AY Honors/Model Boats/Answer Key
1. Do two of the following:
a. Purchase and build one kit for a sailboat 10 to 15 inches (25.4 to 38.1 cm) long and about four to five inches wide and operate boat on the water for at least two minutes.
b. Build a model boat with an electric motor from your own plans or from a kit, size 10 to 18 inches, (25.4 to 45.7 cm) and operate the boat for three to five minutes.
c. Build a model boat 18 to 30 inches (45.7 to 76.2 cm) long from your own plans or from a kit. Install a small bore internal combustion engine .029 or .049 and operate for at least two successful runs of three to five minutes each. Record in writing the operating characteristics of the model and state what you did to improve its performance.
2. Identify and define these words:
a. Displacement
Displacement is the volume of water a boat's hull moves out of the way when it floats. The displaced water is the same weight as the boat as long as the boat is floating. If the boat sinks then the amount of water being displaced is equal to the volume of the boat instead of the weight.
b. Center of gravity
c. Propeller pitch
Propeller pitch is the distance a propeller would move in one revolution if it were moving through a soft solid, like a screw through wood. For example, a 21-pitch propeller would move forward 21 inches in one revolution.
d. Thrust and lift
is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system.
e. Mono hull
The body of the boat.
f. Hydro
something similar to a speed boat. (hydroboat)
g. Bow
The front of the boat.
h. Keel
has two distinct meanings related to two different types of boats: one a riverine cargo-capable working boat, and the other a classification for small- to mid-sized recreational sailing yachts.
i. Transom
The wide, usually flat area at the very back of a boat. This is where an outboard motor is typically mounted. This is also where you usually find the name of the boat on larger vessels.
j. Cavitation
Inefficient low-pressure pockets on propellers form bubbles that collapse against the blades resulting in premature wear. Cavitation causes vibration, noise and serious damage to a propeller.
k. Heeling
Heeling is normal, sideways tipping. Heeling is a result of the force of wind on the sails. Some heeling is inherent in sailing; as the force of the wind is transferred into forward motion, any excess is transferred into sideways motion, some of which is slippage and some of which is heeling. A boat that has too much sail set so that it heels over beyond a certain angle will sail less efficiently.
When a boat is heeled, the center of effort changes. The center of effort is the pivot point of the sails and is related to the center of lateral resistance, which is below the waterline. One way to reduce heeling is to move the center of lateral resistance upwards by raising the centerboard or daggerboard. The boat will have less resistance below the waterline and consequently less heel.
l. Planing
is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift (buoyancy).
