Even the hardest–core sailor realizes it's time to fire up the motor when the winds drop and there's still some distance to go to the slip or the anchorage.
Twenty years ago there were few choices, and they were mostly bad. But there's a reason for that: Internal combustion engines used to power sailboats arguably have the toughest job of any marine engine.
Look aft, and you'll see a saildrive installation under this Arion 29 sailboat.
Consider the proposition: sit in the bilge for hours, days or even months at a time, silent and unused. Then fire up on demand, work hard for a short time, and go back to another long nap. That's a tall order for an engine and its fuel system, and it typically resulted in cranky engines and even crankier sailors.
Today's sailor still faces a tough situation with marine engines but stands a much better chance of getting the propulsion he or she needs, when it's needed. Here's a look at what you can expect if you're buying a new inboard–powered sailboat or repowering a classic.
POWER OPTIONS
There are two ways to power a sailboat with an inboard engine: the traditional straight shaft and prop, and the saildrive. The shaft and prop setup is identical to the one on a conventional inboard powerboat. The saildrive, meanwhile, is an inboard engine with what looks like the lower unit of an outboard engine extending down through the hull.
A straight–shaft arrangement is common on conventional cruising boats, where there is often an extensive keel through which the shaft passes as it leads to the propeller. It's sometimes also installed on boats without full–length keels, using shaft struts for support.
A saildrive installed aboard a Grampian 28 sailboat.
Saildrives are typically installed on racing boats, since they have lower drag. They also may have a slight efficiency advantage because they have a vertical leg extending straight down from the bottom of the boat, which ends in a 90–degree turn aft, and therefore the propeller thrust is transmitted parallel to the direction the boat is traveling. By contrast, in a conventional inboard shaft installation, the shaft exits the bottom of the boat at a downward angle, which means thrust is not parallel to travel; the more the angle, the greater the wasted thrust.
As with all things boat–related, there are advantages and disadvantages to each. Straight–shaft installations employ widely known technology and components because they're so common, for example. And a diver can do some lower–unit maintenance. But, they have higher drag and a less–efficient thrust angle. Other minuses include the fact that alignment is critical to control sound and vibration, and they initially involve higher installation and labor costs. In addition, straight shafts require through–hulls for cooling water.
Saildrives, meanwhile, have lower drag, no alignment issues, and less–expensive installation costs. They don't require through–hulls for cooling water, nor stuffing boxes or shaft seals. But, installation does involve a big hole in the bottom of the boat and often a single, rubber O–ring to seal the opening. And transmission maintenance usually entails a haul out.
A close-up look of a saildrive with a folding prop.
BRAND OPTIONS
Whichever setup works for your needs, you'll likely choose an engine by either Volvo Penta or Yanmar, since they make up about 80 percent of the business worldwide. In the United States, Yanmar has a significantly greater slice of the pie, a fact both companies agree on, though neither would provide an exact accounting.
For recreational sailboats from 25 feet to 50 feet, inboard auxiliaries run from about 9 horsepower to more than 110 horsepower. In an average year, 1,900 to 2,200 inboard auxiliaries are sold, according to Douglas Rose, product manager for Volvo Penta's Americas office in Chesapeake, Virginia. That figure pales in comparison to an average year for I/O engines, of which perhaps 75,000 to 80,000 are sold, and for outboards, of which nearly 100,000 are sold, he says.
Volvo Penta became well known in the United States after it introduced the first stern drive, called the Aquamatic, in 1959. Today its sailboat diesel engines range from 11.8 horsepower to 174 horsepower and are offered in both straight–shaft and saildrive configurations, on sailboats from C&C (saildrive only), Tartan, some of the Sabre line, as well as a number of custom designs. Interestingly, Rose says the company sells more saildrives in Europe than in North America. "The European market has taken to it more readily than the American market," he explains. He speculates that the reluctance on this side of the pond may be due to some early bad experiences with units sold by some companies. Rose notes that these early saildrives were often nothing more than a gas outboard powerhead built on top of an outboard bottom end, and they suffered from disastrous reliability and corrosion problems.
