The dilemma of motor-sailing

IT’S THAT TIME of year again. The wind on Puget Sound is practicing its summer trick of either coming from dead ahead or disappearing entirely. And in the calms we find all kinds of sailboats puttering along under power with their mainsails set and their foresails stowed. It’s called motor-sailing.
The question is: does the mainsail actually help? Is it contributing to forward motion, or is it a parasitic drag?
At first glance the answer seems quite simple: as long as the sail is filled with air, bulging with a business-like curve, it must be sucking the boat forward and adding to the engine’s speed. This must certainly be the case if there is a faint breeze blowing at 45 degrees or more from dead ahead. But what about a dead calm?
When there is no wind at all, the apparent wind caused by the boat’s motion through the water will come from dead ahead. This will make the mainsail flutter uselessly as the boom swings in to the centerline. There will definitely be no advantage in that case, and perhaps a slight disadvantage caused by the drag of the sail.
What then, if you pull the mainsheet traveler to one side or the other and pin the mainsail at an angle so that it fills with the air coming from ahead? This is what many sailors have always done, including me, to keep the mainsail quiet and, perhaps more importantly, to help cut down on rolling; but it has always worried me.
The sail might well be curved in a bulge that looks purposeful, but most of the power that it generates in this position is directed aft, not forward. It’s acting in the same way that a backed squaresail acts, and it’s robbing the boat of forward speed. The faster the motor pushes the boat, the greater the counter-effort.
So what we really should do in a dead calm is drop the mainsail altogether. We don’t, of course, not only because of the extra rolling, and not only because it involves work, but also because a little breeze could spring up at any time, and that would change the situation drastically. Even five knots of wind would change the mainsail from being a big bag of drag to a helpful contributor to forward motion, and we want to be ready to take advantage of it the second it happens.
And so we continue to motor-sail in the age-old way, our brows furrowed with the effort of trying to figure out whether the effort of dropping the mainsail is worth the slight gain in speed that might result. Mostly, I believe, it isn’t. But maybe that’s just wishful thinking.
Today’s Thought
Expecting something for nothing is the most popular form of hope.
—Arnold H. Glasow
Tailpiece
“Dad, if a girl kisses me, should I kiss her back?” “Hell no, son. Kiss her lips.”