6cyl or 4cyl diesel main engine

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bobc said:
Marin, I know from other posts that you're not afraid to do the green thing. I don't think you can buy an EPA rated engine that's non turbo.
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No, I've got nothing against helping out the environment. That's one reason that we'd love to get rid of the Lehmans. But, despite the good advice my engine friend has given me, I just don't want turbocharged engines. If for no other reason than I hate the sound of them.:)

At this point I have no idea if a re-power is in our boat's future or not. One possibility that is probably not at all cost effective is to get a pair of engines from overseas where EPA regulations do not apply. Or perhaps a pair of the Luggers we like can be unearthed somewhere. Or whatever. It's a bridge we don't have to cross yet so it's not something I'm going to spend any time thinking about.
 
:confused: Why all this talk about horsepower? Who cares about the horsepower rating (and # of cylinders)?

The spinny thing in the back moves our boats through the water. The power developed in the engine is provided to the propeller via the gearbox and shaft in the form of torque.

So one could say that torque moves your boat through the water, not horsepower. Horsepower should be thought of the measure of torque over time. HP=T x rpm/5252. Torque and horsepower are joined at the hip by this formula. Keep in mind that torque and speed can be measured, horsepower is then calculated. :socool:

So what, you say. Well, my point here is that lots of different combinations of the two measured variables can create the one calculated variable. (Read that sentence again, there will be a quiz later)

RPM matters (and do people get excited about engine rpm on this forum or what?) Because rpm it is directly linked to the pitch and diameter which make up the efficiency of the spinny thing. And propellers can only be so big, can have certain variables of efficient pitch, have so much swept area, and can only rotate so fast before they cavitate. Also gearboxes can be somewhat limiting in ratios relative to the engines manufactures and reliability of gearboxes are also affected by its thermal efficiency.

Throw in the mass of boat, block coefficient, waterline length, plus available engine room height and width. Don't forget shaft centerline height is relative to your motor mounts. Oh, shaft diameter and length (torsion is our friend and enemy) too. Any parasitic loads like dual alternators or a hydraulic pump?

You can have lots of fun figuring out which engine, gearbox and propeller combination is right for you boat. Then I suppose you can go ahead and see what the rated horsepower is. It won't matter much though, because, you'll never really use it, as it is at WOT.
 
Good post, NS, thanks. But you left out another variable regaring horsepower, one that has always bothered me.

What kind of horse?

Take our engines for example. Ford Lehman, 120 horsepower at 2,500 rpm. So is this 120 Clydesdales? Or 120 Morgans? Or, God forbid, 120 Shetlands? Because depending on the kind of horse, 5252 may not be the right number to use. Perhaps if it's a Clydesdale the number is more like 3535. Where the Shetland might be 8585.

Because the kind of horse your formula is related to is going to make a hell of a difference in the torque available to turn the spinny bits at the back.

Actually, it seems to me that any discussion of horsepower is absolute rubbish because so far as I know, nobody knows what kind of horse it was that served as the "model" for one horsepower way back when. Who says 5252 is the actual correct number? Because if they used a Percheron, for example, well, 120 horsepower can really move something, right? Our wussy Lehmans take on a whole new image if they are 120 Percheron power.

But if the horse chosen to be the model for one horsepower was, say, an all-flash-and-dash-but-no-staying-power quarter horse, well then our two Lehmans don't really amount to much on the power scale.

So while I appreciate your torque explanation, NS, it seems to me that you first have to define just what kind of horse your forumula is based on before your you can start calculating with torque and rpm. Right?
 
I thought horsepower was based on the "miniature" horses used in English/Welsh mines, and not the large Clydesdales or even medium sized "quarter horse."
 
Pretty sure James Watt used mill ponies walking on a turntable and then uprated it to horses.

Also keep in mind he was selling steam engines and not horses...

Even so, he got his name attached to two units of power.
 
Northern Spy said:
Hmmm. Wiki says brewery horses. Very appropriate for my boat.
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Well this changes everything. Have you seen a brewery horse? They're frickin' enormous. Think Budweiser Clydesdale when you think brewery horse. In England before trucks (sorry, lorries), they used horse-drawn wagons to distribute beer. Stacked to high heaven with casks. Same idea as what you see in Munich during Octoberfest. Big-ass wagons loaded with beer casks being pulled by four or more giganic horses all tricked out like pimpmobiles.

If that's what Watt was using, then no wonder the British thought a piss-ant (by US standards) 120 hp, six cylinder Ford Dorset diesel was a gynormous powerplant suitable for the semi-tractors of the day (the day being the late 50s).

We've had it all wrong. We've been laughing at the measily power put in things like E-Types and Morgans and Austin Healeys and MGs and Land Rovers but we had no clue that when they say "68 horsepower" over there (the hp of my 1973 Land Rover), they mean 68 brewery horses, for God's sake. The biggest, baddest, strongest horses God or Allah (or both of them together) ever made.

This casts a whole new light on the British and their engines. I'm gonna treat our FL120s with a whole lot more respect now.
 
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Hmmm. The first steam engines were used in mines to pump water, not to haul beer. I'm skeptical of this "brewery horse" theory.
 
Nobody said anything about steam engines hauling beer. Just that Watt used brewery horses as his power model. Which makes sense because the mine horses were little bitty things bred for the purpose and would not be something one would select as representative of the power of a typical horse. A friend in the UK raises "mine horses" as a hobby and you can put the damn things in the back of a car. I can't see Watt or anyone else using them as the basis for a power figure.

Here's the explanation probably referenced by NS----

Horsepower (hp) is the name of several units of measurement of power, the rate at which work is done. The most common conversion factor, especially for electrical power, is 1 hp = 746 watts. The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses......

"Watt found by experiment in 1782 that a 'brewery horse' was able to produce 32,400 foot-pounds per minute." James Watt and Matthew Boulton standardized that figure at 33,000 the next year.[10]

Most observers familiar with horses and their capabilities estimate that Watt was either a bit optimistic or intended to underpromise and overdeliver; few horses can maintain that effort for long. Regardless, comparison with a horse proved to be an enduring marketing tool.
 
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A 3 cylinder or a 6 cylinder will be smoother than other configurations , even if they install a balance countershaft .

IF you can obtain cruise power with no turbo , the engine will eat a bit more fuel, but save thousands in turbo maint.

KISS is for a reason!

The Deere engines can be bought factory rebuilt at way!!!! under the "marine " price from the tractor folks.

A rebuilt Twin Disc and the next 10,000 hours (assuming some maint and PM) should be easy.

For a 6 cyl I would get an International 360 or 466 , mechanical for cheap , long lasting and smoooth!
 
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Marin said:
Received this regarding my comments on turbochargers from my engine industry friend. Seems my perceptions are a bit off the mark. Thought it might be of interest to the rest of you.

------------------

Marin---

Turbocharging isn't necessarily a bad thing. It is a frequently misunderstood thing though, that is for sure.

Here are some numbers that might be of interest to the forum member you mentioned with the NA John Deere engine in his Seahorse Marine boat.

His normally aspirated engine has a compression ratio of 17.6:1

The turbo version has a compression ratio of 17.2:1

His normally aspirated engine can produce a full load EGT of 1139F.

The turbocharged version will produce a full load EGT of 770F.

The turbo version "breathes" better. The exhaust valves run cooler because valve overlap bathes them in cool air for a period on each exhaust stroke.

The turbo version is capable of producing more horsepower, but that doesn't mean you need to use it.

Turbos on gasoline engines live in Hell and are routinely operated by drivers who treat them like they are a carburetor or a radiator. Ignorance is bliss until the costs of abuse are presented.

Turbochargers lead a relatively comfortable life on a diesel and can easily last the life of the engine, if for no other reason than the way the engine in a recreational "trawler" is operated, long periods at moderate power with an extended period of "cool-down" before the engine (and its lube oil supply) is shut down. Replacing the turbo on a JD 4045 only costs around $700 or so in any event. That should not scare anyone away from higher efficiency and greater available power.

The fear of turbos and the common belief of high expenses and dangers from mistreatment simply don't apply to the units fitted to small diesels on recreational vessels, trawlers in particular.

Here is a PDF with the power specs for the John Deere engine in question.

http://www.deere.com/en_US/docs/eng...R/perf_curve_documents/PT2_01-4045DFM7080.pdf

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Marin, I still believe your original thoughts are more on the mark.

Simply put if you look at th explanation above, you still have to read between the lines and assumptions are made about maintenance, that may not be true for everyone all the time.

How does one get more power out of a given displacement if it is not stressing the engine more????? Oh, we sprinkle on the fairy dust of marketing.

Temperatures, lubrication become even more critical.

Companies push turbochargers for many reasons and customers saving money is certainly not one of them.

JMHO

Richard
 
Wxx3 said:
How does one get more power out of a given displacement if it is not stressing the engine more????? Oh, we sprinkle on the fairy dust of marketing.Richard
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You cannot buy a new diesel for off or on the road or pleasure craft that is not turbocharged. Turbos have been around for 50 plus years and are as much a part of old as well as new diesels. The major engine mfrs offer longer warranties today on their Tier iV diesels than they did 30 years ago on non turbo engines. Increased diesel longevity is all about design, materials and maintenance.

On boats, the biggest problem with old and new turbo engines is with those that have seawater aftercoolers. No way around this maintenance area, just like any other part that comes in contact with sea water.

IMHO, the best thing for repowering a trawler yacht is with a re-man non Turbo Cummins 5.9. Full warranty applies, much simpler than a new JD 4045 or 6068, parts readily available, the most popular 4 stroke diesel ever due to the pickup market and they last "forever." Footprints are much the same as Lehman and Perkins 6s.
 
Yes Tom and a twin engined GB would suddenly have 420 hp. Sounds like an excellent plan for Marin. That would be a bit more than "Spray". He likes speed too.

May be good for many single engined trawlers here. I'd kill the Lehman first though. And killing Lehman's is hard to do.
 
Well, just to add some contrast to the discussion, I'm a big fan of turbo charged, electronically controlled diesels. The turbo ensures there is always ample air for complete combustion, and as mentioned earlier, allows the engine internals to run cooler.

Electronically controlled, common rail diesels idle smoother, run smoother, start right up even when cold, basely smell at all, basely smoke, get better mileage, make less noise, and essentially eliminate light-loading issues. And they accurately report RPM, load %, GPH consumption, etc. The technology has been around for a very long time and is extremely reliable. Yes, they can break, but so can a mechanically controlled engine. Personally, I think the benefits far outweigh risks.
 
twistedtree said:
Well, just to add some contrast to the discussion, I'm a big fan of turbo charged, electronically controlled diesels. The turbo ensures there is always ample air for complete combustion, and as mentioned earlier, allows the engine internals to run cooler.

Electronically controlled, common rail diesels idle smoother, run smoother, start right up even when cold, basely smell at all, basely smoke, get better mileage, make less noise, and essentially eliminate light-loading issues. And they accurately report RPM, load %, GPH consumption, etc. The technology has been around for a very long time and is extremely reliable. Yes, they can break, but so can a mechanically controlled engine. Personally, I think the benefits far outweigh risks.
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Well put! The JD 4045 is actually smoother and quieter than the Lehman 120 that it replaced. I wasn't expecting that -- I was expecting a rougher engine with turbo whine. I enjoy the benefits you list every time I use the boat.
 
twistedtree said:
Well, just to add some contrast to the discussion, I'm a big fan of turbo charged, electronically controlled diesels. The turbo ensures there is always ample air for complete combustion, and as mentioned earlier, allows the engine internals to run cooler.

Electronically controlled, common rail diesels idle smoother, run smoother, start right up even when cold, basely smell at all, basely smoke, get better mileage, make less noise, and essentially eliminate light-loading issues. And they accurately report RPM, load %, GPH consumption, etc. The technology has been around for a very long time and is extremely reliable. Yes, they can break, but so can a mechanically controlled engine. Personally, I think the benefits far outweigh risks.
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The above quote, while I agree with the second paragraph, the first is simply not relevant to the second.

Diesels by design always have ample air (unless you ware a car company that took a gasoline designed engine and made it into a diesel for marketing reasons, but then who could be so stupid to do that??? :banghead:
I digress, having spent a number of years in cold, dark places, like Alaska and even further north, all of the diesel generators we had (cat diesels) ran constantly for 3 months at a time, then down for 1 hour oil change and then another 3 months, anybody would like to guess if turbocharged?

Our heavy equipment, cats, graders, basically did the exact same thing, but some of those were turbocharged because of different needs to occasionally have much more power. And they had far more problems, not every day or even every week, but at least every month.

By point here, everything else being equal, is that a turbo, while increasing power, will always add complexity, more maintenance and more $$$ period.

Richard
 
HP is a great , almost useless yardstick for most trawler owners.

A far better but impossible to obtain is fuel burn per HP ,,,,AT THE RPM / HP THE BOAT WILL CRUISE AT.

Some diesels will make 16- 22 HP per gal of fuel at the WOT loading.

So what?

Yank them back to 1500-1800 with a std prop light load and you're only getting 8-10 HP for that gallon of diesel.
 
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