intake air is choked by the throttle. That makes it smoother.
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Old 08-02-2014, 01:51 AM   #28
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For trawler service, the idle shake is probably the biggest reason the four is avoided. It can be moderated with very good mounting design, but it cannot be isolated completely. Even my best design efforts with a four mounting have been only moderately successful isolating idle shake. Most just opt for a six. A six also has an idle shake, but since it hits three times per rev, you can idle it down lower and still be smooth. Sixes can idle down to around 600, a four even mounted well is lucky to go down below 750 before the shake gets too bad.
I ought to have asked the JD dealer for some hard data to support his smoothness claim, and will try to remember to do that at the next boat show. Interestingly though in view of Ski's comments above, the JD 4045 has a listed 600 rpm idle speed for the Tier 3 engine.
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Old 08-02-2014, 06:31 AM   #29
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Since a well managed boat will spend as little time at idle as it can, the real question is how silently and smoothly the vessel is at normal cruise.

Most modern engines do fine , even at the high load , lower RPM required for best fuel burn.

Modern diesels will not warm up, or stay at operating temps at idle anyway , so most folks will run 700-900rpm on cold start for a min , before getting underway.

The engine has to be just warm enough not to stall when shifted into gear.
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Old 08-02-2014, 10:02 AM   #30
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Ski,
Good post your #27.
I drove a VW diesel when our Golf was in the shop. All day loaner. A 2012 Jetta automatic. It was an amazing car and I loved driving it. The amount of power in town was unbelievable for a diesel.

I have a TSI gas engined VW w manual gears. Diesel is fine in my boat but I prefer gas in a car. My TSI is a brand new engine. A 1.8 turbo but nothing is the same beyond that. There is no external exhaust manifold ... it's built into the aluminum head and exhaust goes directly into the aluminum turbo. Unlike the old 1.8T this boy has some T lag. But no premium fuel required. The power is stunning ... especially in 2nd gear. Millage is listed at 36 hwy. The new TDI is 42.

Two TDI engines would power a 36GB don't you think? That would save over a ton (literally) of weight. Our marine engines are WAY behind the tech curve. Can you imagine how smooth and quiet a TDI 36GB would be at 10 knots?
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Old 08-02-2014, 10:38 AM   #31
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Probably gas something to do with additional balancer shaft(s). The industrial versions (lower tier) of the 4045 has balancer shafts as an option. Can't imagine what that would be like at idle.
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Old 08-02-2014, 10:41 AM   #32
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Most displacement boats might require more HP than the VW can produce for hours on end.

1.8 liters would be about 90 cubic inches , so perhaps 30 HP on a cont basis.

Two might be OK , but headwinds or blue water wave climbing might be slow going.

>Can you imagine how smooth and quiet a TDI 36GB would be at 10 knots? <

Real quiet after a couple of hours on the pin.

Car & motorcycle engines are NOT industrial duty ., so can nor be operated at their rating for very long.

Even most piston aircraft engines can only provide Take Off power for 5 min.

Might be better in a ski boat where full throttle is only to get the skier up.
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Old 08-02-2014, 11:00 AM   #33
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You can buy the 115hp 2.0l TDI VW engine from Mercury. Or with variable vane turbo for 150 and 170 hp.
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Old 08-02-2014, 11:31 AM   #34
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I ought to have asked the JD dealer for some hard data to support his smoothness claim, and will try to remember to do that at the next boat show. ...........
Asking a salesperson why his product is better than others is not the best way to get accurate information.

You would do better to find third party reviews.
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Old 08-02-2014, 11:34 AM   #35
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Ski,
............ Two TDI engines would power a 36GB don't you think? That would save over a ton (literally) of weight. ......
But removing that much weight might change the boat's stability or handling. You might have to replace it with ballast so you would gain nothing.
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Old 08-02-2014, 12:16 PM   #36
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A few months back we were on a boat with a 4045 with 135 HP. I thought the engine was running 1600-1700 RPM when I was at the helm but the wifey thought she was running 1300 RPM when she had the helm. Max RPM is 2600.

You could hear the engine in the background but it was not bothersome at all on deck, down below, or in the pilot house. The sound was just a muted, well it was a bit loud in the engine room.

The only noise problem we heard as from an engine accessory squealing which the owner fixed pronto. That was the only annoying thing we heard. I did not notice any "roughness" from the engine either.

One person took a nap in the cockpit while another fell asleep on the sofa which is pretty close to the ER.

Those of us in the pilot house had no problem having a conversation. The engine was there if you listened for it but that was all. I am sure we would have noticed if the engine STOPPED working but the engines operation was something one did not notice either from noise or vibration.

My two cents is that many full displacement boats have engines with too much HP. I suspect those boats are not running with a large enough load on the engine.

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Old 08-02-2014, 12:32 PM   #37
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With twin Lehmans a GB 36 is heavy. Two tons of noth'in bur engine and gears. I can't imagine that loosing a ton or two would'nt do great good for the GB. It would be like disembarking 20 to 25 people. Much less power would be required to move the boat.

And speaking of power claiming the VW engine would only be capable of 30 continuous hp is ridiculous .. IMO but I don't know what it would really be capable of. My gas VW is 170hp but I don't know what the diesel has. I'm think'in more like 60 or 70 continuos hp . That would be about the same as a single engined GB36. And w all that weight gone it should perform better than the single. It would weigh about as much as a 4cyl Lehman GB36.

But a preview of the future is all I intended.

Dannc,
A romp through the archives will reveal that you are absolutely correct.
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Old 08-02-2014, 01:09 PM   #38
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I am planning to run a 130/140hp VW 1.9 M-TDI sterndrive in my 30' dory.Straight marinized auto engine.It's done quite regularly.
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Old 08-02-2014, 01:54 PM   #39
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Interesting that the 4045 idle is 600. That is much lower than other fours. I'll be impressed if it can run at that speed without shaking.

Anyone have first hand experience with that engine at idle?

Dannc do you remember idle on the boat you were on?

Regarding the TDI, they are fine engines, but with the aluminum head on an iron block there are galvanic issues there. Probably not suitable for trawlers where it is normal for engines to be in service 40yrs plus. Aluminum in contact with coolant is trouble long term, just think of Mani-coolers, Yanmar manifolds, Lehman 275 aluminum bits. The really serious industrial/marine engines (Cat, Detroit, Cummins) you rarely find aluminum in contact with coolant.
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Old 08-02-2014, 03:36 PM   #40
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Black smoke is probably just abad injector. No way I would do a repowner at 2000 hours. Just broken in unless way over propped even then it probably could out live you.
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