The main is a pain
The main sail is your power house. A boat gets most of its momentum from the main; but it is also a giant pain in the rear to put up, take down, put on the sail cover, jibe, and do a whole bunch of other things.
In heavy air, the main is a terror with possible accidental jibes and overpowering events like broaching. In light air, you have just as much chance of jibing while running, but get little benefit from the main with barely enough wind to fill it.
In either scenario, heavy or light air, who is going to steer the boat if you're single-handing and have to climb up to douse the main, wrap it in sail ties and cover it with a sail cover? Even with an auto helm, that's a lot of work and a long time away from the helm.
What if you just doused the main and used the jib? Better still, what if you never put up the main in the first place?
Unlike the main, there is no sail cover, no sail ties and you never have to worry about the accidental jibe with your jib. It sits up on the bow, can catch all kinds of wind on the downwind leg and is a breeze to douse when it’s on a roller furler.
Here’s a little scenario for you:
You’re sailing home and will come into the dock in the next half hour. You don't want to raise the main just to pull it down in 20 minutes to come into dock and you really don't want to wake your crew who have been up all night at the helm. You also don't want to start your motor because that too will wake your crew and she needs as much sleep as she can get cause she is driving home while you sleep in the back seat.
You know you will have plenty of time to fire up the motor when you get inside the breakwater, but for the last half hour while you are in open water with a great breeze at your stern. Why not take advantage of the wind by sailing? Roll out your jib.
You uncleat your roller furler line and give the starboard jib sheet a tug. The jib rolls out on your starboard side and fills with air before you even think to pull it all the way in and your boat pushes forward at 4 knots and you don't make a sound.
Twenty mins later, you spy the safe water mark of the harbor and realize that it's time to get ready to dock the boat. You preheat the motor and turn the key and smell of exhaust fills the cockpit as the boat rumbles to life.
Within a moment your bleary eyed crew stumbles on deck and says, “Thanks for letting me sleep.I needed that.” You nod and smile, knowing that she will be eyes wide open when you are sawing logs in the back seat on the way home.
While your crew readies the fenders and dock lines, you give the roller furling line a yank and the jib tightly rolls up and you motor the vessel into your slip. You just pulled off one the greatest sailing hacks there is.
That’s really how easy it can be sailing on the jib alone. No muss no fuss, no main, no pain, just smooth sailing on the jib alone. Is it unethical? Well maybe, but it's just too damn easy not to do it.
Can I do it on the upwind leg?
The short answer to that is no. The Jib is useless alone on the upwind leg because it needs a main to work due to slot effect.
In the article, Guide to Sail Trimming And Shape, we discuss slot effect saying, “With a jib it (also) needs to have a nice wing shape to it, but in that case it needs to be pulled in concert with the mainsail because it enhances the flow of wind on the backside of the main. This is all under the lift principle which is mostly what is happening when you are upwind sailing.”
On the upwind leg, the jib squeezes the wind on the backside of the main and that causes the main to get more power. If the jib has no main to squeeze the wind on to, it is out of balance and carries too much wind on its back side.
That causes the boat to turn away from the wind because it has no main on the back side of the sailboat to counteract the effort to point it towards the wind. Unfortunately, sailing upwind with the jib alone will only cause you to sail in circles.
Sailing with the jib alone doesn’t work on the upwind leg and makes it kind of unethical because there is no balance between sails when you have only the jib out. Sailing purests might scoff at you if all you ever sailed with was your jib, but in my book, any wind is good wind and if a boat works a boat works so why not do it? The pirates did and look where it got them?
The transition from sail to power
Now I am not saying that jib sailing is gonna be the next Olympic event and there is no way it will win any races. It is a cheap sort of way of harnessing the wind on the sly and is kind of a lazy way to sail, but it works.
It’s particularly nice on days when you're not entirely committed to sailing. For example, light wind days.
Say your cruising along under power and see a tiny little ripple of wind on what is otherwise a mill pond kind of day. You're not sure if the wind will fill in, or if it's gonna be an iron gennie sort of afternoon. You're sick of listening to the motor and the fumes are blowing back into the cockpit and making you nauseous.
You peel out the jib and try it.
Initially the jib fills mostly and you think ok, lets secure the motor and breath a little easier. The motor quiets and the boat slows to a bare motion of 2 knots.
The sun beats down on the boat and it's getting hot and a silence falls over the boat as the jib flaps uselessly in the still air. You should have kept the motor on.
If you had raised the main, your boat would still not be moving at all and everyone would be hot from climbing all over the cabin top to raise it, and now you would have to ask them to lower it. Who wants to be that guy?
Instead, you pulled out the jib and now you can just as easily put it away. You refire the motor and head back to the dock for gin and tonics in yacht club air conditioning, a fine alternative to heat exhaustion and sunburn on a non-wind sort of day - and you’re the hero.
I hate to say it, but I am a lazy sailor and I love sailing with the jib alone. It has its merits and there are days when it's just too hard to put up the main. I wouldn’t recommend doing it every day, and never on the upwind leg, but if the opportunity presents itself, why not take advantage of one of sailing's best little hacks. Do good, have fun, sail far and thanks for reading.