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Main Engine

Main Engine

The engine is a single John Deere 6090SFM85 marine diesel engine . It has been downrated to M1 rating 325HP @2100 RPM and is a 6 cylinder, 9 litre engine. The tier 3 classification means that it has very low emissions.

The standard specification of this engine is with M4 rating. The rating is to do with the profile set up within the engine computer relating to the ratio between torque and RPM. On M4 rating, the engine is tuned to deliver maximum torque at high RPM – so it’s performance is at the high end. The need to have increased RPM to achieve the torque increases the fuel consumption considerably. For a boat which is a slow displacement design, with infrequent need for the high RPM, and continuous steady operation, there are more efficient solutions.

What is RPM and Torque?

The RPM/torque ratio can be compared to trying to ride a bike uphill. You can do this in 1st gear, when you legs are going 19 to the dozen (high RPM) but the pedalling goes very easily (torque). Or, you can climb the same hill in 10th gear, where you are pedalling very slowly (low RPM) but having to use a lot of strength in your legs (torque). The right solution for this depends on the person and the hill you are trying to climb.

In the same way, the right solution for the boat depends on the specific boat and the characteristics of the water the boat needs to push through. There are times when the high end power would be useful such as when fighting against a very strong tide or current. However, in general this is a waste of power and the objective for our boat is to achieve maximum torque at the minimum RPM (the “10th gear” analogy above).

M1 Rating Change

There are schools of thought which suggest that the rating should be left at M4. That high end power is then available to you when needed, and you should control the RPM manually. However, to achieve the optimum at lower RPM the prop needs to be changed. We have opted for a 5 blade prop instead of 4 blades (so it has more “push” through the water). The prop is 2″ bigger than the standard M4 rated prop and the pitch (angle) is also different.

The rating change itself is a straightforward modification and involves profile mapping in the ECU to change the max rpm. The full specification document of the engine gives a more detailed overview. It details the different engine ratings and the situations where they would be used. John Deere will commission the engine and oversee the first engine start in order to validate the warranty.

Engine Controls

The single engine comes with ZF engine controls at the helm and the flybridge. The standard model has been upgraded to the 4100 command head. There’s absolutely no technical reason for this upgrade! The only reason is that the 4100 unit is much smaller and neater. It won’t take up as much valuable space on the helm.

Engine Monitoring

The engine comes standard with analogue engine data which is displayed on a fairly large panel on each helm station. Again, this is taking up a lot of valuable space. We have relocated this analogue panel to the upper dashboard to one side. We intend to keep it as a backup in the case of a problem with our electronics. It will, however, not be our primary engine data tool.

Maretron Ships Monitoring System

Our main engine data will be part of the Maretron ships monitoring system. We will use this system to monitor all the normal readings which are needed. The main ones are of course the RPM, engine temperatures, fuel and starter battery power. However, this system is far wider reaching. It will also provide data to allow us to analyse the performance of the engine. Example of this include:

  • Very accurate fuel usage isolated for the engine (and for each of the generators) separately. This is achieved using a flow rate sensor at both fuel intake and return. The sensor takes temperature differences into consideration in the measurements, and calculates accurate usage.
  • Fuel filters – monitored via a pressure sensor on every filter
  • Actual engine performance data from the engine ECU itself. This uses a J2K100 module from Maretron. The module connects into the J1939 engine network and sucks all the data from it
  • The fuel data is also linked to navigation data to provide a calculated range based on fuel reserves and activity
  • Fuel tank levels are also accurately measures using pressure sensors in the tanks. This is a far more accurate measurement of tank levels than the normal float and sight guages. It is able to calculate based on the irregular shape of the tank.

The system includes a series of user programmable alarms which are both visual and audible throughout the boat. A more detailed description of the Maretron monitoring system is included in the electronics blogs.