Upgrading Your Boat' s Autopilot

Upgrading Your Boat's Autopilot

Thursday, May 5, 2016


Raymarine Pro Ambassador Alan Watson rethinks the autopilot system on his 40-year-old Nelson 42

May 2016

Trinity Star - Underway in the Solent | Raymarine by FLIR

Trinity Star is a Nelson 42, now just over 40 years old. I have owned her for 12 years and in that time have steamed over 7,000 miles and done a great deal to her including fitting new engines and stern gear, rewiring, re-plumbing and several changes of electronics.

In 2014 the navigation system was upgraded to the Raymarine eSeries display, Class B AIS and a new fishfinder module, and in 2015 it was the turn of the autopilot. I had fitted the Raymarine 400G autopilot soon after I bought the boat and it has performed flawlessly for all these years. It can steer the boat better and with less effort than I can, particularly in following or quartering seas when the Nelson can be a bit twitchy.

After some experience with the new Raymarine EV1 heading sensor on another vessel, I decided to upgrade with the expected benefits of more accurate heading information and a better display on the p70 controller as well as improved autopilot performance. The improvement to heading information should in turn lead to better performance on MARPA, which is very dependent on stable and accurate heading information.

System Implications

The 400G autopilot consists of a course computer unit which is connected to the hydraulic rudder actuator, a rudder position sensor, a fluxgate compass and the two control units. The course computer is then connected to the main navigation system via NMEA0183 or SeaTalk. When the main system was upgraded last year, most of the Seatalk was replaced by SeaTalkng, a very straightforward system of ready-made leads and junction boxes based on NMEA2000.

The system has a backbone with spur cables to each unit on the system. For the new evolution autopilot there is a SeaTalkng connection from the course computer, which also connects to the pump and rudder position sensor. The heading sensor and the two control units connect to the Seatalk network rather than to the course computer.

Image: The course computer is connected to the rest of the system via SeaTalkng.
Insert: The new EV1 Heading Sensor.
Course computer | Raymarine by FLIR

Planning the installation | Raymarine by FLIR Image: Initial calibration was a simple process.
Insert: I planned the system carefully, especially measuring the lengths of leads required for the SeaTalk backbone.

Planning the Installation

As the leads are ready-made, some careful measuring is necessary – and it is also worth checking what comes in each box as many contain a lead, and if you buy one of the system kits it comes with quite a selection of leads and fittings. One good piece of news is that the new p70 controller fits the same size panel hole as the old one, saving major carpentry. There are two types of controller, one with buttons intended for sailing vessels and one with a rotary control for power: I went for the rotary one.

The rudder position sensor is the same too, so the old one was left in place (which saved a lot of work). Before I started pulling things apart I noted the heading from the old system to give a starting point for setting up the new and also centred the tiller, athough I could use the alignment mark on the heading sensor which was staying put.

The first task was extending the SeaTalk backbone (blue cables) to the upper helm position where the i70 and the heading sensor were connected. I was grateful that the locking collar for the connections is on the module and not the cable, which meant the cables would go through a 12mm hole. The work to put in the rest of the system was very straightforward and resulted in a simpler system with a big heap of cabling removed.

The SeaTalkng network requires a single source of 12V to power it: this can either be fed direct on to the network via a red cable or can be sourced from the course computer. I elected to use the red cable so that the whole network remains powered even if the autopilot is switched off for any reason, so I made sure that the little slide switch on the course computer was set to ‘off’. The system powered up with no drama, and the initial setup was amazingly simple. All I had to do was tell the system what sort of boat it was fitted to and set the rudder centre point and limits. To do a rough setting of the compass, I rotated the sensor in its mounting until the reading was the same as I noted on the old system, and then clipped in the bezel to lock it in place.


Sea Trial

The final task was to go to sea and set up the compass before seeing how well the system performed. The Evolution will establish and store its own deviation curve over time, but I wanted to get this done immediately. No button pushing is necessary: you just do a few slow circles and then check it has stored a figure (it’s under ‘diagnostics’).

Mine showed 5° of deviation, which was the same as the previous system. It was then a case of setting the compass to align correctly with north. The easiest way to do this is to put on some speed and go with the tide, and set the compass to agree with COG. The heading can then be fine-tuned manually, but I found it was spot-on.

Sea Trial | Raymarine by FLIR Image: The new autopilot picked up the routes and tracks from the chartplotter straight away.
Insert: MARPA is now noticeable more accurate, and you can see that the radar overlay lines up perfectly with the chart.

Having done this, I checked on a couple of transits and then put the radar to overlay the chart plotter. As long as the radar heading line has been set correctly when installed, the overlay should be perfect – and mine was. I then enjoyed myself for the afternoon, playing with my new toy.

The new autopilot held course well, picked up routes from the chart plotter and did everything I expected. The new facility of ‘power steer’, where I was able to drive the vessel from the knob on the p70, could prove useful. It was a fairly calm day but Calshot corner obliged with a few bumps, so I was able to try the course holding from different directions and it lived up to expectations. The last test was of MARPA, and this was particularly pleasing with more stable vectors and data than the old system. Over the season the system will get a thorough testing, but initial results were excellent.

Shop the Blog - Find out more about the equipment mentioned in this blog post:

eSeries Multifunction Display | Class B AIS | Fishfinders | Autopilots | p70 Control Head | SeaTalkng / NMEA 2000 | i70 Instrument Display

This article originally appeared on the Practical Boat Owner (PBO) website. Content used with their permission.

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