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.

Many model boats are pre-built ready to display, while many kits are meant to sit on a shelf, not sail. None of these are useful for this Honor. Try a search for working model boat kits and radio controlled model boats.

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.

You will want to look for a RC or Radio Controlled boat.

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.

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

Thrust is the force exerted by a propeller to move a boat through the water. As the boat moves forward, it may experience lift, which is a force that will raise the boat slightly.

e. Mono hull

The body of the boat.

f. Hydro

A hydroplane (or hydro, or thunderboat) is a fast motorboat, where the hull shape is such that at speed, the weight of the boat is supported by planing forces, rather than simple buoyancy.

A key aspect of hydroplanes is that they use the water they are on for lift rather than buoyancy, as well as for propulsion and steering: when travelling at high speed water is forced downwards by the bottom of the boat's hull. The water therefore exerts an equal and opposite force upwards, lifting the vast majority of the hull out of the water. This process, happening at the surface of the water, is known as ‘planing’.

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

Planing is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydro-dynamic lift, rather than hydro-static lift (buoyancy).