Types of Hulls
The next big decision is which type of hull to choose. If you're planning a scale project, your choice will obviously be determined by the full-size craft you want to model. But sport, racing and sailing boat hull types exhibit very different characteristics. In general, there are two hull classifications: monoplane and hydroplane.
MONOPLANES Monoplane hulls have one continuous surface in contact with the water. This is by far the most common hull type for full-size craft. Monoplane hulls can be divided into two subcategories: deep-vee and shallow-vee.
• Deep-vees. Most RTR monoplane hulls are deep-vees. This conventional layout brings the keel to a sharp point well below the surface of the water. The bottom of the boat is angled upward steeply toward the hull's sides, resulting in a boat that knifes through the water with a comparatively large wetted surface area. This type of hull is stable at all speeds and provides sharper steering response. The downside is that the extra hull surface that contacts the water causes drag that limits top speed. Still, with the right power system and proper tuning, these boats are plenty fast—especially for beginners.
• Shallow-vee hulls are the faster of the two monoplane types because they run with less surface area in contact with the water. The shallower keel vee-angle produces a flatter bottom that causes less drag. The downside is that less contact with the water means less stability, so they are more challenging to control and require more precise trimming. Shallow-vees are very popular for entry-level racing, the so-called Crackerboxes being the most common.
HYDROPLANES Hydroplanes have more than one (non-continuous) surface in contact with the water. They include tunnel hulls, catamarans, outriggers and stepped hydros.
• Tunnelhulls are most often associated with full-size racing boats. They get their name from the raised center section of the hull. Two outer sections (sponsons) sit in the water with a “tunnel” between them. As the boat gains speed, air builds up in this tunnel and raises the boat higher out of the water; this reduces the surface area that contacts the water. This means less drag and higher speeds, while the relatively wide spacing of the sponsons maintains stability. This design provides a good balance of speed and handling for beginners.
• Catamarans (cats) work on the same principle as tunnelhulls and differ only in shape. They have more steeply angled sponsons—much like deep-vee monos with a tunnel along the center. A cat's tunnel tends to be taller and narrower than a tunnelhull's, so it's longer to preserve stability. This, too, is a good beginner design.
• Outriggers are at the top of the performance ladder; their sponsons and main hull are separate pieces. This improves the airflow at high speeds, so outriggers are the fastest RC boats; some even run at more than 90mph! The drawback is that they're designed to work best at full throttle. At slow speeds, they sit too low in the water and don't handle well. Also, they are the least forgiving when it comes to setting the trim.
• Stepped hydroplane hulls have notches perpendicular to the centerline that divide the wetted surface into two or more sections. These notches get the boat up on step faster, and that improves performance. At speed, these notches reduce the wetted area, reducing drag. This hull type includes a diverse group, from simple deep-vees with small steps in the hull, to 3-point hydro racers such as the full-size Miss Budweiser turbine-powered, unlimited hydroplane. At full speed, 3-point hydros ride on two small areas of the forward sponsons and the centrally located propeller at the rear.
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