Sailing Cat Boats
All types of sailboat are a combination of features. The sail configuration of a sailboat is important and may be the most important feature on most sailboats. When it comes to gaff headed catboats; we also need to consider the other features that make the design sail as a performance sailboat. We will use the popular Com-Pac Sun Cat as our example sailboat during this discussion.
Let start at the bottom and work our way up. The Sun Cat has a stub keel for several good reasons. The stub keel holds ballast, provides support for the boat when it on the trailer, hides the centerboard below the cabin floor and provides directional control when motoring and sailing. The down side of a stub keel is drag. The stub keel is a good deal for most cruising boats that live on trailers. The centerboard is a flat metal stainless steel plate. A discussion of how the board works is worth a full paragraph.
A keel is required if a sailboat is going to sail into the wind. If you had a sailboat that only had a center board and you lifted the board while you sailing into the wind, the boat would slide sideways away from the direction of the wind. (Note: The Sun Cat may not do this because it has a stub keel that's works well in big winds.) This feature is a tracking feature provided by a keel and any boat that has a keel would track well including powerboats. The key to understanding your keel is to analyze why a sailboat moved sideways. The force vectors produced by sails when you're on the wind (close hauled) are not in the desired direction. The force vectors want to push you off to leeward. We need something else to make our sailboat point and move into the wind. We know the keel is a tracking device and that works well for tracking (motor or sail), but some keels give us lift like sails gives us lift. When I say lift, I mean power that is generated. Sails gives us sail power or lift going to windward and I want something that will give me more power or lift in a different direction to balance or counteract the direction error generated by the sails. Sorry about the long sentence. If we are sailing on the wind, the sails are moving our boat sideways because that's the best they can do. All sails do that; even the best sails in world will do that. With the centerboard down, the board has more water pressure on the leeward side and less pressure on the windward side and that's the definition of lift. The lift created by the difference between my sails and my boat's heading is keel lift. The lift generated by the board or keel compensates for the sail error and moves our boat and us to windward. What makes this complicated to understand is that the forces are dynamic and change with boat speed and design. A design feature for a centerboard is a board with minimum drag. I think a flat metal board is a good thing for most small sailboats. The rudder and hull of most sailboats provide some lift. I like flat metal rudders. The Com-Pac Sun Cat points well for the reasons above.
Now that we have looked at the bottom of the boat, let's look at the rig. We can divide the rig into three parts. Small, medium and big winds. Really, all sailboats fall into the same three categories. Cat boat adjustments are a little different than sloops. With the cat boat we don't have a jib. With the sloop, the jib is the smart sail and the main is the dumb sail. The reason we call them smart and dumb is that the main sail trim adjustments are based on the wind off the jib. The cat boat has only one smart sail. The main sail on the cat boat has one more adjustment than the main sail on a sloop. And that gaff adjustment is a very important feature. The head of the cat boat's sail where it's attached to the mast is called the throat. We can tension the sail between the throat and the tack and use that same adjustment for most wind conditions. We are going to adjust the gaff for different wind conditions and directions in the following paragraphs.
Sailing on the wind is the most fun and we learn more from that point of sail. The sail should be trimmed over the boat with the mainsheet traveler in the middle of the boat in most wind conditions. Don't trim the sail too close or you will stall your sail. I like tell-tails for sail control. The gaff boom itself will be angled away from the lower part of the sail to provide the twist required by all sails. In light air, the gaff should be adjusted lower providing lots of sail chamber and a good curve from top to bottom. Maximum chamber should be in the middle of the sail. On a sloop, the boom would fall into the cockpit and you would still have a flat sail without any chamber or power. The centerboard works well and is designed for light air and the Sun Cat points well in light air. It points better than some sailboat with two sails. In really light air, sails produce their own surface drag and any sailboat with lots of sail area can become a stationary object.
Medium winds means it's time to bring the gaff up some for a flatter sail and less chamber. The centerboard should stay down, the boat will point well and heeling will be at a minimum. It's a stiff boat. When we get to high winds, it's time to bring the centerboard up and flatten the sail as much as possible with the gaff. One summer, we had two Sun Cats sailing close hauled in 25 knots wind. One boat was reefed and the other boat wasn't. Both boats had the same amount of heel and the same speed. They were both sailing at hull speed. The gaff is really an automatic reefing system. When it blows big time, the gaff falls off and the top the rig loses power. When you have less power at the top of the sail, you heel less. That's a nice safety feature.
Other points of sail are very easy in most cat boats. The Sun Cat has a moderate sail plan and you don't have worry about too much sail going down wind in moderate conditions. I would avoid downwind sailing in big winds in any sailboat. Sometimes you have to tack around from a broad reach on one side to another broad reach on the other side. That's good seamanship and a good idea for any sailboat. Most boats need a little more chamber on a beam reach. The Sun Cat can do this with just a small adjustment by lowering the gaff. Traveler on all boats are used to maintain sail twist. You change the trim angle with the traveler and adjust sail twist with the main sheet. That's too much trouble for most of us unless we are into racing and speed. Most of us can and will adjust the gaff because it's easy. On the sloop, we need to stretch the sail material to make a speed change. That's a lot more work and we normally don't do it unless we are racing or into speed.
The little diagram above has a 3 at the bottom end of the sail. That number is the number of degrees that the sail can be adjusted between a luff and a stall. If we trim our sail outward towards the luff, the force vectors will be pointing a little more towards the boat's course. We could point higher and sail a little faster if we try to sail the luff. Sailing on the edge of a stall will make the boat heel more and slow down. We can see a luff because the sail shakes. We can't see a stall because the sail can be stalled and still look good. Tell-tails on all the batten ends of the sail will show a stall.
Everyone wants to know the answer to the basic question, is the sloop better than a cat boat or is the cat boat better than a sloop? The answer to that question is sometimes. New sailors learning to sail should learn to sail on a sloop. They need to know about the smart sail and the dumb sail and why the sails have those names. The gaff headed cat boat can be a more versatile boat that sails well in almost any wind condition with less effort. The reason that cat boats were used on the Chesapeake Bay as workboats is because they are very strong boats that can be controlled in most wind conditions.
The Sailboat Company
Richlands, NC 910-324-4005