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What percentage power to run and fuel

Old 10-04-2020, 03:14 AM
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Default What percentage power to run and fuel

I just got a 46’ Bertram with Cummins Q series motors. The dealer says home heating oil is fine. He also states that 80-85% power is good for long life of the engines.

Does that sound right? If not, I’m interested in opinions backed by personal experiences. Thanks!
Old 10-04-2020, 05:16 AM
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While home heating oil and diesel fuel are very similar and at times can be just about identical, diesel fuel is a consistent hydrocarbon intended for Diesel engines. Home heating oil is often times a blend of stuff as oil burners don’t really care what goes through them.
In an emergency it would be fine, to do it every day I think is just plain bad advise.

This is easily answered with just a google search, no need for opinions.
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Old 10-04-2020, 05:24 AM
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Had an old Mercedes Diesel that would burn lots of different oils. Lots of guys did veggie oil conversion, used motor oil.....heck I ran Tiki Torch oil in mine.....but I would want to keep good clean fuel in that Cummins.
Old 10-04-2020, 06:07 AM
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Originally Posted by Craig Hili View Post
I just got a 46’ Bertram with Cummins Q series motors. The dealer says home heating oil is fine. He also states that 80-85% power is good for long life of the engines.

Does that sound right? If not, I’m interested in opinions backed by personal experiences. Thanks!
I think what he is saying is your load factor should be around 80% not power. Depending on year of the motors you may not show load on the instruments.
Old 10-04-2020, 06:09 AM
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Oh. I hadn't heard of load factor. Yes, it displays that.
Old 10-04-2020, 06:36 AM
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2 points I like to make
you have $150k worth of engine, I would not risk them by saving a $1.00 a gallon
if you wonder why 20,000 hours marine diesels need full rebuild @ 2,500 hours , keep running them at 80% load.
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Old 10-04-2020, 07:53 AM
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Hopefully that 46 Bertram has QSM-11's and not QSC's as that hull really needs a lot of power to move efficiently.
As far as running them, 70-80% load as a cruise speed is fine and what modern marine diesels are designed for. At the 500 hrs/yr E-rated engines are designed to be run, that is about 12 years until you reach the 6,000hrs before overhaul that is expected.
If you use the boat at the more common 150-200 hours per season, that would be 30-40 years of use. If you are going to use a boat more than 500 hrs/yr, it really should have commercial rated engines.
Old 10-04-2020, 08:42 AM
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A few points: (and yes I am in the marine diesel business)

1. In some areas (including mine in SE NC) our fuel distributor uses the same tanks and trucks for #2 off road diesel and home heating oil. Here it is the same stuff. Check with your local fuel vendor.

2. To figure out best cruise speed, you need to experiment a bit. The QSM11 display should give you %load, gph, rpm and other data. Sometimes you have to toggle screens to get the stuff you want. Take boat out and with clean bottom and normal load, get boat up on plane and add a couple kts, guessing you will be around 17kts and 1500rpm. Write down boat speed, rpm, %load and gph. Add 50rpm and take down the same data. Keep doing that til you get to like 2150, which is the hardest I would like running an 11 long term. (unless a 710 at 2500, that can go higher)

Make a table of the data. Add a column for nmpg. Take boat speed and divide it by total gph.

There will be a sweet spot where nmpg is best, and %load is not too high. Berts like going a bit faster due to the deep vee. Would hope to see a sweet spot of like 23kts at 1900, %load under 80, gph is what it is. Berts feel nice when the get some lift from speed.

3. With sync off, do a full power run, watch rpm and %load. With the 2300rpm version like to see about 2350 and load slightly below 100%. If the 2500 rpm version, want to see 2550 and same with the load.

You do NOT want to run a QSM at high load. That dry manifold will bite you. Best is to under prop it and let it spin up. Some say don't cruise over 20gph. Actually, I like seeing full power at like 2360 (elec gov won't let it much over that) and at that point load below like 95%.

QSM 11 is not common rail. It is unit injected with lots of injector hardware lube oil lubed. It is about as sensitive to fuel quality as a 6-71 (as in, not that much). Common rail picky as heck about fuel quality. QSM is happy with normal filtration.

But don't run them at high load/lower rpm. Really.

Investigated a boat that caught fire with these. Guys ran from Fla to NC with barnacles on the props. Ran their normal 2150. Turns out that was 100% load due to the barnacles. Warped the dry manifolds and a jet of hot exhaust gasses shot out and caught the ER overhead on fire. Lots of damage.



Old 10-05-2020, 06:22 AM
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They are QSC 8.3 is what I have and it is common rail.
Old 10-05-2020, 07:09 AM
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Well, geez, that was a lot of wasted typing. I thought I saw QSM somewhere above. QSC does not have the dry manifold problem, so ignore that. Still good to do the test run and log data at various rpms. Full power rpm will be higher, and that depends on the rating. Some are 2600, some are 3000.
Old 10-05-2020, 07:15 AM
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Lol, sorry about that. I'm new to all this and should've given more info.

The motors are rated for 540HP and they produce about a knot per hundred RPM. I've been running at 2250RPM and get 22-23 kts, the guy before me ran them at 2400 RPM and that gives me 24 kts.

Where is the highest I should cruise them to ensure reliability?
Old 10-05-2020, 07:27 AM
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Probe the exhaust temperature, the temp will increase with rpm until you hit a “sweet spot” and it drops out, that’s where you want to run your engines
Old 10-05-2020, 07:33 AM
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I think the 540 is rated at 2600, but verify on your engine tag up on the timing gear cover.

To answer your question need to know rpm, %load at full power, sync off. If full power is like 2660 at 95%, then 2400 is no problem.

Post %load, gph and boat speed at the two rpms you like.

Berts like speed to lift up, so 2400 might be better.
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Old 10-05-2020, 11:25 AM
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I would not recommend burning home heating oil in your Cummins diesel. While #2 diesel can be used for home heating, not all home heating oil is refined or treated the same as #2 diesel intended for use in an engine. I don't know the requirements for home heating oil but I would be afraid of higher sulfur content, higher paraffin content, and lower cetane rating to name a few. At the very least I would expect shorter filter life. At worst I would expect fuel system issues due to differences in lubricity and potential deposits due to higher sulfur content. A key part of meeting the off highway emissions regulations is the chemistry of the fuel. Clean fuel and regular oil changes are the key to getting a long trouble free service from your engines. I retired in Feb. of 2019 after 40 years of working in design, development, and manufacturing at Cummins Inc.
Old 10-06-2020, 05:03 AM
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Thanks guys. It's diesel fuel only for me.

WOT was 28 kts at 2660 RPM and 99% load. 85% throttle is 85% load and 25 kts at 2400 RPM. 85% seems right. The boat is on plane and efficient.
Old 10-06-2020, 05:18 AM
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Constant 85%load is Not recommended on the QSC's ….. twin 540HP in a 46 Bertram is under powered in todays world.....
Old 10-06-2020, 05:45 AM
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Personally, I would prefer to cruise at 80% power, which is probably 2,350 rpms.
Also be careful to monitor the engine load as the boat ages in the water, with just a little bottom slime and a barnacle or two on the props, you will probably close o 90% load at 2,400 rpm, which is really hard on those engines.
Old 10-07-2020, 01:08 AM
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The boat planes nicely with the motors at 2400RPM 84% load 87% throttle at 22.5 gal/hour each side. The data plate says 2600 is the max rated RPM, but WOT for me made 2640 and 2680 RPM respectively.

1- can I run at 2400RPM reliably?
2- given that I'm able to push just past max RPM, am I propped correctly?

It sucks to think the boat is underpowered with the engines I have, but even if that's true, I'm not changing motors; it's too expensive. How bad is the situation? What's the likely outcome of my running the things at 2400RPM and 83-85% load?
Old 10-07-2020, 07:08 AM
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Running at 2400/22.5gph is certainly running them harder than I would like to see. That's about 420hp.

You are propped correctly, but a little on the heavy side. Would like to see like 95%load at 2660.

Berts are fine boats, but being heavy with a deep vee, they take a LOT of hp to get up.

Will engines be reliable run at 2400? Probably will. These engines (not your particular engines) are proven on the dyno at over 100% rated for like thousands of hours. Brutal test.

But I would not expect them to last as long compared to running a lighter load.

In your favor is that they make a 600hp at 3000rpm, basically the same engine.

Do the data log test run as suggested. Log same numbers for 2000, 2100, 2200, 2300, 2400. Sometimes you get surprises looking at the numbers. Include kts.

How many hours so far? Any problems?
Old 10-07-2020, 07:23 AM
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I'll be back by the boat to run it in a week or so, thanks for your input! The motor were installed in 2008 by the previous owner. He owns Mako Marine in Freeport, NY (on LI) and that's where he ran them. There are about 750 hours on the motors and they haven't had any problems at all. The only thing that I noted was that the starboard side makes 43psi for oil pressure vs. 60psi on the port side (both within normal range, and the previous owner states it has always been that way) and I noticed while playing around with the Vessel View computer while bringing it to NC that the starboard side also makes less boost (30.2psi vs 38.9psi at WOT) and there are differences in the intake temp (84F vs. 61F, cooler on tbe starboard engine).

I did hire a surveyor to evaluate the ship and the motors. He said they were running optimally...but I am scratching my head about the differences. Any thoughts about that?

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