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How do I best run 671TIB's

Crabber50

Member
Have a new to me boat, it is a 61' Tollycraft with 2 671 TIB's they were rebuilt about 500 hours ago and tuned at time of purchase. These are my first diesel motors ever.

The hull speed or efficient speed for the boat is about 10 knots. Here are the specs from the sea trial.

RPM Knots
900 7
1000 8
1200 9.2
1338 10
1500 10.5
1800 12.1
2000 13.2
2156 14.8 Top speed

Am I fine to cruise 90 percent of the time at 1000-1400 RPM and just run her up to 1800 every now and then? Should I ever use WOT?

Really appreciate any advice. Also any help on how to know how many Gallons per Hour I'll burn?

Thank you
 
Detroits are VERY comfortable at 2156. With properly functioning cooling and lube systems and a clean hull, they will do WOT all day, everyday. 1800 to 2150 rpm is the "sweet spot" on the power curve for these engines.

While it certainly won't do them any harm to run at 1400, don't be afraid to open em up when the mood strikes you.

You will need to run a bit to find where you get the best fuel consumption numbers for distance traveled. That usually dictates where a skipper will keep the throttle set. You may actually find that you get more bang for your buck, fuel wise, keeping them somewhere in that power curve.

Congratulations on getting what sounds like a VERY COOL vessel!
 
Need to double check the WOT in Neutral, when the survey was done he said it checked out fine, he is very experienced with DD but it is not in his written report. Thanks for asking as I need to know, should I be concerned that in gear WOT is 2156? The boat is VERY heavy, maybe even 80,000 LBS with Full tanks.
 
Sorry for the delay, finally was able to do a WOT test, result are below

Thank you!

Top RPM in neutralWOT

Port 2245
Starboard 2300

Top RPM in gear WOT
Port 2115
Starboard 2150

Speed overGround 15.4
Current 0
Full fuel and watertanks
4 adults on board
 
It's just my opinion but it IS based on 30 years of working on Detroit Diesels. The difference in NO LOAD rpm and FULL LOAD rpm is known in Detroit Diesel parlance as "DROOP".

Your STBD engine has a DROOP of 150 rpm and, While some might think that is excessive, I think it may be better than an engineering spec sheet listing. DROOP specs for turbocharged 6v and 8v 92 TAC engines was changed from 125 rpm to 175 rpm for dyno testing many years ago. I can't imagine that the inline 6-71 engines, which typically yield less brake horsepower AND torque, would have a smaller DROOP window.


But, since I don't know all there is to know about marine application I will certainly be interested in what others have to say.

I think you have a couple of strong units there and they seem well matched. A slight high speed governor spring adjustment is all it would take for them to probably "mirror" each other. I would personally drop the starboard to 2250 or so rather than bring the port up to 2300. But in the giant scheme of things, it probably doesn't make a big whoop.
 
Jmgo,

Thanks for all yourhelp, it is very appreciated. Enjoyed reading your posts answering otherfolks questions as well.

It is good news thatthe "droop" is not an issue. If my calculations are correct we should be able to travel quiteeconomically at or below 10 knots running 1300 RPM or less. We may even get better than 1 MPG. However due to hull speed the economy goesway down as we increase speed. It seemswe will burning 7 GPH at 1300 RPM (10 knots), but 32 GPH at 2150 RPM (15 Knots)

So we will likely berunning 10 knots or below most of the time, but it is great to know we can run full out if the situation warrantsit. Want to do everything we can to'baby' these engines.

Looking for servicemanuals so I can keep everything in top shape.

Thanks again, as I get more time with them I will be backwith more questions I am sure.

Crabber50
 
Yep, slower is usually cheaper in just about any conveyance you choose except maybe bobsleds. And THAT is ONLY when going downhill! Friction is always working against us except when stopping. And DROOP is just a fact of life and frictional loss when you load 'em up.

That is, at least in my opinion, a pretty BIG boat and there are just SO many factors that come in to play as to why a hull will perform in a given manner with given power plants. Running those 71's at 1300rpm all the time would certainly be considered "babying" and, like any other contraption that goes round and round, the fewer times they do, the longer they will last.

I would, however, put in my operational "parameters" a short, wide open run every so often to keep the oil build up in the blower boxes cleared out. If you are unfamiliar with the 2 cycle aspect of the air charge box and the drains that are necessary to keep the box clear, that is a good portion of the service manual to concentrate on once you have it in hand. Your vessel, most likely, has some sort of "catch" system for the drain oil to return to sump but whatever is there, it needs monitoring and maintaining for good engine health and long life.

One other thought goes to oil pressure. The turbos want/NEED a good, clean, steady supply of oil "up there" at all times. You should see the full 50 to 60 psi at 1300 rpm but it is essential to make sure that it is happening. These turbos will also exceed 100,000 rpm when developing full boost so a good 3 to 5 minutes "spool down" time at idle will maintain some oil on the bearings until they can get slowed down before stopping the engines.

Sounds like a FUN boat! Good luck with her and fair winds!
 
Looking at a DD engine performance chart, would I read the fuel consumption based on actual RPM's achieved? For example 2100 on the chart even though WOT on the chart is 2500? 2100 is 14 GPH per side, 2500 is 24 GPH per side. Just wondering if mine are burning 14 or 24?

Attempted to attach file
 

Attachments

  • 6-71TI Performace Curve 1984.pdf
    88.5 KB · Views: 399
I opened the PDF and I started getting a headache. Not being a bonafide dynamics engineer...I don't do all that well with charts. This thing looks like a test stand data logging chart that has "convergence" of BHP-SHP- propeller load (dyno) and fuel consumption for that injector set coming it at 2500 rpm. What does it mean it the "real world"? In a "given" boat? I don't know.

There is no weight, speed or distance associated with this chart. So, the question of "what work is being done" is only answered in an unknown...propeller load. Which, I imagine is a formula in a book I've never had the displeasure of reading.

MY minds eye is of the engine bolted down in a clean room with hoses and lines and "beakers" of fuel hanging over it like intravenous feed bags while a guy in a white coat in ANOTHER room pours the coals to to her while watching the dials rotate.

This test is done at 2500 rpm plus....something I know they USED to do in the the marine world. The valves will start to float somewhere a bit north of there (around 3,000 rpm) and there is negligible torque gain in "that region" the be had from these engines. I KNOW these things because I was TOLD these things by the boys from DETROIT DIESEL TRAINING CENTER...BURBANK, California. A place that is NO LONGER THERE.

So, I'm sure there are plenty of people that would argue with me on this but, in my opinion, this is like a memo...it's just a chart....not to be taken too seriously.

But, then, I'm just an old mechanic.
 
You are fine to cruise at 1,000 to 1,400 RPM .
The performance chart is just a guide. Every boat is different. It assumes you have the correct size props .
If you happen to be way over propped you will use more fuel than the correct sized props, the governor is going to keep shoving fuel into the engine to get the RPM's you are asking for.
Do the engines have pyrometers? Use ONLY Delo 100, 30 or 40 weight motor oil.
 
100% agreement on the SINGLE weight viscosity oil. Multi-viscosity oils are generally NOT recommended for use in the 2 cycle Detroits. Only in EXTREME cold conditions and the use of block heaters is not convenient have Multi-vis oils been prescribed by DD for their 2 strokes.
Great advice from CASTLE_CAPE!
 
Very happy that it is okay to cruise 1000-1400 as the wife and I have found that range most comfortable and likely affordable, wish knew the fuel burn! Previous owner used Delo 100 40 weight, so I will continue with that. Each engine has two heaters on a thermostat, have them set at 70, turn up to 120 a few hours before we start them.

Attached the survey mechanics results. It has the Pyro data, we have meters at helm but do not know what is good/bad or what to watch for when

The starboard engine starts immediately, but since its tune up the port engine takes 5-7 seconds and often 2 tries. No throttle added when we start.

All of your help is very much appreciated.
 

Attachments

  • Reduced 65 Tolly eng report 9-14.pdf
    257.8 KB · Views: 466
Just MY opinion but keeping the EGT below 900*F is a strategy for long engine life. I get worried If I see 1100 and above although MANY engines withstand this easily even for extended periods. Much of what you are seeing on your pyro gauges will depend on WHERE the sensor is located and what TYPE of thermocouple is used for measurement.

There are many differing strategies for mounting the thermocouples but most have them an inch or two before the turbine side of the charger.

With the numbers represented on your survey, it would seem that you have little to worry about if you are going to be in the 1400rpm operating range most of the time. When you do apply full boost, is when I would say to keep a weather eye on the temps. IE: more rpm = more fuel burned= bigger fire= higher temps.

What caught my eye on this particular survey (besides things like "turbocharger check-good"...huh?)
Is your oil pressures. While they are within the "safe operating minimums" for both engines, l would have expected them to be much higher at the elevated rpms. I don't think it's any cause for alarm and may have a lot to do with WHERE and HOW the senders are plumbed into the system. They should be in the MAIN gallery feed but often are placed in a less "technical" area because of room restrictions. Just something to consider going forward.
 
Need to do some work on the gauges as the surveyors oil pressure results were based on helm gauges, they report lower numbers then the engine room, last time I started the engines I noticed the oil pressure was reported much higher in the engine room. Maybe even 50psi at idle. The tach and volts do not work in the engine room at all.
 
Well.......That is GREAT NEWS! That sounds like they have "proper" oil pressure and the rest is easy. Not all that unusual for the engine room instruments to be the "first to go" as a vessel (and it's skipper) ages. Here is where you will benefit from living in the "digital age". You will be able to buy replacement instruments and senders that are probably MUCH more accurate than what is currently in there. AND, you can have the SAME readings at the helm as are in the engine room if they are installed correctly and the signal wiring reliably routed. No more having to "do the math" to make sure all is well down there!

This boat sounds a little sweeter all the time!
 
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