105.8 GPS, Plotters and Radar Flashcards
When using GPS, a good margin of safety is on longitude and latitude is …
100 meters, notwithstanding most units being far more accurate than that
GPS units don’t need to run continuously (to save battery.) Instead… (four steps)
- Turn on 2. Get coordinates 3. Plot fix on chart 4. Double check 5. Turn back off.
On ocean crossing, do GPS fix every __ __ __ hours. On coastal cruising, do so every ___ ___ ___.
three or four; hour or more
GPS units, in addition to giving you your current position can also provide
speed, direction and COG/SOG
You can usually save ____ ____ _____ to your GPS unit for future use
frequently used waypoints
“Route navigation”
The process of using intermeidate waypoints to avoid certain areas or follow certain paths
What is a GPS-assisted grounding?
GPS operating along does not know where underwater danger points are, or know the skippers margin of safety, or the leeward side of a danger point
If paths are equally available on either side of an obstruction, pass it on the
leeward side
The benefit of the MOB function on a GPS is that it …….. ; however, it must be _____ very soon after the person goes overboard, and does not take into account any ________ moving the MOB.
continuously provides a course heading back to the MOB location; activated very soon; current or wind
The waypoint alarm may not sound on a GPS if you pass…
…. too far from the waypoint
Some GPS units have a waypoint _____ alarm to sound regardless of how far away
abeam
You should always double check that a GPS-generate course or route doesn’t….
…. take you close to any dangers (it just doesn’t know)
Careful of using a buoy’s specific coordinates as a waypoint because (2 reasons):
- Others may be doing the exact same thing
- You might hit it
A waypoint does not have to be a specific object, instead can merely be a
… point of specific lat and long. Double check!
1’ of latitude change is equal to ____ feet
6076
GPS plotters frequently show positions as XXX* XX.XX1’ E/W and that .001 equates to
six feet
SOG and COG – compare to knotmeter and compass reading
Latter take into consideration current and leeway affects
A waypoint log is….
a written down set of waypoints creating a route. A regularly used route can be named and saved in most GPS units
A GPS will always show you the direction and distance to your waypoint, REGARDLESS OF…. The ____-_____ Error function can show you
… how are off you are of a planned route. Could be taking you over a hazard.
Cross Track Error (CTE or XTE)
The purpose of the CTE or XTE function is to show you…
…. how far left or right of your INTENDED route you are.
Sailing on heading 050. COG is 057. Steering to 043 will keep you closer to…., but will have you travelling ….., not _____ back to it.
Instead, you must ___ ____, and steer to something like ____ to reaquire planned route. Then steer ___ to stay on that intended ____ course route.
intended route, parallel to the intended route, tracking
over-compensate, 033; 043; 050
If the boat is stopped, but GPS is indicating SOG and COG, that is a good indication of
drift and set of curret
The importance of setting a departure point in addition to first waypoint is…
… deviation of intended course or CTE can only be measured with a point of origin
GPS can help avoid danger areas by setting an ______ Cirle around it.
If entered, (what will happen?)
Avoidance Circle around it
an alarm will sound
What is the risk in setting an avoidance circle?
Must be SURE that the object at the center is not considered a waypoint destination, but instead something to AVOID. Double/triple check Avoidance Circle settings
In addition to avoidance circles, another way to avoid a danger is to set a warning…
Always build in a…
latitude (or longitude).
… safety margin
On large scale charts (so… small area shown, small number after 1:X)… one can draw additional ______ and ______ lines to provide more precision
latitude and longitude
To avoid rapid fluctations and confusion, most GPS will allow you to calculate the _____ of COG and SOG over a set period of time
average
When you read lat and lon on a GPS, be wary of ____-_____ error.
Focus on the numbers from ___ to ___, and don’t overly worry about ____ of a hundredths or thousands of a _____
over-precision error.
left to right, minute.
1 Minute equals ___ NM or ___ feet
one NM or 6076 feet
0.1 Minutes equals __ NM or __ feet
1/10 of NM, or 607.6 feet
0.01 Minutes equal __ NM or __ feet
1/100th of NM or 60.76 feet
0.001 Minutes equal __ NM or __ feet
1/1000th NM, or 6.076 feet
140 minutes = ___ degrees, ____ NM, and ___ feet
140/60 or 2 degrees 20 minutes, or 2.33 degrees, 140 NMs, and (140x6076) feet
It is important that the GPS ____ agrees with the same on the paper/electronic chart being used.
datum or horizontal datum
The most common horizontal datum is
WGS 84
“WGS 84” stands for and is…
World Geodesic System of 1984, most common lon lat datum
WGS 84, WGS 72, NAD 27, AUSTR 84, GBR 36
All examples of varying horizontal datum around the globe. Be sure GPS is set to the proper one.
Some GPS units can calculate ___ and _____, substituing for Tables __, __, __ in TCTs.
tide and current, 1, 2, 3
Radar is an abbreviation for
Radio Detection and Direction
To measure distance, most radar units have two approaches
- concentric rings of common distance
- mouse/cursor to draw a line
It is useful to compare the shape of coastal ____ on the GPS to the ____
Changing the range of the concentric rings can sometimes..
shape; chart
…bring the shapes shown into alignment
Radar units sometimes display _____ headings, which must be converted into ____ headings for use on a chart
relative; magnetic
The risk of longer ranges (say, 12 miles) on a radar is that _____ objects can be ____.
To avoid issue….
closer; missed
switch between ranges
Which is usually more accurate, a radar’s range detection or direction detection, and why?
range more accurate than direction, since the beam of radio signals sent out are not precise but have width to them.
Verify all fixes with…
soundings
A relative degree marking should include…
the letter R
When taking multiple bearings on another crossing ship, it is important to keep…
… the heading of the boat the same, otherwise successive bearings make no sense
Radar is good but not great. Why?
What can be done to improve on radar bearings, assuming visibility available?
Issued in a wide beam, so not as accurate.
Confirm with visual, handheld bearings
