Be your own skipper

With patience and grown-up help, you can make this model boat designed for kidspace readers.

Building a "tall ship" is a tall order - even if it's only about two feet long. But model sailboat designer Dale Wenninger is confident you can do it. You'll need the right tools and materials, a grown-up's enthusiastic cooperation, and some patience to do it.

You'll also need a plan. And have we got a plan for you! The boats you see in the right-hand photo above are a design called CS Monitor, in honor of this newspaper. After a test sail, in fact, the design was modified especially to cope with the variable winds that blow across the reflecting pool near our offices on the Christian Science Plaza in Boston.

First, a little background.

We thought there was a good story in model sailboats. Wouldn't it be fun to build and sail a model sailboat? Maybe not a fancy remote-controlled one, but one that we could manage.

Enter Dale Wenninger of Swampscott, Mass., a retired restaurant owner. He grew up making boats with his grandfather and brother in Maine. He's especially interested in designing model boats that grown-ups and kids can build and sail together. He was delighted to hear from us. Without our suggesting it, he offered to design a model boat for Kidspace readers.

This is not the sort of boat you can build in an afternoon. It took us about 10 hours to build, once we'd found all the materials we needed. Mr. Wenninger provided a list of materials, plans to print out, and an extensive set of instructions. (We've put all of it - along with construction photos -on our website. See boxed item on this page for the Web address.)

To Wenninger, making sailboats isn't the main thing. He mostly likes "finding ways to help kids make connections with parents and other adults," he says.

He's become the "designated grandfather" to several neighborhood children interested in making model boats. At his local Congregational church, he's organized a mentoring program, in which adult modelers help teenage boatbuilders.

Those sailboats are much bigger than the CS Monitor. They are remote-controlled and require a $200 investment for materials and equipment. They are much trickier to build, too. We wanted a relatively simple, inexpensive model.

Wenninger obliged. Instead of fiberglass, he settled on a wood-and-rigid-insulation construction that is relatively easy to shape. He figures it costs about $10 in materials, based on building three boats. (For one boat, we spent almost twice that.)

Designing a sailboat is hard. Full-size sailboats undergo many tests and revisions. One way to make a good model boat is to pattern it on a full-size one. That's what Wenninger did. He started with the basic shape of the Dark Harbor. The Dark Harbor is "a good little boat from the 1920s with a proven design," he says.

The next and biggest challenge: How to make his gracefully curving hull design relatively easy to make. His solution: Make a hull skeleton out of plywood, and then fill it in with stiff foam insulation.

Remember, you'll need grown-up help and supervision to complete this plan. An adult with some knowledge of power tools would be best. You'll also need access to a thin-bladed saw (coping saw, saber saw, or jigsaw), a glue gun, and a rasp. Wenninger, with his experience working with young people, is confident that the project is well within the abilities of a middle-schooler.

"The biggest obstacle to doing anything," he says, "is getting past the idea that you can't do it."

We visited Wenninger's workshop. Here, he designs and builds model sailboats as well as full-size rowboats and kayaks. Wenninger took us through the project, one step at a time. No advanced woodworking skills are required.

The secret: The rigid foam insulation is easy to shape, but so light that the completed hull, though solid, floats easily.

After the hull skeleton has been constructed and the foam insulation glued in place and shaped, water putty is applied. The putty, mixed to the consistency of cake batter, is slathered onto the hull and smoothed. The putty strengthens the hull and fills in gaps. Strips of fabric mesh are pressed into the putty to strengthen the hull. More putty covers the mesh.

When the putty dries, the hull can be sanded like wood. With persistence and patience, a very smooth surface is attained. (The smoother the hull, the better it glides through the water.) Three coats of paint give the hull a watertight finish.

Putting the mast in the right spot - and making sure it's not cockeyed - is critical. Realizing this, Wenninger included a self-aligning pilot hole for the mast in the hull. (You might notice that the mast is tilted back slightly, or raked. A raked mast is for style, more than anything else. It looks more streamlined and sleek that way.)

A steerable rudder would have been too hard to make. You can adjust the CS Monitor's sails, though, to adapt to wind conditions. (We also tied light string to our boats so we could reel them in.) The first model tipped over too much in the strong, variable winds on the plaza. Wenninger went back to the drawing board and made the keel four inches deeper. That did it.

The sails on the boats shown are made of simple white cotton cloth. You can use colored cloth, if you like. With an indelible marker, you might add a sail number. You can make the sails repel water by spraying them with a fabric treatment like Scotchgard. (Wenninger thought about making waterproof sails out of old shower curtains, but the plastic melted when he applied hot glue.)

Sticking to this project and completing it has several rewards. One is the satisfaction of accomplishment. Another is the fun of sailing the boat. A third is the fact that, no matter how it sails, it sure looks good.

In fact, at the moment we've got our two on display atop some filing cabinets in the office. Pretty cool.

For a printout of the plans for the CS Monitor, send a check for $3 (for postage and handling) to: The Home Forum, The Christian Science Monitor, P02-20, One Norway St., Boston, MA 02115.

Sails don't work the way you think

When you first look at a sailboat sailing, it seems so simple: The wind is hitting one side of the sail, pushing the boat ahead. But if the wind is pushing it, how can a sailboat sail almost directly into the wind? Something else must be happening here.

The wind does push against the sail. More important, the wind also pulls on the sail. This pulling action exerts a much stronger force than the pushing action.

Picture a sailboat sailing upwind. When the wind coming toward the boat hits the sail, the wind is redirected around either side of it. Some of the air flows past the inner curve of the sail, and some of it goes across the billowed-out side. Now the physics of moving air comes into play.

The air going around the two sides of the sail must reach the back of the sail at the same time: That's a law of nature. But because of the curved shape of the sail, the air going around the inside of the sail has a shorter trip than the air going around the puffed-out front. The air going around the outer curve has to speed up. It's now going faster than the air going the shorter route.

The different air speeds are important. The faster-moving air is lower-pressure air. The low-pressure air creates a vacuum on the windward side of the sail, and the sail is sucked toward it, pulling the boat.

Sails and airplane wings work on the same principle. Air flowing around an airplane wing creates lift - upward motion. Air flowing around a sail creates forward motion. (Have you seen pictures of windsurfers who can turn their sails parallel to the water? Their sails become wings, and they fly across the water.)

A sailboat's centerboard, or keel, plays an important role. The keel helps force the boat forward, even as the wind tries to push the boat sideways as it sails upwind.

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