When to Motorsail (and Why You Should)

Motor Sailing · Passage Technique

No sailor admits in the marina bar to how much they motored on the last passage. The logs tell a different story. Survey after survey of offshore cruising fleets — the ARC rally data, Pacific Cup logs, Caribbean 1500 participants — consistently shows that modern cruising boats motor between 25 and 40 percent of total passage distance. On many passages it is more. And the vast majority of that motoring happens with the sails down, the engine working harder than it needs to, and the boat rolling uncomfortably in any leftover swell.

Motorsailing — running the engine with the mainsail up — is the efficient answer to most of those situations. It is faster than motoring alone, more comfortable, easier on the engine, and burns less fuel. The only thing preventing more sailors from doing it is the irrational guilt that comes with running the engine at all.

The Motorsailing Reality: When the Engine Is Going to Run Anyway

The relevant question is not "should I use the engine?" — in light air, dead downwind in a swell, or on a schedule with weather approaching, the answer is almost always yes. The relevant question is "should I leave the mainsail up while the engine runs?"

The answer, with very few exceptions, is also yes. A mainsail raised while motoring does several things simultaneously: it damps the rolling motion that makes motoring in any swell miserable; it contributes genuine forward drive at any apparent wind angle from roughly 40 to 150 degrees; it reduces the load on the engine at a given speed, which means lower throttle for the same hull speed or the same throttle for more speed; and it makes the boat easier to steer in a following sea by adding directional stability that the engine alone cannot provide.

The practical result is a boat that is faster, more comfortable, more fuel-efficient, and better-handling than it would be under engine alone — with no additional crew effort beyond raising the sail that should probably have been up already.

When to Motorsail vs. Sail Pure

The threshold where motorsailing becomes the rational choice varies by boat, crew, and conditions, but several situations make the decision straightforward.

Wind under 8 knots true. Most modern cruising boats — fin-keel designs with moderate to heavy displacement, often underpowered by racing standards — can technically sail in 6 knots of wind. They make 2.5 to 3.5 knots, they roll in any swell, the sails slat as the boat hobby-horses, and the apparent wind drops so much with the boat's movement that the sails become mostly decorative. Running the engine at half throttle, mainsail up and trimmed, produces 5 to 6 knots with a steadier, more comfortable motion. The choice is obvious.

Wind dead ahead with no useful tacking angle. A sailboat cannot sail directly into the wind, and a boat that needs to make good a course of 270 degrees in 10 knots of wind from exactly 270 degrees has no sail combination that helps. The engine goes on. The mainsail should still go up — it will not contribute forward drive, but it will damp the rolling from any leftover sea, and that alone is worth the effort.

Light air in a swell. This is the most miserable of all conditions: a leftover ocean swell from yesterday's blow, 4 to 6 knots of wind, no steerage way, and sails slatting back and forth with every roll. The flogging damages the sail, the hardware, and the crew's patience in roughly equal measure. The engine and mainsail combination steadies everything. This is not motorsailing as a compromise — it is the correct tool for the conditions.

The Mainsail-Up-While-Motoring Argument

Some sailors motor with sails fully furled and stowed because they believe "if the engine is on, we're motoring, not sailing." This is a philosophical position masquerading as a practical one, and it costs them in several ways.

The rolling reduction alone justifies the mainsail. A boat motoring in a beam or quartering swell without a sail up will roll continuously — sometimes uncomfortably, occasionally dangerously. The mainsail, even with no wind to fill it properly, acts as a damper. It slows the roll period and reduces the amplitude. It is not as effective as a proper stabilizer, but it is free, requires no electricity, and is on the boat already.

The speed contribution is real and measurable. At 40 to 150 degrees of apparent wind, a full mainsail on a 40-foot boat adds 0.5 to 1.0 knot over the same engine setting without the sail. Over a 200-mile passage, that is 8 to 16 nautical miles of free distance, or 1.5 to 3 hours off the passage time. At coastal fuel dock prices, the fuel saved by running a lower throttle setting to achieve the same speed is also meaningful.

Engine loading is better with the mainsail helping. A diesel engine running under very light load — the engine turning easily because the boat needs only 2 knots to be barely making way — does not run efficiently. It glazes the cylinders over time, runs cooler than ideal, and deposits carbon more readily. Motorsailing puts a load on the engine without requiring full throttle: the engine works against the sea and the hull resistance, and the sail contributes power alongside it. This is closer to the operating condition the engine was designed for.

The Motorsailing Attitude

The sailing culture has a complicated relationship with engines. Running the motor is coded as failure in a way that is entirely irrational when you trace it to its source. Racing sailors cannot use engines in races — therefore using an engine is "not sailing." Offshore purists built their identities on passages made entirely under sail — and they existed in an era when diesel auxiliaries were less reliable and fuel availability offshore was genuinely uncertain.

Neither of these circumstances applies to the modern cruising sailor. The engine is reliable. Diesel is available throughout the world with very few exceptions. Fuel is cheap relative to the value of arriving on schedule, arriving in daylight, arriving before the weather deteriorates, or simply arriving without the crew being so exhausted that docking becomes dangerous.

The experienced offshore sailor's calculation is not "can I sail it?" It is "what does this crew, this boat, and this passage require?" Exhaustion is a safety issue. Arriving at a reef-lined entrance in the dark because you refused to run the engine is not seamanship — it is pride. Fuel is cheap. Time has real value. The engine is there.

Motorsailing in a Passage: The Weather Timing Trade-Off

The most common offshore motorsailing scenario is the departure or landfall timing problem. You are 80 miles from port. The wind is 6 knots from ahead, building to 25 by afternoon. You can sail — slowly, uncomfortably, with slow progress against the building chop — and arrive after dark in deteriorating conditions, or you can run the engine with the mainsail up at 6 knots and arrive in daylight with sea room to spare before the blow.

Every experienced offshore sailor makes this calculation the same way. Motorsailing to make the port in the weather window is not a compromise of seamanship — it is seamanship. The boat and crew that arrives at the right time, in the right conditions, with fuel and energy in reserve has made the correct decision. The boat that sails proudly into a lee shore at midnight with an exhausted crew in a building gale has made a different kind of mistake.

Engine Wear and the Diesel Load Argument

Diesel engines are designed to run under load. The ideal operating range for most marine diesels is 70 to 80 percent of maximum continuous rated power — enough load to keep combustion temperatures in the productive range, cylinder pressures high enough to seat rings properly, and the turbocharger (if fitted) spinning in its efficient range.

Running at anchor for extended periods — engine at idle to charge batteries, circulate coolant, or run the watermaker — is actually worse for engine longevity than motorsailing at moderate throttle. Idle wear is real: the engine is warm but not hot enough, the rings do not seat properly against the bore, and fuel that does not combust fully washes down the cylinder walls and dilutes the oil film.

Motorsailing at 65 to 75 percent throttle, propeller loaded by real boat speed and sea conditions, is close to the ideal operating condition. The engine is warm, the combustion is complete, the rings are seated, and the alternator is spinning fast enough to charge the house bank properly. You arrive at the next port with a well-exercised engine, charged batteries, and a crew that is not exhausted from a day of slatting sails and slow progress.

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Frequently Asked Questions

What percentage of a typical offshore passage involves motoring and why does this surprise sailors? Survey data from offshore cruising fleets — the ARC rally, Pacific Cup logs, Caribbean 1500 participants — consistently shows that modern cruising boats motor between 25 and 40% of total passage distance. The figure surprises sailors because the sailing culture codes engine use as failure, creating a social pressure that produces underreporting in marina bar conversations but does not change the log entries. The engine is running. The relevant question is whether to leave the mainsail up while it does — and the answer, with very few exceptions, is yes.

Why should the mainsail almost always be raised when motoring? A mainsail raised while motoring does four things simultaneously: it damps rolling motion that makes motoring in any swell miserable; it contributes genuine forward drive at apparent wind angles from 40 to 150 degrees; it reduces load on the engine at a given speed (lower throttle for the same hull speed, or the same throttle for more speed); and it adds directional stability in following seas that the engine alone cannot provide. The practical result is a boat that is faster by 0.5–1.0 knots, more comfortable, more fuel-efficient, and better-handling — with no additional crew effort beyond raising a sail that should probably be up already.

What conditions specifically make motorsailing the rational choice over pure sailing? Three conditions make motorsailing clearly rational: (1) Wind under 8 knots true — most cruising boats technically sail but make only 2.5–3.5 knots with uncomfortable rolling motion; running the engine at half throttle with the mainsail up produces 5–6 knots with steadier motion. (2) Wind dead ahead with no useful tacking angle — the engine goes on and the mainsail damps rolling even without contributing forward drive. (3) Light air in a swell — leftover ocean swell with 4–6 knots of wind produces slatting sails that damage hardware and exhaust crew; the engine and mainsail combination steadies everything and is the correct tool for these conditions.

How does motorsailing affect engine wear compared to motoring alone? Diesel engines are designed to run under load, with the ideal operating range at 70–80% of maximum continuous rated power. Motorsailing at 65–75% throttle, propeller loaded by real boat speed and sea conditions, is close to the ideal operating condition — combustion is complete, rings are seated, the alternator spins fast enough to charge the house bank properly. Running at anchor for extended periods at idle is actually worse for engine longevity: the engine is warm but not hot enough, rings do not seat properly against the bore, and unburnt fuel washes down cylinder walls and dilutes the oil film. You arrive at the next port with a better-exercised engine after motorsailing than after extended idling.

What is the weather timing calculation that makes motorsailing a seamanship decision rather than a compromise? The offshore passage scenario: 80 miles from port, 6 knots of wind from ahead building to 25 knots by afternoon. The pure-sailing choice arrives after dark in deteriorating conditions; the motorsailing choice runs the engine with the mainsail up at 6 knots and arrives in daylight with sea room to spare before the blow. Every experienced offshore sailor makes this calculation the same way. Motorsailing to make the port in the weather window is not a compromise of seamanship — it is seamanship. The boat and crew that arrives at the right time, in the right conditions, with fuel and energy in reserve has made the correct decision.