over powering your vessel

[markpierce]

Smaller engines give the mechanic more room in the engine room/compartment.

 

[FF]

From what I read in National Fisherman slobbering is caused by very low loads causing the piston rings to burnish the cylinder walls.

With no pressure behind the rings to seal properly the rings just slide and polish, instead of scrape.

More frequent oil changes will get rid of the acids caused by the blowby , but only a hone or new cylinders can fix the eventual lack of compression.

This is one of the main reasons noisemakers are of two different sizes on larger boats.

The night load is minor , and would be very hard on the day unit.

This is done even tho 2 identical noisemakers would offer easier servicing and a source of spare parts .

 

[BandB]

This is one of the main reasons noisemakers are of two different sizes on larger boats.

The night load is minor , and would be very hard on the day unit.

This is done even tho 2 identical noisemakers would offer easier servicing and a source of spare parts .

Actually, from what I've seen, been around, or owned, generators seem to be of two different sizes a lot on medium sized boats, 60-80', and the larger generator is used regularly while the smaller one never gets used. I've seen many that would have perhaps a 30 kw and a 7 kw and the 30 would have 1200 hours and the 7 would have 150 hours. So, that is being rethought. Other builders like Hatteras have always gone with two identical. Most 80' Hatteras come with two 27.5 kw or so. Now, above 80' they're almost always identical. A 130' boat would typically have two 92 kw or so. On our 65' Sunseeker, the standard is a single 21.5 kw Onan. We wanted a backup and a 7.5 or so was suggested but we went with identical and haven't regretted it.

I've been in a lot of discussion on sizing of the 2nd generator. Theorists and brokers have often said much smaller. Captains and owners with practical experience have gone the other way. Here's why. Let's take the 80' Hatteras above. A 7.5 or 10 kw generator would be virtually useless. First it would mean not running heat or a/c. Most boats in that range will have them set to come on automatically. But then even without them the chances of overloading would be great. Someone showers, someone else decides to whip up breakfast, another goes to the coffeemaker and lights on all around and a 7.5 wouldn't handle it. Just all the refrigeration is going to load one significantly. We have in the galley a refrigerator over two freezer drawers. On the bridge an icemaker and small refrigerator and in the lazarette, two freezer drawers. Even if one or a 10 kw did, they would always be running at 75-95% load, far worse than any possible underloading. On our 65' Sunseeker, we very seldom ever run at less than 35-40% load which means anything under 12 kw or so would be useless and means 21.5 kw isn't underloaded. Instead, by having two identical, we can share parts and spares, split the usage, always have a backup and put fewer hours on. The night load always includes heat or a/c coming on and off over the course of the night. Even if they weren't absolutely needed for temperature control, they are to maintain air movement and to reduce moisture.

Heating, cooling, showering, cooking, lights on a boat above a certain size are typically used exactly the same way you'd use them in a house. On a larger boat, such as 130' with two 99 kw generators, you will always have enough to keep one generator in a satisfactory load range as you'll never require less than 30-40 kw and not often under 50 kw.

While I do agree that traditionally many mid range trawlers have had one large and one small, that is no longer as common and definitely not common on larger boats. Refrigeration and a/c or heat are the driving forces, but there's a lot of other electricity usage. On an 80', late at night, 8 guests, 2 crew members, you may have 6 or more people showering, using hot water, 4 televisions on, 3 freezers, 1 large and 1 small refrigerator, several phones and tablets charging and then the a/c switching on and off, different units at different times.

I've looked at and calculated on many cruising boats 60' and up and just haven't found the large and small combination to make sense. Then observation has shown on boats with a large and small, the small doesn't get used. Most boats in the 60-70' range still run with just a single generator.

 

[Nomad Willy]

Eric, you have it figured out. Heat and cool oil via coolant with a plate heat exchanger that is mounted on side of engine. The oil always seems to be at least 10F degrees hotter than coolant at low loads and about 15 to 20F at higher loads.

At my low (1500 RPM) to normal (1750 RPM) cruising loads I don't find (measured with IR gun) oil temperatures below 185F once engines have warmed up.

Sunchaser,
This makes no sense to me at all. The coolant is artificially kept higher than it would normally be by the thermostat. The oil has no thermostat and most of the time it sits in the bottom of the sheet metal oil pan w large area exposed to ambient cool air. I don't think I do "get it".

 

[sunchaser]

Sunchaser,
This makes no sense to me at all. The coolant is artificially kept higher than it would normally be by the thermostat. The oil has no thermostat and most of the time it sits in the bottom of the sheet metal oil pan w large area exposed to ambient cool air. I don't think I do "get it".

The temperatures I gave are measured with an IR gun on the oil pan. The plate exchanger was sized by the engine manufacturer to provide adequate oil cooling at full load. Next time I'm on vessel I'll send you some pictures of what is happening.

The first time I saw a plate exchanger for cooling diesel engine oil was about 50 years ago on a Cat loader. Plate exchangers for heating and cooling are used in all sorts of industrial applications going back over a century.

 

[Baker]

Sunchaser,
This makes no sense to me at all. The coolant is artificially kept higher than it would normally be by the thermostat. The oil has no thermostat and most of the time it sits in the bottom of the sheet metal oil pan w large area exposed to ambient cool air. I don't think I do "get it".

At low loads, the oil is heated by the coolant loop. At high loads, it is cooled by the coolant loop. The coolant loop simply moderates the oil temp. ANd the coolant loop is large enough to extract the heat out of the oil system. The coolant is also moderated by the thermostat and allows coolant to heat up in low power situations. Does that help?

 

[psneeld]

Different folks, different strokes...same for some engines....

Here is what my go to engineer says about all of this...

"The article referenced in post #19: Why You Shouldn't Go Easy on a Diesel - Professional BoatBuilder Magazine, supports those who questioned SD's credibility. I have always said the man is .....(not on the money... see note)

The "turbine wheel" shown is a compressor wheel. It is probably fouled by a crankcase ventilation system that vents to the air filter.

The later article mentioned in post #22 is a different version of the same article but shows a turbine wheel. However, there are several reasons that wheel can be sooted and wet, a leaking seal in the turbo itself is likely. That turbo could have been (and probably was) mounted on a generator. All of the conditions illustrated are more common to generators than propulsion engines. The generators which tend to have that sort of problem use the same engines that are used in smaller boats for propulsion. That makes it easy for someone with more experience selling technical articles to content hungry magazines to commercialize the kind of mythology perpetuated on internet boating forums.

It is more fear mongering for food than practical guidance."

Note....I cut a tidbit that wasn't technical.......well it was but I cut it for a different reason...

 

[AusCan]

A couple thoughts:

2 pole generators are much more prone to glazing due to running at constant high speed with light loads. Generators running at 3600 rpm (60Hz) are more at risk than the generators running at 50 Hz (3000 rpm).

Larger generators are often 4 pole running at 1500 or 1800 rpm. There are less glazing issues with these.

 

[Nomad Willy]

Chaser and Baker,
OK got it good now.
The "cooler" is a moderator or stabilizer. Makes me wish I had a "well designed marine engine" but since I almost never run at any other speed except 2300rpm and 50% load my little Mitsu will probably be long lived.

I have thought in the past that removal of the "oil cooler" would be quite beneficial for underloaders. But I see now the cooler in the case of underloader is a heater ... just what is needed. Could it be that a bigger "cooler" would help underoaders keep their oil temp up at low load?

This cooler sounds a bit like multi-viscosity oil. The temperature is stabilized w the cooler and the viscosity is stabilized w the MV oil.

 

[Ski in NC]

Coolant to oil heat exchangers are really elegant. At low power with thermostat closed, coolant is recirced and the oil HX is on the discharge of the water pump, between that and the block. As engine warms up, it does actually put some heat into the oil. Running at high load, the thermostat is open and lots of coolant is going through the coolant HX. This drops the coolant temp coming out of the water pump, so tends to cool the oil. And at high load there is much more heat going into the oil, so this is where you want cooling and you get it.

On little NA engines, you don't really need any oil cooling of any sort. High hp engines have piston cooling jets aiming oil onto the underside of the pistons, and this picks up GOBS of heat. Those engines absolutely need active cooling.

With the oil hx you get oil temps like 190f at light load, 210 at high load, or thereabouts. Pretty tight range, really.

I could go off on a rant about marine engines using sea water to cool lube oil, but that's another topic.

 

[Nomad Willy]

Thanks Ski and all for this really great learning experience for me. As I've said I've been wondering about that for many years.

And incidentally the same or very similar things must take place w trans coolers in the radiator of cars. The marine industry probably picked it up from cars. Probably would promote faster trans warm up.

 

[Jeff F]

Coolant to oil heat exchangers are really elegant. At low power with thermostat closed, coolant is recirced and the oil HX is on the discharge of the water pump, between that and the block. As engine warms up, it does actually put some heat into the oil. Running at high load, the thermostat is open and lots of coolant is going through the coolant HX. This drops the coolant temp coming out of the water pump, so tends to cool the oil. And at high load there is much more heat going into the oil, so this is where you want cooling and you get it.

With the oil hx you get oil temps like 190f at light load, 210 at high load, or thereabouts. Pretty tight range, really.

I agree on the elegance. When I first started following this debate I carefully I reviewed the system in my 6bt. Pretty cool. Came to the conclusion that as long as my coolant temp was at minimum spec I could run at very low loads forever without doing my motor any harm because the oil temp would be kept (heated) to coolant temp in steady low load operation.

 

[BandB]

A couple thoughts:

2 pole generators are much more prone to glazing due to running at constant high speed with light loads. Generators running at 3600 rpm (60Hz) are more at risk than the generators running at 50 Hz (3000 rpm).

Larger generators are often 4 pole running at 1500 or 1800 rpm. There are less glazing issues with these.

Even the small generators we have are at 1800 rpm. Most modern generators are. We have Northern Lights, Kohler, and Onan from 7.5 kw to 99 kw and all are at 1800 rpm.

 

[sunchaser]

Even the small generators we have are at 1800 rpm. Most modern generators are. We have Northern Lights, Kohler, and Onan from 7.5 kw to 99 kw and all are at 1800 rpm.

Panda lovers will squeel at this! Your 1800 units become 1500 at 50 hz. BTW, bigger gensets than yours drop down from 1800 RPM while at 60 hz.

 

[Ski in NC]

Fishcher-Panda, Entec, a couple Onan models and some others did the 3600rpm thing. There was NO love. Ugh...

 

[FF]

There are simpler methods of having warm oil than heating it.

My old MB 300SL had a hopper tank that all the (dry sump) oil was contained in.

The tank had a central sheet metal core that was where the oil was returned to and taken from.

The oil inside the core came up to temp far faster as it was only a few quarts , rather than the full 14 quarts the oil lube system contained.

This simple , no moving parts oil warming system should also work on a wet sump.

"When I see that quote about needing to run at 75% power for best life, he loses credibility. That is nonsense."

I too have read his posts and think he is talking about 75% load of the available HP at working RPM, not WOTat water ski HP rating.

This would explain the long life and good fuel burn of CPP boats.

 

[Jeff F]

The essential part of Steve's argument was that the oil might not be hot enough under light load even though the coolant is. But in my motor I don't think that would be possible, at least in a steady state.

 

[BandB]

Panda lovers will squeel at this! Your 1800 units become 1500 at 50 hz. BTW, bigger gensets than yours drop down from 1800 RPM while at 60 hz.

Yes, I know they become 1500 at 50 hz, but I'm not in a 50 hz part of the world.

I have never had a 3600 RPM generator and never plan to own one.

 

[eyschulman]

This issue of lighter load running has been kicked around on multiple threads on multiple sites and it is the same merry-go-round. All diesel engines are not created equal that is a fact even for our present political environment where most determine facts by which side you take. There does seem to be a good weighting of evidence suggesting that the modern common rail electronic engines run within temp. specs. do not suffer from running in the 40-60% load range and actually will last longer with fewer problems. As to old school diesels it depends, awful lot of variables between engines and how they are used at low loads.

 

[Nomad Willy]

Eyeshulman that may just be the problem ... old engines. Probably over half of the guys here have engines over 25 years old. And most are direct injected .... the advantages and disadvantages I no doubt still have much to learn about. I have an old car (87) but most of our engines are even older than that. But everybody considers that car to be quite old. And most would prefer to rebuild instead of replacing these old engines. So any problem w these old engines will probably be w us for a long time. At some time of course it will be popular to huck'em out but it looks like that's way down the road.