Last Friday I visited the engine for our new boat (next boat). It’s a John Deere 6068AFM75 M2. The standard engine in the Nordhavn 47 and 52 series is a Lugger L1066T.2 with a ZF220A gearbox. Both are great, long lasting components. We chose to move to the John Deere 6068 to get a bit more horsepower, a closer to continuous rating, and increased fuel efficiency. 

On the horsepower front, we moved from the 165 HP of the Lugger 1066 up to 266 HP of the John Deere 6068. The Lugger is a Medium duty rating where the maximum cruise is 200 RPM off of the rated RPM.  It’s not designed to be run at the full 165 HP continuously.  The 6068 is rated at 266 HP and is a M2 rating meaning it can run at 266HP for up to 16 hours in 24 and it can run at 231 HP continuously, without break for the life of the engine. 266HP is arguably more than the boat needs but I like lots of head room and an under stressed engine.

Looking at efficiency, the Lugger produces 165 HP while consuming 9.6 Gal/hour (see http://www.northern-lights.com/PDFs/brochure_pdfs/L1066_series.pdf) which means that it produces 17.188 HP/Gal/hour at rated output. The John Deere produces 266 HP while burning 13.5 Gal/hour (see http://www.deere.com/en_US/rg/ESC/QuickSpecs/MarineProp/6068AFM75_A_S0_R0.html) which means that it produces 19.703 HP/Gal/hour at rated output. The increase in efficiency of 2.515 HP/gal/hour sounds like a small increment but it actually represents a full 14% improvement. 

A 14% reduction in fuel consumption, if realized over the life of the boat represents substantial savings. But, what we find even more interesting is the potential lengthening of the cruising range. +14% is like adding 205 gallons of fuel to the standard 1470 gallons. Engine efficiency varies with RPM and output but manufactures typically only publish numbers for rated output and show curves for the rest.  Matching curves is less precise but it appears matching curves that the advantage of the 6068 is maintained at all cruising output levels.  Given that the 6068 has an aftercooler, we expect higher efficiency. The potential downside is one more component to service.

Essentially both the Deere and the Lugger are the same engine. They both use exactly the same base John Deere industrial engine and both are great engines differing only in optimization points and the 6068 is somewhat more expensive. As with all things marine, decisions like these are a balancing act, there is no one right answer, but we like the set of trade-offs offered by the 6068 and so went with it for this boat.

The new engine produces sufficiently more power that the ZF220A gear box is no longer acceptable. We moved up to the ZF305-2 for this application. It’s a beast.  More than required but it ended up being the best fit with sufficient capacity and I love having more capacity than needed in the mechanical systems.

Our 6068 was at Cascade Engine Center near Seattle last week to have the high output alternators installed and to prepare the engine to Nordhavn’s specifications for installation into the 52. I took some pictures of it in final test prior to being air freighted to China next Tuesday. Ironically it’ll be returning to Seattle on the deck of a freighter when the boat is delivered later this year.

Overall, I like the drive belt as layout installed by Cascade, the engine looks good, runs quietly, and produces close to no smoke even when cold starting. I hope it does as well in service as it looks during its initial test runs.

                                                –jrh

James Hamilton, jrh@mvdirona.com