Tuesday, June 19, 2012

Keeping Upright

Last week, we covered types of sailboats and some of the general principles of sailing. Today, it's time to trot out that law of physics most of us know so well: For every action, there must be an equal and opposite reaction. It's the short way of saying that if you apply force to sails on top of the boat, you want something under the boat opposing that force. Otherwise, you end up with an upside down boat.

These drawings are of the different types of keels that can be bolted to the structure of a sailboat. The important part is that if you're getting into the details of writing about keels, you'll want to know that certain keels go with certain boats. Full keels are usually on blue water cruisers. The fin and bulb keel is popular on racing boats. Coastal cruisers and day sailers can have just about any kind of keel, though most of them will look like C or D.

A keel provides a force to counter the wind in the sails. The more the wind blows and the farther over a boat heels, the more the keel is lifted from vertical. Gravity (and water resistance) wants to push that heavy keel back to vertical. Most of the time, this balancing act is sufficient to keep most boaters out of the drink. But it is entirely possible to overcome the righting moment of the keel. Get too much sail up in too much wind, and you risk a knock down. This is when the force of the wind in your sails overpowers the weight of the keel and the boat falls all the way over on it's side. The sails can end up in the water, as can the sailors. When that happens, though, all of the wind spills out of the sails. The  weight of the keel is hanging out there on the horizontal. Chances are excellent that the boat will right itself. Usually with a crash. The sails will fill again, but if no one is on the helm, the boat will round up  into the wind and come to a stop. In theory. In reality, people occasionally drown this way. Not often, but it happens, especially in transoceanic races.
It's also possible to roll the boat entirely. If you end up in a storm in open ocean, you want to keep your bow to the waves (using a drogue or a storm anchor). If the waves are big enough and they catch you broadside, you can find yourself upside down, your keel vertical in the air and the sails underwater. Most boats go to the bottom when that happens.
Keels do a couple of other things for a sailboat. It's inertial mass that provides 'bite' in the water. This means that the baot is moving, the mass in that keel wants to keep moving. This gives a sailboat the speed and power to tack. In a tack, you sweep your bow across the direction the wind is coming from. It's possible to do that manuever so slowly that you lose momentum, the wind grabs control of you and you end up in irons. Keels help prevent that to a large degree. They're also designed to keep a boat from sliding sideways in the water.
When you're on a beam reach - with the wind coming from the side - the keel in the water that keeps the wind from blowing you off course. (In reality, over long distances, you DO get blown a bit off course - boats do slip sideways a bit regardless of the keel, but in most cases, unless your characters are doing ocean passages, you won't deal with it.) 
Most monohulls (all the sailboats I've shown you so far are monohulls - one hull boats) can enter a marina under power, turn into a waterway and put the engine in neutral and simply glide into their position at dock because of the momentum. Other boats, especially power boats with little hull real estate below the water line skate around on the surface of the water, more at the mercy of the wind. Granted, they have massive engines to make up for that.
If you live near water, it pays to pack a picnic lunch and head down to watch the sailboats on a nice, breezy day. You're especially lucky if the marina has either a junior racing team or a sailing school. Many of these organizations put people in little 12-15' sailboats that can be easily upset. Watch them long enough and you'll see someone push a boat just a little too far. The whole thing will go over (this is a knockdown). The little boat probably won't right itself. The sailor will likely have to swim over, pull the sails off, get the boat upright and then climb back in and set up sails again.

If you're really interested in understanding sailing, look up sailing schools in your area. Most schools have introductory classes for about $100. The aim is to get you out on the water and teach you the basics in a coulple of weekends. It would be enough for you to get a feel for sailing.

Next: multihulls

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