A gust sweeps in and the boat heels sharply. The new sailor's eyes go wide and his knuckles whiten as he clabbers for a handhold, any handhold, in the face of imminent capsize. In choosing to take up sailing, he didn't bargain on capsizing. But the boat doesn't capsize. The gust passes, and the boat comes back up to an even keel. So why didn't it capsize? It felt like it was going to, lying on its side like that, the mast maybe 30 degrees shy of vertical. To answer that good question, we need to look at the unseen parts of the boat below the aterline. But before we do that, let's examine why sailboats heel in the first place. After all, motorboats don't heel.
The wind, even when it's relatively light, exerts real force on the sails as they translate wind force into motive power. You will feel that force spread throughout the boat like a bolt of electricity. Touch a jib sheet under load, and it feels more like an iron bar than a rope. It;s really quite impressive, the pwer contained in those pieces of fabric we call sails. The trouble is, the laws of physics dictate that most of the wind's force-when the wind blows from over the front of the boat-wants to push the boat over on its side. Only a relativey small portion of the wind's force devotes itself to moving the boat forward. In the language of boat design, a degree of force is referred to as "moment", and so here we are talking about heeling moment. So what compensates for the inevitable heeling moment? The answer is that part of the boat you can't see because it's underwater. It's called the keel.
If it's useful, think about sailboat stability in terms of a seesaw. Put a heavy kid on one end, a light kid on the other-the seesaw will be out of balance; it will capsize to the heavy kid's side. But put two kids of even weight on the seesaw, and you have balance. The seesaw is stable. In boats, the force (weight) of the wind in the sails naturally causes the boat to heel, but it won't, under reasonable conditions, capsize, because this heavy chunk of lead, the keel, mounted on the bottom of the boat counterbalances the heeling moment.
Points Of Sail
Please immerse yourself in this illustration. You might find an objecy or a model boat to serve as a visual aid, and turn it through an imaginary wind steady from a single direction. Then perhaps go at it from the opposite perspective-keep the boat's heading stationary and let the wind shift around it. Then take it a step farther by trying to picture where the wind will be if you turn, say, 90 degrees in one direction or another from your present heading. It might even be helpful to set up a portable fan to supply wind, instead of merely imagining it. Whatever your style of learning, focus it at this early stage on understanding points of sail. If the angle changes, either because you turn the boat or because the wind shifts,then you will need to adjust the sail trim accordingly. But for now, the important step is to grasp the general concept of relative wind angles as illustrated in "points of sail".
In Irons - 0 degrees
Close hauled - 45 degrees
Close Reach - 60 degrees
Beam Reach - 90 degrees
Broad Reech - 120 degrees
Running - 150-180 degrees
Sailors shorten them to up or down as indication of both direction and boat heading. You will turn the boat up-towards the wind-or down-away from the wind, which implies of course awareness of the answer to that question. Where is the wind? Say you are sailing with the wind blowing over the starboard side on a beam reach. To takeher up requires a right-hand, or starboard, turn onto a close reach, and the sails would need to be trimmed (pulled in) to the new point of sail. If you take her farther up onto a beat, you would be sailing on a starboard tack. She won't go up any higher. If you try to press her closer to the wind, she will slow down and the sails will begin to flutter, or luff, like flags. Of course the same principle applies with the wind blowing over the port beam. In that case, to take her up requires a left-hand, or port, turn through a close reach onto a port tack. In some cases, depending where you want to go in relation to where the wind meets the centerline of the boat, you will need to turn either the bow or the stern through the "eye" of the wind, the direcion from which the wind blows. Turning the stern through the eye of the the wind requires you to jibe.
On a boat, there is always a windward side and a downwind or leeward side to everthing, including sails. These two words also refer to the direction of things-rocks, buoys, other boats-outside your boat. For instance, you might hear, "The boats to leeward seem to have more wind." Obstructions lying to windward such as rocks, shoals, and anchored boats are less threatening than those lying to leeward, since boats sailing to windward tend to slide sideways or make leeway. However, boats sailing on the downwind side, or in the lee of an island, will experience diminished or disturbed wind.