17. Wind and Rain
The information in this chapter is chiefly to help guide you if the Pilot Chart has been lost from your lifeboat. it will give you some knowledge of what winds you may expect in your latitude, so that you will not be misled by a short variation from the prevailing wind.
The rainy seasons are given to guide you in the rationing of water.
If the prevailing wind is blowing in the direction of enemy territory, the section on the rigging and use of a spritsail is of vital importance to you.
PILOT CHART.--For the price, you cannot obtain more information regarding winds than from a U.S. Hydrographic office Pilot Chart. Again you are urged to provide yourself with Pilot Charts -- at 10¢ a sheet -- as insurance against the possibility of the chart in your lifeboat being lost.
To understand the information on the Pilot Chart, no knowledge of meteorology is needed. Knowing your approximate position, you will be able to find out the average velocities of
winds in your vicinity, and their directions. The trade wind boundaries are distinctly marked.
BEAUFORT SCALE.--You will need this scale in reading the wind roses on the Pilot Charts. The number of feathers on a wind-rose arrow shows the average force of the wind on the Beaufort scale.
Force Wind Velocity, miles per hour 0 Calm Less than 1 1 Light Air 1-3 2 Light Breeze 4-7 3 Gentle Breeze 8-12 4 Moderate Breeze 13-18 5 Fresh Breeze 19-24 6 Strong Wind 25-31 7 High Wind (mod. gale) 32-38 8 Gale 39-46 9 Strong Gale 47-54 10 Whole Gale 55-63 11 Storm 64-75 12 Hurricane Over 75
TRADE WINDS.--The trade winds are steady winds which blow constantly in the same direction. They are caused by differences in temperature between the polar and equatorial regions.
The trade winds blow from subtropical belts of high pressure toward equatorial belts of low pressure. These belts encircle the earth, and
range from 3 degrees N to 35 degrees N, and from the Equator to 28 degrees S. They make seasonal shifts north and south.
The heat of the equatorial region causes the air to rise. Surface currents from cool north and south latitudes flow into the equatorial region, replacing the ascending warm air.
In the North Atlantic, from 20 degrees N to 30 degrees N, south of the Azores and west of Madeira, the NE trade winds blow strongly in summer. These NE trades are especially strong near the Canaries and the Antilles, and can be felt as car north as Gibraltar.
The SE trades blow weakly in the summer months. They are strong during winter, especially along the North Brazilian Coast.
MEAN LIMITS.--The limits of the trade winds vary each quarter -- every three months.
For instance, the mean -- or average -- of the southern limit of the NE trades is 2 degrees N during the first three months of the year, 4 degrees N the second quarter, 10 degrees N the third quarter, and 6 degrees N during the last quarter.
The northern mean limit ranges from 25 degrees N to 30 degrees N, and decreases for the last half of the year.
If you lack a Pilot Chart, you can apply the above variations to the following mean limits--
to determine approximately how far the trade winds in your area, and in whatever season you are sailing, will take you.
North Atlantic Southern Belt 2° N - 10° N Northern Belt 25° N - 30° N South Atlantic Southern Belt 30° S - 25° S Northern Belt 0° - 5° N North Pacific Southern Belt 8° N - 12° N Northern Belt 25° N - 30° N South Pacific Southern Belt 30° S - 25° S Northern Belt 4° N - 8° N South Indian Southern Belt 30° S - 25° S Northern Belt 15° S - 0°
MONSOONS.--The monsoon are winds which blow over the Arabian Sea, Bay of Bengal, China Sea, and along the coasts of Asia. The NE or dry monsoon blows in winter; the SW or wet monsoon blows in summer.
DOLDRUMS.--The doldrums in equatorial belts are areas where light airs, calms, clouds, and rain prevail.
HORSE LATITUDES.--When the heated, rising currents of air of the equatorial region reach an altitude above that of the polar atmosphere,
these currents form a horizontal current which flows toward the poles, just as water flows downhill.
In the temperate latitudes this current of air cools; in the horse latitudes are some descending air currents, fine weather, light and variable winds. The equalizing of atmospheric pressure in these regions results in a calm.
That is why, in the Tropics of Cancer and Capricorn, you may come upon large ocean areas where there is no wind for days.
WESTERLIES.--Westerlies are the prevailing winds you will encounter in the high latitudes. however, you may at times encounter winds blowing north and south; but the general average in high latitudes will be Westerlies.
The high pressure belt in the south contributes strong NW to W winds over an area from 35 degrees S to 65 degrees S. These Westerlies are encountered around the Horn and the Cape of Good Hope. This area, in which storms are frequent, has been dubbed the "Roaring Forties."
In the corresponding latitudes of the North Atlantic and North Pacific, Westerlies also prevail.
SPRITSAIL.--If your are near enemy territory and find that the wind is carrying you in that direction, it is advised that you change your lug sail into a spritsail.
A sprit will allow you to point a little higher to the wind, which will enable you to tack to better advantage than is possible with a lug. However, with a sprit you will not make much speed. For a long distance use a lug sail.
A spritsail rigged from a dipping lug. A: Piece of marlin or grommet made fast around mast and through fore leech bolt rope. B: Clove hitch left open. Eyes on end of snotter fit snugly on oar handle. Two round turns can also be used. Weight of oar will prevent snotter from slipping. C: Yard removed from head. D: Pocket sewed to fit blade of oar. E: Halyard is bent on the nock.--A jib may be added for greater efficiency.
To change the lug sail to a sprit: Remove the yard. Sew a piece of canvas across the peak -- the
after top corner of the sail -- so as to form as pocket. Bend the halyard onto the nock -- the forward top corner of the sail.
Bend two or three lengths of marlin or grommets to the luff of the sail, and fit them around the mast.
With 9 or 12 thread make a snotter -- a short line with an eye splice on each end.
Make two round turns or a clove hitch around the mast with the snotter -- so that the eyes come together.
Fit the blade of your steering oar into the pocket. Put the handle of the oar through the eyes of the snotter. (See detail in drawing.)Bend the tack -- the lower forward corner of the sail -- to the mast and secure.
Haul in the slack of the sheet.
Now you have afore-and-aft sail which will allow you to tack with much more efficiency than with a lug.
RAINFALL.--In rationing your water, it is well to remember that you may have squalls all around you, without a bit of rain coming your way.
RAINY SEASONS.--The following list is given to help you in the rationing of water on a long open-boat trip. You may find yourself short of water in one of these areas, and with no sign of
water in the sky, even though the rainy season may be about to start.
Caribbean, Sea, June
Brazil, northern, January to April
Brazil, May to September
West Indies, July to October
Africa, west coast, S of equator, November to April
Africa, west coast, N of equator, May to October
Hawaiian Islands, December to April
Ecuadorean coast, December to April
South Pacific Islands, November to April
Mexico, Central America, June to October
Arabian Sea, May to September
Bay of Bengal, May to September
China Sea, May to September
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