Swing Keels and Centerboards - SailNet Community
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post #1 of 1 Old 06-27-2002 Thread Starter
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Swing Keels and Centerboards

I have to keep my Catalina 22, which is a swing-keel model, in the water. Will this damage the moving parts of the keel?

Tom Wood responds:
Before we answer your question, let’s differentiate between a centerboard and a swing keel. The difference is often glossed over by builders and owners and it makes a big difference in answering your question.

A centerboard has little or no ballast beyond what will overcome its own buoyancy to make it drop down—in effect, it has almost no weight in the water and exists only to add lateral resistance area to the profile of the boat. A swing keel, on the other hand, has the entire ballast of the boat hinged so that it can be retracted.

As you can see, there is the possibility that every combination conceivable could exist between these two extremes. One boat might have 10 percent of its ballast in the board and be called a swing keel while another might have 50 percent of its ballast in the board and be termed a centerboard boat. Most boats have at least some of their ballast in the keel box.

With one caveat to be discussed below, there is no reason why leaving a centerboard or swing-keel boat in the water will harm it. In reality, most centerboards are not damaged by water, but by land—as in running aground. With the board up this can jam debris into the trunk, wedging the board in the up position, but with the board down, running aground induces levered stresses that can break the board, damage the trunk, and shear the pivot pin away. Some boards protrude below the bottom of the keel box when in their fully up position and these are difficult to block up properly for land storage or transportation, and they're also a problem when taking the hard.

There are minor inconveniences when leaving a centerboard boat in the water. Marine growth loves the slot in the keel that houses the board and, depending on the width of the slot, barnacles or shellfish can be the devil to remove. If left to grow fat and sassy, shellfish can make the board inoperable. Painting inside a narrow trunk with antifouling paint isn’t much fun either. I once had an old centerboard sloop that had to be hauled twice each season and lifted high in the air so that I could lower the board and scrape the inside of the trunk. Coarse sandpaper glued to a semi-flexible piece of plywood was an excellent tool, but I always wished for armpit-length rubber gloves when applying the paint.

The most common problem associated with swing keels and centerboards occurs with the pennants designed to raise and lower them. Like all pieces of running rigging, they wear out. But because centerboard pennants are immersed in salt water, they wear out fast. The effects of marine growth and salt corrosion make this a very rapid process regardless of whether line or flexible wire-rope is used. So it is wise to examine and replace the pennant on a regular basis and carry a spare for when it does break—note I use the word "when" and not "if."

And now for that caveat. A heavily ballasted centerboard or swing keel can do an immense amount of damage if the keel is stored in the retracted position and the pennant parts. I used to repair several of these each season, and in one case the boat was submerged before the problem was discovered. Designs of boards vary widely, but most have the ballast located as low as possible (or aft when the board is up) with the pivot pin as far forward as possible. This creates a situation of tremendous leverage. If the board is suddenly released, it falls fast until something stops it—and that something is usually the forward end of the centerboard case in tandem with the pivot pin. This is no problem for the pure, lightweight centerboard, but you can see how a half ton of lead on a four-foot lever arm might cause quite a jolt. Cracked fiberglass and bent pivot pins are the usual result.

Many smart owners leave their heavily ballasted swing keels mostly lowered while the boat is in the slip. This way, if the pennant does break while they are not on the boat, the board doesn't fall far and will do little or no damage. It has the side benefit of adding stability to the boat at the dock. The drawback is that some boards rattle around in their cases unmercifully when not side-loaded with the pressure of sailing.

Another method of avoiding the falling-board syndrome is a variation on the old centerboard owner’s emergency patch for a broken pennant. When the pennant breaks, two people can work the board back up into its trunk slot with a length of line. The two form a loop over the bow and work aft, one person on each side of the boat, see-sawing the line under the keel until the board is all the way up. The two ends of the line are then fastened to cleats or winches on each side of the boat. I had to smile as I was writing this since it used to be so common to see centerboard boats sailing blithely around Florida and the Caribbean with these bandages running down the sides of the boat in a very unseamanlike manner.

I have seen swing keel boats sitting at the dock with such a "centerboard pennant preventer" (if you’ll allow me to coin a new nautical term) in place as a standard practice. The rope is bound to quickly become slimy from growth, but it’s got to be a good deal cheaper than an emergency yard bill for a cracked centerboard trunk.

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