Simrad NAC vs AC Autopilot Computers: What the Names Mean

What the NAC and AC names mean on a listing

When you read a Simrad autopilot listing, the letters NAC or AC in the title are model-line names for the autopilot's computer. The computer is the part that receives heading information, reads your course commands, and sends steering signals to the drive unit. In Simrad's naming, NAC stands for the course computer line, with models like NAC-1, NAC-2, and NAC-3. AC stands for the actuator control unit line, with models like AC12 and AC42.

Both names point to the same job: the box between your control head and your drive. Neither name alone tells you which drive, which control head, or which network cables are in the box. The model name is the first clue, and the maker's product page for that exact model is the source you need for the rest. For a broader look at how autopilot computers fit into a complete system, see the best marine autopilot guide.

Processing power: what the model numbers suggest

Model numbers within a line often indicate the position of the unit in the family. A NAC-1, NAC-2, and NAC-3 are three models in the same line. A higher number does not automatically mean a better computer for your boat, because the right unit depends on the steering system and the drive you plan to use. The maker's page for each model states the steering types and drive units it supports. Compare two models only on those stated details, not on the number alone.

The same logic applies to AC12 and AC42. The number is a model identifier, not a measure of processing speed. Any claim about how fast a unit computes, how quickly it responds, or how much power it draws would have to come from the maker's page. If the listing does not state it, you cannot assume it. When you compare two computers, focus on the core pack contents and what the listing actually includes.

Connectivity and the network

Autopilot computers connect to the rest of the boat's electronics over a marine network. The common standard is NMEA 2000, a CAN-based network for sharing data, commands, and status between instruments. The NMEA 2000 standard describes a low-cost, bidirectional, multi-transmitter network with no central controller, meaning each certified device can send and receive data over a single channel.

NAC and AC units are designed to work in a networked helm, where a chartplotter, control head, and heading sensor all share data. What the listing should tell you is which network connections the unit has, whether it includes a network cable, and which control heads or sensors the maker lists as compatible. If a listing says the unit is NMEA 2000 certified, that is a stated detail. If it says the unit connects to a proprietary network, that is a stated detail too. The maker's page is the only source you should trust for these claims. For more on how autopilots talk to chartplotters, see the integration guide.

How to read a Simrad NAC or AC listing

A listing title usually begins with the brand and the model, for example a NAC-1 or an AC42. The next words tell you what is in the box: a core pack with just the computer, a complete pack with a control head and a drive, or a unit sold without a drive. Look for the words 'no drive' or 'requires pump' in the title, because they signal that you must supply the drive separately.

If the listing mentions a control head, the head may be included or sold separately. The words 'w/o GHC' or 'w/o controller' are a sign that the control head is not in the box. Read the bullet list for the steering type the unit suits, such as hydraulic steering, mechanical steering, or a specific engine helm system. What the listing does not say is just as important: if a detail is missing, ask the seller or check the maker's page before you order. For a full walkthrough of reading autopilot listings, see the complete pack guide.

Why the boat's steering decides the choice

The NAC and AC computers do not steer the boat by themselves. They send signals to a drive unit, and that drive must match the steering already aboard. Hydraulic steering needs a hydraulic pump, mechanical steering needs a linear or rotary drive, and a boat with an electronic helm needs a unit designed for that helm system.

So when you compare a NAC with an AC, your first question is not which model number is higher. The first question is which drive your boat needs, and which computer the maker lists for that drive. The steering type is the deciding factor, and the maker's page for the computer is the place to confirm it. For help matching a drive to your steering, see the hydraulic autopilot guide or the sailboat autopilot guide.

How to choose between a NAC and an AC for your boat

Start by writing down your boat's steering type and the drive you plan to use, either an existing drive you will keep or a new drive in the pack. Then compare the NAC and AC models on the stated details: the steering systems the maker lists, the control heads the unit works with, and the network connections it has. If you already have a drive, a core pack that includes only the computer and the sensor may be enough. If you are building a system from scratch, a complete pack that names the drive and the control head saves you the work of matching parts yourself.

When the listing is clear about what is in the box, you can decide. When it is not, treat the missing detail as a question for the seller, the dealer, or the maker's page. The right computer is the one the maker says suits your steering, not the one with the higher model number. For a comparison of Simrad model lines on stated details, see the Simrad autopilot guide.

What to pick for your situation

Questions

Is a NAC computer more powerful than an AC computer?

No listing or maker page can be summarized by a single rule. NAC and AC are two model-line names for autopilot computers. The right unit for your boat depends on the steering type and the drive, not on a ranking of model numbers. Check the maker's page for the steering systems each model supports.

Can I use a NAC computer with an AC drive?

The computer and the drive must be matched according to the maker's stated details. A listing may name the drive units that work with a specific computer. If it does not, the maker's page for that model is the source to confirm compatibility.

Does a NAC or AC computer include the control head?

Not always. Read the listing title for words like 'w/o GHC' or 'w/o controller,' which mean the control head is not in the box. Complete packs name the control head, while core packs often leave it out.

What does a NAC or AC listing mean by 'no drive'?

It means the computer is sold without a drive unit. You must supply your own drive, either an existing one on your boat or a new one bought separately. Match the drive to your steering type using the maker's page.

Which network does a Simrad NAC or AC computer use?

Most modern autopilot computers connect over NMEA 2000, a CAN-based network standard for marine electronics. The listing may also name a proprietary network. The NMEA 2000 standard describes how certified devices share data over a single channel.

How do I know if a NAC or AC unit fits my steering system?

The maker's page for the exact model is the only reliable source. It states which steering systems the unit suits, such as hydraulic, mechanical, or an electronic helm. A listing that does not state this leaves you with a question for the seller or the dealer.