Chapter 6

Hulls And Their Characteristics

There are three basic types of sailing hulls, A each one more or less ideal for its particular use, yet the Indoor Yacht Club boys will argue far, far into the night about the relative merits of the trio of types plus innumerable variations of each. In the majority of cases, the amateur orators don't know what they are talking about. You hear that round-bottom boats invariably turn over, that V-bottom craft pound themselves to pieces, and that flat-bottom jobs are good only for rowing around a park lake. All of which is stark nonsense.

In the first place, the round-bottom boat (Fig. 1) isn't round. If it were, it would turn over with suitable alacrity. The so-called round-bottom boat does have sections—that is, crosswise shapes—that are curved all the way from keel to sheer line. In fact, some of the larger boats (Fig. 2) have curves that are of S form from keel to deck edge. A far better term for such boats would be "curved-bottom," but let's not attempt to reform boating nomenclature.

Round-bottom boats are fast, but there is no reason to believe that they are faster than the other types in the smaller sizes. Many of the speediest one-design boats—that is, boats built from identically the same design—are of V-bottom form. Another common fallacy is to consider that the round-bottom is a more expensive type of craft. Under the mass-production methods used by professionals for the construction of a number of the popular makes of sailing craft, the round-bottom hull is considerably cheaper to build. It is a paradox that the amateur finds the round bottom more difficult and expensive to build. That is because he does not have the permanent molds and the steam-bending equipment found in the professional yards. If you are going to buy a professionally built boat, you should be able to get a better price for a round-bottom than for a V-bottom boat of the same size. Notice that we said that you "should'' get a better price. Actually, the poor builder will tearfully tell you that he must charge more because the boat is sectionally curved.

Under normal conditions, a round-bottom boat does not have quite as much stability as a V-bottom. She may not be able to carry as much sail without heeling objectionably. To increase her stability, ballast may have to be added, less sail carried, or more skill used by the skipper. These points, of course, assume that boats of both types are of equal size and weight.

It is also said that the round-bottom boat is stronger. She may well be slightly lighter for a given strength, but otherwise there is little, or nothing, to prove the assertion that a well-built round-bottom boat will outlive an equally well-constructed V-bottom. The argument that one type pounds more than the other falls flatter than a newlywed's cake when viewed in the light of the surfaces presented to the water at the normal angle of sailing heel. True pounding comes from a relatively flat surface coming ker-smash against the surface of the water.

If you should sneak into a boat yard in the dark of the moon and saw a V bottom in half you would find, upon looking at the result of your wickedness, that a section through the boat was composed of four straight, or almost straight, lines (Fig. 3). The two bottom lines would start at the keel and branch upward to form a squatty letter V. Where the tips of the arms join the sides—a point a bit below the water line—would be a sharp corner known as the chine. Above the chine, the sides would be almost vertical right on up to the deck edge, or sheer line. In some V bottoms, the sides above the chine are slightly curved to improve appearance. The line from chine to keel is usually straight.

Sketch such a section and then see how, on paper, you can easily change the hull from a V-bottom to a round-bottom. Sketch in curves to round off the sharp chine corners and the result will invariably be a pretty good round-bottom shape (Fig. 4). You have eliminated small triangular sections at the places where the bottom lines meet the sides. Those small sections are responsible for the added stability previously mentioned. They act somewhat like the bilge keels often fitted to ships to prevent their rolling. On the other hand, the corners that add to stability can hardly be claimed to increase the sailing ability because they prevent the flow of water alongside from being the even, smooth stream that it should be. However, the situation is not quite as serious as it may sound. Some of the fastest of the small sailing boats have sharp chines. One of the reasons why the corners do not cut speed is that they reduce wetted surface by throwing the bow wave outward rather than allowing it to rise upward along the hull. In this connection, it must be understood that water flowing alongside a hull has considerable resistance. In fact, this friction is enough so that if you look very closely, you will see that a film of water is being carried along with a boat in motion.

Make this experiment. When your boat is sailing along at a good clip, place the flat "of your palm against the planking and slowly move your hand down into the water. If you are really sailing fast, you will find that the water within a half inch or so of the hull is being carried along with the boat. Now move your hand into the water a few inches beyond the hull and see the difference. If the action of a chine can throw some water away from the boat rather than having it climb up the side, you will save the drag of the excess water.

This might be a good place to say something about the so-called "planning" sailboat. Owners of some sailing craft fondle around with the idea that their boats are planning, just as a power-driven hydroplane skips along the surface of the water. It is the carefully considered opinion of this writer that any such claims are wishful thinking and nothing more. In this, we are speaking of planning in its true technical sense. That means the bodily lifting of the entire boat at high speed. Not one motorboat in 20 that is said to plane actually does so. What happens, in both fast sailboats and many motorboats, is that the speed is sufficient to lift the bow due to the increased pressure of the water. The crew feels the boat lift, the wave formation changes because the sharp bow has been lifted out, and the sensation is that the entire boat has risen in the water. In some cases, the actual speed does increase, but in any case, the change in the wave formation gives the appearance of increased speed. What has happened is that the boat has changed trim, she is sailing on a new water line with the bow higher than before. The stern is actually a bit lower, but this situation is not readily apparent, so the crew may be pardoned for believing that the boat is planning when such is not actually the case. We do not believe any sailing boat ever built has actually planed. If it pleases the owners to believe that bit of vivid imagination, no real harm is done. But, on the other hand, the chap who would rather be right than wrong is going to be in better company if he does not go around boasting that his sailboat planes. If it does, and he can prove it, his fortune as a yacht designer is made.

Editor's Note. The position that Mr. White takes above is, to say the least, a controversial one. Your editor believes, as do most ardent sailors, that several one-design sailboats actually plane when reaching.

The are bottom (Fig. 5) is relatively uncommon, the most popular boats of that type being the famous Star, Lightning and Comet knockabouts. In all basic elements, it is similar to the V bottom. There is still the chine corner, but the bottom lines, instead of forming a flattened letter V, are very much a flattened letter U. Perhaps it would be better to say that the bottom up to the chine is the shape of a shallow saucer. There is no reason to feel that the arc bottom has any point of superiority over the V bottom. Having slightly more wetted surface, it is technically inferior.

Of all boat types, the flat bottom (Fig. 6) is the most popular (and least attractive from just about every viewpoint). Its main virtue is ease of building, particularly if the bottom planks run across the bottom rather than fore-and-aft. Obviously, you have chine corners where bottom and sides meet. The above might indicate that the flat-bottom boat does not have technical virtues. This is not true in cases where the hull shape can be modified. For example, the world-famous Down East dory, used by commercial fishermen for rough-water work, is actually a flat-bottom. Another example of modification can be found in the boats Hans Brinker and Flying Dutchman, which have appeared in MECHANIX ILLUSTRATED and How To BUILD 20 BOATS (Fig. 7). These boats are Americanized versions of a Dutch type that has been used for centuries in the waters of Holland and the North Sea. In many respects, they are similar to the American dory. They differ radically from the conventional flat-bottom boat in that the flat portion is relatively narrow although the width of the hull on deck is more than usual. This result is effected by giving the sides an abnormal flare. The conventional flat-bottom boat may have a width on deck of only a few inches more than its width on the bottom. The sides, at the amidships point, are almost vertical. The dory and the Dutch type have the sides set at such an angle that there may be as many more feet of beam between bottom and deck widths as there are inches of difference in the ordinary flat-bottom boat.

Experience has taught that boats of this modified flat-bottom form are not only extremely seaworthy but may also be quite fast. There is considerable doubt that this particular type of underbody can truthfully be called flat-bottom because the flat portion is relatively so narrow. Probably the term "dory bottom" comes closer to being correct.

In all of this discussion, you must remember that we are considering the hull shape in section, not as it looks when viewed from one side. When you look at a beached boat from one side, the profile is relatively the same irrespective of whether she is round, V, or flat-bottom. The lines of the bottom, the chine (where there is one), and the sheer are usually more or less curved, being higher at the ends than amidships. There are some exceptions to this rule in regard to the sheer, or curve formed by the edge of the deck, but the underbody lines invariably are curved with the ends higher than the middle portion.

Where boats vary in their profiles, the main differences involve the amount of exposed keel. Within reasonable limits, the hull itself will be the same no matter whether the boat has a full keel, a fin keel, or a centerboard.

Most of the popular small sailing boats have centerboards: wooden or metal plates working up and down in slots cut through the keels (Fig. 8). To prevent water from entering the boat, an enclosure, called a centerboard trunk, is built over the slot (Fig. 9). The board works inside this trunk and can be raised or lowered to suit conditions. Most centerboards are fitted with pins at their forward, lower corners. At the after, upper corner of each, there is a chain or line arranged to control the depth of the board. When at anchor, when sailing in very shoal water, or when sailing before the wind, the board is drawn up into the trunk so that little, if any, of it projects below the bottom of the boat. No boat will sail well when the board is raised unless dead before the wind.

It is a common fallacy to believe that the object of the centerboard is to provide ballast, thus helping to keep the boat from turning over. Few centerboards have much effect upon stability. Their entire duty is to provide additional area below water to prevent the boat from being shoved sideways by the wind. Technically, this is called lateral-plane area and designers figure it out very carefully as there is a strict relationship between the amount and location of lateral-plane area and the sail area and location. A further discussion of the value of lateral plane will be found in another chapter.

Another type of centerboard also requires a slot and trunk, but is not hinged. It is bodily raised or lowered. In fact, it can be entirely lifted out when the boat is not being sailed (Fig. 10). Adjustments are provided so that the depth of the board below the bottom can be controlled and often the trunk and slot are considerably longer than the board is wide so that the latter can be shifted forward or aft to provide perfect balance in relation to the center of sail pressure. Devices of this type are known as dagger centerboards.

Obviously, the value of the centerboard is that it can be raised when the boat is in shoal water or when the craft is hauled out. Many boat owners follow the sport on waters that vary in depth from a few inches to many feet. The man who keeps his boat drawn up on the beach, or sometimes anchors in water not over a foot in depth, must have a center boarder because any other type would have too much draft. On the other hand, center boarders are often used irrespective of their advantage in draft. Even if you do all your sailing in waters that are many feet in depth, the day may come when you are driven on a sand bar or, torn from a mooring in a storm, come to rest on the beach. The chances are that a centerboard boat can be easily gotten afloat again. A craft with a permanent deep keel presents a more difficult problem.

Are You Ready To Move Onto The Next Lesson? Click Here...