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Old 11-17-2017, 01:28 AM   #21
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Post below courtesy of Bob Sinter. Bob, as most of you know, is in charge of training, customer support, application engineering for Northern Lights.

"40 - 60% load is the sweet spot for almost any diesel engine. Sub 30% loads are almost always problematic, although some engines are more forgiving than others. 2 GPH pencils out to about 40 HP. You can get away with 30% load in any diesel for a while. But, it will virtually always lead to “wet stacking”, where exhaust byproducts condense in the water-cooled parts of the manifold, turbocharger (if you have one) and the exhaust system, regardless of whether it's wet or dry. Low loads also cause grossly high volumes of crankcase vapor blowby which overwhelms the vapor/mist coalescer systems and is aspirated into the air intake, creating smoke and soot. It also is the root cause of a lot of engine oil leaks.

In general terms, diesel engines tolerate low loads in this order, from most tolerance to least: 1.Naturally aspirated, non emission rated 2. Turbocharged, no after cooler 3. Turbocharged, jacket water (antifreeze) after cooler 4. Turbocharged, jacket water after cooler, emission certified 5. Turbocharged, seawater after cooled, non emission rated 6. Turbocharged, jacket water, second circuit keel cooled after cooler 7. Turbocharged, seawater after cooled, emission rated 8. High power density seawater after cooled (above 50 HP per liter)

With only a few exceptions, many passagemaking full displacement boats have at least twice as much power installed as they need. Experience has shown that is less than desirable. The trend toward more appropriate sizing is reflected in a number of new builds that are being specified with 4 cylinder engines where sixes were used previously and less installed HP overall. Robert Beebe’s Passagemaker firmly established the historical precedent in proper engine size for passage making yachts with its single 120 HP Ford-Lehman. That's the reality. Obviously, bigger, heavier boats require more power, but probably not as much as you think. In the absence of running at more appropriate loading, which is unfortunately incompatible with best cruising range, a daily WOT run is the second best thing - you may need to increase the time at or near WOT to give the engine a chance to heat up and clean itself out if you have wet stacking, smoke or oily looking drips near the turbo."
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Old 11-17-2017, 01:36 AM   #22
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If buying an older boat which may require re-powering during your ownership, it is much easier to swallow the bill for new little 50hp baby rather than 2 x 300 hp diesels.
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Old 11-17-2017, 02:29 AM   #23
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If you don't plan on exceeding hull speed and normally cruise efficiently one knot slower, there is no need to exceed 80 HP. (Have a four-cylinder, naturally aspirated John Deere.)
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Old 11-17-2017, 07:30 AM   #24
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If you don't plan on exceeding hull speed and normally cruise efficiently one knot slower, there is no need to exceed 80 HP. (Have a four-cylinder, naturally aspirated John Deere.)


Problem is Mark thanks to decisions of a past administration that excellent US built engine is no longer available for sale in the US.
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Old 11-17-2017, 09:14 AM   #25
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But obviously many other 80hp engines are.

I’ve heard of Bob Sinter. The Northern Lights people seem to have figured it out.

Larry (healhustler) seems to have arrived at the same conclusion. “I hope our prolific member OCDiver pipes in here. He spent the time and money refitting his 45' Cherobini Independence from a 380 Cummins to a small John Deere for "trawler speed only" aspirations. Before the refit, I was with Ted coming across the Okeechobee Waterway and asked him to nail the big 380 to see what the boat would do. It got to 9 knots or so and was looking at the sky. The wake was beyond huge, but that was pretty much it. At a sedate 7.5-8 knots, the boat was the ideal cruiser. Even though the hull is a semi-displacement design, the 380 was still not enough to get it on top. Now with the modest HP John Deere, it's the perfect trawler. From time to time, money, determination and the sacrifice of a couple of knots can make a better boat out of a good one.”

A real trawler person waits for the tide to change or is a planner (like Sunchaser) and arrives at the approprate time not to need more power than what is required to drive the boat. For SD that’s about exactly 7hp per ton of displacement.
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Old 11-17-2017, 09:26 AM   #26
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While I appreciate Bob Sinter's thoughts and I believe he is right for constant rpm generator engines, I do not believe he is right on his load requirements for propulsion engines.

I can not understand why it is ok to run an older Lehman at 50 hp (40% of 120) but it is not ok to run a 370 hp Cummins of the same displacement at 50 hp (14% of 370). What is the difference?

Yes the Cummins has three times the cooling capacity and a turbo and aftercooler. But the thermostat takes care of keeping the engine warm and the turbo and after cooler might as well not be there at the low rpms it takes to make 50 hp. Yes the fuel injection pump and injectors of the Cummins can provide three times the fuel as the Lehman and at low power that injection system is operating well down on its operating curve so its spray pattern might not be as good. But then lets talk about the QSB whose common rail injection system solves all of that.

Why can't you run a Cummins QSB 380 at 50 hp? Dodge pickup trucks do it all day long at a steady 60 mph.

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Old 11-17-2017, 10:51 AM   #27
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I'm with you David. Good analysis. I have yet to see an engine in trawler service suffer from low load running. Yes, they can wet stack, but that is easily resolved with a clean-up hard run.

I have had generators glaze the cylinders from light load. But those are a different situation. Constant rpm.

On a propulsion engine, as you go down in load so does the rpm. So the specific load (considering rpm) is actually higher. A FL 120 or Cummins 370 making 40hp at 1200 is 33% for the FL, 11% for the Cummins, but that is only referring to max hp at rated rpm. What matters more is what can the engine make at full power at 1200? Maybe 60hp? So now the load looks much more reasonable.

On a gennie it is always 1800. Once the AC's cycle off at night, there is almost zero load and it runs at say 5% load all night. Even then, most do not suffer. Some do, but on a percentage basis the number is still very low.

If I am spec'ing an engine for a boat I would shoot for 50-70% comparing cruise hp to rated hp. But that is not the only consideration. On planing boats, the weight and size penalty of a larger yet lightly loaded engine may be a bigger consideration. On a trawler, the vibration of a four cyl may push the choice to the smoother six. But there are not many low hp sixes out there unless you go to an obscure brand which creates its own problems.

So sometimes all things considered, the best (least bad) choice is to go with a larger engine in the trawler. The Deere 4cyl have balance shafts, so that that can be a good option.

But all this only applies if you are building or repowering. The point I guess I am trying to make is that if shopping used, don't be freaked out by something with way more power than needed for hull speed. Other than a few minor operating considerations (power up occasionally) and a bit more maintenance (aftercoolers) you should not have any problems, nor burn but a little more fuel.
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Old 11-17-2017, 11:59 AM   #28
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My addition may be pointless. I understand your concerns about too much engine.

I,m in that boat also.

Too much engine for my 32'er. My engine now is old (40yrs) V555 Cummins @217 hp, yet it has done fine at 7 -8k. for the last 30 years. Originally powered to plane but cannot because we carry too much, er, stuff.

If you buy a boat with what you consider to be too much hp it doesn't mean it has to be used. Yes run it up for 10-15 minutes once daily on a long run to clean it up if concerned.

NOT WOT. Not needed. Just bring it up to a point where it is working harder on a slow PLANE or just on to the lower portion of the hump.

For a good normal cruise speed stay just below,10-15%, the hump speed , and it will be loaded sufficiently to be fully at operating temps which is what is important. That has also "derated" the engine.


As pointed out you will have a tad more mtc. with a seawater cooled after cooler but not that big deal unless ignored.


Stop worrying so much about the engine hp unless you are in the position to spec. exactly what you want or do a repower. Just learn to run and maintain it smartly and whatever you have will serve well.

I strongly suggest you add one of the most important guages, EGT. It will tell you ,with some experience, just how hard you are operation g the engine, overloading or easily.

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Old 11-17-2017, 12:01 PM   #29
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David and Ski, doesn't the Cummins(6 series) have a coolant cooled oil cooler? Does that help in what we are talking about? When everything gets up to 180 degrees I would think that would help. My little 4LH Yanmar had a seawater cooled oil cooler. I had a bitch of a time changing oil on that thing because I could never get the oil temp up to help the oil flow. That would not have been good to run that engine slowly all the time.
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Old 11-17-2017, 12:06 PM   #30
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Let's face it, most folks buy used boats and live with the engine that came with it.
If some buy a custom new build, they usually follow the recommendations of the builder.
Repowering? We all hope to sell the boat before that happens.
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Old 11-17-2017, 12:14 PM   #31
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Yup all gauges in the 40 to 60 % range and all is perfect.

This is true with your car too.
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Old 11-17-2017, 12:19 PM   #32
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Quote:
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David and Ski, doesn't the Cummins(6 series) have a coolant cooled oil cooler? Does that help in what we are talking about? When everything gets up to 180 degrees I would think that would help. My little 4LH Yanmar had a seawater cooled oil cooler. I had a bitch of a time changing oil on that thing because I could never get the oil temp up to help the oil flow. That would not have been good to run that engine slowly all the time.
Yes, I believe the Cummins does have a coolant cooled oil cooler. My Yanmar 6LY has a sea water oil cooler but it will fully warm up to operating temps while just making 50 hp at 1,600 rpm, which gives my 7 kt typical cruising speed. But the oil is probably cooler than on the Cummins.

Some engines I believe even have thermostatically controlled oil coolers. Don't know which.

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Old 11-17-2017, 12:41 PM   #33
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Not to ruffle any feathers , or get kicked off the Trawler forum , but has anyone ever heard of someone really loading up a trawler with a semi displacement hull with a lot of horse power ? I mean to really get it up and over . I have a 1979 ms 34 . This boat is new to me but have run many commercial fishing boats with almost the same hull (why I bought the 34 )and by not being speed demons ,we usually get up easy to 18 to 19 with a 380 hp with boat balanced correctly . Yes ,I am enjoying going slower and yes, I enjoy the fuel economy and no, I am not repowering . Just wondering if anyone did it and what was the result?
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Old 11-17-2017, 01:15 PM   #34
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Little rusty, but I believe it has been done with that hull. Maybe it was Jay Leonard had a 270 cummins. I remember something about 20-21kts it became a bit squirrelly.

Been years, but I had same hull and remember doing the research. It was on the old mainship yahoogroups.
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Old 11-17-2017, 01:22 PM   #35
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Ski and David

Can only but agree with your posts 26 and 27. I'd add my confusion as to why Sinter states a marine after cooler increases the chances of glazing. Cooing the charge air would seem a positive in improving engine performance whether NA or Turbo with after cooler.

Todays common rail diesels do a very good job of controlling fuel under light load conditions. To the point sport fishing boats can fish for hours on end at near idle. Possibly Sinter wrote his comments a few decades ago.

And as Baker says, the coolant cooled oil coolers work well in keeping oil up to temperature under light loads. No mention by Sinter as to keeping oil temps up in the + 180F range.
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Old 11-17-2017, 02:56 PM   #36
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Let's face it, most folks buy used boats and live with the engine that came with it.
Repowering? We all home to sell the boat before that happens.
Actually - When I bought my boat I knew the original raw water cooled 36 hp Volvo may not last long, but the boat was what I wanted and the price was right. The engine overheated if I pushed it hard, was a bit smokey, parts were hard to find, and I never felt I could trust it completely. Especially here where there is no tow service, and I don't see another boat all day.

A year later, I wasn't upset when I checked the dipstick and found it frothy white. I didn't even investigate the problem. For less than 16K I was able to replace the engine & gearbox and replace my fuel tanks while the engine was out. Now I have a boat I can trust 100%.
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Old 11-17-2017, 04:44 PM   #37
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Ski and David

Can only but agree with your posts 26 and 27. I'd add my confusion as to why Sinter states a marine after cooler increases the chances of glazing. Cooing the charge air would seem a positive in improving engine performance whether NA or Turbo with after cooler.

Todays common rail diesels do a very good job of controlling fuel under light load conditions. To the point sport fishing boats can fish for hours on end at near idle. Possibly Sinter wrote his comments a few decades ago.

And as Baker says, the coolant cooled oil coolers work well in keeping oil up to temperature under light loads. No mention by Sinter as to keeping oil temps up in the + 180F range.
Anecdotal example: our 26-footer's 1998 260hp Volvo KAD44P diesel.

Not common rail, but an early electronic engine. Turbocharged, supercharged, clearly a #8 in Bob Sinter's scale.

It has 6502 hours on it so far. After cruising at mostly at 3000-3400 RPM for its first two years, we've run for the last 4500-5000 hours at 1300-1400 RPM, 6-7 knots, more than 95% of the time, putting out ~30 hp? Running just hard enough to keep temps up to 175-180. Runs as well as when first broken in, burns no more oil, smokes no more, shows no sign of deterioration, oil analysis fine, etc.
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Old 11-17-2017, 04:59 PM   #38
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Wouldn’t have mattered

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Did he have trim tabs ?
I have twin, is 330s on the by Ocean Alexander 456, and loaded for a winter in the Bahamas which means cases of wine beer Gin, etc we can only get 11 or 12 kn out of our boat. Empty, she will do 15.

Perhaps if I threw the head of lettuce overboard we could make more speed.
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Old 11-17-2017, 06:18 PM   #39
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I have twin, is 330s on the by Ocean Alexander 456, and loaded for a winter in the Bahamas which means cases of wine beer Gin, etc we can only get 11 or 12 kn out of our boat. Empty, she will do 15.

Perhaps if I threw the head of lettuce overboard we could make more speed.
Tuffy question, Got a water maker on board? reduce the FW by half or more.

What are you doing with lettuce on board?
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Old 11-17-2017, 07:52 PM   #40
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Sunchaser wrote;
“And as Baker says, the coolant cooled oil coolers work well in keeping oil up to temperature under light loads. No mention by Sinter as to keeping oil temps up in the + 180F range.”

IMO if the lube oil temp is kept up to 180 and a heavy load is put on the engine every several hours for a few minutes one should be good to go.

BUT I seriously question if an engine coolant will keep the lube oil up to 180. That little cooler is going to replace the heat of a big fairly hard working engine? ..... but if it can ......
Perhaps it’s a solution to the underloading issue. I’m still glad I can run my engine at 50% load w/o too much fuel burn and w/o too much noise.
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