Power ratings and a new engine decision: Need some help

[Garpow2026]

Hello...I am posting this question as I am soon to launch a new build for a full displacement trawler and am struggling to find 'layman's' explanations or much of anything around the 2 questions posed below on ower ratings and JD and Cummins. I am hoping that this crew which is very experienced in boats and engine option decisions would be willing to share your thoughts and do a little educating. So please excuse the lack of diesel know how and bear with me... the boat is a 65' LOA trawler with a 18' foot beam and roughly 120,000lb displacement, 5' 8" draft. JD6090 was the quoted engine but after some research I have changed this to the following: JD6138AFM85 with the M2 rating @ 425 (bhp) - primarily from feedback about the advantage of the water cooled jacket approach. My first question is M1 vs M2 rating. My understanding is both these are Continuous use ratings the difference being full power rating of the M2 of 16 to or 24 hrs and then 80% power for the other 8hrs vs M1 continuous full power. My thought being the extra horsepower would be valuable in a pinch to up the top end by a knot or so - I understand that comes with a high fuel cost so please do not beat me up on that one as I appreciate that but still feel the extra power could be worth it for local cruising or emergency situations and 80% of that power might drop this boat to 7 knots or so still very respectable if running all day or night. I understand that the hull speed is a little over 10 knots and cruise is 7-8.5 likely with both engines but at full throttle I could get more out of the M2 rating and then as required pull the RPM's back for the required period and still travel at the cruise speed of the M1. Here are the numbers:

Performance Rating Power KW (bhp) Rated Speed (rpm) Rated fuel consumption L/hr(gal/hr)
M1 272 ( 365 ) 1800 76.7 ( 20.3 )
M2 317 ( 425 ) 1900 86.2 ( 22.8 )
M1 - Typical annual usage (hr) Unrestricted
M1 - Typical full-power operation (hr) Uninterrupted
M1 - Typical load factor >65%
M2 - Typical annual usage (hr) 000-5
M2 - Typical full-power operation (hr) 16 of each 24 hr
M2 - Typical load factor <=65%

I would appreciate others thinking on this one as I can pick either engine rating at this point. The last question is a little different but related. I was in a version of the boat that had a Cummins QSM11 and I loved the smaller size of that engine for ease of maintenance and the extra space it delivers over the larger JD. Cummins also has an equivalent type rating of Heavy Duty vs continues use that creates the same question as above. Any thoughts on Cummins vs JD would be welcome as well for this purpose.

Pardon the long explanation. Any experiences and input/information would be so helpful! Thanks...

 

[Jeff F]

I've studied the JD ratings carefully.

The load factor is essentially average load, so if you ran the M2 at 80 - 100% load for most of the time you could exceed that threshold and an M1 would be more appropriate. But in practice recreational trawlers spend lots of time under low loads, so don't have trouble staying well under that load factor. That would be average gph of under 2/3 of maximum rated.

I'd choose the M2.

 

[twistedtree]

Great questions. I think M2 is fine for a trawler, even one that is heavily used. Time spent at higher loads just won’t be very often.

I’m a bit confused by the jacketed bs non-jacketed comment comparing the 6099 to the 6135. It is a 6135, not 6138, right? I believe both have jacketed exhaust manifolds and turbos. And I think the AFM models are both coolant cooled after we coolers (that’s a mouthful, isn’t it), not seawater cooled. The SFM would be seawater cooled, if I’m remembering all this correctly.

Will the engine be heat exchanger cooled, or keel cooled?

As for Deere vs Cummins, wars have been fought over that question. I would pick whichever fits your application better. I went through this about 5 years ago and wrote a blog article called “mirror mirror in the wall, which is the fairest engine of all” that might help sort through what’s a best fit for you. It’s on MVTanglewood.com. I don’t think you can go wrong with either.

 

[Garpow2026]

Thanks for insights and I think they both make sense and I was leaning towards to M2 rating. My understanding was the 6135AFM85 is jacket' cooled and this results in easier maintenance and better reliability then the model originally quoted which was a 6090SFM85...so I may very well of misspoken on the 'water' aspect and appreciate you clarifying. I will hit your blog as well and read up and I do also get the 'wars have been fought' comment over the engines - never simple answers I know and big fans for all the brands. It is a learning experience! Thanks again for your thoughts.

 

[Comodave]

JD and Cummins are both excellent engines. I would look to which brand has better support in your intended cruising area and go with that engine.

 

[cafesport]

They haven’t published the data yet but I have it on good authority Lugger is back in the propulsion game with engines of those power and ratings again. Should be seeing something at the Miami show. I would give them a call and see what they would recommend for your build. I would also go with their generators on a new build.

 

[Garpow2026]

Great questions. I think M2 is fine for a trawler, even one that is heavily used. Time spent at higher loads just won’t be very often.

I’m a bit confused by the jacketed bs non-jacketed comment comparing the 6099 to the 6135. It is a 6135, not 6138, right? I believe both have jacketed exhaust manifolds and turbos. And I think the AFM models are both coolant cooled after we coolers (that’s a mouthful, isn’t it), not seawater cooled. The SFM would be seawater cooled, if I’m remembering all this correctly.

Will the engine be heat exchanger cooled, or keel cooled?

As for Deere vs Cummins, wars have been fought over that question. I would pick whichever fits your application better. I went through this about 5 years ago and wrote a blog article called “mirror mirror in the wall, which is the fairest engine of all” that might help sort through what’s a best fit for you. It’s on MVTanglewood.com. I don’t think you can go wrong with either.

Thanks again and I did list your website. Great information and so well written. I am learning a lot. I am interested in the comments on Victron and Maretron issues. Is the issue with NMEA compatibility with those two companies or is it they interfaces specifically between Maretron and Victron. I am planning effectively the same system for my boat with Lithium battery bank, solar panels etc and would hate to note end up with the monitoring I am hoping for. By chance, did you entertain Boening? I know they are well used on Flemings. Anyways, you have a new follower and appreciate your level of detail and thought processes around your boat (you clearly learned a ton from your previous boats). I am actually going to reach out to my builder on the PH window concept and see if I can reduce window panes and improve visibility. Thanks! Oh..I see Vermont in your profile! I live in Shelburne!

 

[Garpow2026]

They haven’t published the data yet but I have it on good authority Lugger is back in the propulsion game with engines of those power and ratings again. Should be seeing something at the Miami show. I would give them a call and see what they would recommend for your build. I would also go with their generators on a new build.

Thanks as I know Lugger has many followers. I will do some research.

 

[sunchaser]

Garpow
Props move boats according to Tony Athens. That said, to efficiently use the M2 vs the M1 rating on the JD's, your vessel would require different props as the power vs RPM rating is different at each M rating.

Some years ago when looking at a new build Nordhavn in the 120,000 + lb range the JD 6090 was perfectly adequate at the M2 rating. There are over 60 N55/60s equipped with the JD 6081s or 6090s and I've not heard they are underpowered. A detailed eyes on look at the Nordhavns in this size range may be helpful.

The JD6135 is about 1,000 lbs heavier than the 6090 and with a larger footprint. The exhaust run diameter would be larger as would be cooling lines. During long low RPM passage runs where fuel economy is critical, the larger engine may well run too slow for the hull design thus being less fuel efficient (brake mean specific HP) and not achieving proper internal temperatures.

Who is the builder? They're knowledge and expertise for the hull and props hopefully included a good NA who should have ready answers for the HP question. Will the vessel have a get home engine? If so, the main engine dimensions and shaft layout will be a factor.

Lastly, the Cummins vs JD question is with lots of info on Boatdiesel and Seaboard. In this era, engine electronics are a major consideration especially when it comes to design, diagnostics and lightning protection. Good luck with your decision making, there are no bad choices.

 

[twistedtree]

Lugger is definitely back and showed engines at FLIBS and METS. Datasheets should be available.


I see now that it's the 6090SFM, which I believe is a sea water cooled aftercooler, so that's probably what people are talking about. Just be aware that there is (or was) a 6090AFM with coolant cooled aftercooler just like the 6135AFM. I had on in my N60.


I think the devil will be in the details. To meet emmissions, right around when I built (2018-2020) some engines were emerging with split circuits for engine and aftercooler cooling, I believe to allow the aftercooler to run cooler. That mean two keel coolers for a keel cooled boat. I don't recall which engines had which, nor whether it's changed since then, but it was getting more and more complicated.


I actually wouldn't worry about a seawater aftercooler. If you aren't maintaining that, you will be maintaining a keel cooler. No matter how you slice it there is maintenance involved, and having owned both keel cooled and sea water cooled engines, I'm convinced the grass isn't greener on either side of the fence. You might have some slight personal preferences, as I did, that pushed me towards sea water cooling, but they really are just personal preferences, not something that makes one system "better" than the other.



And I'd be remiss if I didn't bring up Scania as an option. I remain very pleased with mine.


Let's take up Victron+Maretron+NMEA is a separate thread dedicated to that topic.

 

[rslifkin]

I actually wouldn't worry about a seawater aftercooler. If you aren't maintaining that, you will be maintaining a keel cooler. No matter how you slice it there is maintenance involved, and having owned both keel cooled and sea water cooled engines, I'm convinced the grass isn't greener on either side of the fence. You might have some slight personal preferences, as I did, that pushed me towards sea water cooling, but they really are just personal preferences, not something that makes one system "better" than the other.

Not necessarily. You can have an engine with a seawater pump, heat exchanger, and wet exhaust, but a coolant loop aftercooler. Or the aftercooler can be in the seawater side of the loop (better cooling but more maintenance).

 

[twistedtree]

Not necessarily. You can have an engine with a seawater pump, heat exchanger, and wet exhaust, but a coolant loop aftercooler. Or the aftercooler can be in the seawater side of the loop (better cooling but more maintenance).

Yes, agreed. And sea water heat exchanger, yet dry exhaust, etc. The combinations are seemingly endless.

 

[guy with a boat]

We have a Deere 6090AFM75 (325hp) in our N63 which is 68’ OA and 140,000+ lbs. I can tell you as one data point that I wouldn’t have any use for additional power in this boat, and it would only make it more difficult to keep it reasonably loaded. The only time it sees 80% or higher load is when I run it up to exercise it. Then engine has an M2 rating and, again, I’ve not come close to needing the higher rating. We are at right around 4,000hrs and 26,000 miles in our 2015 boat, so it gets used a bit. No complaints from here.

 

[Garpow2026]

Garpow
Props move boats according to Tony Athens. That said, to efficiently use the M2 vs the M1 rating on the JD's, your vessel would require different props as the power vs RPM rating is different at each M rating.

Some years ago when looking at a new build Nordhavn in the 120,000 + lb range the JD 6090 was perfectly adequate at the M2 rating. There are over 60 N55/60s equipped with the JD 6081s or 6090s and I've not heard they are underpowered. A detailed eyes on look at the Nordhavns in this size range may be helpful.

The JD6135 is about 1,000 lbs heavier than the 6090 and with a larger footprint. The exhaust run diameter would be larger as would be cooling lines. During long low RPM passage runs where fuel economy is critical, the larger engine may well run too slow for the hull design thus being less fuel efficient (brake mean specific HP) and not achieving proper internal temperatures.

Who is the builder? They're knowledge and expertise for the hull and props hopefully included a good NA who should have ready answers for the HP question. Will the vessel have a get home engine? If so, the main engine dimensions and shaft layout will be a factor.

Lastly, the Cummins vs JD question is with lots of info on Boatdiesel and Seaboard. In this era, engine electronics are a major consideration especially when it comes to design, diagnostics and lightning protection. Good luck with your decision making, there are no bad choices.

Lots of great information. I missed the size difference on the 6135 and the 6090 so great heads up. The size difference was one of the reasons I was considering the Cummins QSM11 over the JD. I am 6'3" (won't mention the other number!) and access in the engine room always an important concern and one that the smaller engine makes a noticeable difference. I have seen the boat - Selene 60- with both engines. I need to push JTM (the builder) on their preferred approach. The prop being sized and appropriately linked with the engine is on my list as well. Thanks for the input.

 

[sunchaser]

Lots of great information. I missed the size difference on the 6135 and the 6090 so great heads up. The size difference was one of the reasons I was considering the Cummins QSM11 over the JD. I am 6'3" (won't mention the other number!) and access in the engine room always an important concern and one that the smaller engine makes a noticeable difference. I have seen the boat - Selene 60- with both engines. I need to push JTM (the builder) on their preferred approach. The prop being sized and appropriately linked with the engine is on my list as well. Thanks for the input.

I’ve spent time in the ER in a S60 with Cummins power. Space and access is precious so the JD 6135 would not improve things.

 

[Jeff F]

Props move boats according to Tony Athens. That said, to efficiently use the M2 vs the M1 rating on the JD's, your vessel would require different props as the power vs RPM rating is different at each M rating.

I generally agree, but in this case they bump max rpm between the M1 and M2. You can overlay prop demand curves for the two and IIRC they're pretty much identical until M1 max rpm.

 

[sunchaser]

I generally agree, but in this case they bump max rpm between the M1 and M2. You can overlay prop demand curves for the two and IIRC they're pretty much identical until M1 max rpm.

The difference between the M1 vs M2 is 100 RPM and 52 HP. Me, I'd definitely prop the vessel differently to take full advantage of the 15% greater HP of the M2.

 

[rslifkin]

The difference between the M1 vs M2 is 100 RPM and 52 HP. Me, I'd definitely prop the vessel differently to take full advantage of the 15% greater HP of the M2.

Prop load grows exponentially with increased RPM, so you wouldn't necessarily need more prop to use the extra power.

At one point I was looking at propping for a Cummins QSB. It turned out the 380hp version actually would need 2 inches *less* prop pitch to reach governed RPM than the 355hp version if you geared them the same, as the 380hp version revs 200 rpm higher than the 355 (3000 rated, governed to 3070 vs 2800 rated, governed to 2870). Turning the extra RPM with the same prop would have needed significantly more than an extra 25hp. The 425hp version turns the same RPM as the 380 and would want the same pitch prop as the 355. In this example, props were assumed to be 22" diameter, 1.77:1 gear ratio, boat speed at WOT of 27, 28, or 30 kts depending on engine choice. The 355 and 425 wanted a 26 pitch prop, the 380 would only want 24 pitch.

I ran similar numbers for a JD6090SFM85 at the M1 rating (325hp at 2100 RPM) vs the M2 rating (375hp at 2200 RPM). Assuming a 10 kt boat speed at WOT for M1, 10.5 kts at WOT for M2, 4 blade prop, and a 2.5:1 gear ratio, the calculator says the M1 would want a 37x24 prop. M2 would calculates as wanting the same prop. So the extra 50hp is just enough to turn the extra RPM with a small increase in boat speed accounted for.

 

[dannc]

Not sure there is a right or wrong answer for M1 vs M2.

Many people choose an M2 rating for full displacement trawlers. The reason I seem to see most of the time for picking M2 is in case one needs the extra HP.

My issue with that reasoning is that there is not that often that much HP difference between M1 and M2. In the JD engine case listed it is only 60 HP. 60 HP is not going to buy much extra speed as one get up towards hull speed.

On the other hand, if one was fighting current to get somewhere, is the extra HP which is only going to gain a bit of speed, more important than having the M1 rating and just running WOT? Will the time allowed to run WOT on M2 be enough to get where one needs to go? Which is more important, the extra HP or the time allowed to run WOT?

If one really needs the extra HP to deal with wind, wave, and/or current at sea, is one really going to use that HP? For instance jogging into a storm vs running down wind with a series drogue or putting out a parachute anchor an laying too?

These are really specific use cases and how often will one really run into them?

Flip side, if one needs to run at some given engine load, having the extra HP in the M2 engine means one is burning more fuel than one would with the M1 engine. This would something one would have to do all of the time vs the previous scenarios which may never happen at all....

So my thinking is that the M1 engine is a "better" choice than an M2 for a full displacement hull for the boats and engine combinations I have considered. Having said that, either M1 or M2 works.

For the HP being discussed, Scania makes some interesting engines that are EPA Tier III rated.

Later,
Dan

 

[Jeff F]

Flip side, if one needs to run at some given engine load, having the extra HP in the M2 engine means one is burning more fuel than one would with the M1 engine.

In this case they're identical engines with identical props. One is allowed to run a bit faster at WOT. They're going to have the same fuel usage at less than WOT.

There really is no downside.

 

[Garpow2026]

I’ve spent time in the ER in a S60 with Cummins power. Space and access is precious so the JD 6135 would not improve things.

Agree. I have been inS60s with both and the open free space is much better with the Cummins. That said, as noted above the 6090 is smaller footprint but has a different injection (common rail cs electronic). Constant trade-offs. Thanks.

 

[Garpow2026]

Garpow
Props move boats according to Tony Athens. That said, to efficiently use the M2 vs the M1 rating on the JD's, your vessel would require different props as the power vs RPM rating is different at each M rating.

Some years ago when looking at a new build Nordhavn in the 120,000 + lb range the JD 6090 was perfectly adequate at the M2 rating. There are over 60 N55/60s equipped with the JD 6081s or 6090s and I've not heard they are underpowered. A detailed eyes on look at the Nordhavns in this size range may be helpful.

The JD6135 is about 1,000 lbs heavier than the 6090 and with a larger footprint. The exhaust run diameter would be larger as would be cooling lines. During long low RPM passage runs where fuel economy is critical, the larger engine may well run too slow for the hull design thus being less fuel efficient (brake mean specific HP) and not achieving proper internal temperatures.

Who is the builder? They're knowledge and expertise for the hull and props hopefully included a good NA who should have ready answers for the HP question. Will the vessel have a get home engine? If so, the main engine dimensions and shaft layout will be a factor.

Lastly, the Cummins vs JD question is with lots of info on Boatdiesel and Seaboard. In this era, engine electronics are a major consideration especially when it comes to design, diagnostics and lightning protection. Good luck with your decision making, there are no bad choices.

This is really good information and very usable for my thought process. Beyond size, there are functional difference between the 2 engines primarily the injection method that I had gotten guidance was a better solution on the 6135 being the electronic controlled injection technique versus the common rail method on the 6090. I need to check on the Cummins on these aspects. Thanks for the detailed response as it is great information.

 

[Garpow2026]

Not sure there is a right or wrong answer for M1 vs M2.

Many people choose an M2 rating for full displacement trawlers. The reason I seem to see most of the time for picking M2 is in case one needs the extra HP.

My issue with that reasoning is that there is not that often that much HP difference between M1 and M2. In the JD engine case listed it is only 60 HP. 60 HP is not going to buy much extra speed as one get up towards hull speed.

On the other hand, if one was fighting current to get somewhere, is the extra HP which is only going to gain a bit of speed, more important than having the M1 rating and just running WOT? Will the time allowed to run WOT on M2 be enough to get where one needs to go? Which is more important, the extra HP or the time allowed to run WOT?

If one really needs the extra HP to deal with wind, wave, and/or current at sea, is one really going to use that HP? For instance jogging into a storm vs running down wind with a series drogue or putting out a parachute anchor an laying too?

These are really specific use cases and how often will one really run into them?

Flip side, if one needs to run at some given engine load, having the extra HP in the M2 engine means one is burning more fuel than one would with the M1 engine. This would something one would have to do all of the time vs the previous scenarios which may never happen at all....

So my thinking is that the M1 engine is a "better" choice than an M2 for a full displacement hull for the boats and engine combinations I have considered. Having said that, either M1 or M2 works.

For the HP being discussed, Scania makes some interesting engines that are EPA Tier III rated.

Later,
Dan

The real world scenarios are endless and I appreciate the practical decision that go along with the technical aspects! Thanks for jumping in.

 

[twistedtree]

Stepping back to look at this, I think you are likely over-powering. My previous N60 was dimensionally the same as Guy with a Boat's N63, 65' LOA, 120,000 LBS, virtually identical to your S60. Like Guy's boat, it was powered by a Deere 6090, 325 hp. Speed would top out around 10 kts, plowing a lot of water. More power would not have been useful.


My current N68 is 71' LOA, 200,000 lbs, and is powered by a 400 hp Scania. It too will top out around 10 kts, and I don't think more power would be of much use in this boat either.


I think a Deere 6135 (425hp, 13 liter) is overkill in an S60. The 6090 is a good fit, I think. If I were looking for an alternative, I would be looking at a Cummins QSL9 (9 liter), not a QSM11. I think the QSM11 (12 liter) is similarly overkill. A Scania DI-9 (9 liter) would be a good fit too with continuous duty ratings of 300 and 350hp. 13 liters just seems really overkill, and the extra space consumed will impact daily use, where you will never use the extra HP.

 

[Garpow2026]

Stepping back to look at this, I think you are likely over-powering. My previous N60 was dimensionally the same as Guy with a Boat's N63, 65' LOA, 120,000 LBS, virtually identical to your S60. Like Guy's boat, it was powered by a Deere 6090, 325 hp. Speed would top out around 10 kts, plowing a lot of water. More power would not have been useful.


My current N68 is 71' LOA, 200,000 lbs, and is powered by a 400 hp Scania. It too will top out around 10 kts, and I don't think more power would be of much use in this boat either.


I think a Deere 6135 (425hp, 13 liter) is overkill in an S60. The 6090 is a good fit, I think. If I were looking for an alternative, I would be looking at a Cummins QSL9 (9 liter), not a QSM11. I think the QSM11 (12 liter) is similarly overkill. A Scania DI-9 (9 liter) would be a good fit too with continuous duty ratings of 300 and 350hp. 13 liters just seems really overkill, and the extra space consumed will impact daily use, where you will never use the extra HP.

I am starting to think the same thing based on the different conversations. I will take a look at the QSM9 and the Scania for comparison. It is clear that the balance of finding the right power is important. Appreciate the further thought and input.

 

[Hobbit]

So just for comparison sake we have a 57' trawler around 90,000 lbs full load with 18' beam. Its powered by a single Cat D333 1968 diesel rated at 215 Hp. We run around 1600 rpm doing 7.5 to 8 kts and burn 4.0 US gals/hr. So it seems to me from the engines you are looking at they have more than the required power and might very well be over powered IMHO. I could push it up to 9+ kts but I'm sure this would be double or triple the fuel.

 

[OldDan1943]

What engine is in there now and why are you considering a change?
Using the same brand and rating may allow something closer to a “drop in’ replacement.
IMO, based upon my N46, Luggar 120hp, go with the one that gives you more space to work