How much engine do I really need?

[North Baltic sea]

I have witnessed this re-programming. Cummins tech shows up with his computer, plugs it into the engine ...... Presto ! no other changes. Just for a laugh get a quote from Cummins for that engine as a 220 and a 340. The price difference will shock you.

Chip tunig pay about 450$ all cummins qsb series engines

https://www.chipexpress.com/products/cmd-cummins-mercruiser-diesel/qsb/

Add torque and power, but does the machine and the gearbox withstand increased power?

NBs

 

[Irish Rambler]

The trim tabs will stop it 'squatting' under heavy throttle. My own personal opinion is that I'd reset the engine for extra torque at 250 that should give you 10 knots comfortably and simply plan your passages using tidal streams to help you along.
If you ever slip the boat check the prop size for maximum dimension to give you power.

 

[Fletcher500]

I have witnessed this re-programming. Cummins tech shows up with his computer, plugs it into the engine ...... Presto ! no other changes. Just for a laugh get a quote from Cummins for that engine as a 220 and a 340. The price difference will shock you.

I did a quick search on the web and could not find anything from a reliable technical source to confirm this. All of the engine manufacturers (Cat, Cummins, Deere, etc) sell standard blocks, and then offer up-ratings from there on the same block with RPM/Fuel changes. I would still think the Turbo, after cooler, and possibly other major changes (Bore/Pistons for a major change from say 250-550) would be needed in addition to any programming. Do you have any technical data from Cummins you can share?

 

[DavidM]

I went through this discussion with Tony Athens in the early days of QSBs when I was dithering between a Yanmar 370 and a QSB ??? for our new Mainship 34T.

Tony said that there is absolutely no difference in the mechnical components between a 220 hp and 380 hp version of the QSB series engines. I could buy the 220 and if I later wanted more power I could pay $$$ to have the chip upgraded to the 380. Cummins would also supply a new data plate for the upgrade.

I decided to go with the Yanmar, primarily because at the time it was $10,000 cheaper than the 380 hp Cummins.

David

 

[dhays]

I have a 2007 Mariner Seville Pilot House 37 (Helmsman 38) which I bought in 2015. The PO had the Cummins QSB 5.9 re-programmed from 220 HP to 380 HP. He also has Bennett trim tabs. I guess he thought he might get her up on a plane, but at 40,000 lbs. fully loaded, no way was she ever going to plane. I can cruise at 7-8 knots on 3 GPM , but if I firewall it, I only get up to about 11-12 Knots but I am burning 17 GPM . I have had very few occasions where I pushed it that hard, other than to "blow it out" now and then. We do have some very strong tidal currents in my area, especially going through narrow passages against max flood/ebb, and actually needed the extra power, but I'm pretty sure boat would have been fine with the 220 HP configuration. Does anyone want to buy a set of used Bennett trim tabs? Or can anyone explain what possible good they are on an 8 Kt boat?

I have a Cummins OSB 5.9L 380hp engine in my 43’ North Pacific. My understanding is that while the engines can be chipped from 220 to 380, Cummins designs the supporting systems to support the higher HP. So a reflashed 220->380 is not the same as an engine designed for 380hp. There are plenty here who know far more about the Cummins than I who can correct me if needed.

My boat came with large Bennet trim tabs. I drive my boat slow and most of the time the trim tabs make very little difference. However, at certain throttle setting and certain conditions, adjusting them carefully can give me maybe a 1/4 knot improvement in speed at a reasonable cruise speed. If you play with them, you may, or may not, find that they can be helpful. If I was to commission a boat like mine now, I would eliminate the trim tabs.

 

[DavidM]

By supporting systems, I believe that means transmission, prop shaft and prop. Other marinization systems like R/W pump, main heat exchanger, after cooler, lube and fuel coolers are the same for all hp levels according to Tony Athens.

David

 

[sunchaser]

DM
How about exhaust run diameter and ER ventilation? We're speaking of a theoretical 50% or so increase in gas volumes to match much higher fuel burn.

 

[Adagio43]

I started this thread because I didn’t understand why the big range in HP was offered in the same model SD trawlers. I had only owned sailboats in the past and planning was something you did for a few seconds downhill on the face of a wave. Now that I was making the switch from sail to power I thought it was time to start asking questions. I want to thank all of the respondents for their time and efforts to educate me.

After reading through all of the replies this is what I have come up with. If I have gotten some of it wrong please correct me.
1. With enough HP you can get some moderate SD trawlers to plane but you are not going to like the fuel burn (4-5 times more than at 8Kts to achieve 10-12knts).
2. I always knew that diesels like to work and should be run at approximately 80% of WOT or at least “blown out” on a regular basis. This is a lot easier and cheaper to do on a 15K pound displacement sailboat with a 50-75HP Diesel than a similar size SD trawler with 220- 370HP Diesel. I use to run my sailboat at 2400 - 2600 RPM’s and burn 3/4 GPH. It seems most trawlers are run at 1700-1900 RPMS (we’ll below 80% of WOT) and burn 3-4 GPH. Anything higher only buries the transom and accomplishes little other than adding to the fuel burn.
Hence why the 370HP engine if 220 HP would get the job done. (At this point you may have guesses that I am looking at Nordic Tug 32-34 with 6 series Cummings diesels).
3. If you can’t run the engine at 80% of WOT then blowing it out on a regular basis was important along with an Exhaust Gas Temperature (EGT) gage to keep track of things.

Some people argue for the higher HP to fight tides and have get home capabilities. Maybe it’s my sailboat background and I appoligise for it but this just
does not work for me. In my experience when it blows up the last thing I want to see is land and something to hit. Also, who goes through Hells Gate against the current.
(As a side note: I always trusted my sails over my engine so this will be an interesting transition for me.)

Now a new player has entered the scene, Trim Tabs. They can help to keep the stern from burying at higher RPM thus improving MPG but dependent on displacement/HP ratio. Also helpful to improve trim for sea conditions and payload. Question: can they be worthwhile in improving MPG to justify running at closer to 80% of WOT?

Let my education continue. And once again thanks to everyone for their responces.

 

[North Baltic sea]

I started this thread because I didn’t understand why the big range in HP was offered in the same model SD trawlers. I had only owned sailboats in the past and planning was something you did for a few seconds downhill on the face of a wave. Now that I was making the switch from sail to power I thought it was time to start asking questions. I want to thank all of the respondents for their time and efforts to educate me.

After reading through all of the replies this is what I have come up with. If I have gotten some of it wrong please correct me.
1. With enough HP you can get some moderate SD trawlers to plane but you are not going to like the fuel burn (4-5 times more than at 8Kts to achieve 10-12knts).
2. I always knew that diesels like to work and should be run at approximately 80% of WOT or at least “blown out” on a regular basis. This is a lot easier and cheaper to do on a 15K pound displacement sailboat with a 50-75HP Diesel than a similar size SD trawler with 220- 370HP Diesel. I use to run my sailboat at 2400 - 2600 RPM’s and burn 3/4 GPH. It seems most trawlers are run at 1700-1900 RPMS (we’ll below 80% of WOT) and burn 3-4 GPH. Anything higher only buries the transom and accomplishes little other than adding to the fuel burn.
Hence why the 370HP engine if 220 HP would get the job done. (At this point you may have guesses that I am looking at Nordic Tug 32-34 with 6 series Cummings diesels).
3. If you can’t run the engine at 80% of WOT then blowing it out on a regular basis was important along with an Exhaust Gas Temperature (EGT) gage to keep track of things.

Some people argue for the higher HP to fight tides and have get home capabilities. Maybe it’s my sailboat background and I appoligise for it but this just
does not work for me. In my experience when it blows up the last thing I want to see is land and something to hit. Also, who goes through Hells Gate against the current.
(As a side note: I always trusted my sails over my engine so this will be an interesting transition for me.)

Now a new player has entered the scene, Trim Tabs. They can help to keep the stern from burying at higher RPM thus improving MPG but dependent on displacement/HP ratio. Also helpful to improve trim for sea conditions and payload. Question: can they be worthwhile in improving MPG to justify running at closer to 80% of WOT?

Let my education continue. And once again thanks to everyone for their responces.

Hi,

I would like to reply to point 2. I have verified the facts, and manufacturer Cummins is ok to drive 380hp common-rail engine 24/7 whenever just about 50hp load does not need to blow the engine high rmp, the second paragraph is see how linear fuel consumption vs the speed of the SD frame can be.



These readings are the CM smart craft on the NT37 Computer, water and fuel 100%, 5 persons in boat.

NBs

NBs

 

[FF]

"It seems most trawlers are run at 1700-1900 RPMS (we’ll below 80% of WOT) and burn 3-4 GPH."

The incorrect rule of thumb of 80% power is not measured against WOT.

It is measured against the HP available at the selected operating RPM .

"80%" of 2100 RPM, 1800RPM and 1500RPM will be quite different numbers.