SAR Chapter 5 Answers to Review Questions

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SAR
Chapter 5 Answers to Questions
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Chapter 5 - Answers to Review Questions
1. Why is the ability to tow safely an important
skill?
Because an Incident that is Non-Distress may
become a Distress   if towing assistance is not
performed safely
2. What are the two situations when towing can be
hazardous?
Very Calm Waters, or Open Ocean
3. What are the principal decisions a Coxswain
can make while on an assist mission?
Actions that effect the Safety of his Crew, or
the Crew,   Passengers or vessel needing
assistance
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Chapter 5 - Answers to Review Questions
4. Why does smooth-water instability occur?
A sway of the towed boat causes the forefoot to
become an effective rudder and the towed boat
veers off to one side
5. Why is a towed boat more stable when there is
some wind and chop?
Chop - or wind - causes the towed boat to rock
thus canceling the tendency to veer off
6. When smooth-water instability occurs how may
it be counteracted?
Use a Stability Bridle, a drogue on the towed
boat, or an along-side tie
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Chapter 5 - Answers to Review Questions
7. What are the three types of forces involved in
every towing evolution?
Acceleration, Steady, Shock
8. In a marginal situation what is the purpose of
tow planning?
To be sure the Maximum Peak Force does not exceed
1500 pounds for a large vessel or 850 pounds for
a small vessel
9. The Maximum Peak Force contains what two
components?
Steady Force and Shock Force
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Chapter 5 - Answers to Review Questions
10. What is a reasonable upper limit on tow
forces?
1500 pounds for a large vessel 850 pounds for a
small one
11. Why is stretch necessary in a towline?
The stretch reduces the instantaneous force when
the two vessels have different speeds
12. Why is stretch undesirable in a towline?
The stretch stores energy which can cause damage
if the line breaks
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Chapter 5 - Answers to Review Questions
13. What is a gravity drop?
The vertical distance the broken end of the line
drops before it reaches the other end
14. For the same diameter does 3-strand or double
braid have the greatest strength?
Double Braid
15. For the same diameter does 3-strand or double
braid have the greatest stretch?
3-strand twisted
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Chapter 5 - Answers to Review Questions
16. For the same diameter does 3-strand, or
double braid have the greatest amount of stored
energy?
3-strand twisted
17. For the same diameter does 3-strand or double
braid have the largest gravity drop?
Double Braid
18. A properly made eye splice has about what
percent of line strength?
90
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Chapter 5 - Answers to Review Questions
19. A bowline has about what percent of line
strength?
60
20. A sheet bend has about what percent of line
strength?
55
21. Why are poly lines inappropriate for large
towing loads?
Their low coefficient of friction makes cleating
very difficult
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Chapter 5 - Answers to Review Questions
22. What is the mechanism of chafe in synthetic
line?
Synthetic line rubbing against metal melts the
strands
23. What chafe point is often neglected in a
towline?
The eye splice or bowline connected to the bow of
the boat being towed
24. If a towline parts, where is the break most
likely to occur?
Boundary Corner Points Center Track Line
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Chapter 5 - Answers to Review Questions
25. What is meant by Speed-Length Ratio of One?
A speed such that the speed in knots divided by
the square root of the waterline length in feet
Is numerically ONE
26. What is the proper towing speed for boats
with the following waterline lengths? 23ft, 38ft,
44ft.
5 kn, 6 kn, 7 kn
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Chapter 5 - Answers to Review Questions
27. For an Auxiliary vessel with Maximum Cruise
of 2000 RPM with a slip of 30 making 18 knots
what is the Maximum RPM for the following Tow
Speeds?
5 knots
slightly less than 1320
6 knots
slightly more than 1320
7 knots
slightly less than 1420
8 knots
slightly more than 1420
28. The Steady Force graph assumes what
Speed/Length ratio?
ONE
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Chapter 5 - Answers to Review Questions
29. What determines the amount of the Steady
Force, provided the Speed/Length Ratio is 1?
Only the characteristics of the towed boat
30. Estimate the Steady Towing Force for the
following
15 Lw outboard
less than 50 pounds
20 Lw I/O c/c
50 pounds
35 Lw diesel c/c
240 pounds
27 Lw sailboat w/outboard
70 pounds
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Chapter 5 - Answers to Review Questions
31. What does the appearance of waves indicate to
the Coxswain?
Whether he has to deal with Swells or Wind Waves
32. In long rolling swells what is the best
technique to avoid large shock forces?
Use a very short towline
33. What is the shape of Wind Waves?
Trochoidal, or peaked
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Chapter 5 - Answers to Review Questions
34. What does the Coxswain use as a measure of
Wind Waves?
The Average Period
35. How is the average period of Wind Waves
measured?
Count the number of crests that pass in a
measured amount of time. Divide the elapsed time
in seconds by the number of crests that have
passed to get the Average Period
36. What is the standard towline length when
there are significant wind waves?
200 feet for a large vessel 100 feet for a small
one
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Chapter 5 - Answers to Review Questions
37. What is the Steady Force for the following
30 Lw Cabin Cruiser
155 pounds
32 Lw Sailboat
115 pounds
24 Lw Sailboat
50 pounds
44 Lw Cabin Cruiser
500 pounds
38. If the Standard Shock Force is 600 pounds
what is the Adjusted Shock Force if the Auxiliary
vessel is using Double Braided towline?
600 x 1.6 960 pounds
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Chapter 5 - Answers to Review Questions
39. If the Average Period is 7 seconds, what is
the Shock Force for
40 Lw Vessel 35 Lw Distress
1550 pounds
35 Lw Vessel 40 Lw Distress
1550 pounds
30 Lw Vessel 45 Lw Distress
1300 pounds
1300 pounds
45 Lw Vessel 30 Lw Distress
40. What is the Relative Wind Direction Factor if
the tow is 45º off the wind?
0.7
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Chapter 5 - Answers to Review Questions
41. What are the two characteristics of most
Auxiliary boats that makes them less than totally
satisfactory for towing?
Incorrect pitch on the props, and no tow post
ahead of the rudder and prop(s)
42. For a gasoline-engine vessel with vacuum
gauges what is the minimum reading that should be
allowed during a tow?
7 inches mercury equivalent
43. How can a twin-engine vessel with a knotmeter
be sure the engines are not overstressed during a
tow?
Tow no faster with two engines than the speed
that can be obtained with full throttle using
only one engine
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Chapter 5 - Answers to Review Questions
44. What is the maximum continuous RPM for a gas
engine?
75 of red line (or max RPM that can be achieved)
45. What is the maximum continuous torque for a
gas engine?
75 of maximum rated torque
46. What is the maximum continuous RPM for a
diesel engine with a yacht rating?
90 of the maximum RPM that can be achieved with
full throttle
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Chapter 5 - Answers to Review Questions
47. When is a bridle on the towing vessel
desirable or necessary?
When directional control is difficult without a
bridle
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Chapter 5 - Answers to Review Questions
48. Using the Seascape Tow Planning Worksheet,
what is the Maximum Peak Force for the following
towed vessels with the corresponding sea
conditions, using 200 ft towline? Vessel
wave period towline
15 Lw outboard 5.0 sec
3-strand
Steady lt 50 lbs Shock 450 lbs Max lt 500
lbs
20 Lw c/c
5.6 sec Double Braid
Steady 50 lbs Shock 600 X 1.6 960 Max
1010 lbs
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Chapter 5 - Answers to Review Questions
48. Using the Seascape Tow Planning Worksheet,
what is the Maximum Peak Force for the following
towed vessels with the corresponding sea
conditions, using 200 ft towline? Vessel
wave period towline
35 Lw diesel c/c 4.3
sec Double Braid
Steady 245 lbs Shock 250 X 1.6 400 Max 645
lbs
27 Lw sailboat 7.1 sec
3-Strand
Steady 70 lbs Shock 950 lbs Max
1020 lbs
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Chapter 5 - Answers to Review Questions
49. When should the skipper do formal Tow
Planning?
When the wind and sea state indicate that the tow
safety might be marginal
50. Why is an Auxiliary vessel engine(s)
certainly overloaded if the skipper tows at 75
of redline RPM?
The tow is a load that the boat designer did not
contemplate and thus the 75 of maximum rated
torque is reached before the 75 redline RPM is
reached
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End Of
Chapter 5 Answers to Questions