Windvane or Autopilot 2014


In preparation for some ocean voyaging at the end of 2014, a backup autopilot or a windvane was high on our list of priorities.

Our previous yacht, Kukka, had a windvane, a Hydrovane. It was a great piece of equipment which did double duty as both a windvane to steer the yacht, and as a backup in case the main steering should decide to call it a day

Enki, however, has something that Kukka did not have.....stern davits. This has complicated the decision. And at twice the displacement, a windvane on Enki would have to be that much larger and more robust. We toyed with the idea of having a Hydrovane installed and then shipping it only for the ocean passages. Careful measurement of the locations of our davit arms, our wind generator and radar poles and the vertical height/size of the vane were beginning to suggest that clearances might well become a problem especially with trade wind sailing when the vane tilts forward.

We had seen several yachts with quite complex and large s/s structures for a Monitor windvane that could fold and swing to one side....but then the davits could not be used. With our larger RIB and decent sized outboard, we (and my degenerate spine) do like the ease an convenience of our Simpson davits.

We won't be cruising oceans endlessly, much as we might wish we could have that option. There's the Atlantic and the Pacific, probably once only. Possibly four months of open ocean sailing calling for some kind of backup to the existing Raymarine and Mamba system. Our emergency tiller is a pretty robust affair. We have a decent-sized battery bank, wind and solar as well as a generator to keep it charged. We weighed up the cost, the bulk and the complications of a windvane against the alternative, a second independent autopilot driving the rudder directly.

Enki has a Lewmar Mamba steering system. It's balanced and sensitive. The electric Mamba bevel head autopilot motor drives the steering rods before they enter the Mamba gearbox. Here the power is geared UP to drive the rudder through a draglink. If we wanted to bypass the gearbox (in case THAT failed......a few have) for this independent autopilot we would need a pretty hefty drive unit for this 20 ton yacht. Not having much in the way of experience with hydraulics, we opted for the Lewmar Mamba direct drive. It's at least as beefy as the biggest of the Raymarine and Lecomble and Schmidt hydraulic/electric linear drives, and after all it's just a big starter motor from a Bulgarian truck, isn't it. Simple? Hope so.

We called in the good folks from Marlin in Marmaris yet again to build a sturdy mounting platform for the drive unit and to do the necessary measuring and geometry to make sure that it would all function as planned. The job involved lots of upside down work under the after cabin bunks and that genius Ismail from Marlin fabricating and aligning the draglink geometry to the rudder stock. It says a lot for the talent of the man that despite NO flat surfaces in that area, an angled rudder stock and doing all of the measurements and angles with his head literally down a hole, it did not need a single shim to get the alignment of the draglink spot on.

We chose a Raymarine ACU 400 course computer with a p70 control head. Whilst this is an NMEA 2000 based system, SeaTalk ng, and the venerable Enki still utilises SeaTalk 1 for all her navigation instruments and plotters, some creative thinking was needed to avoid conflict and complications with the data and power paths if this new unit was to operate with SeaTalk 1.

Raymarine in Sydney were of great assistance when I visited them earlier in the year. Colin Woodfield guided me through the potential pitfalls and solutions. Steve Morris from the Australian Lewmar agents sourced the drive unit for us and could not have been more helpful. This new system is only intended as a backup in case the primary autopilot drive or Raymarine course computer fails, or if the Mamba steering system fails.We have, however, tried to design the installation so that the old course computer can switch to the new drive and vice versa. That will involve a couple of switches, as well as making sure that the SeaTalk1 bus no longer gets its power from the original course computer, but rather from a dedicated 12V supply. This way it can be accessed by both autopilot course computers.
I will complete the wiring etc through this season whilst Diana mops my brow, soothes my nerves, counsels me against uttering too many expletives and passes tools and cool drinks.

The one irritation that became apparent was testament to my lack of experience in this kind of enterprise.....I was a pharmacist, not an engineer, after all!

Raymarine course computers have an internal fuse that determines whether 12v or 24V powers the autopilot drive clutch. The existing Mamba drive is 24V drive, BUT 12V clutch (why, I don't know). In my excitement at finding the new drive in stock and available in 24V and at a fair and reasonable price, I jumped in without checking on the clutch voltage. It turns out to be 24V not 12V. Lewmar do make what I should have bought.

So to make the old computer run the new drive or vice versa, one has to either switch a fuse inside the Raymarine unit from 12 to 24V. Or perhaps changing the clutch output on the original to 24V and using a small 24V to 12V converter to the original drive? that might make switching between system components easier? I'll have to sleep on that one.

Ismael and his new apprentice.....he is a great teacher this man.

Mamba gearbox, draglink to rudder and primary course computer

Laying out the pieces

Ismael and Mehmet talking it through

The new drive, draglink and fitting for rudder stock

Mounting under port side after berth.....still more layers of epoxy to come

In place
Geometry looks good
One more job off the job list


  1. It seems to me that it would have been simpler to add another Mamba drive motor as a spare and if you wish another spare AP controller if you wish. That way two bolts and two terminals would have replaced the motor and control unit would just be a matter of turning one off and the other on. It could remain on the Network if you wish.

    I have the Mamba steering, Mamba motor and Simrad AP brains but my thought for a backup would just buy some additional units to replace in case.

    Am I missing something?

    1. A late reply...sorry. My criteria were to have a totally separate electrical system and a backup system to drive the rudder directly.
      The isolation of the second unit, if not live and not permanently connected electrically, could provide some protection in case of a power surge or a lightning strike.
      The second drive unit could steer the boat in case a component of the Mamba failed, as some gearboxes have done in the past.