105.5 Correcting for Current and Leeway

Question 1

“Waypoint”

Answer 1

point on a chart with precise L&L

Question 2

“Route”

Answer 2

series of waypoints connected

Question 3

“COG”

Answer 3

Course Over Ground – actual course boat has gone from last waypoint

Question 4

“CTE” or “XTE”

Answer 4

Cross-Track Error – usually in feet then miles, left or right of desired course btw waypoints

Question 5

“SMG” or “SOG”

Answer 5

Speed Made Good or Speed Over Ground – actual speed you are making over ground through the water

Question 6

“VMG”

Answer 6

Velocity Made Good – speed directly towards next waypoint regardless of course changes

Question 7

“CTS”

Answer 7

Course to Steer – GPS determined course to arrive at next waypoint

Question 8

“Course”

Answer 8

intended direction of travel

Question 9

“CMG” or “COG”

Answer 9

“Track Made Good” or “Course Made Good” actual path of boat over the sea bottom. “Track” includes the effects of current

Question 10

Heading or “CTS”

Answer 10

direction you must steer in order to correct for current and stay on the DR line

Question 11

“Set”

Answer 11

direction TOWARD WHICH current flows. Set = 180 degrees, water is flowing toward 180 degrees.

Question 12

What is difference between “Set” and Wind Direction

Answer 12

Set is expressed as TOWARD; Wind is expressed as FROM. Set of 180 degree, wind of 360 degrees are both moving in the same direction

Question 13

“Drift”

Answer 13

Is the speed of the current

Question 14

“Leeway” is the combined influence of (not current)

Answer 14

wind and waves

Question 15

“Boat Speed”

Answer 15

is the speed of the boat through the water, and ignores current

Question 16

Boat Speed ignores what?

Answer 16

current

Question 17

SMG or SOG is actual speed boat moves over

Answer 17

the ground under the water – so takes into effect current

Question 18

Knot speed reads 6. From ahead, a 2 knot current. What’s happening?

Answer 18

4 knots of true speed or SOG

Question 19

Triangles (vector diagrams) can be used for two purposes related to currents

Answer 19

1. Determining heading to offset current

2. Determine set and direction of current that pushed you off speed

Question 20

Explain using vector / triangle diagram to determine course to take across current

Answer 20

1. Plot basic DR line
2. Vector line from departure point using DIRECTION from the set in degrees; and using LENGTH measured in MILES from the drift.
3. From tip of new vector, use calipers set to your boat speed (use miles from longitude scale for knots) to find intersection with DR line.
4. Connect those points; that is course to head
5. The distance between the departure point and the intersection point represents true boat speed

Question 21

The output of a vector / triangle diagram to determine heading to sail is a ___-____ situation.

Answer 21

one-hour. But heading and speed will be correct for entire length of trip provided current doesn’t change

Question 22

A “big” deviation between a DR position and a three-point fix would be ___ % and likely due to ____

Answer 22

15% or more; current

Question 23

Explain using vector / triangle diagram to correct course heading when off DR line

Answer 23

1. Get fix at a certain time and plot DR position for that same time
2. Line between those two gives you the SET only of the current, not drift
3. Draw line from fix back to origin point and find the 1 hour DR position. Connect a vector to the newly drawn line at same SET angle.
4. The distance of that Vector is the Set.
5. Now use other vector triangle method to get new course
   - new line to destination
   - advance the vector to current fix position
   - line from tip of vector through the one-hour point ahead
   - direction of that new line is the heading to destination
   - on the new direction line can calculate true boat speed

Question 24

Always use ___ speed when plotting a current triangle

Answer 24

Boat

Question 25

The current set and drift in a triangle represents cumulative effects of (4 things)

Answer 25

ocean currents, tidal currents, leeway and minor steering errors

Question 26

Tidal Current Tables can give you ___ and ____ at different locations. Can be used in _______ _______.

Answer 26

set and drift at different locations. Can use in triangle calculations

Question 27

River currents are affected by (two weather aspects) and can change based on channel ___, ____ and ____.

Answer 27

rainfall; melting snow/ice; depth, width, shape (curves)

Question 28

Tidal Current Tables, cruising guides and other sources of current information usually give SET of currents as a

Answer 28

TRUE direction, rather than a Magnetic. (WHAT?) So plot the set using the outer rose.

Question 29

Even in areas of no tidal, river or ocean current, you may want to adjust heading to accommodate

Answer 29

leeway

Question 30

To measure just leeway, use handheld on the ___ line, add ___ degrees, compare to boat heading get difference. To compensate, steer the boat the amount of difference ____ ____ the wind.

Answer 30

wake; 180; higher into