Apparatus For Trimming Sails

Abstract

A pressure-sensitive device is provided for aiding a sail-boat skipper in trimming a sail for maximum efficiency and speed. The device includes air-pressure sensors located on opposite sides of the sail and means for comparing the pressures so that the sail may be trimmed to provide a maximum pressure differential. In one embodiment the sensors are a pair of static tubes, each having one end operatively associated with one side of the sail and the other end in communication with a housing having a flexible diaphragm which moves in response to change in the difference in air pressure on opposite sides of the sail. The diaphragm is coupled to a dial-type indicator for indicating these changes.

Description

BACKGROUND OF THE INVENTION

This invention relates to a device for aiding a sailboat skipper in trimming his sails for maximum speed and efficiency. A laminar flow of air over the sail's curved surface creates a negative pressure on the forward or leeward side of the sail, producing a suction effect which the boat's hull in turn transforms into forward motion.

Proper trim of the main sail and other sails produces maximum efficiency and speed. Oftentimes the skill of a skipper is measured by his ability to maintain the sails trimmed so as to produce maximum speed. The skipper trims a sail by letting the sail out until it luffs and then bringing the sail back until the luff is cancelled. Luffing, efficiency and speed are related to the air foil effect achieved by the shape of the sail which is, in turn, related to the air pressures on opposite sides of the sail. Indicators are presently available for measuring boat speed relative to the water so that the sails can be trimmed to achieve maximum indicated speed; see U.S. Pat. No. 3,349,615. Indicators are also available for measuring the strain of the mast which is caused by the sail driving forces. By trimming the sail the driving force can be maximized as determined by maximizing the strain on the mast. Devices for measuring the mast strain are disclosed in U.S. Pat. No. 3,157,148.

None of these prior art devices measure or compare the air pressure on opposite sides of a sail which pressure determines the shape of the sail and its orientation, and thus its efficiency and the speed of the boat. Maximum efficiency and speed are achieved by maximizing the difference in pressure on opposite sides of a sail for any given heading.

Therefore, it is an object of this invention to provide means for sensing the air pressures on opposite sides of a sail.

It is another object to provide means associated with the air pressure sensors for indicating the difference in air pressure on opposite sides of a sail.

It is a further object to provide means for indicating when the sails have been trimmed to produce a maximum difference in the air pressures.

These and other objects of this invention will be apparent from the following description and appended claims.

SUMMARY OF THE INVENTION

By virtue of this invention there is provided means for measuring the air pressures on opposite sides of a sail and comparing and displaying these pressures. In one embodiment static tubes sense the air pressures on opposite sides of a sail and an aneroid barometer may be provided for measuring the respective pressures. In another embodiment, comparator means are provided for comparing the pressures on opposite sides of the sail and displaying the differential so that a ready determination may be made of the maximum difference.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an elevational view of a sailboat having a main sail and showing the location of one sensor forward of the sail;

FIG. 2 is a top plan view showing the location of the sensors on opposite sides of the sail;

FIG. 3 is a diagrammatic view showing a pair of aneroid-type barometers, each adapted to be coupled to one sensor;

FIG. 4 is a diagrammatic sectional view of an apparatus adapted to be coupled to both sensors to display pressure differences;

FIG. 5 is a diagrammatic sectional view showing another apparatus for displaying pressure differences in which the pressure differential causes the movement of a flexible diaphragm which is coupled to an electrical-type indicator; and

FIG. 6 is a sectional view taken along line 6--6 of FIG. 1 showing the sensors positioned on opposite sides of the sail.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawing, the sailboat 10 includes a hull 12, mast 14 and sail 16 with the wind direction as shown by arrow 18.

The air pressure sensors 20 and 22 are mounted to the sail in positions for sensing the pressure on opposite sides of the sail at approximately th center of pressure thereof. With the sail in the position as shown in FIG. 2, the sensor 20 senses the air pressure on the forward or leeward side of the sail while the sensor 22 senses the air pressure on the rearward or aft side of the sail. The sensors 20 and 22 are substantially identical hollow tubes, viz. static tubes having open sensing ends 24 and 25, respectively, which are bent downwardly so as to prevent the inflow of water. The sensing ends are positioned so as to open generally downstream with respect to the air flow over the sail and thereby substantially eliminate momentary fluctuations in pressure. The other end of each sensor extends downwardly from its position on the sail and terminates at a point near the hull 12, where it is connected to instruments as described hereinafter. The connection between the sensors and instruments may be flexible to accommodate movement of the sail, such as reefing, raising and lowering.

In a first embodiment, a pair of dial indicator aneroid barometers 26 and 28 are provided, each of which is connected to one of the sensors. For example, the barometer 26 is connected to the forward sensor 20 via tube 26a to measure the air pressure sensed thereby, while the barometer 28 is connected to the aft sensor 22 via tube 28a for measuring the air pressure sensed by it. The skipper, after determining his heading, trims the sail by adjusting it so that the readings on the barometers 26 and 28 provide a maximum difference. This maximum difference indicates that the difference in air pressure on opposite sides of the sail has been maximized so that maximum efficiency and speed have been obtained.

In an alternative embodiment, in order to provide a single instrument for the skipper to read, rather than two separate barometers, the forward sensor 20 is connected to an expansible air-tight bellows 30 via tube 30a. The bellows 30 is enclosed within and supported by an air-tight housing or pressure chamber 32 which communicates with the aft sensor 22 via tube 32a. Through a series of linkages and gears, as are well known in the art and indicated by line 34, the expansion or contraction of the bellows 30 is indicated by a mechanical pointer 36. The indicator is calibrated so that the center of the scale 38 represents zero pressure differential and the maximum pressure differentials, positive or negative, are indicated by opposite ends of the scale. When the pressure on both sides of the sail is the same, the bellows 30 is in an initial position and the indicator 36 points toward the zero setting. If, as in FIG. 2 the sensor 20 senses a low pressure and the sensor 22 senses a higher pressure, the bellows contracts. If the pressure conditions are reversed so that the sensor 20 senses a high pressure and the sensor 22 a low pressure, the bellows 30 will expand. Thus the indication provided by the pointer 36 represents the difference in pressure sensed at the sensors 20 and 22. Therefore, the skipper need only adjust his sail until he achieves the maximum difference which is indicated by the greatest swing of the pointer 36 to either side of the scale 38 from the center.

In yet another embodiment, the sensors 20 and 22 are connected to an air-tight housing 39 or enclosure which includes a flexible dividing wall or diaphragm 40 that divides the housing into a pair of air-tight chambers 42 and 44. The chamber 42 is connected to the sensor 20 via tube 42a and the chamber 44 is connected to the sensor 22 via tube 44a. The pressures within the chambers 42 and 44 are related to the pressures sensed by the sensors 20 and 22 and if the pressures are approximately equal, the flexible dividing wall or diaphragm 40 assumes a center position. However, if the pressures change so that the pressure in chamber 42 is greater than that in chamber 44, the diaphragm will move toward chamber 44, while if the pressures are reversed, the diaphragm 40 would move toward and into the chamber 42. Thus the movement of the diaphragm 40 is related to the differences in pressures in the chambers and thus the difference in pressures is sensed by the sensors 20 and 22.

Mechanical display means similar to that shown in FIG. 4 can be connected to the diaphragm so as to display the difference in pressures. Electrical means 46, generally, can also be used. The means 46 include a pair of piezoelectric crystals 48 and 50 which respond electrically to variations in the respective varying forces applied thereto and are positioned on opposite sides of the diaphragm 40 and in contact therewith. The crystals are electrically connected to a translator 52, as is well known in the art, and the translator's output then becomes the input to display means 54 which can include pointer 54a and scale 54b. Movement of the diaphragm 40 which is related to variations in the pressure conditions at the sail, causes variations in the forces applied to each of the crystals 48 and 50. This variation in forces is sensed by the translator 52. The skipper, as before, trims his sails to obtain a maximum difference as shown by the display 54.

It will be appreciated that numerous changes and modifications can be made to the embodiments shown herein without departing from the spirit and scope of this invention.

Claims

What is claimed and desired to be secured by Letters Patent of the United States is:

1. In combination with the main sail of a sail-boat the improvement which comprises a first static port means positioned on one face of the sail at substantially the center of pressure thereof, a second static port means positioned on the other opposite face of the sail, the said port means being substantially opposite one another to sense the respective static air pressures existing on both sides of the center of pressure, a device for translating the respective pressures into intelligence representing the respective air pressures, differential means responsive to said difference in air pressures and presenting the same as a measure of the trim of the sail and means providing communication between said port means and differential means.

2. The combination in accordance with claim 1 wherein the port means open downwardly to preclude entry of water.