Holy torque Batman!.

As we wait for the final days of our boats build to slowly march by, I have been on the search for any information about any gear associated with it.
One chart I've glossed over was the engines performance specs.
As I have no idea exactly how torque impacts the propeller in water equation, I've ignored the subject.
When I finally focused on the numbers I stopped in my tracks.
This baby puts out just shy of 1200 pounds feet of torque!
I'm impressed!
Bruce

https://cumminsengines.com/uploads/docs/Marine_SiteContent_en_Binary_Asset_attachments_Products_Commercial_Propulsion_QSB6_7_Performance_Curves_FR94127_480_3300_HO_PC_Tier3-02OCT2013.pdf

Have a light hand on the throttle or your fuel tanks will get small quite quickly. What do you guess the torque/HP/fuel consumption to be at 8 or so knots? Maybe 15 - 20% of rated full load?

Which raises another question, how do the designers adjust rudder and stabilizer designs for these varying speed ranges? This question covers more builders than AT.

sunchaser said:

Have a light hand on the throttle or your fuel tanks will get small quite quickly. What do you guess the torque/HP/fuel consumption to be at 8 or so knots? Maybe 15 - 20% of rated full load?

Which raises another question, how do the designers adjust rudder and stabilizer designs for these varying speed ranges? This question covers more builders than AT.

Click to expand...

Until a NA or Marine engineer answers....

My guess is all boats have to go slow....thus a large enough rudder to turn against expected current, wind.... but small enough not to increase drag enough to penalize higher speeds.

Also I believe, there is less drag on a larger surface slightly turned than a smaller surface turned more to produce equal force.....maybe a small difference but think I remember something like that from aerodynamics class.

Based on my experience....most of the time the combo seems right...but some TFers have felt the need to modify their rudders for slow speed manuevering.

I know some 38 foot Sea Rays that were really hard to slow control due to their small props and rudders.

So even power at idle avaiable due to a large prop may be mixed in the calculations.

Ultimately I would think the calculations lean more to control than speed......then on the first model that hits the water, keep shaving down the rudder till you see better speed performance if at all until controllability becomes an issue.

Speaking of that spec sheet, before you take final delivery, make certain that the boat easily attains the full rated RPM of 3300, preferably more up, the the governed limit of 3375. And that should be with full fuel, full tanks, loaded for war. It's very common for boats to be over-propped and unable to reach full RPM. With a high output engine like this, that will significantly impact longevity, and I think will void the warranty. Getting 470hp out of a 6.7l engine is pushing it hard at 70hp/l. My 8.3L QSCs were rated for 500hp (60hp/l), and my 9l Deere is rated for 325hp (36hp/l). What you have is fine - don't get scared - but just know you need to be sure it's not over propped. And be sure to observe the allowed duty cycle which is no more than 1hr at full throttle out of every 8hrs of operation, and reduced throttle must be 3000 RPM (300 below rated max) or less. That's unlikely to be an issue with typical trawler operation, but still important to know.

IMO many sea rays were hard to control at slow speed because they used tunnels. great for speed but not so good for slow operation.

twistedtree said:

Speaking of that spec sheet, before you take final delivery, make certain that the boat easily attains the full rated RPM of 3300, preferably more up, the the governed limit of 3375. And that should be with full fuel, full tanks, loaded for war. It's very common for boats to be over-propped and unable to reach full RPM. With a high output engine like this, that will significantly impact longevity, and I think will void the warranty. Getting 470hp out of a 6.7l engine is pushing it hard at 70hp/l. My 8.3L QSCs were rated for 500hp (60hp/l), and my 9l Deere is rated for 325hp (36hp/l). What you have is fine - don't get scared - but just know you need to be sure it's not over propped. And be sure to observe the allowed duty cycle which is no more than 1hr at full throttle out of every 8hrs of operation, and reduced throttle must be 3000 RPM (300 below rated max) or less. That's unlikely to be an issue with typical trawler operation, but still important to know.

Click to expand...

As this is the first of the American Tugs delivered with this engine combination, Cummins will be aboard for the sea trial to certify the engine package installation. American Tugs has delivered a number of 5.9 480 HP powered 395's but this is the first of the 6.7's. I am told that Cummins will not certify the package if it is over propped.
This will be an interesting sea trial with lots of instrumentation and I can't be there!
Bruce

sunchaser said:

Have a light hand on the throttle or your fuel tanks will get small quite quickly. What do you guess the torque/HP/fuel consumption to be at 8 or so knots? Maybe 15 - 20% of rated full load?

Which raises another question, how do the designers adjust rudder and stabilizer designs for these varying speed ranges? This question covers more builders than AT.

Click to expand...

No idea how they adjust for additional speed ranges but owners of other 480 hp 395 have no complaints and I've asked!
One interesting note is that the 480 hp equipped boats are actually the most fuel efficient of the series, ar least below the additional speeds allowed by the higher power. If you open it up, you pay!
Bruce

As this is the first of the American Tugs delivered with this engine combination, "Cummins will be aboard for the sea trial to certify the engine package installation. American Tugs has delivered a number of 5.9 480 HP powered 395's but this is the first of the 6.7's. I am told that Cummins will not certify the package if it is over propped.
This will be an interesting sea trial with lots of instrumentation and I can't be there!
Bruce"


It is good to see that the engine specs clearly call out acceptable EGT readings. A good thing to monitor to ensure that overloading is not present at any rpm now of in the future. Please consider the value of this gage/reading and if it is not part of your install already the value of adding that feature.

smitty477 said:

...It is good to see that the engine specs clearly call out acceptable EGT readings. A good thing to monitor to ensure that overloading is not present at any rpm now of in the future. Please consider the value of this gage/reading and if it is not part of your install already the value of adding that feature.

Click to expand...

It is not something that we added to the boat during the build but...
I may add one at a later date.
This boat is being delivered in such a complete form that there is little left for me to do!
I understand the importance of egt so it is on my list.
Bruce

"It is not something that we added to the boat during the build but..."


It may be part of your existing engine package ...

smitty477 said:

"It is not something that we added to the boat during the build but..."


It may be part of your existing engine package ...

Click to expand...

Depending on the engine data display that you have, it may be included. My boat was not equipped with one of the Cummins Smartcraft displays and I have found that I wish I have it. I am considering adding a Seaboard SMX display if I can figure out how. After almost a year of powerboat ownership, I have decided that the more engine data the better.

Bruce B said:

It is not something that we added to the boat during the build but...
I may add one at a later date.
This boat is being delivered in such a complete form that there is little left for me to do!
I understand the importance of egt so it is on my list.
Bruce

Click to expand...

EGT gauge is nice to have. But with that QSB you get real time GPH display. Both sort of tell you the same thing, engine load. If GPH is above normal, with normal being the prop load curve on the data sheet, EGT could be high too. If GPH is at or below prop curve data, EGT will be fine.

Still, EGT is a nice helm gauge to have. But that GPH reading is super valuable.

Experience with these has shown them to be pretty accurate, too.

Nice engine. QSB, QSC and QSL have really impressed me. And they have been out long enough to get some good history.

smitty477 said:

"It is not something that we added to the boat during the build but..."


It may be part of your existing engine package ...

Click to expand...

Sigh,
I have to say, I've read all of the manuals and materials I can find on equipment used on this boat but the Cummins stuff is organized in a way that makes it difficult. I don't believe that I have seen this but I'll go look again.
I also learned that our engine will use a new Mercruiser/Cummins control panel that is different than previous versions. The new planet appears to be a Simrad
based panel that Mercury calls VesselView 7.
Aparrently Cummins and Mercury are in the process of parting ways too and future engines will use a different NMEA based system for engine monitoring.
Still lots to learn here...
Bruce

Bruce B said:

As this is the first of the American Tugs delivered with this engine combination, Cummins will be aboard for the sea trial to certify the engine package installation. American Tugs has delivered a number of 5.9 480 HP powered 395's but this is the first of the 6.7's. I am told that Cummins will not certify the package if it is over propped.

This will be an interesting sea trial with lots of instrumentation and I can't be there!

Bruce

Click to expand...

That's ideal.

Bruce B said:

Sigh,
I have to say, I've read all of the manuals and materials I can find on equipment used on this boat but the Cummins stuff is organized in a way that makes it difficult. I don't believe that I have seen this but I'll go look again.
I also learned that our engine will use a new Mercruiser/Cummins control panel that is different than previous versions. The new planet appears to be a Simrad
based panel that Mercury calls VesselView 7.
Aparrently Cummins and Mercury are in the process of parting ways too and future engines will use a different NMEA based system for engine monitoring.
Still lots to learn here...
Bruce

Click to expand...

Will the Garmin plotter and displays interface with the Simrad based VV7.

sunchaser said:

Will the Garmin plotter and displays interface with the Simrad based VV7.

Click to expand...

It is my decision to do or not.
Not sure yet...
Bruce

IF this new engine has a high pressure fuel system, go to Pro Boat Builder and read the fuel filtering requirements .

FF said:

IF this new engine has a high pressure fuel system, go to Pro Boat Builder and read the fuel filtering requirements .

Click to expand...

We have a good system aboard the boat.
I drive a Ram truck with one of these engines so I am aware of the importance of clean fuel...
Thanks,
Bruce

"We have a good system aboard the boat."

That meets the Pro Boat builder specks?

That exceeds Cummins specs.
This is not the first of these boats built. There are a couple hundred of them out there now.
Have not heard of issues by owners and I've been asking.
They do some interesting things in the fuel system for some interesting reasons that I never understood.
I am happy with the design and I am not easy to please!
Bruce

Bruce B said:

We have a good system aboard the boat.
I drive a Ram truck with one of these engines so I am aware of the importance of clean fuel...
Thanks,
Bruce

Click to expand...

No doubt the Cummins in your AT has the same nameplate as your pickup, but there the boating world similarity ends.

I'd guess that 90% (or higher) of the diesel engine issues we boaters encounter are directly tied to the marine environment and related hardware. This 90% that can shut us down involves heat exchangers, raw water pumps, scaling and fouling, after coolers, propulsion systems, fuel delivery and exhaust systems to name a few.

As your wonderful new vessel's engine ages it will begin to mimic those that are already entering the teenage years and beyond. The marine engine environment treats no nameplate kindly. It is immune to ethnicity, political leanings and propaganda. The marine diesel loves a good initial in vessel setup, proper care, lots of attention and seed money.

If only my boat's engines could be dry land stored, as well pampered and easily cared for as my truck's.

Bruce B said:

That exceeds Cummins specs.
This is not the first of these boats built. There are a couple hundred of them out there now.
Have not heard of issues by owners and I've been asking.
They do some interesting things in the fuel system for some interesting reasons that I never understood.
I am happy with the design and I am not easy to please!
Bruce

Click to expand...

I would expect this to be the case. There are a lot of QSB (what you have, right?) and QSC engines in marine service for over 10 years now, and the filtration is well specified by Cummins. 10 micron external, plus the on-engine filter which I think is 2 micron.

Do you have the dual racor setup? That makes filter swap trivial if you need to do it while underway, and allows for continued operation while you replace the plugged filter element. But even that I think is overkill for most cruising.

Yes, there is a dual Racor set up for the engine.
We also chose to include the optional vacuum gauge mounted at the helm so that we can keep an eye on things.
As to diesel reliability in the marine environment, this may be be the largest marine engine I've cared for but it certainly is not the first.
Having spent my life in the business of auto maintenance, I've amassed a little knowledge along the way and I'm at very least "capable".
I've personally seen to the care of far fussier machinery than this and I like maintaining machinery more than most people like a good beer and a ball game.
My background and almost perverse interest in mechanical things won't allow me any kind of magic ability to avoid problems but it should allow me to spot them sooner and certainly avoid the more common lack of maintenance induced failures.
Bruce

There are LOTS of Q series running with simply the filtration system Cummins specified. Very few injection system failures that I have heard of, and my ear is pretty close to the vine.

I consider the Cummins specs for filtration adequate. If you want to put additional filtration on, or if your tanks are full of crap, nothing wrong with adding more. If my tanks were full of crap, I would consider it.

Ski in NC said:

There are LOTS of Q series running with simply the filtration system Cummins specified. Very few injection system failures that I have heard of, and my ear is pretty close to the vine.

I consider the Cummins specs for filtration adequate. If you want to put additional filtration on, or if your tanks are full of crap, nothing wrong with adding more. If my tanks were full of crap, I would consider it.

Click to expand...

Wow, people skip the external filter? I guess I shouldn't be surprised.

Bruce should also be free from crap in his tank for a long time.

twistedtree said:

Wow, people skip the external filter? I guess I shouldn't be surprised.

Bruce should also be free from crap in his tank for a long time.

Click to expand...

No, the spec includes a 10mic external filter. A racor 10mic primary, on engine secondary.

Ski in NC said:

No, the spec includes a 10mic external filter. A racor 10mic primary, on engine secondary.

Click to expand...

OK, I misunderstood. I thought you were saying that people commonly omitted the external 10 micron racor (or other brand of your choice), and just ran with the on-engine filter.