105.7 Fog Navigation Flashcards
Single most important tool in fog navigation is your
DR plot, as its processes do not change when fog sets in
Second most important tool in fog navigation is the
depth sounder
Depth meter is also know as a
fathometer
Six things a fathometer can do in heavy fog 1 with DR plot 2 re: depth 2 re: bottom 1 re: getting a fix
- Verify DR position
- Run along a depth contour
- Find a charted object on a depth contour
- Position by bottom features
- Avoiding the depths of underwater objects
- Establishing a fix by a line of soundings by plotting on a separate piece of paper and finding its fix
A fathometer can get a “fix” by a series of soundings by ……….. but cannot be done when the bottom is …..
… recording the series distances on a separate piece of paper and then finding its fit on the chart
flat or unchanging by much
“Visual” bearings in fog can be done using a handheld compass and…
…. facing the sound you hear directly
In heavy fog and hearing a charted fog signal around you, what three elements can be used to determine position
- DR position
- Magnetic bearing of sound
- Fathometer
Two or more charted fog signals around you…
… can create a fix by intersecting their magnetic LOPs. Verify with DR position and fathometer
In preparation for one-day facing fog navigation, in clear weather one should practice…
… identifying the mag direction of charted sound (buoy bell) for hearing bearings, or sighted bearings using a handheld.
When taking a sound bearing to a charted fog signal, the boat should be kept…
… on a steady course.
In heavy fog and under power, it is wise to intermittently…
turn off the engine and listen. Every five to fifteen minutes
In heavy fog a crew member should be stationed ahead of the mast (careful of the jib) to…
… listen for sounds away from the noise of the engine or cockpit
In heavy fog, skipper should dial up ____ _____ for themselves and the crew
safety processes
In heavy fog, the sounds of shipping vessels could indicate a nearby…
shipping channel. Take a bearing compare to chart
In fog, the sounds of airplanes could indicate…
…. a flight path. Check chart for airports.
In fog, the sounds of a ferry could indicate…
…. a nearby ferry route. Take bearing and check the charts
Particularly important, so that other boats can “see” you, to raise a ….
… radar detector, if not already flying
In fog, the sound that has terrified sailors throughout the ages is the sound of
… breakers dead ahead.
In fog navigation, keeping the sound of breakers along the side of the boat is dangerous since….
… skipper will not be able to detect a slow rising in the noise over time.
The sound of breakers can be used to navigate along a coast line by…
… zigzaging into and away from the sound of the breakers (much like zig zagging along a depth contour
As with a depth contour zig zag, skipper must be sure to avoid ___________ when zig zagging on breakers
…. underwater dangers
In fog, certain non-buoy sightings through the fog can help. These include (three):
- Shipping or ferryboats
- Color of fog (green or lighted means land)
- Marine life (birds fly outbound in morning, to land in evening)
In fog, changes in wind and water patterns…
… can indicate nearby land (choppy swells from land pushing back on water; interrupted wind flows)
What is the difference between a masthead light and a masthead running light?
A masthead light is white and turned on on a sailboat when at anchor. A masthead running light is tricolor and used when sailing.
How is taking a sound bearing on another vessel similar to taking a sight bearing?
If it remains in a fixed position off of boat (say 60% off the bow) then collision is possible
If on a potential collision course with a shipping vessel, turn to the other boat’s
stern. Sail behind it (though careful as there may be another vessel behind it following same track)
A large ship’s fog signal can be heard up to ____ miles away, but as it gets closer…
… the direction of the sound can become less clear. Lesson: Begin recording bearings early.
A strong current is defined as anything over ___ knot
one
When we plot our DR position which has been corrected for current and/or leeway, it is called an…
….estimated position
Procedure to take current/leeway into effect on DR plotting….
and remember to use….
- Plot normal DR line from departure to destination
- Plot a Situation 1 triangle to get heading to sail and TRUE boat speed
- Use TRUE boat speed to plot likely EPs along the route
In estimating ETAs at points along the plotted DR it is important to use _____ boat speed, which take into consideration both ____ and ____
TRUE; current and leeway
In fog, a “safety valve” heading toward a coast should be adjusted to be even further…
… upwind
If fog sets in, ok to change intended DR plot to be less long legged to
shorter legs from buoy to buoy
When in complete doubt as to position, it is an acceptable navigation decision to…
…anchor and wait it out.
The correct signal for a boat anchored in fog is
dot dash dot in one minute intervals
What is the first thing to do when fog is threatening or when night is about to fall?
Take a DR position
As a safety valve, a general rule is to steer the boat __-_____ or __-_____ of the destination
upwind or upcurrent
When possible, you should pass rocks, reefs or dangers on their….
downwind or down-current sides (i.e., so the boat would be pushed away from them)
When in fog during the daytime, skipper should turn on…
… running lights
If under power in fog, stop and listen at
five to 20 minute intervals (shorter if in more congested areas)
When approaching a harbor with limited visibility, have the ______ ready so it can be immediately _____ to avoid being pushed _____ ______.
anchor; dropped; further aground.
Insurance records show that the three most common reasons for groundings are:
- Failure to keep track of soundings
- Failure to keep a DR plot
- Failure to follow buoys correctly.
Best to right on lon / lat minutes to the….
hundreths place so XX.XX’
I don’t agree with the printed answer to question Ch 7, 4A of 140 on page F-4.
Believe the correct answer is 148 degrees.
For the test, when answering regarding soundsing, don’t interpolate.
Write nearest sounding, if shallower water exists, write “nearby X ft”, or after sounding indicate “range X to Y”
ALWAYS in working through problems, be very careful when combining Relative Bearings
with Magnetic Bearings.
When asked to go to the “center” of a harbor, if no buoy then a point equidistant from nearest points of land.
True
Do the indicated miles of a lighthouse matter more or less than the indicate height of the light?
Matter less, as the height off the ground determines distance seen. An airplane might see the light from the designated mileage. For boat, must combine the visual distances of height of eye with height of light (assuming just coming into view on the horizon.) Square root of height x 1.15
