SEAMANSHIP CH. 6

HEAVY WEATHER

HEAVY WEATHER

The reading material for this lesson will be found in CHAPMAN; SEAMANSHIP, Boat handling under adverse conditions in the CHAPTER ON SPECIAL SEAMANSHIP TECHNIQUES

AND

Text in your student study guide.

Unless you are experienced in HEAVY WEATHER and know

exactly what you are going to do……..

The best advice for someone going out in a boat in HEAVY WEATHER is………….DON’T!

If you are caught out, or feel you have to go, this chapter has some useful pointers for you.

WIND WAVES

1. Nearly all waves are caused by the wind blowing over the surface of the water; fresh or salt

2. The longer and the stronger the wind blows, the higher the waves.

3. When the wind blows from the same direction for an extended period of time, the waves will tend to run in that same direction.

4. .NOTE: WIND directions are given as “FROM” where it is coming.

All other directions are given as “where it is going to…”

Example: Wind comes from the south. Seas will run to the north.

NON-WIND WAVES

THERE ARE TWO KINDS OF NON-WIND WAVES:

1. SEISMIC: Produced by internal shock waves below the earth’s surface. (EARTHQUAKE)

2. TIDAL: Produced by internal shock waves within the ocean floor, which are MOVING waves and attain incredible heights. (Also caused by Earthquakes)

CLASSIC or IDEAL WAVE

PARTS OF THE WAVE1. A vertical cross-section looks like a normal sine wave

2. The “crest” is the TOP of the wave.

3. The TROUGH or TROF is the bottom of the wave

4. The HEIGHT is measured from the TROF to the CREST

5. ONE “WAVELENGTH is defined as the horizontal distance from one crest to the next crest.

WAVE PARTS (CONT’D)

1. The “SLOPE” or STEEPNESS of the wave is measured from the CREST to the TROF, in a straight line.

2. Putting numbers to the wave picture allows us to talk about the significant features of the wave(s).

WAVE HEIGHT1. The greater the height, the more “unstable” it tends to

become (ready to break).

2. Large waves tend to move somewhat slower

3. Height is academic. Remember, a 5 ft. wave is almost over your head when you are standing up in the boat!

4. Wave heights are notoriously over-estimated.

5. Waves over 3 ft. become troublesome and over 5ft. become difficult for small boats and their operators to safely and properly handle.

WAVE HEIGHT WARNINGS

Wave heights of 4-6 ft. or higher usually will be warned for in a SMALL CRAFT ADVISORY (SCA) issued by the NATIONAL WEATHER SERVICE, NOAA.

WAVE VITAL STATISTICS

1. The PERIOD becomes extremely useful and important to the boater because this is the wave speed, in TIME.

2. If you know the WAVE PERIOD , it is possible to make significant heading changes or even “ come about” without seriously endangering your vessel or crew.

3. Knowing the wave period will significantly help you judge your approach speed to a dock or another vessel or to a person in the water awaiting rescue.

SURF1. Surf is caused by breaking waves which became unstable due to

the rising up of the floor of the water body.

2. Friction with the bottom causes the wave bottom to move slower than the wave top. This makes the wave “lean” into the direction of motion.

3. It doesn’t take much of a “lean” before the wave can no longer hold itself together and the top crashes ahead of the bottom.

4. This “breaking’ can occur anywhere the physics are present but the actual beach or reef is where we see it most plain.

5. On the open sea, breaking waves are common with wind speeds above 30 kts.

WAKES1. Wakes (waves) caused by another boat, can be a definite hazard

to your vessel and vice-versa!

2. BOW WAKES: The wake generated by the bow of the vessel. It tends to remain on the forward portion of the hull and care should be taken not to generate a LARGE wake here. They can be damaging to other vessels.

3. STERN WAKES: By far, the most dangerous to other vessels. Attention must be paid to the stern wakes of other vessels, especially those of meeting and passing vessels in close quarters and close to shallow water or a beach.

4. SOLUTION: REDUCE SPEED IMMEDIATELY.

BOW & STERN WAKES

EFFECT OF WIND

1. The more water you draw, the greater your hull and keel will resist the side forces of the wind and the less sideways motion you will have due to the wind pushing your boat.

2. The less hull you have in the water, the greater the effect of the wind and resulting sideways motion or LEEWAY, especially at low hull speeds.

3. The more cabin structure and “freeboard” you have, the greater the LEEWAY (side motion from the wind).

4. Sideway motion is known as “LEEWAY”( a skidding motion of the hull)

5. LEEWAY should be watched and overcome at all times, unless you count on it for maneuvering purposes.

DRAFT & LEEWAY

1. “A”, having a deeper draft has more resistance to LEEWAY (side-way motion) than “B”.

2. However, because “A” has more of the hull exposed to the water than “B”, “A” will be more adversely affected by CURRENT.

EFFECT OF CURRENT

1. Much more will be said about current in a later course.

2. Current can be effective both with the wind and against it.

3. While currents may be “wind driven” they usually are deep within the water and their effect is independent of the wind.

4. A deep-draft vessel will receive the greatest effect from the current because the current has that much more of the vessel to act on.

5. Minimizing the effect of the current requires lining the hull up WITH the direction of the current flow, much as with the effect of the wind.

6. Often times, wind and current will produce a tricky, even dangerous safety situation for steerage and special caution is required.

WIND & CABIN PROFILES

LEEWAY EFFECT

1. Vessel “A”, with it’s large superstructure of exposed hull and freeboard makes an ideal surface for the wind to “push” against and shove the hull off to one side( the LEE or downwind side).

2. Vessel “A” would be a much more difficult vessel to steer, at low hull speeds.

3. Vessel “B” has much less exposure to the wind with a much lower profile and that much less wind resistance and leeway.

4. Vessel “B” would be a much easier vessel to steer with much less leeway, at low hull speeds.

EFFECT OF WIND ON HULL PROFILES

1. In the previous slide, it is easy to visualize the reason for the increased effect of the wind on hull “A”, due to the amount of surface area the wind has to work against.

2. It is also easy to see that the low-profile open boat will have much less wind effect due to the lesser amount of surface for the wind to interact with.

3. Vessels with large profile areas such as “A”, sometimes become difficult to control in small, tight, maneuvering areas such as docking and getting in and out of a slip. Houseboats have a very large sail area.

MINIMIZING THE EFFECT OF THE WIND

1. To achieve the minimum effect of wind on the boat, it is necessary to face the bow INTO the wind.

2. The more the bow drifts away from the wind ( next slide ) the GREATER the effect of the wind on the vessel’s heading and the greater the difficulty of steerage ( maintaining a desired heading)

3. Minimizing the effect of the wind takes PRACTICE – PRACTICE – PRACTICE under variable loads, headings and hull speeds. It is a matter of “finesse”and an integral part of the “SEAMAN’S EYE”.

WIND AND YOUR BOAT

A. At the TOP: Minimum effect.

B. Moving down-scale, wind effect increases on the hull.

C. Finally, at the bottom, wind effect is at a maximum (broadside).

HEAVY WEATHER TACTICS1. When wind and seas are becoming more and more difficult to

manage, it is time to employ some different tactics.

2. Left to drift, power boats tend to face their sterns INTO the wind. This is NOT good.

3. When wind and seas are HIGH, control of the vessel’s heading may not be possible.

4. One of the best solutions to maintaining the boat’s heading in rough seas, high winds, or when adrift, is the use of a SEA ANCHOR”

THE SEA ANCHOR(DROGUE)

THE SEA ANCHOR1. A simple device which captures water and holds it or slows it’s

flow through it, thus slowing down the drift speed of the hull, when it is deployed.

2. It also helps to check the “yaw”, producing more stable headings.

3. When deployed from the bow, it is called an “anchor”.

4. When deployed from the stern, it is called a “drogue”.

5. SEA ANCHORS are extremely effective, if they have been “adapted” to your vessel’s specifications.

6. Several different types of sea anchors follows:

PARACHUTE SEA ANCHOR

SAIL TYPE SEA ANCHOR

JURY RIG SEA ANCHORS

JURY RIGS1. Jury rigging is the art of making something for a specific

purpose, out of anything you can find to do the job.

2. In a time of need, sea anchors can be fashioned ( jury rigged ) out of almost anything that you can get to suspend itself reasonably close to the surface of the water; right on top is better.

3. Anything that can reasonably capture water, thereby slowing the motion of the boat, will work.

4. The more water it can catch and hold, the more effective.

5. Usually, there are plastic buckets, tarps, sail cloth, canvas remnants, pieces of sheet plastic or similar items you can fashion a sea anchor out of, Including a hatch cover or door. Any length of rope to attach it, will work.

DEPLOYING A DROGUE FOLLOWING SEAS

DEPLOYING THE SEA ANCHOR

WHERE YOU DON’T WANT TO BE

The following two slides focus attention on two situations where you NEVER WANT TO BE:

1. The BROACH and

2. A PITCHPOLE

Good seamanship practices, a SEAMAN’S EYE and a continuing alertness and understanding of the effects of the impending weather situation on your vessel, can prevent such a situation.

LITTLE OR NO RECOVERYFROM THE BROACH

PITCHPOLINGABOUT AS BAD AS IT GETS

REVIEW QUESTIONS NO. 11. The time it takes two wave crests to pass the

same point is known as the___________

a. scan

b. second trip

c. period

d. span

REVIEW QUESTIONS NO. 2

2. The uninterrupted expanse of water over which the wind blows is called the _______

a. stretch

b. fetch

c. path

d. trof

REVIEW QUESTIONS NO. 3

3. A sea anchor___________

a. is a heavy anchor for use in open water

b. is highly effective regardless of method or skill employed in it’s use.

c. is usually cone-shaped of canvas or other cloth material and prevents excessive yawing when properly deployed.

d. is easily handled.

REVIEW QUESTIONS NO. 4

4. The angular measure from the trough to the crest of the wave is the____

a. pitch

b. slope

c. spill

d. swell

REVIEW QUESTIONS NO. 5

5. Nearly all waves are caused by______

a. cycloidal action

b. the wind blowing across the surface

c. earthquakes

d. swell over changing bottom conditions

REVIEW QUESTIONS NO. 66. If forced to operate a power boat in heavy seas, _____

a. alter course to run in the trough or the waves where the sea is calm.

b. alter course to run just ahead of the crest of a very high wave since waves are always spaced farthest apart there.

c. alter course to run broadside to wind and waves since rolling motion is more comfortable than pitching motion

d. slow speed and alter course to run into wind and waves at approximately 45 degree angles.

REVIEW QUESTIONS NO. 7

7. A “warp” is____________

a. used in place of a drogue

b. used when running abeam of the seas

c. streamed from the bow

d. usually made of heavy planking so that it

will float.

REVIEW QUESTIONS NO. 8

8. Running with high seas abeam is most likely to cause a vessel to____

a. hog

b. jibe

c. pitchpole

d. broach

REVIEW QUESTIONS NO. 9

9. Of the waves caused by boats, which is the most dangerous?

a. Bow wave

b. Beam wave

c. Mid-ship wave

d. Stern wave

REVIEW QUESTIONS NO. 10

10. When you have too much weight aft, your vessel will tend to____

a. roll

b. slew

c. yaw

d. pitch

END CHAPTER 6