29Firefox

There are a lot of options out there but the boat is going to have to be designed from the ground up. Buzzi has a 42 foot RIB on the market that will go 70 knots with a pair of Cat C-15 ACERTs. Those are some pretty big motors. But it's hard to pick up babes with a rubber boat.

mthill

That doesn't address the point he made about weight. A C9 Acert, according to the Cat handbook I have in front of me, with an E rating will make 567bhp @ 2500rpm. But the thing weighs a ton...literally. Dry weight is 2086 lb. Add oil, coolant, etc and it's probably 2200+ lb. Those C15s are 50% more.

I know it's been beaten to death here, but the Duramax probably offers the best chance for lighter weight with performance, primarily due to its generous use of aluminum in its construction.

Take one straight out of a truck and it's under 1000 lbs. Dump the heavy VG turbo, cast iron manifolds, iron EGR valve body, EGR cooler, and other unnecessary stuff. Put marine appropriate parts in its place (CAC, turbo(s), aluminum water-jacketed manifolds, etc) and you've got a marine diesel at ~1200 lbs. What does a 525EFI weigh?

Rather than discuss the (de)merits of its durability in a marine application, let's just agree that we simply don't know yet since no one has done it. It's a 200k+ mile engine in a truck. How that translates into marine life is only a guess at this point. I'd rather have data than speculation.

HabanaJoe

I'll agree to that mthill - on paper it sounds good, let's see one and then we'll see how it works.

Jassman

I'll let U know when we R done

29Firefox

Yup a C-15 ACERT weighs a ton and a half dry. The marine high output version puts out about 850hp max and will cruise all day at 700hp. 200k+? The warranty is for 500k and properly maintained there are many documented cases of TBOs of a million miles on OTR truck engines.

Not intending to wiz on your parade but remember one thing. The more Horsepower an engine puts out the more heat it puts out. The more boost you run the more heat you have to scrub out of the intake air. You are gonna need 500 hp worth of intercooling and aftercooling.Thats some big heat exchangers and after coolers. Cummins is still kicking that problem around thats why were still waiting on the QSB 600 model to get released.

Also who's data sheet you looking at? A C-7 is only good for about 420hp tops.

mthill

Comparing TBOs between engines with completely different intended uses isn't really fair I suppose. It goes both ways. You can design an engine for 1,000,000 mile or a 1/4 mile TBO. Each will have their compromises.

Intercooling isn't trivial, but some (a lot) of that can be improved by design. If you don't have to work the air so hard to get it in the cylinder, you won't have so much heat to take out. Cummins will need a lot more boost to get 600hp than a dmax. It's well proven. Combine that with sub-optimal compressor design and you have an intercooler design that's near impossible to package.

QSB 600? How about a 550? 120 hp jump from the 480 is a pretty big bite. Where's the 6.7L? The bump in displacement certainly can't hurt anything.

C7? I don't remember mentioning a C7...

29Firefox

Hmmmmmm who incorrectly threw out the statement about the TBO of a C-15 truck engine.

It goes like this. You have to burn a certain amount of fuel to create a certain amount of horse power. You need a proportionate amount of air to burn that fuel. With a smaller displacement engine you have to compress the air more to get the correct amount in to produce the desired horse power. The inverse is also true. The fact is your going to have to burn 500 hp worth of fuel and air to get 500 hp no matter the displacement. Burning the same amount of fuel and air is going to produce the same amount of heat. So your going to need the same amount of cooling capacity for both engines. No way around it. Cummins is still working on it. The Duramax boys will have to work out the same problem.

It goes way back. Uncle sam wants a 600hp. Cummins has had the ECM program written for a 600 hp model since the QSB first came out. 600 hp is the brass ring. Thats why the Navy SEALS were drooling over the Banks tuned QSB.

ROFLMAO.... you stepped right in that one. I first brought up the C-15..... I'll use your words "C9? I don't remember mentioning a C9..."

I've seen some Boat Show flash displays. Some pics here and there on the internet. But I haven't seen a few hundred Duramax installations on the water for a few years so we can get feed back. Or how how about some destructive testing to see where the actual limits are. Like Joe said "on paper it sounds good, let's see one and then we'll see how it works."

Njawb

The volumetric efficiency and brake specific fuel consumption curves are not invariant across all engines.

mthill

Firefox, we must be misreading each others posts. That's the only explanation for your most recent response.

I didn't misstate the TBO of a C15, I've never even considered what it might be. I mentioned the TBO of a dmax at 200k miles in a truck. Nothing more. My follow up point was that it's not fair for either engine to be compared to the other. They (dmax and C15) were designed with completely different applications in mind.

I brought up the C9 because it fits with the earlier request for 550-600 hp. In Cat's line, it fits the bill. I have no idea where any reference to a C7 in this context came from. Perhaps you misread? It doesn't really matter.

I couldn't agree more about not seeing hundreds of dmax engines installed in boats. That is exactly my point as well. I want to see data. Until someone does it, discussion of if suitability as a marine engine is speculation at best. People are working on it...

mthill

Sort of. As najwb said, it's slightly more complicated than that. I'll admit that BSFC isn't all that different, by VE can have a reasonable impact.

That said, dealing with the heat of combustion has little to no impact on aftercooler capacity. The heat you're referring to (fuel energy) simply passes out the exhaust stream or is transferred to the exhaust cooling water. If that's raw water, it also goes overboard. If the exhaust cooling is closed, it impacts the jacket water heat exchanger.

I like data so, in a QSB, running in a "marine" style build, has a fuel energy distribution about like this (round numbers):
10% coolant
10-12% aftercooler
20-25% exhaust
10% cooled exhaust
10% oil (cooled pistons)
~35% horsepower

The power is the easy one to calculate if you know your fuel burn rate accurately. Diesel fuel at 18000 Btu/lb (LHV) * burn rate (lb/hr) / 2548 (convert btu/hr to hp) will give you the potential energy of the fuel in hp. Divide your actual hp with this and you get efficiency.

From Cummins QSB480 data sheet, at rated power, fuel consumption in 26.1 gal/hr. 7.001 lb/gal gives 182.7 lb/hr.
18000*182.7/2548 = 1290 hp. 473/1290 = 36.6%.

Essentially, I agree with your assessment that is won't be very much different for a dmax, although slightly easier to handle the aftercooler and a slightly better overall efficiency.