Old iron is out!!!!!!!

[Texastailboard]

Really looking to see how your project turns out, we have been considering a repower on our 52. Just haven’t finished our cosmetic stuff we have currently started on.

[krush]

.. Maybe just a bit lower cruise since JD wants me cruising at 50% load. That would technically be 64% but the Deere torque curve is really flat through here making tons of torque down to 1400 RPM before falling off. The 500 HP JD makes more torque than the 670 HP QSM by just a bit at 1800 but at 1400 it's over 10% more.. We are back at that displacement thing but torque turns the prop. So that's how I got here, big displacement, low HP and high torque I hope will equal a lightly loaded happy engine. FYI the JD is basically the same displacement as the 12V71N that it's replacing. 13.5 vs 13.96. Make about the same HP at 300 less RPM. Can't find a torque spec so not sure of that but at 3500 lbs lighter there is just not way I won't get a slight bump in performance with all the other benefits of a modern engine. Well that's the plan anyway. We all know how the best laid plans work out sometimes.

If you toss out the torque thoughts and data and do your analysis with HP only you will come to much more clear conclusion. The torque does not matter...and that is exactly the reason you can't find a torque curve for the old detroits.

The engine makers provide a HP vs RPM curve that shows you what rated HP the engine can reliably make at a given RPM. However, in a boat application with a fixed propeller, the prop demand curve will likely never line up with the engine HP curve (prop is exponential, engine is mostly linear). Cummins marine usually provides a generic "prop demand curve" on their engine plots to give you an idea what the HP vs RPM output will be in a generic boat.

Prop size/pitch will shift that prop demand curve around. The usual goal is to have the prop demand HP be equal tot he engine HP output at rated RPM. However, there are unique cases where somebody may "overprop" to increase cruise efficiency (see this thread (wow, it's been over 10 years since that discussion!): https://www.samsmarine.com/forums/sh...g-Engines-Slow)

[nautibake]

The 3500 lbs is total not per side. The JD pair is about 1000 lbs heavier than a pair of Cummins. The 3500 Lbs is about a 5% weight reduction in my boat. The other thing is that by going to a 7 degree gear box the engines will sit lower in the hull than the Detriots did. I don't believe the weight difference will matter especially when coupled with sitting them lower in the hull. I'm certianly hoping that is true. With so many boats out there with Cummins running I think if it made a big difference we'd have heard about it by now. I haven't ran the calculations but I feel certian that the change in weight will have much less effect on stability than say a full tuna tower.

I'm finding a great deal of inspiration from your project (have to admit, also a welcome distraction from watching Dorian). I grew up driving a 1958 JD tractor pulling hay mower, hay bailer and 5-ton hay wagon. I have imagined a repower to CAT or Cummins but for some reason never even considered the Deere. I have a 1977 Hatt 58 MY. Although I don't like to admit it, I primarily cruise with a trawler profile like many here. Do you think the M2 or M3 version of your engine would be a good match? I cannot get close to getting on plane with my current DD 8V71TI's. 2400 lbs of gyro stabilizers and an 850 lb tender all basically on the stern I assume are the main reasons. I would like the option of occasionally getting up to 18 - 20 knots to get somewhere (or to get away from something). I know many more details would need to be analyzed, but just curious if you thought these would fit the profile for a 58MY.

Also, without disclosing anything specific, do you mind sharing approximately what the street price is to buy those engines? And the ZF gears?

In any case, look forward to seeing your progress, and good luck!

[harnett]

Interesting that you said that. I grew up sitting on a JD tractor in the fields to so there was definitely some history with JD there. I know of at least one 53MY with JD 8 liters running around. The owner has nothing but positive things to say about them and he says she runs on plane great. I can only imagine with the 13.5 liters a 58 would fly. As for price they were a bit more that Cummins recons but more or less the same as the Cat C12. I'm going to keep everyone post but it's going to be a bit longer than I thought. I didn't order my engines until I had the old ones out and had test fit a CNC template I made. I was really worried about the oil pan hitting the hull. All my measurements said it was ok but I was to scared to place the order until I knew. The order is in but they are telling me I may not see them until Nov. 12V is a stock item but 24V that I wanted is special order and takes a bit longer. Not that I don't have lots of engine room cleaning and preping to do anyway. Still hoping for a 2019 launch. We'll see.

[nautibake]

Interesting that you said that. I grew up sitting on a JD tractor in the fields to so there was definitely some history with JD there. I know of at least one 53MY with JD 8 liters running around. The owner has nothing but positive things to say about them and he says she runs on plane great. I can only imagine with the 13.5 liters a 58 would fly. As for price they were a bit more that Cummins recons but more or less the same as the Cat C12. I'm going to keep everyone post but it's going to be a bit longer than I thought. I didn't order my engines until I had the old ones out and had test fit a CNC template I made. I was really worried about the oil pan hitting the hull. All my measurements said it was ok but I was to scared to place the order until I knew. The order is in but they are telling me I may not see them until Nov. 12V is a stock item but 24V that I wanted is special order and takes a bit longer. Not that I don't have lots of engine room cleaning and preping to do anyway. Still hoping for a 2019 launch. We'll see.

Thanks harnett, good luck getting your engines in and installed. Really looking forward to your progress. it’s hard to believe those engines will make that much HP on such low fuel flows, but wow that would be amazing. I won’t have any issues with space.

[Rocco]

Did the 24v JDs show up in November as promised? Curious how the project is going.

[harnett]

No they are a little behind. Production date got changed to Dec. 7th. I am pretty much ready with everything else waiting on the engines to arrive. I'll keep everyone posted.