18 Boater s Pocket Reference: Chapter 1 Basic Terminology

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1 18 Boater s Pocket Reference: Chapter 1 Basic Terminology Flybridge Pilothouse or Wheelhouse Mast Salon or Cabin Portuguese Bridge Bow Stern Cleat Cockpit Freeboard Transom Gunwale Hull Draft Chine Hull Rudder Propeller Shoe Keel Length at Waterline (LWL) Length Overall (LOA) FIGURE 1-1: Powerboat Side View

2 26 Boater s Pocket Reference: Chapter 1 For planing in very rough water, the deep vee was developed with a deadrise often greater than 20 degrees to allow the Deadrise Angle Chine boat to cut through the waves. The deep vee requires more power to get on plane than flatter hull designs. It tracks very well in all types of seas, so much so that it can be difficult to turn. Another development in vee shape hulls is the modified vee, which has a deadrise decreasing from forward to aft. This gives it a sharp entry for cutting through waves and a flatter stern section to aid in planing. When only one deadrise angle is specified for a modified vee, it is normally given as the deadrise at the stern. Other Hull Forms Cathedral Hull The cathedral hull is a planing hull that eliminates some of the slamming action associated with flat hulls while retaining much of the efficiency of the flat hull. This design also tracks well and provides high initial stability. Sailboat Hull The sailing monohull is characterized by a deep keel that reduces slipping sideways (leeway) from to the force of wind. It can be rounded or vee shape with a hard or soft chine. Trimaran The trimaran is usually associated with sailboats and consists of a main hull with two outriggers, one on each side, that provide high initial stability. The main hull and outriggers can be any of the three primary types of hull designs, and can be designed for displacement or planing use. The outriggers allow the use of long slim hulls, which are faster than hulls that have a wide beam.

3 Righting Arm + Boat Design and Construction 33 Catamaran Flat Bottom Powerboat Capsize Zone Degrees Heel FIGURE 1-7: Stability Curves Cruising Sailboat t Capsize Ratio or Capsize Screening Value The capsize screening value (CSV) was developed after the 1979 fastnet storm in the Irish Sea where several boats capsized and several lives were lost. Generally a boat is considered suitable for offshore use if the CSV is less than 2.0. The higher the CSV is above 2.0 the more likely a boat is to capsize in adverse conditions. Notice that this means the hull should not be too wide for a given displacement. The curve in figure 1-8 represents the CSV at 2.0. The safe area is below the curve. Boats that fall above the curve are considered unsafe for offshore use. Beam (ft) Capsize Screening Value Not Good Good CSV = Displacement ( x 1000 Lbs ) FIGURE 1-8: Capsize Screening Value = 2.0

4 36 Boater s Pocket Reference: Chapter 1 Prismatic Coefficient (CP) The CP is a ratio of the volume of water displaced by the boat to the volume of a prism like shape with a length = LWL and constant cross-section equal to the maximum cross-section of the boat (below the waterline). Solid line shows hull volume displaced Waterline Dotted line shows prismatic volume = maximum cross-sectional area times length at water line. Area of maximum cross-section FIGURE 1-9: Prismatic Coefficient To better explain this, figure 1-9 shows the two volumes used in calculating the prismatic coefficient. The numerator is represented by the solid line and indicates the volume actually displaced by the vessel. The denominator is represented by the dotted line and shows the volume of the maximum boat cross-section times the length of the boat at waterline. Equation 1-5 is used to calculate the prismatic coefficient. CP = D (Volume) MS LWL D (Lb) / 64 = MS (SqFt) LWL (Ft) = D (Kg) / 1025 MS (SqM) LWL (M) Where: CP = Prismatic Coefficient D = Displacement Volume (Seawater) MS = Midship Section = Underwater Area of the Maximum Hull Section LWL = Length at Waterline EQUATION 1-5: Prismatic Coefficient. Both the numerator and denominator are volumes and may be expressed as either imperial or metric units as long as both

5 42 Boater s Pocket Reference: Chapter 1 Relativity of Boat Sizes and Measurements As boat size changes there are certain relationships between different boat measurements that generally remain constant. These have been called by various names, such as Froude s Law of Comparison or the Law of Mechanical Similitude. Some of these are: Linear dimensions (such as beam and draft) vary proportionally to length (L). Areas will vary as the length squared (L 2 ). This includes wetted surface area and sail area. Resistance varies with wetted surface area. Speed varies as the square root of length ( L). Weight, displacement, and volume vary as length cubed (L 3 ). Corollary: Cost varies with the displacement and therefore as the length cubed (L 3 ). A boat that is twice as long as another boat will: Have twice the beam and twice the draft. Have four times the sail and wetted surface area. Travel 2 or 1.4 times faster (displacement hull speed) Displace eight times as much. Cost eight times as much! Boat Construction Hull Materials General Today most recreational boats are made from fiberglass, which in the last 50 years has all but replaced wood as the material of choice for hull construction. In addition, some recreational boats are constructed from either steel or aluminum, or a combination of both. Wood The structural properties of wood make it an ideal material for use in building boats. It is easy to work with and provides excellent strength for its weight without being too brittle (it will deform to some degree before shattering or failing). Wood construction is skilled labor intensive, so it does not easily lend itself to assembly line construction techniques. In addition, wood is susceptible to damage by water, particularly rot. These two factors have led to the demise of wood as

6 46 Boater s Pocket Reference: Chapter 1 Another similar in concept technique is the Vacuum Infusion Process (VIP). This was developed as a sufficiently different alternative to SCRIMP so users would hopefully not have to pay fees to TPI. The cloth is laid and covered with plastic, but with channels left open in foam core material so a vacuum applied at one end will draw epoxy from a drum at the other end through the channels. Over a period of hours the lay-up becomes completely saturated with the resin. The latest and most sophisticated system to be developed is the Virtual Engineered Composite (VEC ) system developed by Genmar ( This system uses an inside mold as well as the usual outside mold. The VEC system allows placement of stringers and boat floor so the entire structure is constructed as one piece in one step. The inner mold is lowered and resin is then injected under pressure rather than by vacuum. Computer control of all aspects of the process throughout the injection and curing steps, with more than 500 variables being monitored, ensures high quality and consistency from one hull to the next. The method is being used to produce boats up to 24 feet (7.3m) in length. Structural Properties of Fiberglass Let s add an additional complication to fiberglass boat construction. Fiberglass is actually quite a heavy material, with stiffness much less than aluminum on a pound for pound basis. As a result, building boat hulls from solid fiberglass, especially in larger boat sizes, yields a heavier boat, which is not conducive to a planing or semi-displacement design. In order to solve this problem and add strength to the fiberglass hull form, a lightweight core is added in between two layers of fiberglass. So now we place a layer of gelcoat, a layer of fiberglass, a relatively thick layer of lightweight material, and a layer of fiberglass. Note the deflection in the two different cases shown in figure The sandwich construction bends much less, showing greater structural rigidity and strength. FIGURE 1-13: Comparative Flexure of Solid and Cored Fiberglass By adding a lightweight core, we can considerably reduce the amount of fiberglass used and end up with the same structural strength albeit with one major caveat. The thinner

Bowrider Photo of an LXi 208 (Courtesy Larson Boats) The bowrider is an all-purpose runabout with an open bow that allows seating forward in the bow. The boat in the picture is a sterndrive model.

7 56 Boater s Pocket Reference: Chapter 1 boats with outboard or sterndrive (also called inboard/outboard or outdrive) propulsion. There are many variations of these with special designs for such diverse activities as water skiing, river running, racing, fishing, etc. Some examples of runabouts follow. Bowrider Photo of an LXi 208 (Courtesy Larson Boats) The bowrider is an all-purpose runabout with an open bow that allows seating forward in the bow. The boat in the picture is a sterndrive model. Outboards models are available as well, and jet drives have also become more popular in recent years. This type of boat can be used for skiing and fishing and is almost always made of fiberglass. This boat type with a sterndrive is the most popular model of runabout for general purpose use. Cuddy Photo of a Cabrio 220 (Courtesy Larson Boats) The cuddy style of runabout has a forward enclosed cuddy cabin. In smaller boats this would contain vee berths and in larger models can include a toilet with shower as well as a

66 Boater s Pocket Reference: Chapter 1 Pilothouse Photo of a Krogen 44 (Courtesy: Kadey-Krogen Yachts) The pilothouse design is characterized by a raised pilothouse

There may or may not be a flying bridge as shown in the above drawing.

8 66 Boater s Pocket Reference: Chapter 1 Pilothouse Photo of a Krogen 44 (Courtesy: Kadey-Krogen Yachts) The pilothouse design is characterized by a raised pilothouse separated from the salon. Typically there will be a cabin in the bow as well as a guest cabin under the pilothouse. There may or may not be a flying bridge as shown in the above drawing. The Krogen 44 shown in the picture is a full displacement hull design and is suitable for ocean passages. Sedan Photo of a 390 Trawler (Courtesy Mainship Trawlers) The sedan has the salon and cockpit on one level with the helm being located in the forward part of the salon. A second helm located on an open bridge above the main bridge,

9 Boat Design and Construction 71 Ketch Like the yawl, the ketch is two masted and has a mizzenmast shorter than the main. The mizzenmast is taller than the mizzenmast of a yawl, is located forward of the rudderpost, and has a sail with up to half the area of the mainsail. Some have gaff rigged main and/or mizzen sails and often have more than one foresail (like a cutter). Schooner A schooner has two and sometimes more masts with the aft mast being the taller mast. The schooner usually has two or more headsails.

Rapido 60. Number:

Rapido 60. Number: Rapido 60 Make: Model: 60 Length: Rapido 60 ft Price: $ 1,200,000 Year: 2015 Condition: New Location: United States Hull Material: Number of Engines: 1 Fuel Type: Composite Diesel Number: 4887218 201 Shipyard