two engines or one

[backinblue]

My Son loves to say ‘An Engineer will spend 100’s of man hours to screw a Technician!’
I now understand.

How so? I don't get it. Maybe the technician doesn't fully understand the engineering or the design parameters of the equipment they are working on? Not putting anyone down, I've worked as both.

 

[Datenight]

Before this gets all out of hand let me step in as a "qualified petroleum engineer' because there are lots of misconceptions about engine oils. First thing, just to clarify, the field of Petroleum Engineering specifically refers to engineers who specialize in oil production, not lubricants. I spent 36 years in field, a majority of this time leading R&D teams developing lubricant formulations. In any case, these teams consist of mechanical engineers (including myself), chemical engineers, and chemists. In any case modern engine oils cost millions to develop. R&D in this field is in the hundreds of millions per year. It is a very high technology investment field...

...This is a very short outline of modern engine oils. The key is to buy a viscosity and performance level suitable for your engine. In boats many of us have older engines so the modern multigrade oils have way more performance and durability than they need.

Thank you Slomo, very good explanation.

Rob

 

[backinblue]

+1 for SloMo!

 

[psneeld]

Anyone with lots of experience running marine diesels for a hundred hours a week, not a year, knows better than to listen to the vast majority of drivel in these oil threads.

I tend to believe what commercial guys run in their engines (not all as some are just dumber than rocks too), not some recreational boater turned magazine article writer.

 

[LovetoBoat]

How so? I don't get it.

On cars - I say this all the time - as an example have you ever worked on a car or truck that has the oil filter can up? You can not help but get oil dripping down - I prefer the filter as a pendent hanging down.


There are lots of examples where the engineer could not possible work on their own vehicles or they would not have designed it that way... Tight quarters so you can not get a ratchet or box wrench on the nut...



The technician in this term is the user.



YMMV but I have been known to curse the engineering...

 

[backinblue]

On cars - I say this all the time - as an example have you ever worked on a car or truck that has the oil filter can up? You can not help but get oil dripping down - I prefer the filter as a pendent hanging down.


There are lots of examples where the engineer could not possible work on their own vehicles or they would not have designed it that way... Tight quarters so you can not get a ratchet or box wrench on the nut...



The technician in this term is the user.



YMMV but I have been known to curse the engineering...

I've actually have heard some people say they like the filter up on top of the engine because it's so easy to service. Most oil should drain and if you are careful, you probably won't spill any. Again, I doubt the engineer did that because he was stupid or to make it difficult to service. Maybe it was the only place it would fit given various engine compartments that the engine would need to accomodate.

 

[rslifkin]

I've actually hhave heard some people say they like the filter up on top of the engine because it's so easy to service. Most oil should drain out of it and if you are careful, you probably won't spill any. Again, I doubt the engineer did that because he was stupid or to make it difficult to service. Maybe it was the only place it would fit given various engine compartments that the engine would need to accomodate.

Up top and easy to access is good, but if it's a canister filter, it should be hung on a mounting bracket. Or if it's upside down, it needs a catch tray built into the mount with a good way to collect the oil from a tray. Filters that unavoidably coat half the engine in oil when removed are a poor design.

 

[phillippeterson]

I make far less mess with one of my vehicles, vehicle A, that has the oil filter on top. I unscrew it, lift it a little, let a few drops fall in the housing then turn it over and remove it.

The oil filter hanging below the engine on my other vehicle, vehicle B, drips all over me when I remove it and continues dripping for a while.

When removing the filter from vehicle A I don't even need gloves.

 

[slowgoesit]

Thank you Slomo, very good explanation.

Rob

Another thanks for someone (Slomo) who: A) writes concisely B) Appears to know what he is talking about, and C) Has the professional credentials to actually be knowledgeable in the field! Too bad he didn't wade in on the first page before the rest of us had to weed through all the drivel!

 

[Art]

Before this gets all out of hand let me step in as a "qualified petroleum engineer' because there are lots of misconceptions about engine oils. First thing, just to clarify, the field of Petroleum Engineering specifically refers to engineers who specialize in oil production, not lubricants. I spent 36 years in field, a majority of this time leading R&D teams developing lubricant formulations. In any case, these teams consist of mechanical engineers (including myself), chemical engineers, and chemists. In any case modern engine oils cost millions to develop. R&D in this field is in the hundreds of millions per year. It is a very high technology investment field.

Hello Slowmo...

Pleasure to read your input; from a person who really knows. And, owning a Tolly puts you in top position too!

If you would; your input/feeling on the following: I put 4oz of ZDDP [zinc level increasing] liquid in each of my several classic aged gasoline engines at each oil change. I also add 4 more ounces ZDDP at 1/2 way between oil change. What do you think about added lubrication capability of ZDDP? From what I understand ZDDP zinc adds a thin molecular barrier coating between metal parts.

I appreciate your posts! - Art

 

[catalinajack]

Up top and easy to access is good, but if it's a canister filter, it should be hung on a mounting bracket. Or if it's upside down, it needs a catch tray built into the mount with a good way to collect the oil from a tray. Filters that unavoidably coat half the engine in oil when removed are a poor design.

Geez, I have a pair of Lehman 120s with the filters up. I simply punch a couple of holes in the case which let's the oil in the filter drain into the sump. Takes just a few minutes. No muss, no fuss.

 

[Hammond Eve]

trying to wrap up

all this has been very helpful. it is clear that in general the multiviscosity characteristics of oil are not understood by every user. half of my initial proposition was in response to past queries where a two engine captn wondered how it would be to run just one. I tired to answer that and was reinforced, it works great. on a trawler ,one engine half the petro consumption, hardly a drop in the range, as the speed drops from abougt 8.3 mph to 7 mph, so unless we are in an awful hurry using the engines singly is very economical. on mine, the steering was ok but a bit cockeyed. So a catamaran operator opined that his works just fine and goes straight, ok, but that would be expected with a cat, i expect. My bottom was cleaned so that not an issue. The forum has spoken and i cannot support the veracity of 3400 rpm, it must be as expected at 2200, bad tac. but running smoothly i am in the speed range or the rest of yalll, at 7-8 mph, so i will use the gps to get at this speed for cruising. My engines are worn out, that seems to be a fact. I am disinclined, being 81 yrs old in a 48 yr old abused boat, to do anything very invasive on the engines if i can limp along for a few more years, and all this oil info yall have provided gives me reason to believe limping along is dooable. so, thank you, most helpful

 

[backinblue]

No disrespect here, and I own a single engine boat, but I don't think you use half the fuel by running only 1 engine. To move your boat at a certain speed, say 7 knots, requires a certain amount of energy. That energy is contained in the fuel. Engines are not 100% efficient so may you gain a little by running only 1 engine, but at the same time if you have to counter steer to go straight, you area adding drag from the rudder. There is probably also additional drag from a non-powered prop. So bottom line (IMO and I'm sure more knowledgeable people will weigh in) you can run 1 engine hard, or 2 engines at half speed and use approximately the same fuel at hull speed. I know this is an over generalization and I don't want to get deep in the science of efficiencies vs RPM, etc, just pointing out that shutting down 1 engine doesn't half your fuel consumption.

 

[rslifkin]

No disrespect here, and I own a single engine boat, but I don't think you use half the fuel bu running only 1 engine. To move your boat at a certain speed, say 7 knots, requies a certain amount of energy. That energy is contained in the fuel. Engines are not 100% efficient so may you gain a little by running only 1 engine, but at the same time if you have to counter steer to go straight, you area adding drag from the rudder. There is probably also additional drag from a non-powered prop. So bottom line (IMO and I'm sure more knowledgeable people will weigh in) you can run 1 engine hard, or 2 engines at half speed and use approximately the same fuel at hull speed. I know this is an over generalization and I don't want to get deep in the science of efficiencies vs RPM, etc, just pointing out that shutting down 1 engine doesn't half your fuel consumption.

Agreed. The fuel consumption benefit is from the reduced speed with 1 shut down. Slowing down the same amount with both running will lead to very similar fuel consumption (within a few percent) in most cases.

 

[backinblue]

Agreed. The fuel consumption benefit is from the reduced speed with 1 shut down. Slowing down the same amount with both running will lead to very similar fuel consumption (within a few percent) in most cases.

On the other hand, if he is ok with the slightly slower speed and the engines are near end of life, maybe it's a good way to reduce engine hours. I just don't know if pushing an engine harder for less hours is a good or bad thing in terms of life.

 

[Hammond Eve]

pushing engine

that certainly would be true, to some extent. i did not push any engine. i assume that my bad tac was relatiely useful so one engine or two i used the same rpm. for that rpm, one engine got about 7 mph, with 2 engines it got about 8.3 mph, not 4.15 mph.

 

[Art]

Just wondering ... what's the average amount of fuel use difference?? [considering the loaded engine was turning correct size, well balanced prop.

Engine having no load in neutral, running at 1500 rpm - vs - same engine with load in gear running at 1500 rpm.

And, for the engine with load... would it take more fuel at 1500 rpm when tied at dock or while moving through water?

Concerned people want to know!

 

[backinblue]

that certainly would be true, to some extent. i did not push any engine. i assume that my bad tac was relatiely useful so one engine or two i used the same rpm. for that rpm, one engine got about 7 mph, with 2 engines it got about 8.3 mph, not 4.15 mph.

No worries, that makes perfect sense. Your boat is much more efficient at 7 knts then 8.3 therefore you are seeing better fuel economy. The point is that running both engines at 7 knots boat speed should be relatively the same mpg as running 1 at 7 knots. To get 7 knots with 2 engines, you can run them both at a lower rpm than 1 engine at 7 knts. Make sense?

 

[backinblue]

Just wondering ... what's the average amount of fuel use difference?? [considering the loaded engine was turning correct size, well balanced prop.

Engine having no load in neutral, running at 1500 rpm - vs - same engine with load in gear running at 1500 rpm.

And, for the engine with load... would it take more fuel at 1500 rpm when tied at dock or while moving through water?

Concerned people want to know!

Moving through the water takes more fuel. More work is being done = more energy required = more fuel. When you put the engine under load, it will require more fuel to maintain the same RPM.

 

[Art]

Moving through the water takes more fuel. More work is being done = more energy required = more fuel. When you put the engine under load, it will require more fuel to maintain the same RPM.

Of course, understood... but, what's the average fuel use difference between no load at 1500 rpm and with load at 1500 rpm. 25% more / 50% more - ???

 

[rslifkin]

Just wondering ... what's the average amount of fuel use difference?? [considering the loaded engine was turning correct size, well balanced prop.

Engine having no load in neutral, running at 1500 rpm - vs - same engine with load in gear running at 1500 rpm.

And, for the engine with load... would it take more fuel at 1500 rpm when tied at dock or while moving through water?

Concerned people want to know!

In neutral would take the least fuel, moving significantly more, and tied to the dock at the same RPM even a bit more (prop load is higher when the water around the prop is stationary rather than moving).

 

[backinblue]

Of course, understood... but, what's the average fuel use difference between no load at 1500 rpm and with load at 1500 rpm. 25% more / 50% more - ???

Depends on easily your boat moves through the water at that RPM. How much drag, how much displacement, etc. In other words, how much work is required for the engine to maintain 1500 RPM as a particular boat moves through the water. Think about your car coasting down a hill at 1500 RPM as compared to climbing a steep hill at 1500 RPM. Lots more throttle (gas pedal) required for the same engine RPM.

 

[Art]

that certainly would be true, to some extent. i did not push any engine. i assume that my bad tac was relatiely useful so one engine or two i used the same rpm. for that rpm, one engine got about 7 mph, with 2 engines it got about 8.3 mph, not 4.15 mph.

OK - So... now that posting contributors have well established the pertinent point [indisputable fact] that any more load placed onto any engine [i.e., load for whatever cause or reason] means using more fuel to attain rpm and speed; which proportionally increases engine wear and tear.

Therefore, I feel we can assure you Hammond Eve... having two last-gasp engines... just go quite slow [using one or both engines] and engine life will be expanded with fuel use diminished!

Happy Boating Daze! - Art

 

[backinblue]

Just a final point because I can't resist. We tend to judge engine life by hours, when in fact a better indication would be total revolutions of the engine, e.g. an engine running 1000 hours at 3000 RPM will have more wear than 1000 hours at 1500 RPM because it's got twice the number of cycles on the engine. So Hammond Eve may extend the life by reducing the number of cycles, i.e. running 2 engines at a reduced RPM and load than running only 1.

 

[Art]

Just a final point because I can't resist. We tend to judge engine life by hours, when in fact a better indication would be total revolutions of the engine, e.g. an engine running 1000 hours at 3000 RPM will have more wear than 1000 hours at 1500 RPM because it's got twice the number of cycles on the engine. So Hammond Eve may extend the life by reducing the number of cycles, i.e. running 2 engines at a reduced RPM and load than running only 1.

Good point!!

 

[SteveK]

Just a final point because I can't resist. We tend to judge engine life by hours, when in fact a better indication would be total revolutions of the engine, e.g. an engine running 1000 hours at 3000 RPM will have more wear than 1000 hours at 1500 RPM because it's got twice the number of cycles on the engine. So Hammond Eve may extend the life by reducing the number of cycles, i.e. running 2 engines at a reduced RPM and load than running only 1.

Very good point. We also use engine hours as an indicator of boat usage. I can run all day say 12 hours but have only spent one day on the boat.

 

[FF]

AS the load counts , and is mostly unknown ,life time fuel consumption would probably be best for judging engine life. But hard to know on a used boat

Total RPM was part of old tachometers,engine hours is sometimes used , and the old standard piston miles can be figured if the boat usually has a single cruise RPM.

All these methods are guesstimates , actual engine condition can be estimated by starting a cold engine , casting off and watching the engine temperature that the white smoke in the exhaust stops.

 

[SteveK]

AS the load counts , and is mostly unknown ,life time fuel consumption would probably be best for judging engine life. But hard to know on a used boat

Total RPM was part of old tachometers, engine hours is sometimes used , and the old standard piston miles can be figured if the boat usually has a single cruise RPM.

All these methods are guesstimates , actual engine condition can be estimated by starting a cold engine , casting off and watching the engine temperature that the white smoke in the exhaust stops.

OK, that is an incomplete statement. What temp tells you good, bad or perfect.

 

[Hippocampus]

IMHO- Engines are most efficient at a particular limited range of loads. Not rpm, not speed of vessel nor other factors mentioned above. This is particularly true for mechanically, pre common rail engines. The greater efficiency of controlled pitch props is that you can have a easy indirect measure of load via exhaust temperature which allows you to keep the engine in its most efficient loading range by varying pitch. Engines do less well if bogging or overrevving with no or low loads. Most engine systems (gearing, prop size and pitch) are set up so at cruise you’re using a fraction of the actual HP the engine could develop. Depending upon which engines were placed in the boat in a two engine set up under one engine you could raise the loading outside the range where there’s the best efficiency. This would be more likely to occur in boats running exclusively at displacement speeds. There there’s little reason to massively over power the boat. With SD or true planing boats that’s not commonly done as to run over hull speed or get up on plane does require that additional HP and torque. That extra HP may only be required for planing boats on the hole shot or only on occasion when SD boats exceeds hull speed but it’s still necessary for it to be there.
So if the twin initially was set up to be used as a displacement hull and engine selection was appropriate to expected loading then running one engine would be inefficient. The increased loading would also accelerate wear beyond what running two engines would produce as at the same speed loading (and amount of fuel running through the engine) would be halved. This assumes initial spec was appropriate to expected usage.

 

[Art]

IMHO- Engines are most efficient at a particular limited range of loads. Not rpm, not speed of vessel nor other factors mentioned above. This is particularly true for mechanically, pre common rail engines. The greater efficiency of controlled pitch props is that you can have a easy indirect measure of load via exhaust temperature which allows you to keep the engine in its most efficient loading range by varying pitch. Engines do less well if bogging or overrevving with no or low loads. Most engine systems (gearing, prop size and pitch) are set up so at cruise you’re using a fraction of the actual HP the engine could develop. Depending upon which engines were placed in the boat in a two engine set up under one engine you could raise the loading outside the range where there’s the best efficiency. This would be more likely to occur in boats running exclusively at displacement speeds. There there’s little reason to massively over power the boat. With SD or true planing boats that’s not commonly done as to run over hull speed or get up on plane does require that additional HP and torque. That extra HP may only be required for planing boats on the hole shot or only on occasion when SD boats exceeds hull speed but it’s still necessary for it to be there.
So if the twin initially was set up to be used as a displacement hull and engine selection was appropriate to expected loading then running one engine would be inefficient. The increased loading would also accelerate wear beyond what running two engines would produce as at the same speed loading (and amount of fuel running through the engine) would be halved. This assumes initial spec was appropriate to expected usage.

Yes! And, I say...

Good running engines each have their own sounds [language] while running well [i.e., good]. I this post... the term "good running engine" includes engine condition, engine tune and gearing/load placed on the engine. With those 3 levels of requirement set at their best positions to meet the definition of "good running engine" - engine sounds [their own language] become important to understand and to adjust throttle as well as rpm to locate their best sound.

So... IMO, for boats especially, if we listen carefully to good running engine's sound we can tell if the engine is being run too hard [strained] or run too easy [overly relaxed]. The magic is to run the engine right in the middle of those two sound emitting engine performance conditions. I call this letting the engine "lope along"; which means it is running at its most comfortably efficient speed. Listen to your engine they do talk - to each of us; if we learn how to listen to their language. And, twins [both in equally good condition] should nearly always be run in a synchronized "lope along" power output level.

Engines love to last for us if we learn to love their most comfortable performance levels and adhere to running them at those levels.