Wednesday, April 30, 2008

Compass (Magnetic North)

The Magnetic North Pole, that the needle or card on your compass points towards, is not located at the geographic North Pole.

Depending on your location, there is almost always an angular difference between True North and the direction your compass is pointing.

This angular difference is called Variation. To find out how much variation there is in your area, look at your marine chart. There will be two (2) red circles on the chart, one inside the other. Each circle is marked in one degree increments from 000o to 359o. The 000o on the outer circle is pointing towards True North. The 000o on the inner circle is pointing toward Magnetic North.

The angular difference Variation between these two directions, for that area, is printed in degrees and minutes, either East or West, in the middle of the two circles. This is called a Compass Rose. The variation between True and Magnetic direction is equally the same for all boats operating in a given area.Each compass may, or may not, be influenced by electrical currents or electrical fields on your boat. This influence can cause additional compass error called Deviation. Most deviation can be eliminated by adjusting your compass. This was talked about in a earlier blog.

Compass North:

When you need to convert True Direction to Compass Direction or vice versa, just set up the formula this way.

True 100°
Variation 10° W
Magnetic 110°
Deviation 5° E
Compass 105°

Remember when going from True to Compass, you add West Variation and Deviation and subtract East Variation and Deviation. The opposite is true if you are going from Compass to True.

If you are having problems with your Global Positioning System (GPS) and your compass don't forget you can program them to use either True direction or Magnetic direction. If your GPS is giving you True direction, while your compass is giving the Magnetic direction you will be off course.

Also don't forget the direction the boat is traveling through the water (heading) can be different from the direction it is moving over the face of the earth, due to wind and current.

Breaking Strength of Lines

For the purpose of the USCG License exams, all lines are measured by circumference. To convert use the formula's below.

The basic breaking strength factor for manila line is found by multiplying the square of the circumference of the line by 900 lbs.

(900 lbs. X circumference2 = breaking strength)

Circumference = p PI (3.14) X diameter

Example, if you had a piece of ½" manila line and wanted to find the breaking strength, you would first calculate the circumference. (.5 X 3.14 = 1.57) Then using the formula above:

1.572 X 900 = 2,218 pounds of breaking strength

To calculate the breaking strength of synthetic lines you need to add one more factor. As mentioned above, a comparison factor has been developed to compare the breaking strength of synthetics over manila. Since synthetics are stronger than manila an additional multiplication step is added to the formula above.

(comparison factor X 900 lbs. X circumference2 = breaking strength)

Comparison chart for synthetic lines.

Line Material

Comparison Factor (greater than manila)


Using the example above, the breaking strength of ½" nylon line. First convert the diameter to circumference, then write the formula including the extra comparison factor step.

2.5 X 1.572 X 900 = 5, 546 pounds of breaking strength

Knots and splices will reduce the breaking strength of a line by as much as 50 to 60 percent. The weakest point in the line is the knot or slice, but a splice is stronger than a knot.

Tuesday, April 29, 2008

Propeller Facts

Marine propellers work by converting power produced by your boat's engine to thrust. As a propeller rotates, it draws water from ahead (the suction side) and pushes it out astern (the discharge side). It is this force that propels your boat.

Any given prop's size is described by two numbers. A propeller that is sized 20" x 24". The first number in this case, 20 represents the diameter of the propeller. Diameter is a critical dimension when converting engine horsepower to thrust.

The larger the diameter of the prop, the larger the column of water in which it's working. To calculate the correct diameter of any prop, measure the distance from the center of the propeller to the tip of one of the blades, and then multiply by two.

The second number (24 represents the pitch. Pitch is the distance the propeller moves through the water with each complete revolution. There is a certain amount of slippage between the prop and the water, so the distance actually traveled will be less than the distance.

Propellers come with 2, 3, 4 or 5 blade configurations. Having enough blade area is an important factor in transferring horsepower to thrust. Too little blade area causes high blade loading, making the prop incapable of using all the available power from the engine. This leads to cavitation, vibration and even pitting of the prop. To much blade area puts excessive load on the engine and does not allow it to produce its maximum hp.

Using a four-blade prop instead of a three-blade prop has several advantages. Your boat will accelerate and come up on plane faster, and stay on plane at lower rpm's. You experience less vibration with a four-blade prop. You will also have an increase in speed at mid-range rpm's, but there will be less speed at wide open throttle.

Cupped propellers - Have an extra curve on the trailing edge of their blades, which enables the prop to cut through water better. A properly cupped propeller should give your boat a higher top speed or allow you to go faster at the same rpm's.

The four most common materials with which propellers are made are:

Composite - Very durable and some models allow you to replace a single damaged blade instead of the entire prop. they do have more flex in them than a metal prop, so they lose some performance.

Aluminum - The most common material used in outboard and I/O installations. They are relatively easy to repair and have the lowest initial cost. They also have some flex in them with a small loss in efficiency.

Stainless Steel - These props have higher performance than composite or aluminum and have less flexing, but are more expensive to purchase and repair.

Bronze - Has high performance and good durability. These props are mostly used on inboard installations, such as ski boats, cruisers and yachts. They have a higher cost but are easy to repair.

Monday, April 28, 2008

Stability for Small Boats

As your boat sits at its mooring, two basic forces are at work. Gravity, and buoyancy, which effectively moves your boat upward to the point equal to the weight of the amount of water the boat is pushing out of the way.

The amount of each force exerted is determined by the weight of the boat. A cubic foot of fresh water weighs 62.4 lbs., while a cubic foot of salt water weighs 64 lbs. If you look at a cross-section of your boat's hull, sitting level in the water, you can imagine two theoretical points. The Center of Gravity (CG) will be in the very center of the entire hull space. The other point, the Center of Buoyancy (CB), will be in the center of underwater portion of your boat.

When the CG and the CB are vertically aligned, the boat is level. If your boat is constructed properly, and your gear is stowed correctly, the CG should always stay in the same place. The CB, however, will change position any time the boat begins to list because the amount and shape of the boat under water changes.

The Center of Gravity and the Center of Buoyancy is called the righting arm. The weight of the boat is pushing down at the CG and the weight of the water is pushing up at the CB. This situation creates a rotating force or motion that is called the righting moment.

As long as the force of buoyancy is able to return the boat to an upright position, the situation is called a positive righting moment. If for any reason, the Center of Gravity should shift outside of the Center of Buoyancy, it creates a negative righting moment and the boat is going to capsize.

The ability of any boat to right itself is called stability. It should be evident to anyone that stowing gear and installing equipment on a boat takes thought. Both should be as low in the boat as practical. It's an absolute necessity to make sure that neither can suddenly shift from one side of the boat to the other. Besides careful stowing, another rule to remember is NEVER run parallel to large waves in a boat that is overloaded or too small for the situation. As the waves cause the boat to roll from one side to side, the positions of the GC and the CB are constantly changing. Even a small change during the rolling, such as gear shifting or a passenger moving to the low side, will create a negative righting moment.

Sunday, April 27, 2008

Traditional Navigation (Currents and Swells)

Ocean swells are a crucial guide in sailing. Navigators recognize up to eight different swells, one from each octant of the compass. Dominant and most reliable are those from the north, northeast, and east, associated with the tradewind season, winter in the Northern Hemisphere. During the summer, swells come from the southeast and south.

The different swells have characteristic intervals. Navigators take advantage of opportunities to check the direction of swells against the stars. When two swell systems are moving across each other, like the converging wakes of motorboats, they make peaks where they come together. The navigator can steer by the alignment of these peaks or "wave nodes," as they are called.

Currents reveal themselves by the shape of the waves. A current flowing against the wind produces steeper waves, one flowing with the wind flatter waves. The direction and strength of a current may also be revealed by the pattern of ripples on the surface of the water. Currents make a significant difference for how a navigator adjusts his course in actual voyaging.

When setting out, the navigator lines his vessel up with landmarks on the island of departure according to whatever alignment is indicative of his particular star course. He then trims his sail to hold that course and keeps track of the angle of progress in relation to swells or "wave nodes."

When he reaches the point of "one tooth," where the island of departure is visible as only a single point on the horizon, he sights back to see how the island lies in relation to the course he is maintaining. If it is in direct alignment, no compensation for current is necessary, if it is out of alignment, he uses the degree of shift to estimate the strength of the current.

There are working rules for how to adjust one's course. For example, a navigator may adjust his course by half a compass position for each full compass position the island has shifted out of alignment.

Application of navigational lore also requires fine tuning the systems of knowledge and adapting them to local conditions.

The course directions given in "Island Looking" and other training exercises are not in fact the ones a navigator actually follows, unless he has never made the particular voyage before. They indicate where one island lies in relation to another but do not show how best to travel between them.

In practice, a navigator may begin with one star course and change to another course at some "drag" point along the way. Adjustments must also be made for currents and changing conditions as they are met. Sailing against the wind is likely to require planning a series of tacks from drag to drag.

The navigator must learn how to make all these adjustments of course for the voyages he actually expects to make. Years of sailing experience are necessary to develop skill as a navigator.

Traditional Navigation (Predicting Weather)

Weather conditions are equated with the months of a sidereal calendar. Though called "moons," these months are independent of the moon.

In most calendars there are twelve or thirteen months of unequal length, each named for a star. A month begins when its star stands about 45 degrees above the eastern horizon just before dawn, when to look at it one must tilt one's head back to the point where one feels a roll of skin forming at the back of the neck. It continues until the next month star reaches the same position.

After each month begins, one or two "fighting stars" make their first appearance above the eastern horizon just before dawn. If there is one such star in the month, it will "fight" (bring stormy weather) for five days after the next new moon first appears in the west at sunset. If there is another fighting star in the same month, it will make stormy weather in the last five days of the moon's cycle that began in that month.

What is a fighting star in one month may be the star for which a subsequent month is named, but not all fighting stars designate months. More immediate weather conditions are forecast from the color of the sky at sunrise and sunset and the shapes of the clouds.

Saturday, April 26, 2008

Estimate Distance Traveled (Western Pacific)

To estimate distance traveled and to keep track of his position during a voyage, a navigator uses what he calls "dragging" or "drags." It involves using an island other than his destination as a point of reference.

For example, on a voyage from Puluwat to Tol, in the Truk Islands, the island of Pisaras serves as reference. The course from Puluwat to Tol is almost directly east on the rising of Altair. Pisaras lies, out of sight, 120 miles (190 kilometers) northeast of Puluwat on the rising of Vega and a like distance northwest of Tol on the setting of Vega. As the voyager goes the 150 miles (245 kilometers) from Puluwat to Tol, Pisaras is "dragged" from the rising of Vega through the rising of Cassiopeia, the rising of the main star in Ursa Major, the rising of Kochab in Ursa Minor, Polaris, and on through their respective settings to the setting of Vega on arrival at Tol. Each next compass position to which Pisaras is "dragged" begins a new leg or "drag" of the journey.

The whole journey in this case is divided into eight "drags." Estimating the headway he is making, a navigator keeps track of his progress from one "drag" to another. As changing conditions affect his progress, he need adjust his reckoning only from one "drag" to the next. This way it is easier to keep overall track of progress made and expectation of landfall.

Every course between islands has an island or seamark of reference that serves to divide the journey into "drags." Ideally, the end of the first "drag," the "drag of visibility," corresponds with the point at which the island of departure ceases to be visible, and the end of the second, the "drag of birds," corresponds with the most distant point at which land-based birds feed at sea. Similarly, the next to last is the one at which land-based birds again appear, and the last one begins when the island of destination becomes visible.

Imaginary places can serve as points of reference for "dragging" as well as real ones, since real places that serve as such points are always too far away to be visible. For the trip north from the Carolines to Guam and Saipan, there are no conveniently located islands. Here "ghost islands" are used as reference.

Sailing Direction Exercises

All sailing directions are kept in relation to the sidereal compass, as are the relative locations of all places of interest, including numerous seamarks as reefs, shoals, and marine life. To memorize this large body of information the Carolinians have developed various exercises.

"Island Looking" is the name of the most important exercise. With it, navigators and their pupils endlessly rehearse their knowledge of where islands are located in relation to one another. One takes an island and then goes around the compass naming the places that lie in each direction from that island. Then one takes another island and does the same. As they sit around the boathouse in the evening, older men quiz the younger men and one another. In reciting "Island Looking," a beginner gives the name of the nearest island that lies in a given compass direction from the hub island. As he goes around the compass, if no island lies in a particular direction, he so indicates. Later, the student learns to include reefs and shoals and, finally, living seamarks, filling most of the compass directions from each focal island. The sidereal compass here shows the places named on the compass directions as one looks out from Woleai Atoll.

Another exercise, "Sea Knowing," involves learning the names of all the sealanes, called "roads," between the various islands and reefs. To speak of sailing on the "Sea of Beads" is to indicate travel between Woleai and Eauripik on the star course between "Rising of Fishtail" (in Cassiopeia) and "Setting of Two Eyes" (Shaula in Scorpio). Referring only to the names of sealanes, those in the know can tell one another where they have been traveling and leave the untutored in the dark.

The exercise called "Sea Brothers" groups sealanes that lie on the same star compass coordinates. Thus on the course from "Rising of Fishtail" to "Setting of Two Eyes" lie the several sealanes that connect the islands of Pisaras and Pulusuk, Pikelot and Satawal, West Fayu and Lamotrek, Gaferut and Woleai, and Woleai and Eauripik. A navigator may forget the sailing directions from Woleai to Eauripik but remember that the Woleai-Eauripik sealane is "brother" to the West Fayu-Lamotrek sealane. His remembering the star coordinates for the latter allows him to retrieve the forgotten coordinates for the former.

Friday, April 25, 2008

Sidereal Compass (Traditional Navigation in the Western Pacific)

After learning the compass points, a student of navigation is taught all their reciprocals. The reciprocal of the rising of Vega in the northeast, for example, is the setting of Antares in the southwest. For every reciprocal pair a student must then learn what other reciprocal pair lies at a right angle to it. A compass star on the beam can serve as a guide when the star on which one's course is set is not visible.

A feel for the angular distances from one to another of all the compass points enables a navigator to maintain his course at the appropriate angle to any visible compass star or any other visible star known to rise and set at about the same place as a compass star. To be able to use the stars this way is essential, the navigator shifting from one to another as they rise and set in the course of a night. When no stars are visible, as in daylight or in overcast at night, a navigator still orients himself with reference to the star compass. Knowing the compass direction of wind and ocean swell, he can keep track of where he is headed.

Sailing Direction - All sailing directions are kept in relation to the sidereal compass, as are the relative locations of all places of interest, including such numerous seamarks as reefs, shoals, and marine life. To memorize this large body of information the Carolinians have developed various exercises.

"Island Looking" is the name of the most important exercise. With it, navigators and their pupils rehearse their knowledge of where islands are located in relation to one another. One takes an island and then goes around the compass naming the places that lie in each direction from that island. Then one takes another island and does the same. As they sit around the boathouse in the evening, older men quiz the younger men and one another. In reciting "Island Looking," a beginner gives the name of the nearest island that lies in a given compass direction from the hub island. As he goes around the compass, if no island lies in a particular direction, he so indicates. Later, the student learns to include reefs and shoals and, finally, living seamarks, filling most of the compass directions from each island. The sidereal compass here shows the places named on the compass directions as one looks out from Woleai Atoll.

Another exercise, "Sea Knowing," involves learning the names of all the sealanes, called "roads," between the various islands and reefs. To speak of sailing on the "Sea of Beads" is to indicate travel between Woleai and Eauripik on the star course between "Rising of Fishtail" (in Cassiopeia) and "Setting of Two Eyes" (Shaula in Scorpio). Referring only to the names of sealanes, those in the know can tell one another where they have been traveling and leave the untutored in the dark.

The exercise called "Sea Brothers" groups sealanes that lie on the same star compass coordinates. Thus on the course from "Rising of Fishtail" to "Setting of Two Eyes" lie the several sealanes that connect the islands of Pisaras and Pulusuk, Pikelot and Satawal, West Fayu and Lamotrek, Gaferut and Woleai, and Woleai and Eauripik. A navigator may forget the sailing directions from Woleai to Eauripik but remember that the Woleai-Eauripik sealane is "brother" to the West Fayu-Lamotrek sealane. His remembering the star coordinates for the latter allows him to retrieve the forgotten coordinates.

Traditional Navigation in the Western Pacific

We know that all people, if raised in the appropriate environment, prove capable of learning to speak any language and to think and operate effectively in the context of any culture. But what about different people's traditional bodies of specialized lore? Are they organized in similar ways, or not? Cognitive psychologists are interested in understanding how specialists mentally process and store their knowledge so that they can retrieve it as needed.

Traditional navigators of the Central Caroline Islands provide a case in point. The Carolinian art of navigation includes a sizable body of knowledge developed to meet the needs of ocean voyaging for distances of up to several hundred miles among the tiny islands and atolls of Micronesia. Lacking writing, local navigators have had to commit to memory their knowledge of the stars, sailing directions, seamarks, and how to read the waves and clouds to determine currents and predict weather.

Before Europeans entered Micronesia, the known world of Carolinian navigators extended from Palau and Yap in the west to Ponape in the east and from Saipan and Guam in the north to Nuquoro and Kapingamarangi in the south. Their sailing directions also included places beyond this region in the west, south, and east, but these lay outside the limits of intentional voyaging and were mostly mythical rather than real places. Knowledge of such distant places met no practical need but served to show off one's learning.

Within Micronesia, the low islands of the coral atolls are where navigation and seafaring have been known and practiced. People living on the high islands of this region - Palau, Yap, Truk, Ponape, and Kosrae - did not maintain seafaring traditions and depended on the atoll dwellers for trade and ocean travel. Puluwat, Pulap, and Satawal, all west of Truk, were where Carolinian navigation was most highly developed, and where it continues to be in active use today.

Basic to the entire navigational system is the "star structure," as the navigators call it. Observed near the equator, the stars appear to rotate around the earth on a north-south axis. Some rise and set farther to the north and some farther to the south, and they do so in succession at different times.

The "star structure" divides the great circle of the horizon into 32 points where the stars (other than Polaris) for which the points are named are observed to rise and set. These 32 points form a sidereal (star) compass that provides the system of reference for organizing all directional information about winds, currents, ocean swells, and the relative positions of islands, shoals, reefs, and other seamarks. The diametrically opposite points of this compass are seen as connecting in straight lines through a central point. A navigator thinks of himself or of any place from which he is determining directions as at this central point. Whatever compass point he faces, there is a reciprocal point at his back.

Thursday, April 24, 2008

Ocean Surface Currents

Currents reflect the horizontal movement of water and tides reflect vertical movements. These currents influence the your vessel's position.
The horizontal movement is caused by the gravitational pull of celestial bodies. But there are other factors:

1. Differences in water temperatures caused by heating and cooling due to the earth's atmosphere.

2. Differences in salinity caused by rain, evaporation and estuaries.

3. Wind induced friction.

4. The Coriolis force which is a consequence of the earth's rotation.

Major oceanic surface currents include the subtropical gyres centered on 30 degrees latitude in each of the major ocean basins. The earth's rotation (origin of the Coriolis force) and the change in wind direction with latitude from the east in the tropics and from the west at mid-latitudes cause the circulation of the gyres to be clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The well-known Gulf Stream in the Atlantic and its counterpart in the Pacific, the Kuroshio Current, are strong currents that carry heat northward from the tropics. The deep oceanic currents are caused primarily by water density differences and in general return the water back towards the tropics.

To predict the behavior of major ocean currents, references are available. The Sailing Directions Planning Guides contain some information on normal locations and strengths of ocean currents. The Pilot Charts are the best reference for predicting the direction and speed of these currents. On these charts, arrows indicate the direction of the prevailing current, a number printed above the arrow indicates the average speed. Since this information is based upon averages, it won't predict the actual ocean current encountered with 100% accuracy.

Ocean surface currents need not be considered in coastal areas. Usually, when close to the continental shelf, the horizontal movement of water is defined by two terms:

1. Tidal stream or tidal current gravitational.

2. Current rivers, wind.

In order to predict tidal stream one needs to use tide tables.
Tidal streams are described by drift / rate and set, in which drift / rate is the speed and set is the direction of the current.

Boat Trailering

It is said about 70% of all boaters keep their boats on a trailer. The trailer that your boat sits on is the last thing on your maintenance list and the last thing on your mind. I have seen several rigs, boat and trailer, leave the hitch and, come to a grinding stop on the boat ramp.

Here are a few tips to keep in mind when getting ready this season.

Inspect:Inspect the frame for any signs of cracking, weld failures or loose or missing bolts. If there are signs of rust or corrosion, clean with a wire brush and paint with a primer.

Trailer Coupler: Make sure the trailer towing ball is the same size as the coupler. Also, be sure to check the locking mechanism on the coupler and lubricate it with light oil.

Winch: Unroll the winch cable or strap and inspect for any signs of fraying or other wear. If you happen to find any, replace it. Do not put your face or head anywhere near the winch handle.

Bunks and Rollers: When your boat is off the trailer, check to make sure that all bunks and rollers are in working order. Non-functional bunks or rollers can do some bad things to the bottom of your boat.

Tie-Down Straps: Remember, your winch is NOT a tie down strap You need an additional chain to hold the bow in place. Also vital to have are either transom tie downs or gunwale tie downs.

Wheel Bearings: Because trailer wheel bearings are submerged in water frequently, they are prone to failure. Be sure to repack your wheel bearings. When you stop to check your load or at a gas station, touch the wheel hub. It should be warm, but not hot. Make sure that your tires are properly inflated. Too much or too little pressure in trailer tires can cause major problems.

Lights: Check your trailer lights before leaving. Work the vehicle's turn singles and push on the break pedal to make sure that all the lights on your trailer are working. Note: Before you back down the launch ramp, disconnect the trailer lights from the tow vehicle. If you don’t do this, the thermal shock from submerging the hot lights into the colder water, will probably blow out the light bulbs.

Safety Chains: Make sure the safety chains are crossed under the coupler. If you use “S” hooks (they are not legal in some states) make sure you attach them with the open end of the hook facing toward the trailer.

Tongue Weight: Have you ever followed a vehicle towing a boat trailer that is “wagging” back and forth behind the tow vehicle? That occurs because they have too much weight behind the trailer axel (wheels) and have created negative tongue weight. The tongue weight of the trailer on the ball should be between 5–15 % of the total weight of the trailer and boat.

These are just a few tips on trailer maintenance and how to have a safe boat trailering.

The Marine Head

There are three types of marine sanitation devices (MSDs) in these days. The type you use will depend on the size of your boat, and how and where you use your boat.

    Type I MSD - A flow-through treatment system that disinfects fecal coliform bacteria to no more than 1,000 parts per 100ml and discharges no visible floating solids.
    Type II MSD - A flow-through treatment system that disinfects fecal coliform bacteria to no more than 200 parts per 100ml and discharges no more than 150mg per liter of suspended solids.
    Type III MSD - A holding tank which performs no treatment, but simply holds waste material for pump-out into a shore-based facility.

On boats under 26 feet, used basically for day trips or over-nighters, a portable head with its own built-in holding tank will probably be your best choice.

They are not, however, legal in some locations, so be sure to check the state or provincial laws where you plan to go boating.
For the owner who plans to spend considerable time cruising, or who frequently has guests aboard, a Type I or Type II treatment system may be the best choice if you are operating outside a Declared Federal No Discharge Zone. If you plan to operate inside a No Discharge Zone - the entire Great Lakes, for instance - you have no choice. The boat must be equipped with a Type III system. All sewage, whether treated or untreated, must be kept in a holding tank and emptied only at a shore-side pump-out facility. No Discharge Zones mean exactly that. Failure to comply can result in major fines and/or jail time.
Besides types of MSDs, you may also choose between a manually operated macerator/pump and an electrically operated macerator/pump. Electrically operated heads are very nice, but bear in mind that, if you lose power, you won't be able to use them.
Odor from holding tanks can be a real problem. Make sure your holding tank is properly vented. I have heard horror stories where unvented tanks have exploded on a hot day. Seriously.

Treating your holding tank with chemicals is a must! Which chemical is best? Ask ten different boaters that question and you will most likely get ten different answers. In my opinion, the chemicals that actually alter waste composition, rather than merely masking the odor with perfume, are the best choices.

One of the best ways to ruin your whole day is to spend it dismantling your marine head in order to get it unclogged. Here are some tips to prevent that from happening:

1.Periodically check all the head's hoses and clamps.

2. Use only toilet paper made specifically for use in marine heads.

3. Show and tell for new guests:

    Demonstrate the proper way to operate the head's pump.
    Ask that they use as little toilet paper as possible.
    Ask that they don't put anything down the head that hasn't first been eaten.
    Ask that, if access to shore facilities is available, they use those instead.

4. If you have a holding tank, empty it often.

Wednesday, April 23, 2008

Chart Datums

The chart datum is the level of water that charted depths displayed on nautical charts are measured from. The chart datum is generally a tidal datum; that is, a datum derived from some phase of the tide. Common chart datums are lowest astronomical tide and mean lower low water.

Depths are usually described with respect to low water reference planes yielding lower charted depths, which are safer and heights are shown with respect to high water reference planes (again, yielding lower vertical clearances on the chart, which are safer). As such, the chance that the observed depth or vertical clearance beneath a bridge is smaller than the charted depth or height is rather small.

Here are some chart datums and their abbreviations:

MHWS : Mean High Water Spring

HW : High Water

MHWN : Mean High Water Neap

ML : Mean Level

MLWN : Mean Low Water Neap

MLWS : Mean Low Water Spring

LAT : Low Astronomical Tide


Tide: The vertical rise and fall of the surface of a body of water caused primarily by the differences in gravitational attraction of the moon, and to a lesser extent the sun, upon different parts of the earth when the positions of the moon and sun change with respect to the earth.

Spring Tide: The tidal effect of the sun and the moon acting in concert twice a month, when the sun, earth and moon are all in a straight line (full moon or new moon). The range of tide is larger than average.

Neap Tide: This opposite effect occurs when the moon is at right angles to the earth-sun line (first or last quarter). The range of tide is smaller than average.

Range: The vertical difference between the high and low tide water levels during one tidal cycle.

Tidal Day: 24 hours and 50 minutes. The moon orbits the earth every month, and the earth rotates (in the same direction as the moon's orbit) on its axis once every 24 hours.

Tidal Cycle: One high tide plus a successive low tide.

Semi-diurnal Tide: The most common tidal pattern, featuring two highs and two lows each day, with minimal variation in the height of successive high or low waters.

Diurnal Tide: Only a single high and a single low during each tidal day; successive high and low waters do not vary by a great deal. Such tides occur, for example, in the Gulf of Mexico, Java Sea and in the Tonkin Gulf.

Mixed Tide: Characterized by wide variation in heights of successive high and low waters, and by longer tide cycles than those of the semidiurnal cycle. Such tides occur, for example, in the U.S. Pacific coast and many Pacific islands.

Chart Datum or Tidal reference planes: These fictitious planes are used as the sounding datum for the tidal heights.

Drying Height: Clearance in meters (or feet in old charts) above the chart datum.

Charted Depth: Clearance in meters (or feet in old charts) below the chart datum.

Observed Depth: Height of tide + charted depth: the actual depth in meters.

Height of light: The height of light above the bottom of its structure.

Elevation: The height of the light above the chart datum.

Rule of Twelve: Assuming a tidal curve to be a perfect sinusoid with a period of 12 hours. The height changes over the full range in the six hours between HW and LW with the following fractions during each respective hour: 1/12 2/12 3/12 3/12 2/12 1/12.

Rule of Seven: The change from spring range to neap range can be assumed linear, each day the range changes with 1/7th of difference between the spring and neap ranges. Hence, the daily change in range = (spring range - neap range)/7.

Master or Mate NMT 200 GT Any Waters Exam

These questions are from a Merchant Marine Examination for Master or Mate No More Than 200 Gross Tons Any Waters. Answer's are highlighted in red.

All of the deck license examination modules are randomly generated. The examination questions do not follow in the same question sequence as those found in the Deck Officer Study Guide. Therefore, you must NEVER memorize lists of answers. This technique will not produce the desired results. The U. S. Coast Guard computer system is not programmed with an answer randomization capability but many of the questions in the test bank use identical question stems and/or similar answers with the answers rearranged in a different sequence; therefore, you must NEVER memorize answers by letter identity alone. New questions and updated examination modules will be generated by the U. S. Coast Guard in order to reflect changes in national and international regulations, shipboard procedures, or evolutionary changes in the marine industry. You must always be prepared to demonstrate your proficiency and knowledge of the subject matter rather than your mastery of the rote memorization of the questions themselves.

1. When underway and proceeding ahead, as the speed increases, the pivot point tends to ?

A. move aft
B. move forward
C. move lower
D. remain stationary

2. Your radar indicates a target, however, there is no visible object at the point indicated. A large mountain, approximately 50 miles away on the same bearing as the target, is breaking the horizon. You should suspect the radar target is caused by ?

A. a submerged submarine
B. ducting
C. sub-refraction
D. ionospheric skip waves

3. Leeway is the ?

A. difference between the true course and the compass course
B. momentum of a vessel after her engines have been stopped

C. lateral movement of a vessel downwind of her intended course
D. displacement of a vessel multiplied by her speed

4. In some parts of the world there is often a slight fall in tide during the middle of the high water period. The effect is to create a longer period of stand at higher water. This special feature is called a ?

A. apogean tide
B. double high water
C. perigean tide
D. bore

5. Prevailing winds between 30N and 60N latitude are from the ?

A. east
B. west
C. north
D. south

6. You are doing a williamson turn. Your vessel has swung about 60° from the original course heading. You should ?

A. put the rudder amidships and check the swing
B. stop the engines and prepare to maneuver to pick up the man in the water
C. shift your rudder
D. increase to maximum speed

7. Under the IALA Buoyage Systems, a cardinal mark may NOT be used to ?

A. indicate that the deepest water in an area is on the named side of the mark.
B. indicate the safe side on which to pass a danger
C. draw attention to a feature in the channel such as a bend, junction, bifurcation, or end of a shoal.
D. indicate the port and starboard sides of well-defined channels

8. In waters where the cardinal system is used you would expect to find danger ?

A. lying to the south of an eastern quadrant buoy
B. lying to the south of a northern quadrant buoy
C. lying to the east of an eastern quadrant buoy
D. beneath or directly adjacent to the buoy

9. Which factor is most likely to impair the strength and durability of synthetic line ?

A. Dry rot
B. Mildew

C. Sunlight
D. Washing with mild soap

10. The velocity of a rotary tidal current will be decreased when the Moon is ?

A. at apogee
B. new
C. full
D. All of the above

11. Nylon line can be dangerous because it ?

A. breaks down when wet
B. kinks when wet

C. is not elastic
D. stretches

12. The maneuver which will return your vessel in the shortest time to a person who has fallen overboard is ?

A. engine(s) crash astern, no turn

B. a single turn with hard rudder
C. a williamson Turn
D. two 180 degree turns

13. All oil spills must be reported to the ?

A. U.S. Corps of Engineers
B. U. S. Coast Guard
C. local police
D. local fire department

14. If you must swim through an oil fire, you should NOT ?

A. wear as much clothing as possible
B. enter the water feet first
C. swim with the wind
D. cover eyes with one hand when entering the water

15. Air temperature varies with ?

A. the altitude above sea level
B. the season of the year
C. the latitude or distance from the equator

D. All of the above

16. A safe fuel system must ?

A. prevent engine overheating
B. have proper air/gasoline fuel mixture ratio

C. be liquid and vapor tight
D. supply sufficient air to the intake manifold

17. The shut off valve at the gasoline tank which can be operated from outside the tank space ?

A. controls the amount of gasoline to the engine
B. shuts off the gasollne supply at the tank
C. is used if the gasoline tank leaks
D. All of the above

18. Automatic identification systems (AIS) are expected to broadcast all of the following information EXCEPT ?

A. Port of origin
B. Name of vessel
C. Course and speed over ground
D. Draft of vessel
19. If you fail to notify the Coast Guard of an oil spill, you may be imprisoned up to ?

A. 1 year
B. 2 years

C. 3 years
D. 5 years

20. When using the rain water collection tubes on a liferaft, the first collection should be ?

A. passed around so all can drink
B. poured overboard because of salt washed off the canopy
C. saved to be used at a later time
D. used to boil food

Tidal Movements

The tide is the vertical rise and fall of the sea level surface caused primarily by the change in gravitational attraction of the moon, and to a lesser extent the sun.
As the earth spins on its axis the centrifugal force results in slightly deeper water near the equator as opposed to shallower water at the poles. In fact it causes a flow from the poles to the equator.
The earth is also in orbit around the sun (one revolution in one year) creating not only another centrifugal force but also a gravitational interaction. These two yield a bulge on the night site (centrifugal) and a bulge on the day site (gravitational) both of them moving as the world turns. Therefore certain places on this world will experience two high and two low tides each day.

With these forces alone, we would not have spring tides and neap tides. Spring tides have higher high tides and lower low tides whereas neap tides have lower high tides and higher low tides. Hence, the range (difference in water level between high and low tide) is much larger in a spring tide than in a low tide.
These differences in range can be explained if we include the moon into our earth-sun system. The moon and the earth orbit each other around a point inside the earth, creating a centrifugal and a gravitational bulge. Despite the sun's immensely larger mass, the moon exerts a 2.25 times larger gravi­tatio­nal attraction, since the moon is much closer to our earth.It is the combined effect of the sun and moon that creates spring and neap tides. When aligned with the earth they combine their attraction and otherwise they counteract their attraction.

The time difference between spring tide and neap tide is normally 7 days and is in accordance with the phases of the moon. Yet, water has mass and therefore momentum. Moreover, it is a viscous fluid that generates friction if moved. Therefore, the actual spring tide lags a day or so behind a full moon or new moon occurrence.

So, tidal movements result in a Tidal day of 24 hours and 50 minutes containing one tidal cycle, namely two highs and two lows. This basic pattern may be distorted by the effects of landmasses, constrained waterways, friction, the Coriolis effect, or other factors. Predictions are possible and we expect the the next day's high tide to come about 50 minutes later.
If you look closer at the orbit of the moon, it reveals that the moon is not always in the equatorial plane, resulting in three types of tides.

Semi-diurnal tide: Featuring two highs and two lows each day, with minimal variation in the height of successive high or low waters. This type is more likely to occur when the moon is over the equator.

Diurnal tide: Only a single high and a single low during each tidal day, successive high and low waters do not vary by a great deal. This tends to occur in certain areas when the moon is at its furthest from the equator.

Mixed tide: Characterized by wide variations in heights of successive high and low waters, and by longer tidal cycles than those of the semi-diurnal cycle. These tides also tend to occur as the moon moves furthest north or south of the equator.

Tuesday, April 22, 2008

Navigation Terms

Line Of Position (LOP): The points along which a ship's position must lie. A minimum of two LOP's are necessary to establish a fix. It is standard practice to use at least three LOP's.

Range or Distance LOP: Obtained by using a stadimeter, sextant or radar. A circle equal in radius to the measured distance is plotted about the navigation aid, the ship must be somewhere on this circle.

Running fix: A position determined by crossing lines of position obtained at different times and advanced or retired to a common time.

Dead reckoning: Determining a position by plotting courses and speeds from a known position. It is also used to predict when lights become visible or to determine the set and drift of a current. DR positions are drawn in advance to prevent sailing into danger. A DR position will be plotted:

1. Every hour on the hour

2. At the time of every course change or speed change

3. For the time at which a (running) fix is obtained, also a new course line will be plotted

4. For the time at which a single LOP is obtained

5. And never draw a new course line from an EP position

Estimated position: The most probable position of a craft determined from incomplete data or data of questionable accuracy. Such a position might be determined by applying a correction to the dead reckoning position, as for estimated current; by plotting a line of soundings; or by plotting a LOP of questionable accuracy.

Double angle on the bow: A method of obtaining a running fix by measuring the distance a vessel travels on a steady course while the relative bearing (right or left) of a fixed object doubles. The distance from the object at the time of the second bearing is equal to the run between bearings, neglecting drift.

Four point fix: A special case of doubling the angle on the bow, in which the first bearing is 45° right or left of the bow. Due to angular spread this is the most precise isosceles fix.

Special angle fix: A construction using special pairs of relative angles that give the distance travelled between bearings as equal to the navigation aids' range abeam.

Distance from horizon: The distance measured along the line of sight from a position above the surface of the earth to the visible horizon.

Sensible horizon: The circle of the celestial sphere formed by the intersection of the celestial sphere and a plane through the eye of the observer, and perpendicular to the zenith-nadir line.

Visible horizon: The line where Earth and sky appear to meet. If there were no terrestrial refraction, visible and geometrical horizons would coincide. Also called : apparent horizon.

Geometrical horizon: Originally, the celestial horizon; now more commonly the intersection of the celestial sphere and an infinite number of straight lines tangent to the earth's surface and radiating from the eye of the observer.

Dipping range or Geographic range: The maximum distance at which the curvature of the earth and terrestrial refraction permit an aid to navigation to be seen from a particular height of eye (without regard to the luminous intensity of the light).

Elevation: The height of the light above its chart datum in contrast to the height of the structure itself.

Chart Datum: Officially: Chart Sounding Datum: An arbitrary reference plane to which both heights of tides and water depths are expressed on a chart. In the same chart heights can be related to other datums than depths.

Vertical sextant angle: The method of using the subtended angle of a vertical object to find its range.

Index error: In a marine sextant the index error is primarily due to lack of parallelism of the index mirror and the horizon glass at zero reading. A positive index error is subtracted and a negative index error is added.

Estimation with horizon: Estimation of heights using the horizon: All tops crossing the horizon and with bases at sea level are on eye level.

Monday, April 21, 2008

What Recreational Boaters Should Know

Commercial vessels, including towboats and tugboats. Operate 365 days a year, 24 hours a day.

The speed of a ship, towboat, or tugboat can be deceptive. A tow can travel one mile in seven minutes,a ship even faster, and it generally takes 3/4 to 1 1/2 miles to stop. For example, if a water skier falls a thousand feet in front of a moving tug or tow, the skier has less than one minute to get out of the way.

Large vessels must maintain speed to steer, and they must stay in the channel it's the only place deep enough for them to operate. Many channels are unmarked. On some waterways, the channel extends bank to bank, so expect vessel traffic on any portion of the waterway.

A pilot's "blind spot" can extend for hundreds of feet in front of deep-draft ships, tugboats and towboats pushing barges.

In narrow canals a tug's or tow's powerful engines can cause a smaller vessel to be pulled toward the tow when passing alongside.

"Wheel Wash" is a strong underwater current caused by towboat or ship engines that can result in severe turbulence hundreds of yards behind a large vessel.

A tug without barges in front could be towing a log raft, barge, or other objects on a long submerged line behind it, which lie low in the water and are difficult to see. Never pass closely behind a tugboat.

Sailboating on inland rivers can be hazardous, and sailboaters and wind surfers should know that a tow or tug can "steal your wind", so you won't have the same Wind you started with when executing a sailing maneuver near a commercial vessel.

Operating in adverse weather or low visibility can prove extremely dangerous. Why take a chance?

Ships, towboats and tugboats use VHF radio channels 13 and 16. If you are unsure of your situation, or their intentions, feel free to contact them. Remember, you are sharing the waterways with vessels operated by highly trained and conscientious professionals. If you have a true emergency, or need information, they can and will help if properly contacted.

Avoid sailing in the commercial ship channels, especially in poor visibility. Obey Rule 9 of the ColRegs for conduct in narrow channels by keeping to the starboard side of the channel and crossing only when this does not impede the passage of a large vessel that can safely navigate only within the narrow channel.

Do not underestimate the speed of ships. If you boat is slow, allow sufficient time to take effective evasive action in the vicinity of large ships.

Be visible. At night make sure your navigation lights can be seen. If you see the navigation lights of a vessel and you think you have not been seen, get out of the way. Use torches, search lights or a spotlight on sails, or fire a white flare to indicate your position. Carry a radar reflector high on your boat. Remember, from the bridge of a loaded container ship or large tanker, the captain or pilot will lose sight of you a third of a mile ahead, although you can see the ship at all times!

Be alert. Look around every so often, especially astern.

Keep watch at night. Even on a clear night you will have difficulty seeing a big ship approach. You might see it first as a black shadow against a background of shore lights, or as a growing shadow – at that point you are not far apart. Remember that your lights will not be easily spotted from the ship.

Watch the ship’s lights. If you see both sidelights, you are dead ahead – MOVE OUT FAST. You must be sure of your position and be aware of other vessels operating around you.

Know whistle signals. Five or more short blasts on the whistle is the “Keep Clear” signal. Check and see if it is for you - and if it is - GIVE WAY. Three short blasts means “My engines are gong astern”.

Know flag signals and shapes. A large ship which displays a cylinder on her yardarm during the day or three red lights in a vertical line at night indicates that the ship is severely restricted in her manoeuvrability. Give her a wide berth.

True and Apparent Wind

A operator aboard a vessel moving through still air will experience apparent wind, which is from dead ahead and has an apparent force equal to the ship’s speed.

Note: Apparent wind, as measured from a moving vessel, is the force and the relative direction from which the wind blows.

If the actual or true wind is 0, and the speed of the ship is 10 knots, the apparent wind from dead ahead is 10 knots. If the true wind is from dead ahead at 15 knots, and the ship’s speed is 10 knots, the apparent wind is 15 + 10 = 25 knots from dead ahead. If the ship makes a 180 degree turn, the apparent wind is 15 - 10 = 5 knots from dead astern.

Wind vanes and anemometers measure only apparent wind. There is always the problem of converting apparent wind to true wind. There is more than one method of making a wind vector to find the true direction and true speed of the wind. The maneuvering board helps finding speed and direction of the true wind.

Note: You are always in the center of the maneuvering board.

Example: Your ship is on a course of 030° , speed 15 knots. The apparent wind is from 062° , speed 20 knots.
Required: Direction and speed of the true wind.


1. Draw the ship’s true course and speed line on the plotting sheet from the center of the board in the direction of the ship’s course (030° ). The length of the line equals the ship’s speed (15 knots) (use the 2:1 scale).

2. Label the center of the plotting sheet "e" for the ship’s true course, and "r" at the end of the ship’s speed line. (This line "er" is one side of the wind vector.)

3. Using parallel rules, measure the direction from which the apparent wind is blowing (062° ).

4. Move this line to the tip of the ship’s course and speed line "r".

5. Draw a line from "r" in the direction the apparent wind is blowing. The length of this line is equal to the speed of the apparent wind (20 knots).

6. Label the end of this line "w." (This line "rw" is the second side of the wind vector.)

7. Draw a line from the center of the maneuvering board "e" to point "w." (This line "ew" is the third side of the wind vector.)

8. Measure from "e" to "w" to find the true direction of the wind.

9. Measure the distance from "e" to "w" to find the true speed of the wind.

Solution: Direction of the true wind is from 109.5° ; speed of the true wind is 10.8 knots.

Note: Measure wind from the direction it is blowing.

Sunday, April 20, 2008

Departing A Pier Under Sail

After raising your sail, the boat should be on the leeward side of the pier, in irons (pointing towards the wind), and as close to the end of the pier as possible. To leave the pier you have to "back out of irons". Backing a boat is fairly simple. When you are sailing forward, a motion of the tiller in one direction will cause the bow to turn in the opposite direction. However, when going backward, hold the tiller over to the same side as you want the bow to go. While steering backward, let the sheet hang loose, keep the tiller centered until you have backed far enough so that you won't hit any other boats when you swing your boat around and go forward.

When you have backed far enough away from the pier, push the tiller over hard in the direction that you want the bow to turn and wait until the bow has turned approximately 45 degrees from the wind, center the tiller again and sheet in until the luffing of the sail stops. If the tiller is brought back properly, and the sail is trimmed properly you will be sailing. This to takes some practice, but once you get the hang of it it will beable to do this from any pier and under most conditions.
Once you do this a few times it is really impressive and you can watch everybody's mouth drop open.

Coming Into A Pier Under Sail

When approaching a pier for a landing under sail, the jib should be dropped some distance away, according to your judgement. This will slow the boat's speed but keep maneuverability. Lines and fenders should be ready to use, just as they would be for a land­ing under power.

You must have an idea of how far the boat will coast after the last sail is lowered or allowed to luff, and before the boat loses maneuverability. You can practice this in open water by heading the boat up into the wind and allowing the sails to luff, and observing how far she car­ries
her way. A lightweight, centerboard boat will stop in the water almost immediately, while a heavy keel boat travel for several boat lengths before stopping, de­pending on wind and sea conditions.

When the boat is judged to be the right distance from the dock, she is brought into the wind with the sheets freed, and sails luffing. The boat will coast in with maneu­verability. The right distance will vary with each boat, and wind and sea conditions. Ideally, the boat will lose way and come to a stop of her own accord and within reach of the pier, and lines can be put ashore and the boat secured.
If the landing looks like its going to be bad, turn away from the pier, and get away and try making another approach. This does take some practice and you need to know your boat and how it acts under different conditions.

Saturday, April 19, 2008

Sail Trim and Shape

Hoisting the sails: Before leaving the dock, you should determine the amount of sail needed. If high winds are expected, it is best to reef or decrease sail area at the dock than forced to reef while underway. The mainsail usually has between one and three reefing points that allow its size to be decreased. The jib might have roller furling (a foresail that can be rolled around the headstay) which can be used to reduce its size. If not, the size of the jib hoisted will have to be determined before setting sail.

Mainsail: If you leave the dock under power, secure the halyard to the head of the mainsail and remove the mainsail's cover. This allows rapid hoisting of the sail, if the motor dies. Make sure the boom vang and sheets are loose to allow the boom to elevate to the proper height. If hoisting a full sail, make sure the Cunningham and reefing lines are also loose. You should also adjust the outhaul before hoisting the mainsail. Once the mainsail is hoisted, loosen the boom toping lift so the mainsail can assume the proper shape and swing freely from side to side. Do not turn off your motor until after the sails are hoisted.

Jib: There many sailboats, and most charter boats, now use a roller furling system for the jib. The roller furling line is uncleated and pulling the jib's sheets the jib is unfurled. Tension should be kept on the roller furling line to keep the line from tangling as it is rolled on the drum. If the jib has to be hoisted, it is usually attached to the forestay using "hanks". The size of the jib is based upon wind conditions.

Control of the sails: The two most commonly used lines by the sailor to control the sails are the halyards and sheets. The halyard is mainly used to hoist the sails and the sheets used to control sail position in relation to the wind. Both of theses lines will also change the sail's shape. Other lines are present to adjust the sail's shape as the sail is eased out or trimmed toward midline. The angle of the sailboat in relationship to the wind is called the point-of-sail. When turning a sailboat, the boat is taken from one point-of-sail to another by adjusting the rudder and sail trim. The closer you sail to the wind, the closer the sails are pulled or trimmed to the midline of the boat. As you sail away from the wind, the sails should be let out.
Winches are used to help trim the sail and adjust lines under the force of the wind. Many winches have a self-feeding cleat on the top, which allows you to pull a line in under force without slippage. Be careful using a winch to pull in a line which should be pulled in by hand, the jib's roller furling line. If these lines are not pulled in easily, it usually means that they are caught.

Taking down the sails: Before you take down the sails the motor should be turned on. The halyard should not be removed and the sail cover should not be placed on the mainsail until the boat is at dock. If the motor fails, the sails can be quickly hoisted. There are two basic methods of taking down the mainsail, heading into the wind and heaving-to.

First method, the boat is first placed in a deep broad reach sailing almost directly away from the wind so the mainsail is shielding the jib's front sail's wind. This decreases the wind pressure on the jib and allows for easier furling. The jib is rolled in, keeping some tension on the sheets to tighten the roll and to keep the sail from flogging (strong whipping of the sail caused by the wind). Under power, the boat is then headed into the wind and the mainsail is lowered and flaked over the boom.

Second method, the boat is heaved-to and the mainsail is let out until it is luffing. In this method, the mainsail is lowered first over the boom. Since the boom is out over the water, the mainsail is taken straight down and may be flaked after the boat reaches the dock or once the mast is secured back to midline. The jib is then furled. When heading into the wind, the wind may forcefully pull the jib out. In a strong wind, the boat is placed into a deep broad reach. The sheets are loosened and the jib furled.

In heaving-to, the forward motion of the boat is slowed, the bow of the boat is turned through the wind but the jib is not released on the windward side the jib is backed. The mainsail is then eased out and the boat is now turned into the wind. Two opposing forces now exist. The jib pushes the boat away from the wind but the rudder pushes the boat into the wind. The boat comes to a near standstill, drifting slowly to leeward.


For sails to do their best, they need good a good flow of air across them. It is easy to choke your sails by trimming them too tightly, and prevent them from being all that they can be. Sails need airflow across them to create lift. Here are some things you can try the next time your out sailing.

When sailing upwind, pull in the jib and main the way you normally do. Then ease them out a bit. Remember the old saying: When in doubt, let them out.

As you sail upwind, try this:

First Ease the main Let it out until you get a nice "bubble" in the luff (up by the mast) which refuses to stay full.

Keep the bubble fairly small, though, and try to keep the area from about one foot behind the mast to the back of the mainsail full. Look at the telltales on the back of the main (pieces of yarn) and try to get them streaming straight back from the sail.

Next Ease the jib Let it get some shape at the front. Again, telltales will tell the tale, so try to get the inside ones falling down or generally lethargic (stalled) and the ones on the outside of the jib streaming back. What you are looking for is a jib with a nice rounded front and a thinning exit to the leech of the jib.

Now Drive for speed Fall off a bit. Steer slightly downwind and don't try to head as far into the wind as you know the boat will go. Give her some air, and let that increase in air move over the sails. Steer to the heel of the boat. When you are heeling more, turn upwind slightly. Turn down when the boat stands up.

If you are racing, have the crew bring in the jib, then the main, with your increasing boat speed. Then try to head closer to the wind without losing speed.

Friday, April 18, 2008

Sailboat Rigging - Lines and Spars

Mast - The main and highest spar in the center of the boat to which the jib and mainsail are attached.

Boom - The horizontal spar which extends aft (backwards) from the mast to which the foot of the mainsail sits.

Standing Rigging - Supports the mast and includes the Backstay,

Headstay, Shrouds - Shroud Lines or cables which give lateral stability to the mast.

Spreaders - Horizontal spars which spread the shrouds from the mast.

Headstay - A line or cable which supports the mast from the bow of the boat. If the line does not reach the top of the mast then it is also called a forstay.

Backstay - A line or cable which supports the mast from the stern of the boat.

Boom Topping Lift - A line which extends from the boom to the mast. Supports the boom when the mainsail is taken down.

Running Rigging - Lines which control and adjust the sails.

Halyard - A line used to raise a sail.

Sheet - The line which is used to adjust a sail against the force of the wind. The mainsail has one sheet. The jib has two, a working (leeward) sheet and a lazy (windward) sheet.

Boom Vang - A line which places downward tension on the boom.

Outhaul - Places backward tension on the clew of the mainsail. When tightened it will flatten the lower one-third of the mainsail.

Reefing Line - A line used to shorten the sail.

Winch - A device used to tighten a line.

Cleat - A metal or plastic device used to secure a line.

Mizzen - The smaller aft mast on a yawl or a ketch.

Chain Plate - A metal plate that a shroud is attached Block A device used to change a line's direction.