Reply
 
Thread Tools Display Modes
 
Old 05-05-2015, 10:29 AM   #81
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,380
Quote:
Originally Posted by FF View Post
"
Except BMEP is not given for the majority of engines , till you get up with the big stuff..
I have found that for engines made during the past decade that this information is readily available. I say this because during this period I have considered vessels powered by JD, Cat, Cummins and Perkins Sabre - all with prop curves and BSFC data readily available. Since all these guys make bigger engines it is likely an across the board decision and required for Tier XX certifications.

For older engines not so easy to find same.
__________________
Advertisement

sunchaser is online now   Reply With Quote
Old 05-05-2015, 11:29 AM   #82
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
Wxx3,
You wrote that the lower the rpm of a diesel the greater efficiency of a diesel compared to gasoline. Who cares about gas power in trawlers? But very true.

As for our diesel engines aren't they most efficient at about 2/3rds to 3/4 of rated rpm? With a typical propeller load of course.

And isn't a turbocharged engine most efficient w the turbo at medium boost? Turbo engines at near the top end aren't relatively efficient IMO but more efficient somewhere below high boost and max power but above the point where the turbo just starts working. Below that speed a turbo is like a dog dragging a broken leg.

It's a matter of how much heat is generated and how much heat is lost. Bigger engines at slower speeds (in our range of power) are much better at radiating (losing) heat and thus energy and efficiency.

These are the reasons I thought a small turbo diesel working at a load and rpm of about 2/3rds to 3/4 of rated rpm would be most efficient.

And if this is true the diesel and especially the turbo-diesel is ideally suited for our boats if operated two thirds load/rpm. A bigger heavier slower turning engine would weigh more and even it's extra weight would decrease it's efficiency. A 10% increase in boat weight = about a 10% increase in fuel burned.
__________________

__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-05-2015, 02:08 PM   #83
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 3,890
A good rule of thumb is the most efficient rpm for a diesel is to find peak torque on the full load curve, and see what rpm that is. Then cruise at that rpm at part load.

For engines in the 5-8 liter range, it's usually around 1400-1700rpm.

High rpm engines, rated at 3000+ rpm usually do not have very good bsfc at higher rpm. At high rpm, pumping losses go way up.

Really big slow engines are not that good either. Too much friction and heat loss.

Turbos do not necessarily inprove efficiency. But they allow a smaller engine to make more power, and the smaller engine saves fuel by being lighter and having lower pumping and thermal losses from the smaller size.

If the exhaust driven turbine was coupled to the crank, that would improve efficiency. But the energy in pumping more air in is not captured as a net effect on the crank.

Best efficiency usually comes from picking a hp rating not at the top of the range for a given block, maybe a notch or two or three down. Match hp needed by boat to mid range, say 50-70% of what engine can develop at full. This also tends to lead to long engine service life.

Hard to do with small engines down in the under 100hp range, there just are not many options out there.
Ski in NC is online now   Reply With Quote
Old 05-05-2015, 02:42 PM   #84
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
Ski I'm really getting into this post.

So the turbo dosn't ever (rpm or load wise) at some point produce more work per gallon of fuel? Just permits us to use smaller engines? That seems like a lot of money spent for a very little gain. I see smaller engines and less weight as a plus but most here view it the other way around.

Re pumping losses Yanmar's 55hp JH engine was rated at 3800rpm but it seems through advertising by other small engine manufacturers that low rpm was beneficial Yanmar suddenly changed the 55hp JH to 3000rpm. Same power .. just lower rpm. Seemed impossible to me.

Higher rpm has advantages. Like lower side loads on pistons against the cylinders. Less force is required w more strokes. And torsional vibration should be less as there are more strokes w less intensity.

I know some engines do have turbos connected to the crank .. DD?. But it's always a trade .. back pressure for X. If the trade is worth it .. it's justifiable.

"50% to 70%" .. I agree. Shooting for 60 to 65.

When I shopped for an engine for Willy I thought there were quite a few engines to select from. All mostly alike though except possibly Yanmar.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-05-2015, 06:14 PM   #85
Guru
 
ranger42c's Avatar
 
City: Maryland
Country: USA
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 3,160
Quote:
Originally Posted by Ski in NC View Post
A good rule of thumb is the most efficient rpm for a diesel is to find peak torque on the full load curve, and see what rpm that is. Then cruise at that rpm at part load.

For engines in the 5-8 liter range, it's usually around 1400-1700rpm.

Hmmm.... Full load peak torque for our 6CTAs is indeed right at 1700 RPMs. Looks like fuel consumption (prop curve) at 1700 RPMs would be about 7 GPH, per engine. Don't have our speed tests file here, but I'll compare that as soon as I can. Seems to me, the hull is a pig at 1700 RPMs, though...

-Chris
__________________
South River, Chesapeake Bay
ranger42c is offline   Reply With Quote
Old 05-05-2015, 06:25 PM   #86
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 3,890
1700 might be a happy spot for the engine, but might be horrible for the boat!!

My boat is ok but not great at 1700, but likes 1900-1950. Close enough for me.

Both engine AND boat must be happy with cruise rpm.

Just a rule of thumb. Real sea trial data are much better.
Ski in NC is online now   Reply With Quote
Old 05-05-2015, 07:21 PM   #87
Guru
 
LarryM's Avatar
 
City: League City, TX
Country: USA
Vessel Name: Pelago
Vessel Model: Wellcraft 3300 Coastal
Join Date: Aug 2011
Posts: 843
Quote:
Originally Posted by manyboats View Post
Re pumping losses Yanmar's 55hp JH engine was rated at 3800rpm but it seems through advertising by other small engine manufacturers that low rpm was beneficial Yanmar suddenly changed the 55hp JH to 3000rpm. Same power .. just lower rpm. Seemed impossible to me.

"50% to 70%" .. I agree. Shooting for 60 to 65.

When I shopped for an engine for Willy I thought there were quite a few engines to select from. All mostly alike though except possibly Yanmar.
Eric,

The 4JH3E was 2.0L - 56HP @ 3,800 RPM. The 4JH4E was increased to 2.2L with advertised power of 55HP @ 3,000 RPM and the current 4JH5E is 2.2L with advertised power of 53HP @ 3,000 RPM.

The factory recommends propping the 4JH3E to 3,900RPM and operating at 2,900RPM. This is 75% rated RPM and under 50% rated HP on the propeller power curve. It is also is at the lower end of the Specific Fuel Consumption curve. This actually looks pretty conservative.

It seems the smaller, higher-speed diesels are optimized for the speeds at which they operate.

As for the later engines having lower rated engine speeds, I'm sure the market demanded less noise. Direct injection Yanmars can be somewhat noisy, but are very smooth.

Ski,

As it turns out, 2,900 RPM is absolutely the sweetest for the engine and boat. The structural and shaft vibration just melt away. The sound even drops 2 dBA in the pilothouse.

The torque is beginning to fall off at that speed though.

Attached is a performance chart for the 4JH3E that demonstrates these numbers.
Attached Images
 
__________________
Larry
M/V Pelago
LarryM is offline   Reply With Quote
Old 05-05-2015, 08:24 PM   #88
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
That's wonderful Larry.
Here my memory was not so good but generally speaking fairly correct.
It's interesting that the lowest fuel burn and highest torque are miles apart on the Yanmar.o It would seem that perhaps it varies a lot on what engine is being scrutinized. I've heard often that the power and torque usually or often comes at the (roughly) same engine speed. I think engine manufacturers tend to try to get the torque down low and the efficiency tends to run high.
Thanks very much for the excellent information. Our small engines don't get much attention here as the Perkins and Fords are so numerous.
Re what Ski presented I'm glad we don't have a turbocharger to deal w but if we did we could have a lighter and smaller engine.

Are we off topic yet?
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-05-2015, 10:06 PM   #89
Dauntless Award
 
Wxx3's Avatar
 
City: New York, NY
Country: USA
Vessel Name: Dauntless
Vessel Model: Kadey Krogen 42 - 148
Join Date: Jan 2013
Posts: 2,313
Quote:
Originally Posted by manyboats View Post
That's wonderful Larry.
Here my memory was not so good but generally speaking fairly correct.
It's interesting that the lowest fuel burn and highest torque are miles apart on the Yanmar.o It would seem that perhaps it varies a lot on what engine is being scrutinized. I've heard often that the power and torque usually or often comes at the (roughly) same engine speed. I think engine manufacturers tend to try to get the torque down low and the efficiency tends to run high.
Thanks very much for the excellent information. Our small engines don't get much attention here as the Perkins and Fords are so numerous.
Re what Ski presented I'm glad we don't have a turbocharger to deal w but if we did we could have a lighter and smaller engine.

Are we off topic yet?
Ski is essentially correct, but I think you are missing the point about turbos.

Turbos work well in an application which requires a broad rpm range.

Our engines don't.

On the plane to Ireland.
Our engines don't

Gotta go
__________________
M/Y Dauntless, New York
a Kadey Krogen 42 Currently https://share.delorme.com/dauntless
Blog: https://dauntlessatsea.com
Find us: https://share.delorme.com/dauntless
Wxx3 is online now   Reply With Quote
Old 05-05-2015, 10:18 PM   #90
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 3,890
Quote:
Originally Posted by LarryM View Post
Eric,

The 4JH3E was 2.0L - 56HP @ 3,800 RPM. The 4JH4E was increased to 2.2L with advertised power of 55HP @ 3,000 RPM and the current 4JH5E is 2.2L with advertised power of 53HP @ 3,000 RPM.

The factory recommends propping the 4JH3E to 3,900RPM and operating at 2,900RPM. This is 75% rated RPM and under 50% rated HP on the propeller power curve. It is also is at the lower end of the Specific Fuel Consumption curve. This actually looks pretty conservative.

It seems the smaller, higher-speed diesels are optimized for the speeds at which they operate.

As for the later engines having lower rated engine speeds, I'm sure the market demanded less noise. Direct injection Yanmars can be somewhat noisy, but are very smooth.

Ski,

As it turns out, 2,900 RPM is absolutely the sweetest for the engine and boat. The structural and shaft vibration just melt away. The sound even drops 2 dBA in the pilothouse.

The torque is beginning to fall off at that speed though.

Attached is a performance chart for the 4JH3E that demonstrates these numbers.
The problem with the attached curves is the BSFC curve at the top is for full power all through the rpm range. Throttle on the stops throughout. Not realistic for a boat. A better curve would show bsfc along the prop load curve. That would be something we could use.
Ski in NC is online now   Reply With Quote
Old 05-05-2015, 11:16 PM   #91
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
Richard wrote;
"Turbos work well in an application which requires a broad rpm range."
Hmmm? I would'a thunk the opposite. Turbo's don't really do much till you get to the upper end as I understood it. Haven't had a turbo diesel and don't contemplate getting one so have no need to know but I'm like a curious cat and want to know. I had a great turbo gas Jetta VW that had a lot of turbo-lag. 3 to 5000rpm was really strong. Drove a Cummins truck w a turbo and the lag was there but mild compared to the VW. But I know you know a lot more than me on this so I'll twist my head around it. Thanks for the course change.

Re what Yanmar said on cruise rpm I feel it supports my "small engine turning up" theory but Yanmar says some strange things. My head is still in the small engine turning fast camp for efficiency but I know mid-range engine speeds can produce great economy.

Products are made to support the latest trends like fuel efficiency. Get a high number whatever the cost on the sticker in the window of cars. My Jetta had an EPA rating of 36mpg hwy and it delivered but top gear (5th stick shift) was too tall for me. I rarely used it.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 05-05-2015, 11:17 PM   #92
Guru
 
LarryM's Avatar
 
City: League City, TX
Country: USA
Vessel Name: Pelago
Vessel Model: Wellcraft 3300 Coastal
Join Date: Aug 2011
Posts: 843
Quote:
Originally Posted by Ski in NC View Post
The problem with the attached curves is the BSFC curve at the top is for full power all through the rpm range. Throttle on the stops throughout. Not realistic for a boat. A better curve would show bsfc along the prop load curve. That would be something we could use.
Ski,

Do you have any idea why the BSFC at prop load curve is so difficult, if not impossible to find? I understand the prop load curve is rather arbitrary as well.
__________________
Larry
M/V Pelago
LarryM is offline   Reply With Quote
Old 05-05-2015, 11:27 PM   #93
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,380
Check out this diesel and associated information. And like most modern (last 50 years anyway) engines turbocharged. 50% thermal efficiency, 102 RPM, 2 stroke, 5 million ft pounds of torque, whew!

http://wartsilasulzer-rta96-c-engine.htm
sunchaser is online now   Reply With Quote
Old 05-05-2015, 11:49 PM   #94
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 7,986
Quote:
Originally Posted by sunchaser View Post
Check out this diesel and associated information. And like most modern (last 50 years anyway) engines turbocharged. 50% thermal efficiency, 102 RPM, 2 stroke, 5 million ft pounds of torque, whew!

http://wartsilasulzer-rta96-c-engine.htm
Link won't open... for me.
Art is online now   Reply With Quote
Old 05-06-2015, 03:06 AM   #95
THD
Guru
 
City: Seattle
Country: US
Join Date: Apr 2012
Posts: 1,142
I have seen pieces on that engine, about 45 feet tall and 70 or so feet long IIRC. I think if you google it, you can find a you tube on it.
THD is offline   Reply With Quote
Old 05-06-2015, 05:28 AM   #96
Dauntless Award
 
Wxx3's Avatar
 
City: New York, NY
Country: USA
Vessel Name: Dauntless
Vessel Model: Kadey Krogen 42 - 148
Join Date: Jan 2013
Posts: 2,313
Many boats,

I was rushed, so didn't explain well.

First, I'm not sure there is a significant difference between gas and diesel turbo engines on how it relates to the turbo.

EPA has really skewed the market in that the consumption test, mpg, has a significant amount of idle time.

Idle kills gas engines when it comes to consumption, therefore car makers developed turbos, which allowed for a smaller engine, thus less consumption at idle, while giving the engine "V8" power under heavy load.

In that sense, a turbo charged engine was significantly more fuel efficient at max hp as well as at idle.

Seemingly a win-win.

But, it's only a win if the engine is well maintained and not abused, eg turned off without some cooling off time.

Also, costs significantly more to build and much more to fix.

The cost difference would never be returned in fuel savings.

So for over the road use, turbo charging makes a lot of sense.

Watch the rpms of your car during a normal commute. It's up and down all the time.

But boats are driven differently. Fast or slow, boats are usually run in a small range of rpms, or maybe two ranges, but seldom more.

Thus in a boat, it is easier to spec an engine to the boat and it's intended use.

Now, we do see a lot of turbo charged boats.
Why, since diesels consume very little at idle?

I don't know, but am guessing that turbo charged diesels exist in boats, mostly because it is such a small market compared to over the road applications, where having a smaller engine is an advantage in being able to fit it into an engine compartment, be it a truck or car.

And in the horsepower wars, that's probably a big advantage.

Also, size also matters in boats, so turbo engine helps that and 99% of boat owners don't care about fuel consumption, or are members of TF, but do like more hp, even if it's wasted.
__________________
M/Y Dauntless, New York
a Kadey Krogen 42 Currently https://share.delorme.com/dauntless
Blog: https://dauntlessatsea.com
Find us: https://share.delorme.com/dauntless
Wxx3 is online now   Reply With Quote
Old 05-06-2015, 06:29 AM   #97
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,537
"Do you have any idea why the BSFC at prop load curve is so difficult, if not impossible to find? I understand the prop load curve is rather arbitrary as well."

IF the mfg used real observed BMEP at various loads ( NOT theory prop curve numbers, or simply peak HP numbers) folks would be able to select an engine on the basis of how well it should work in a specific boat.

For a specific type boat , one engine would be the clear winner.

This is called a fuel map , and is harder to come by than plans for a T-88 small nuke.

Turbos will add to Hp when needed for hill climbing , or in marine applications give somewhat better fuel burn per HP IF the unit is operated with positive boost and a proper EGT from the load.

The danger/hassle with turbos is two fold.

The turbo and all its inter-coolers hurts efficiency till the engine is on the turbo.

No boost is bad , but 5-30 lbs will help , depending.

The other hassle is after a big high boost load the turbo is hot , usually glowing red.

The turbo must be allowed to cool down enough so its lube oil does not burn or coke .

In this case 5 min of idle to help the turbo life is worth the idle time slight hassles from no load running.

Many folks will spend more time ideling than is required for cooling attempting to enter their slip.
FF is offline   Reply With Quote
Old 05-06-2015, 07:43 AM   #98
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 7,986
My question is to the many intones that for turbo powered engines it is always a good idea to let the engine (turbo) cool at idle for 5 minutes after heavy turbo load:


How often (when ever - in boats) does any boat owner simply shut down their engine immediately after applying heavy load to the turbo?


As FF mentions in last sentence of post #97... just idle time for slip entry is usually more than needed. I add that even the minutes of idle for anchoring or canal travel to fuel dock is ample cooling time.


So again I ask, cause I'd like ta know - How often (when ever) does any boat owner simply shut down their engine immediately after applying heavy load to the turbo? Sport fishers, ocean racers, rescue boats??? Who could/would possibly go from heavy turbo load to complete engine shut-down without at least some to several or more minutes of low RPM cooling time?

Makes me think that the premise of too hot turbo shut down often mentioned is 99% an non plus. Am I correct... ?
Art is online now   Reply With Quote
Old 05-06-2015, 08:36 AM   #99
Guru
 
BandB's Avatar
 
City: Fort Lauderdale
Country: USA
Join Date: Jan 2014
Posts: 13,185
Quote:
Originally Posted by Art View Post
My question is to the many intones that for turbo powered engines it is always a good idea to let the engine (turbo) cool at idle for 5 minutes after heavy turbo load:


How often (when ever - in boats) does any boat owner simply shut down their engine immediately after applying heavy load to the turbo?


As FF mentions in last sentence of post #97... just idle time for slip entry is usually more than needed. I add that even the minutes of idle for anchoring or canal travel to fuel dock is ample cooling time.


So again I ask, cause I'd like ta know - How often (when ever) does any boat owner simply shut down their engine immediately after applying heavy load to the turbo? Sport fishers, ocean racers, rescue boats??? Who could/would possibly go from heavy turbo load to complete engine shut-down without at least some to several or more minutes of low RPM cooling time?

Makes me think that the premise of too hot turbo shut down often mentioned is 99% an non plus. Am I correct... ?
I've seen high performance boats, pull into a marina quickly, docking quickly, shutting down and the occupants gone. Typically performance boats that would have turbos. Sport fishers do it too. Now those in the know, don't. But you did answer your question, I think.

However, one other group. Some newcomers. They've been taught over the years that you shouldn't leave your car running. They also feel like they're wasting "gas" if just idling at the dock. So, for them it's education to diesels and to letting a boat engine properly warm up and cool down.
BandB is online now   Reply With Quote
Old 05-06-2015, 09:04 AM   #100
Guru
 
City: Carefree, Arizona
Country: usa
Vessel Name: sunchaser V
Vessel Model: DeFever 48
Join Date: Apr 2008
Posts: 6,380
The whine I hear is due to a world filled with turbo diesels.

Turbo-diesel - Wikipedia, the free encyclopedia
__________________

sunchaser is online now   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 09:55 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012