Two questions

Paul Osterberg

We we are in the process of substituting the old B&G instruments with Raymarine instruments.

The new NMEA 2000 backbone system should be grounded. You who have NMEA 2000 how did you ground your system?

We are also putting in a new modern computer for the old and still well working Autohelm autopilots. If I remember right the clutch for both the linear and rotar drive is on 12 v and not 24 v. Anyone who can confirm that clutch should be 12 v

Paul on SY Kerpa SM 259

Herbert Lackner

Hi Paul, we changed all electronics to raymarine 4 years ago. I removed the ground after having strange behaviour of the system, is running fine now since 4 years without ground. Was in contact with raymrine to find out what the problem was and in the end they recommended not to ground it...

Herbert, KALI MERA, SN120

Alan Leslie

In the NMEA 2000 scheme there is a DRAIN wire and a SHIELD.
The recommendation is that both should be connected to GROUND at ONE POINT ONLY.
Problems have been caused it seems by earth loops where the drain and / or shield have been grounded at more than one point.
On most boats the ground connection is connected to battery -ve which maybe the cause of these earth loop problems as they now effectively have multiple ground connections.
Amel boats do not have a connection between battery -ve and ground.
So on our boats, my instinct tells me that the drain and ground should be connected to ships ground to eliminate interference problems from RF....from VHF or SSB for example 
However if the NMEA 2000 system has issues as you have said, then disconnecting that ground connection is not going to harm anything....and if there are issues it may be worth disconnecting the drain or ground from ships ground to see if either makes any difference. In any event you won't damage any equipment by doing that.
Just what I think...I may be has been known !
Elyse SM437
Malumu Bay, Beqa

Paul Osterberg

Herbert and Alan
Thank you, I will start by not connecting the shield then if I run into problem I know where to start digging
Paul on SY Kerpa SM 259

Thomas Peacock

We have also put some Raymarine instruments in the past 2 or 3 years. You only asked two questions, but I may drone on and give you more answers; I can only hope that at least two of them are correct.

We first replaced the original RM autohelm electronics with RM ACU-400, but left both mechanical drives in place. I used the Raymarine suggestion of hooking up the new fluxgate (also has an inertial system) and the main computer box using their proprietary SeaTalk-NG network. My understanding is that STNG uses the same communication protocols as NMEA 2000, just different connectors and cables. There is nothing to suggest that STNG needs to be grounded. I did not replace the rudder sensor that resides in the aft berth, it looked identical to the one that shipped with the new unit. Everything went fine for a year; I then updated the software, and the autohelm began to continuously turn the boat in circles. Changing the “A” and “B” power connections in the ACU-400 seemed to fix the problem (we were in blue water at the time). Later, the problem came back, I then disconnected the rudder sensor from the ACU-400, and things have been fine since then. I hope to get around to putting the new rudder sensor on, hopefully that will work, perhaps the old one was not compatible with the software update. However, the system functions quite well without the sensor.

The clutches are indeed 12V; the ACU-400 has a switch that allows you to choose. The computer can be powered by either 12V or 24 V. It also feeds 12V to the STNG.

We then installed a RM chart plotter, eS series, which works both by knobs and well as pinch-screen (like a smart phone). Very happy with it. 

Shortly before departing to the Caribbean, the original B&G instruments were fried (long story). I would have gone with RM instruments, but was concerned about the depth sensor fitting exactly into the through-hull for the old unit. Hence, I went with new B&G instruments. The B&G uses NMEA-2000; Raymarine sells an adapter so that STNG and NMEA-2000 can co-exist on one network. The NMEA-2000 is powered by the STNG, which gets its power from the ACU-400. All instruments play together very well, and display each other’s data. All power for the B&G instruments comes from the network alone.

We then added a RM AIS transceiver, using the “Marocain” labeled VHF antenna inside the mizzen mast. No problems. 

Finally, the original Furuno radar died three months ago at the age of 18 years. The new Raymarine CHIRP unit, which is all solid state, no warm-up needed, with some modifications of the original Furuno brackets, fit on the mizzen. It feeds right into the RM chart plotter, so there is no radar display down by the nav station.

Hope some of this is of use.

Tom Peacock
SM 240 Aletes
Rock Hall, MD  USA