Sailboats generally use a mechanical drive system that’s selected based on the boat’s displacement, says McGowan. Buyers need to keep in mind that the boat’s light-ship displacement, the weight often cited in sales brochures, doesn’t account for cruising gear. To compensate for creature comforts, McGowan recommends adding 20 percent to a vessel’s displacement to account for additional diesel, water and blackwater tankage, as well as anchors, chain, tools and other essentials. “If the drive unit is too small to handle the weight of the boat, it has the potential to fail at the worst time,” he says.
In addition to maintaining an efficient course, modern autopilots typically offer advanced steering options, ranging from man overboard (MOB) recovery routing to modes that hold the bow into the wind. Additionally, some manufacturers offer “economy” and “precision” driving modes, which are important for, say, long, windless passages, or when navigating a constricted channel. When operating in economy mode, the system will accept a greater cross-track error in order to reduce power and fuel consumption, while the precision mode ratchets down cross-track error but requires more active rudder management.