Boat handling (pgs 85-97) Flashcards
What are the center of buoyancy and the center of gravity?
A boat’s center of buoyancy always acts straight upward, at the center of the underwater portion of the boat (i.e. it moves from port to starboard as the boat keels). A boat’s center of gravity pulls straight down, and shifts in whatever direction weight is added. You want the center of gravity to be as low as possible.
What is listing?
If there is a change in the boat’s attitude due to an uneven distribution of weight, it has a list.
What are stiffness and tenderness?
If the center of gravity is low, a boat rights itself rapidly and is said to be stiff. If the center of gravity is high, a boat rights itself slowly and is said to be tender.
What is loll and how can you tell it from list?
Loll occurs when the center of gravity and the center of buoyancy directly counteract each other, and the boat has no righting ability. This is a dangerous situation where the boat could capsize easily. You must not mistake loll for list - moving weight to the other side of the boat might correct list, but it will make the boat more unstable in the case of loll. If the boat adopts a lean to one side for no apparent reason, and takes on a sluggish, rolling motion, suspect loll. Move weight lower in the boat.
How does loose water affect stability?
Loose water reduces a boat’s stability by moving the boat’s center of gravity from side to side as it rolls back and forth. To avoid this, try to ensure tanks are either topped up or completely empty.
How does one keep a boat stable?
Make sure water can easily drain off the deck. Try to avoid carrying equipment on deck. Know your boat’s natural rolling period, and be alert to any changes in its motion. If the boat seems less stable, reposition weight lower down. Stow heavy gear as low as possible, spread weight to the outer parts of the boat, and secure everything well.
What does the propeller do?
When the boat is put ahead, the propeller thrusts water astern causing forward motion. Right-handed propellers (most of them) causes the boat to turn slightly to port. The opposite occurs when the boat is put astern.
What does the rudder do?
The rudder steers the boat. If the rudder is turned to starboard, pressure increases on the starboard side of the rudder and decreases on its port side, turning the boat to port. When going backwards, port rudder will cause the stern of the boat to turn to port, resulting in clockwise motion.
What are the effects of pivot points, wind and tides on boat handling?
When turning, a boat pivots around a point forward of center, called the pivot point. When turning backwards, the pivot point moves well aft. In tidal flow, one can increase maneuverability at slow speeds by ‘stemming the tide’ - traveling into the tidal flow. The effects of wind depend on the interaction between the area above the waterline ahead or behind the pivot point. When not moving, a boat will tend to turn beam into the wind. When moving forward, if the area aft of the pivoting point is larger than forward, the boat will try to round up into the wind. If the area aft of the pivoting point is smaller than forward, the boat will try to pay off away from the wind. When moving backward, the boat generally tries to bring its stern into the wind.
How do you anchor a boat?
Select a good location on your chart - free of hazards, away from prohibited areas. Take into account the depth, the kind of anchor you have and protection from the weather. Approach at slow speed. Lower the anchor to the seabed until it just touches the bottom. Slowly pay out the anchor line as the boat moves to stern.
How do you check whether you’re dragging anchor?
Check whether the depth at your position has changed, and whether your position has changed relative to local landmarks.
What do you do if your anchor is fouled?
In good weather, try pulling at the anchor from different directions, and/or using your engine to apply force. In bad weather, consider cutting the anchor line and buoying it for later retrieval.
