How to: Installing an Inboard Autopilot

Problem: how do you install an inboard autopilot on a boat with such cramped hindquarters that finding somewhere to put a drive unit is next to impossible?
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Photos by Pip Hurn

Photos by Pip Hurn

The Cable Guy

Problem: how do you install an inboard autopilot on a boat with such cramped hindquarters that finding somewhere to put a drive unit is next to impossible? Well, you don’t—you install a wheelpilot, which is what I did, and I was happy enough with it over several seasons of coastal sailing. Then I started thinking about more ambitious passagemaking, and suddenly the case for a belowdecks autopilot became overwhelming.

In the meantime, I still had the same problems—the rack-and-pinion steering system on our 1970s 34-footer has no quadrant to which an autopilot drive can be linked, and it would be impossible to install a conventional tiller arm on the rudderstock without the hassle and expense of dropping the rudder out of the boat in order to machine a keyway. Even then, there is not enough room under the lazarette for a conventional linear drive unit, even if I could find someone about a third my size with triple-jointed arms to get down there and install the thing.

It was enough to make me give up on the idea—until I came across the Canadian company Octopus Products. Not only does Octopus make a range of hydraulic and electric autopilot drives, it also offers a blindingly simple piece of equipment that looked like it would solve all my problems. 

Octopus’s RS drive adapted from its sterndrive control units, links a Bowden (push-pull) cable to an electric drive unit. At one end, the exposed inner cable is inserted into the drive unit. At the other, the cable terminates in a stainless steel rod that runs through a linear drive connector and hooks up to a tiller arm. This connector has to be able to take all the thrust, while the drive unit, which can be mounted anywhere and in almost any position—as long as the cable bends are not too sharp—takes no thrust at all. It’s ingenious in its simplicity. 

The beauty of the Octopus drive is that you can mount the drive unit anywhere the cable can reach. Illustration by Alastair Garrod

The beauty of the Octopus drive is that you can mount the drive unit anywhere the cable can reach. Illustration by Alastair Garrod

I had a local welder make up the tiller arm that fits neatly on top of the rudderstock.

I had a local welder make up the tiller arm that fits neatly on top of the rudderstock.

A number of autopilot manufacturers now offer this drive as an option with their autopilot units, and—joy of joys—you can get it bundled with the Simrad AP24/AC12 pilot I had been eyeing up. Simrad calls it the SD10 drive, and it develops a maximum thrust of 400 pounds, compared to the 770 pounds of the Simrad hydraulic pump, which is specified for 30-45-foot boats. This should be more than adequate for almost any sailboat up to the recommended limit of 37 feet and 15,000 pounds displacement.

I soon determined that if I devised a tiller arm to fit on top of the rudderstock, which was squared off to accept the emergency tiller, I would be able to hang the linear drive connector from a bracket bolted to the cockpit structure. There, it would not impinge on the stowage space in the lazarette and, importantly, be out of the way of the bulky items stowed there. Equally important, there would be no need to install a rudder feedback unit since one matched to my Simrad electronics mounts to the Octopus drive unit.

The linear drive connector can be mounted at any angle, as long as the rod at the end of the cable remains perpendicular to the tiller arm at mid-stroke. The bracket is fabricated from 5/16in aluminum plate, bolted together with 1/4in machine screws and fastened securely to the cockpit coaming.

The linear drive connector can be mounted at any angle, as long as the rod at the end of the cable remains perpendicular to the tiller arm at mid-stroke. The bracket is fabricated from 5/16in aluminum plate, bolted together with 1/4in machine screws and fastened securely to the cockpit coaming.

Onlinemetals.com supplied a length of aluminum box section with internal dimensions of 1in x 1in, to which a local welder attached a 12in length of 3/8in x 2in aluminum bar that came from my workshop box of bits. I then drilled a hole in this bar exactly 10in—as specified by the Octopus instructions—from the center of the rudderstock to take the fitting for the cable end.

It took a little bit of trial and error to make a bracket that worked, but on the second try, I got the linear drive connector mounted exactly in line with the end of the tiller arm. The latter had to be installed pointing astern, but the AP software compensates for that. If need be, the drive rod can quickly be disconnected and the tiller arm removed to allow the emergency tiller to be used.

I spent more time agonizing over where to put the motor because there was not enough room in the engine bay to mount it on one of the bulkheads there. After rejecting the notion of putting it in the cockpit locker to port—too much likelihood of damage—that left the quarterberth as the only option. However, locating it there had the added benefit of letting the electrical cables reach the autopilot computer without the need to extend them. Some thoughtful previous owner had also already drilled holes for cables through the after bulkhead, so it was easy enough to snake the drive cable back to the lazarette. The standard 6ft cable proved too short, so Octopus sent the optional 9ft cable.

After much indecision, I mounted the motor above the quarterberth; it is through-bolted to the cockpit coaming.

After much indecision, I mounted the motor above the quarterberth; it is through-bolted to the cockpit coaming.

I’m still debating whether to make up a cover for the motor or leave in its industrial glory as a piece of functional art. After all, as in most boats, Ostara’s quarterberth serves mainly as somewhere to stow things I don’t have room for anywhere else—washboards, sail cover, etc.

As for the rest of the installation, the hardest part was running cables around the boat. I mounted the RC42 rate compass almost amidships, below the starboard pilot berth The AC12 course computer went on the bulkhead at the foot of the quarterberth. 

The AP24 display controls the course computer

The AP24 display controls the course computer

This project was my introduction to Simrad’s proprietary Simnet version of NMEA 2000 cabling, which involved plugging the cables from the AP24 control head and the compass into a “multi-joiner” or backbone strip, from which a third cable was connected to the course computer. I also had to add a Simnet Terminator (resistor) at each end of the “backbone.” I ran a power cable from the DC distribution panel to the AC12, along with a standalone grounding cable that I connected directly to the boat’s ground terminal. The strip required its own power supply, which I spliced into the feed to the AC12. Then I connected the wires from the drive unit motor—two for the power supply, two for the clutch—and another three from the rudder feedback module. Finally, I aligned the two red dots on the rudder feedback unit as specified in the Octopus instructions, and screwed it into place on the motor.

I confess I had to call Simrad’s tech support partway through all of this. I’m far from an electronics expert, but I’ve installed instruments, plotters and autopilots before, and I found some of the instructions in the Simrad manual quite confusing. Thankfully, my problems turned out to be little ones. The point is, with electronics installers charging up to $150 per hour, you can save a considerable amount of money by taking on such projects yourself. Even if you’re not electronically inclined, you can accomplish the time-intensive tasks like running and securing cables and mounting the fluxgate compass.

Finally, I flicked on the circuit breaker labeled “Autopilot” and the AP24 display came to life. All I had to do now was commission the new autopilot system—but that’s another story…

Resources

Simrad

Octopus Marine

The cable is coiled on the cockpit sole, ready to be installed

The cable is coiled on the cockpit sole, ready to be installed

Cable Life

Octopus quotes a 200-hour life for its cables, which is not much if you are crossing an ocean. A 9ft cable, such as the one I fitted, costs $140. You could look at that as an annual expense. You also need to make sure the drive connection is well greased—there are two grease nipples to keep the sliding rod and the pivoting mount lubricated—so this system needs more maintenance than most types of autopilot drive. Nevertheless, the RS drive is a great solution for boats that cannot take a conventional hydraulic or linear drive. Aside from being easy to install it is also cost-effective, at around $1,200—and it can be used with almost any brand of autopilot control head and course computer.

The Simrad AP24/AC12 combo is a descendant of the well-known Robertson brand. Among the features I liked is the no-drift mode that compensates for set and drift— particularly valuable when motoring in rocky waters—and the programmed-in integrated turn patterns, which could prove a life-saver in a MOB situation. You can also set it to follow a depth contour line, which could be useful in fog, and it has an advanced steer-to-wind function that combines information from the wind instrument and the plotter.

Of course, you need to link it to instruments and a chartplotter to access these functions but it will also work just fine as a standalone unit.

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