Title:
SELF RIGHTING VESSEL
United States Patent 3585952
Abstract:
A self-righting vessel is provided in which flotation means, which may comprise the sail of a sailing vessel, is so positioned and proportioned to the vessel that no matter what position the vessel assumes as the result, for example, of winds or waves, the vessel will right itself.
US Patent References:
Boat construction
Kinte - September 1938 - 2131627
Airborne lifeboat
McCarthy et al. - August 1954 - 2686323
Boat construction
Kinte - September 1938 - 2131627
Airborne lifeboat
McCarthy et al. - August 1954 - 2686323
Application Number:
04/794588
Publication Date:
06/22/1971
Filing Date:
01/28/1969
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
114/122, 114/39.290, 114/39.250
International Classes:
B63B22/18; B63B22/00; B63B43/02; B63H9/00
Field of Search:
114/121,122,39 9/3
Primary Examiner:
Blix, Trygve M.
Claims:
I claim
1. A vessel capable of righting itself in the water including a hull of raftlike porportions having a deck and a bottom, said vessel having its center of gravity located in a predetermined region,
2. The invention as expressed in claim 1 in which said float is rigid and is shaped to act as a sail.
3. The invention as expressed in claim 1 in which said float comprises a curved elongated member of streamlined cross section.
4. The invention as expressed in claim 1 in which said float comprises at least two curved elongated members each having streamlined cross sections, the concave sides of said members facing each other.
5. The invention as expressed in claim 1 wherein the buoyancy of said hull and said float and the weight of said counterweight are proportioned such that said center of gravity is beyond the instant center of buoyancy in a direction away from said float for substantially all positions of said vessel in the water.
1. A vessel capable of righting itself in the water including a hull of raftlike porportions having a deck and a bottom, said vessel having its center of gravity located in a predetermined region,
2. The invention as expressed in claim 1 in which said float is rigid and is shaped to act as a sail.
3. The invention as expressed in claim 1 in which said float comprises a curved elongated member of streamlined cross section.
4. The invention as expressed in claim 1 in which said float comprises at least two curved elongated members each having streamlined cross sections, the concave sides of said members facing each other.
5. The invention as expressed in claim 1 wherein the buoyancy of said hull and said float and the weight of said counterweight are proportioned such that said center of gravity is beyond the instant center of buoyancy in a direction away from said float for substantially all positions of said vessel in the water.
Description:
BACKGROUND
This invention relates to self righting vessels.
All vessels experience tilting moments due to the effect of wind or waves thereon. These tilting moments are particularly a problem in the case of sailing vessels, since the sail, which is above the surface of the water in which the vessel is floating must be designed to catch the wind to provide propulsion to the vessel. The tilting moment may be in almost any direction with respect to the direction of travel of the vessel. The stability of the vessel is improved in a known manner by using a counterweight below the hull of the vessel and by shaping the hull so that the center of buoyancy (the center of gravity of the displaced water) is horizontally displaced very rapidly as the vessel tilts slightly. The center of gravity of the vessel and the center of buoyancy now act together as a couple to right the vessel. With practical hull design, the stability of the vessel is limited to a relatively small tilt angle. Beyond a certain angle of tilt, the gravitational force acting through the center of gravity of the tilted vessel and the buoyancy force acting through the center of gravity of the displaced water would comprise a couple that actually causes capsizing of the vessel. The vessel can float even though it is overturned if it is provided with airtight spaces therein. However, when an unmanned vessel such as a meteorological instrument platform is overturned, its usefulness is substantially destroyed even though it may still float.
It is an object of this invention to provide a vessel which will right itself no matter how far the vessel has been tilted.
SUMMARY
In accordance with the invention a float or buoyancy member is fixed to the deck of a vessel whereby the bloat is normally out of the water, and preferably a counterweight is fixed to the bottom of the vessel. The flotation, provided by the buoyancy member and by the hull of the vessel, and the gravity force provided by the loaded vessel and the counterweight are so located and proportioned that the vessel will right itself no matter how far it is tilted. If the vessel is a sailing vessel, the buoyancy member and the sails of the vessel may be advantageously combined. For small degrees of tilt, as in normal operation, known stability producing means, such as a hull which provides great shift of the center of buoyancy with small tilt of the vessel is made use of.
DESCRIPTION
The invention may be better understood upon reading the following description in connection with the accompanying drawing in which:
FIG. 1 is a front elevation of a vessel built to include an embodiment of this invention,
FIG. 2 is a cross section of FIG. 1 on line 2-2 thereof,
FIGS. 3 and 5 are diagrammatic showings which are useful in explaining the operation of the vessel of FIG. 1, and
FIG. 4 is a graph whose curves are useful in explaining the operation of the vessel of FIG. 1.
Turning first to FIG. 3, a sailing vessel including conventional stabilization is illustrated, having a raftlike hull 10 including a compartment 20 providing airtight buoyancy spaces between a deck 14 and a bottom 18 and having a mast 12 extending upwardly from the deck 14 of the hull 10. A conventional sail 13 is shown hung from the mast 12. A combined fin and rudder member 16 extends downwardly from the bottom 18 of the hull 10. A counterweight 23 may be fixed to the bottom of the member 16. The hull 10 may have hollow portions (not shown) in addition to the compartment 20 for containing the payload. The compartment 20 may (if the vessel is an unmanned remotely controlled vessel) also contain radio responsive means (not shown) to change the sail and rudder positions so as to maintain the vessel on a desired course.
When the vessel of FIG. 3 is in a vertical position, the buoyancy force upwardly through the center of buoyancy CB of the displaced water and the gravity force acting downwardly through the center of gravity CG of the vessel are in the same vertical line and there is no tendency for the vessel to tilt. As shown in FIG. 4, curve 22, at zero tilt angle there is no righting moment; however, none is needed.
When the vessel is tilted a small amount to the right as viewed in FIG. 3 for example, due to the raftlike configuration of the hull 10 of the vessel, the quantity of water displaced on the right by the hull 10 is greater than the quantity displaced on the left by the hull 10 and the center of buoyancy shifts to the new position C'B'. The upward force due to this new center of buoyancy C'B' and the downward force due to the position of the center of gravity CG comprise a couple which produces a righting moment such as that exhibited by the part of curve 22 that is above the zero line in FIG. 4. As the tilt becomes grater, the righting moment is at first proportional to the tilt angle. This is due to the fact that as the vessel tilts through small angles the center of buoyancy of the displaced water goes horizontally away from the center of buoyancy of the untilted vessel. For small angles of tilt, the vertical line through the instant center of buoyancy C'B' and the tilted line through the center of gravity and also through the center of the vessel meet at a point M called the metacenter. As long as the center of gravity of the vessel is well below the metacenter, the vessel is stable for small tilt angles whether the position of the center of buoyancy (the center of gravity of the displaced water) is somewhat higher or lower than the center of gravity. However, as the tilt becomes greater the righting moment reaches a maximum and then decreases to zero as the center of buoyancy of the displaced water comes back in a horizontal direction. A point is soon reached, often at a tilt angle substantially less than 90° when the force provided by the instant center of buoyancy and the force of gravity acting through the center of gravity of the vessel comprise a couple which is in a direction to tip the vessel further, as shown by the part of the curve 22 of FIG. 4 that is below the zero line. It is noted that the curve 22, while it reaches zero again at about 180°, is never positive again, whereby once a vessel such as that of FIG. 3 has capsized it will never right itself. By providing a heavier counterweight such as 23 of FIG. 3, the vessel may be made to right itself from somewhat large angles of tilt as shown by the dotted line 26 in FIG. 4. However, the vessel even so counterweighted will, for sufficiently large angles of tilt exhibit a negative righting or a capsize moment, as shown by the portion of the curve 26 that is below the zero line, and this vessel will never right itself.
FIG. 1 illustrates a vessel which does not exhibit a negative or capsize moment at any angle of tilt. The hull 10 including the compartment 20, having the deck 14, the bottom 18, the combined fin and rudder member 16, and the counterweight 23 are the same in FIGS. 1 and 3. In FIG. 1, a pedestal 28 which may be rotatable with respect to the hull 10, is provided which extends upwardly from the deck 14. The center point of a bracket 30 is fixed to the top of the pedestal 28. The ends of the bracket 30 are bent to fit the lower ends of the floats or buoyancy members 32, 32 which are constructed to be rigid. The upper ends of the floats 32, 32 are fixed together by another bracket 34. The floats 32, 32 are similarly curved bodies whose concave sides face each other. Since in the disclosed embodiment, the floats 32, 32 act as sails, they are given cross sections such as that shown in FIG. 2, that is, the sections of the float are streamlined, having rounded front ends and sharp rear edges and being symmetrical about centerlines passing through the sharp rear edges. Also, since the floats 32, 32 act as sails, rotation of the pedestal 28 causes rotation of the sails comprising the floats 32, 32 without changing their relative configuration, with respect to the hull 10. This rotation may be accomplished either by hand or by a motor (not shown) in the compartment 20 connected to the pedestal 28 by gears or the like which are also not shown. When the vessel of FIG. 1 is tilted, its righting moment goes up and down as shown by the curve 36 of FIG. 4. This righting moment never becomes negative because the upward force due to the buoyancy provided by combination of the hull 10 and the floats 32, 32 when they are immersed in water combines with the downward force of gravity through the center of gravity of the vessel to produce only righting moments, at any tilt angle whatever. As shown at the point corresponding to 180° of the curve 36 of FIG. 4, the righting moment is zero. That is, if the vessel is tilted exactly 180° it could conceivably, in absolutely motionless water and atmosphere float in this position and will not right itself. However, the buoyancy of the floats 32, 32 is more than sufficient to support the entire vessel, therefore, the slightest tilt away from 180° will result in the vessel righting itself. The curve 38 results when the counterweight 23 is made smaller. It is seen that with a lesser counterweight 23 the vessel may still be self-righting. However, if the weight 23 is too small the righting motion may drop to zero or even become negative at tilt angles near 90°. Therefore, the weight 23 must be properly chosen.
It is also possible for the vessel, if of inadequate weight, to be stable in a position where it lies in the water at a tilt angle somewhat greater than 90°, the float 32 being in contact with the water and the weight 23 being out of the water, as shown in FIG. 5. This is due to too great buoyancy of the hull 10 in comparison with the vessel weight. Care must be taken that the buoyancy of the hull be such that when one or both floats 32, 32 are just touching the water that the center of gravity CG of the vessel is beyond the instant center of buoyancy CB in a direction away from the float 32, to avoid this undesired stable position of the vessel. If the hull 10 has less buoyancy it would be deeper in the water in FIG. 5 and the instant center of buoyancy would move to the right as viewed in FIG. 5 whereby the center of gravity would be to the left (instead of to the right) of the instant center of buoyancy, and the forces produced by the weight acting through the center of gravity and the floating action acting through the center of buoyancy would right the vessel. It has been found that the total weight of the loaded vessel should be close to, but not less than, half the total buoyancy that the vessel would provide were it submerged to the deck line. Ballast should be added when necessary to provide this weight.
A self righting vessel such as disclosed in FIG. 1 may have dimensions in accordance with the following table.
Circular hull diameter 9.0 feet
Nominal payload 1000 pounds
Nominal displacement 1800 pounds
Total hull buoyancy below deck 3600 pounds
Height of sail bottom above deck 2 feet
Height of deck above waterline 0.4 feet
Depth of fin bottom below deck 5.4 feet
Depth of center of gravity below deck 1.2 feet
Sail height above mast 8.5 feet
Combined span of two airfoils 18.9 feet
Radius of curved span 6.0 feet
Airfoil chord 3.0 feet
Airfoil thickness 0.90 feet
Calculated sail displacement 2250 pounds
To avoid stability of the vessel in the position shown in FIG. 5, the vessel having these dimensions should have the nominal weight of approximately 1800 pounds. If the vessel with payload does not weigh 1800 pounds it should be ballasted to this weight. Larger weight will require a larger vessel for other dimensions of the vessel, corresponding weights will be evident.
This invention relates to self righting vessels.
All vessels experience tilting moments due to the effect of wind or waves thereon. These tilting moments are particularly a problem in the case of sailing vessels, since the sail, which is above the surface of the water in which the vessel is floating must be designed to catch the wind to provide propulsion to the vessel. The tilting moment may be in almost any direction with respect to the direction of travel of the vessel. The stability of the vessel is improved in a known manner by using a counterweight below the hull of the vessel and by shaping the hull so that the center of buoyancy (the center of gravity of the displaced water) is horizontally displaced very rapidly as the vessel tilts slightly. The center of gravity of the vessel and the center of buoyancy now act together as a couple to right the vessel. With practical hull design, the stability of the vessel is limited to a relatively small tilt angle. Beyond a certain angle of tilt, the gravitational force acting through the center of gravity of the tilted vessel and the buoyancy force acting through the center of gravity of the displaced water would comprise a couple that actually causes capsizing of the vessel. The vessel can float even though it is overturned if it is provided with airtight spaces therein. However, when an unmanned vessel such as a meteorological instrument platform is overturned, its usefulness is substantially destroyed even though it may still float.
It is an object of this invention to provide a vessel which will right itself no matter how far the vessel has been tilted.
SUMMARY
In accordance with the invention a float or buoyancy member is fixed to the deck of a vessel whereby the bloat is normally out of the water, and preferably a counterweight is fixed to the bottom of the vessel. The flotation, provided by the buoyancy member and by the hull of the vessel, and the gravity force provided by the loaded vessel and the counterweight are so located and proportioned that the vessel will right itself no matter how far it is tilted. If the vessel is a sailing vessel, the buoyancy member and the sails of the vessel may be advantageously combined. For small degrees of tilt, as in normal operation, known stability producing means, such as a hull which provides great shift of the center of buoyancy with small tilt of the vessel is made use of.
DESCRIPTION
The invention may be better understood upon reading the following description in connection with the accompanying drawing in which:
FIG. 1 is a front elevation of a vessel built to include an embodiment of this invention,
FIG. 2 is a cross section of FIG. 1 on line 2-2 thereof,
FIGS. 3 and 5 are diagrammatic showings which are useful in explaining the operation of the vessel of FIG. 1, and
FIG. 4 is a graph whose curves are useful in explaining the operation of the vessel of FIG. 1.
Turning first to FIG. 3, a sailing vessel including conventional stabilization is illustrated, having a raftlike hull 10 including a compartment 20 providing airtight buoyancy spaces between a deck 14 and a bottom 18 and having a mast 12 extending upwardly from the deck 14 of the hull 10. A conventional sail 13 is shown hung from the mast 12. A combined fin and rudder member 16 extends downwardly from the bottom 18 of the hull 10. A counterweight 23 may be fixed to the bottom of the member 16. The hull 10 may have hollow portions (not shown) in addition to the compartment 20 for containing the payload. The compartment 20 may (if the vessel is an unmanned remotely controlled vessel) also contain radio responsive means (not shown) to change the sail and rudder positions so as to maintain the vessel on a desired course.
When the vessel of FIG. 3 is in a vertical position, the buoyancy force upwardly through the center of buoyancy CB of the displaced water and the gravity force acting downwardly through the center of gravity CG of the vessel are in the same vertical line and there is no tendency for the vessel to tilt. As shown in FIG. 4, curve 22, at zero tilt angle there is no righting moment; however, none is needed.
When the vessel is tilted a small amount to the right as viewed in FIG. 3 for example, due to the raftlike configuration of the hull 10 of the vessel, the quantity of water displaced on the right by the hull 10 is greater than the quantity displaced on the left by the hull 10 and the center of buoyancy shifts to the new position C'B'. The upward force due to this new center of buoyancy C'B' and the downward force due to the position of the center of gravity CG comprise a couple which produces a righting moment such as that exhibited by the part of curve 22 that is above the zero line in FIG. 4. As the tilt becomes grater, the righting moment is at first proportional to the tilt angle. This is due to the fact that as the vessel tilts through small angles the center of buoyancy of the displaced water goes horizontally away from the center of buoyancy of the untilted vessel. For small angles of tilt, the vertical line through the instant center of buoyancy C'B' and the tilted line through the center of gravity and also through the center of the vessel meet at a point M called the metacenter. As long as the center of gravity of the vessel is well below the metacenter, the vessel is stable for small tilt angles whether the position of the center of buoyancy (the center of gravity of the displaced water) is somewhat higher or lower than the center of gravity. However, as the tilt becomes greater the righting moment reaches a maximum and then decreases to zero as the center of buoyancy of the displaced water comes back in a horizontal direction. A point is soon reached, often at a tilt angle substantially less than 90° when the force provided by the instant center of buoyancy and the force of gravity acting through the center of gravity of the vessel comprise a couple which is in a direction to tip the vessel further, as shown by the part of the curve 22 of FIG. 4 that is below the zero line. It is noted that the curve 22, while it reaches zero again at about 180°, is never positive again, whereby once a vessel such as that of FIG. 3 has capsized it will never right itself. By providing a heavier counterweight such as 23 of FIG. 3, the vessel may be made to right itself from somewhat large angles of tilt as shown by the dotted line 26 in FIG. 4. However, the vessel even so counterweighted will, for sufficiently large angles of tilt exhibit a negative righting or a capsize moment, as shown by the portion of the curve 26 that is below the zero line, and this vessel will never right itself.
FIG. 1 illustrates a vessel which does not exhibit a negative or capsize moment at any angle of tilt. The hull 10 including the compartment 20, having the deck 14, the bottom 18, the combined fin and rudder member 16, and the counterweight 23 are the same in FIGS. 1 and 3. In FIG. 1, a pedestal 28 which may be rotatable with respect to the hull 10, is provided which extends upwardly from the deck 14. The center point of a bracket 30 is fixed to the top of the pedestal 28. The ends of the bracket 30 are bent to fit the lower ends of the floats or buoyancy members 32, 32 which are constructed to be rigid. The upper ends of the floats 32, 32 are fixed together by another bracket 34. The floats 32, 32 are similarly curved bodies whose concave sides face each other. Since in the disclosed embodiment, the floats 32, 32 act as sails, they are given cross sections such as that shown in FIG. 2, that is, the sections of the float are streamlined, having rounded front ends and sharp rear edges and being symmetrical about centerlines passing through the sharp rear edges. Also, since the floats 32, 32 act as sails, rotation of the pedestal 28 causes rotation of the sails comprising the floats 32, 32 without changing their relative configuration, with respect to the hull 10. This rotation may be accomplished either by hand or by a motor (not shown) in the compartment 20 connected to the pedestal 28 by gears or the like which are also not shown. When the vessel of FIG. 1 is tilted, its righting moment goes up and down as shown by the curve 36 of FIG. 4. This righting moment never becomes negative because the upward force due to the buoyancy provided by combination of the hull 10 and the floats 32, 32 when they are immersed in water combines with the downward force of gravity through the center of gravity of the vessel to produce only righting moments, at any tilt angle whatever. As shown at the point corresponding to 180° of the curve 36 of FIG. 4, the righting moment is zero. That is, if the vessel is tilted exactly 180° it could conceivably, in absolutely motionless water and atmosphere float in this position and will not right itself. However, the buoyancy of the floats 32, 32 is more than sufficient to support the entire vessel, therefore, the slightest tilt away from 180° will result in the vessel righting itself. The curve 38 results when the counterweight 23 is made smaller. It is seen that with a lesser counterweight 23 the vessel may still be self-righting. However, if the weight 23 is too small the righting motion may drop to zero or even become negative at tilt angles near 90°. Therefore, the weight 23 must be properly chosen.
It is also possible for the vessel, if of inadequate weight, to be stable in a position where it lies in the water at a tilt angle somewhat greater than 90°, the float 32 being in contact with the water and the weight 23 being out of the water, as shown in FIG. 5. This is due to too great buoyancy of the hull 10 in comparison with the vessel weight. Care must be taken that the buoyancy of the hull be such that when one or both floats 32, 32 are just touching the water that the center of gravity CG of the vessel is beyond the instant center of buoyancy CB in a direction away from the float 32, to avoid this undesired stable position of the vessel. If the hull 10 has less buoyancy it would be deeper in the water in FIG. 5 and the instant center of buoyancy would move to the right as viewed in FIG. 5 whereby the center of gravity would be to the left (instead of to the right) of the instant center of buoyancy, and the forces produced by the weight acting through the center of gravity and the floating action acting through the center of buoyancy would right the vessel. It has been found that the total weight of the loaded vessel should be close to, but not less than, half the total buoyancy that the vessel would provide were it submerged to the deck line. Ballast should be added when necessary to provide this weight.
A self righting vessel such as disclosed in FIG. 1 may have dimensions in accordance with the following table.
Circular hull diameter 9.0 feet
Nominal payload 1000 pounds
Nominal displacement 1800 pounds
Total hull buoyancy below deck 3600 pounds
Height of sail bottom above deck 2 feet
Height of deck above waterline 0.4 feet
Depth of fin bottom below deck 5.4 feet
Depth of center of gravity below deck 1.2 feet
Sail height above mast 8.5 feet
Combined span of two airfoils 18.9 feet
Radius of curved span 6.0 feet
Airfoil chord 3.0 feet
Airfoil thickness 0.90 feet
Calculated sail displacement 2250 pounds
To avoid stability of the vessel in the position shown in FIG. 5, the vessel having these dimensions should have the nominal weight of approximately 1800 pounds. If the vessel with payload does not weigh 1800 pounds it should be ballasted to this weight. Larger weight will require a larger vessel for other dimensions of the vessel, corresponding weights will be evident.