US3895592A

US3895592A - Boat lift

Info

Publication number: US3895592A
Application number: US431855A
Authority: US
Inventors: Arthur Shelley King
Original assignee: Individual
Current assignee: LOESS Corp A CORP OF; LOESS Corp A MO CORP
Priority date: 1973-01-24
Filing date: 1974-01-09
Publication date: 1975-07-22
Anticipated expiration: 1992-07-22

Abstract

One embodiment of a boat lift utilizes elongated, upendable floats of polyurethane material which project more deeply into the water when the floats are upright than when they are prone. Attachment of the carriage of the lift to the floats adjacent their ''''sinking ends'''' causes the carriage to be submerged when the floats are upright and to be raised for supporting a boat when the floats are in their prone positions. A second embodiment of the lift utilizes hollow pontoons which may be filled with water or air to cause submersion or flotation of the lift and which are rotatable between float positions in which air supplied to the pontoons is trapped therein, and sink positions in which air is allowed to exhaust from the pontoon while water flows thereinto. Diametrically opposed air pockets on the outside of the pontoons cause automatic return thereof from their sink positions to their float positions, and outlet tubes projecting downwardly from the pontoons when the latter are in their float positions prevent air from escaping from the pontoons during rough water conditions.

Description

United States Patent 1 July 22, 1975 King 1 1 BOAT LIFT [76] Inventor: Arthur Shelley King, 8021 Cherokee Ln.. Leawood, Kans. 66206 [22] Filed: Jan. 9, 1974 [21] App]. No.: 431,855

Related US. Application Data Primary ExaminerTrygve M. Blix Assistant ExaminerCharles E. Frankfort Attorney. Agent, or FirmSchmidt, Johnson. Hovey & Williams [57] ABSTRACT One embodiment of a boat lift utilizes elongated, upendable floats of polyurethane material which project more deeply into the water when the floats are upright than when they are prone. Attachment of the carriage of the lift to the floats adjacent their sinking ends" causes the carriage to be submerged when the floats are upright and to be raised for supporting a boat when the floats are in their prone positions. A second embodiment of the lift utilizes hollow pontoons which may be filled with water or air to cause submersion or flotation of the lift and which are rotatable between float positions in which air supplied to the pontoons is trapped therein, and sink positions in which air is allowed to exhaust from the pontoon while water flows thereinto. Diametrically opposed air pockets on the outside of the pontoons cause automatic return thereof from their sink positions to their float positions, and outlet tubes projecting downwardly from the pontoons when the latter are in their float positions prevent air from escaping from the pontoons during rough water conditions.

11 Claims, 8 Drawing Figures PATENTEDJUL 22 ms SHEET N mb BOAT LIFT CROSS REFERENCES This is a continuation-in-part of my co-pending application Ser. No. 326,536, filed'lan. 24, 1973, entitled BOAT LIFT and now abandoned.

This invention relates to an improved boat lift for use in storing a boat in an elevated position. above the water. so that the boat may remain free of algae and similar collections about its hull when not in use.

An important object of the present invention is to provide a boat lift which is not only extremely effective in raising boats of various sizes and displacements, but is also relatively inexpensive to fabricate and relatively simple to operate.

Another important object of this invention is to provide a boat lift which eliminates the need for pneumatic equipment often associated with conventional lifts for pumping air or water into and out of flotation compartments of the lift through the provision of one or more upendable floats which serve to raise or lower the lift by virtue of the difference in their flotation properties when the floats are upright as compared with a prone position. To this end. advantage has been taken of the fact that the floats must displace the same amount of water in either an upright or a prone position. but a selected point on one of the floats may change positions drastically from above the water to well below the same when the float is shifted from one position to the other. Therefore. by connecting the floats to the boat carriage of the lift at such preselected points on the floats. the carriage will move in accordance with its mounting points between submerged and elevated positions when the floats are operated between their upended and prone positions.

An additional important object of the present invention is to provide a boat lift embodying the flotation concepts above set forth wherein all floats of the lift may be operated in unison and by an individual positioned within a boat overlying the lift.

A further important object of the instant invention is the provision of a second type of boat lift. pneumatically operated. wherein pontoons of the lift are rotatable between float positions in which air is trapped within the pontoons to maintain the boat out of the water and sink positions in which the trapped air is exhausted from the pontoons and water is allowed to fill the same for submerging the lift.

A still further important object of this invention is to provide pneumatically controlled pontoons as aforesaid. having means for resisting the escape of trapped air from the pontoons even during rough water conditions when the pontoons tend to rise and fall. leaving the undersides thereof periodically open to the atmosphere.

Another important object of this invention is the provision of means for automatically returning the pneumatic pontoons from their sink positions to their float positions.

An additional important object of the instant invention is the provision of a pneumatic boat lift which may be submerged by an individual located within a boat supported by the lift.

In the drawings:

FIG. 1 is an elevational view showing one version of the lift of the present invention with a boat in position thereon. alternative positions for the upendable floats of the lift being indicated by solid lines and in broken lines respectively;

FIG. 2 is a top plan view of the lift;

FIG. 3 is a rear elevational view of the lift and boat;

FIG. 4 is an enlarged, fragmentary elevational view of one of the floats showing the pivotal axis of the float located at one end thereof rather than between its ends as in FIGS. l3;

FIG. 5 is a view similar to FIG. 1 ofa second version of the lift. alternative positions of the lift being indicated by solid lines and broken lines respectively;

FIG. 6 is a rear elevational view of the lift and boat of FIG. 5;

FIG. 7 is an enlarged. fragmentary end view of one of the pontoons illustrating its manner of operation; and

FIG. 8 is an enlarged, cross-sectional view of one of the floats taken along line 88 of FIG. 5.

The lift 10 illustrated in FIGS. 1-4 is designed to accommodate a boat 12 and has a main frame or carriage 14 provided with a pair of fore-and-aft extending, laterally spacedapart sections 16 which are interconnected by anumber of cross-pieces 18. Rings 20 or the like at the forward ends of carriage sections 16 adapt the lift 10 for securance to a dock or the like. and suitable roller and guiding

structures

22, 24 and 26 engage the hull of boat 12 when it is supported by carriage 14.

Four upendable. elongated floats 28, preferably blocks of polyurethane material. are swingably mounted on carriage 14 by virtue of a pair of fore-andaft spaced. transversely extending torque members 30, each of which is rotatably mounted on the sections 16 by suitable bearing means 31. Each member 30 has a pair of mounting plates 32 at opposite ends thereof for rigid attachment to corresponding floats 28 at preselected points along the lengths of the floats 28 for movement with the members 30 when they are rotated. Each pair of the floats 28 interconnected by the member 30 is provided with a crank 34 rigidly affixed to its corresponding member 30 for applying torque thereto when crank 34 is actuated. A fore-and-aft extending link 36 operably interconnects the two cranks 34, and a second link 38 operably connects the rearmost crank 34 with a hand lever 40 pivotally coupled with carriage 14, whereby cranks 34 may be operated in unison upon swinging of lever 40. Preferably, the lever 40 is so situated that a person disposed within boat 12 may conveniently operate the same to actuate cranks 34. A spring-loaded latch assembly 41, associated with hand lever 40, releasably holds lever 40 in either its forwardmost position illustrated in FIGS. 1 and 2, or its rearmost position shown in phantom in FIG. 1, thereby retaining the floats 28 in either their prone or upright positions.

As above set forth, the members 30 may be secured to the floats 28 at any of a number of selected positions along their lengths. the position chosen being determined after due consideration to the size and weight of the boat which will be accommodated by lift 10. In this respect, FIGS. 1-3 illustrate the members 30 joined to their corresponding floats 28 at points between the opposed ends of the floats 28, while FIG. 4 illustrates an arrangement wherein a member 30 is secured to its float 28 on one end of the latter. The point of attachment of members 30 to their floats 28 is important inasmuch as such attachment points serve as the axes of rotation for the floats 28, thereby positively affecting the degree of flotation of the lift in the manner hereinafter made apparent.

Operation of the lift 10 is based upon the fact that the floats 28 will extend more deeply into the water when placed on end than when laid on their sides in prone positions. While it is, of course, understood that the displacement of the floats 28 is the same regardless of whether they lie in prone positions against the water or stand on end in upright positions, nonetheless. by careful selection of points adjacent the sinking ends of the floats 28 for attachment of the carriage 14, the latter may be held out of the water as shown in FIGS. 1 and 3 when the floats are in their prone positions, and held in a submerged condition as shown by broken lines in FIG. 1 when the floats 28 are in their upended positions. Therefore, it is but necessary to select a point of attachment of carriage 14 to the floats 28 which is sufficient to accommodate the weight of the boat intended to be used in connection with lift 10. It should be apparent that by selecting a connection point on the very end of each float 28 as shown in FIG. 4, the carriage 14 will be more deeply submerged and will rise slightly less out of the water than when the carriage 14 is attached in the manner of FIGS. l-3.

When it is desired to remove the boat 12 from the water it is but necessary to shift the hand lever 40 rearwardly from its FIG. 1 position so that the cranks 34 operate in unison to swing floats 28 from their prone positions to their upright positions. The carriage 14 is thereby fully submerged, and the upright floats 28 provide guides for centering boat 12 is overlying relationship to the submerged carriage 14. The boat operator need then only swing the hand lever 40 forwardly to lower floats 28 to their prone positions, hence raising carriage 14 and lifting boat 12 completely out of the water.

The boat 12 and lift 10 may be left in this condition for prolonged periods with the assurance that the boat 12 will remain high and dry.

It has been found that an additional benefit is obtained by locating the attachment points of the carriage 14 to floats 28 closely adjacent or at the sinking end of the floats 28. This advantage is noted during swinging of the floats 28 from their upended positions to their prone positions at which time the floats 28 tend to return themselves to their prone positions once their respective centers of gravity have passed a true vertical relationship with the pivot point of the floats 28. In this manner, the effort required to shift lever 40 is held to a minimum, hence facilitating the overall operation of lift 10 and making it possible for individuals of all ages and physical characteristics to use the same.

It is to be further noted that the floats 28, because of their convenient locations on opposite sides of carriage 14, may serve as convenient walkways for persons entering or leaving boat 12 when the latter is raised. In this respect, it is of course desirable that the floats 28 be of sufficient size to locate their upper surfaces above the waterline when floats 28 are in their prone positions. Moreover, a rectangular configuration for the floats 28 provides a flat walking surface compared to other nonpolygonal configurations.

With reference now to FIGS. 5-8, a second embodiment of the boat lift is therein disclosed and denoted by the numeral 42 for supporting the boat 12. The carriage 44 of lift 42 is substantially identical to carriage 14 with the exception that carriage 44 is adapted for use not with the solid upendable floats 28 of lift 10, but rather for use with pontoons 46 which are responsive to the introduction of air or water thereinto to control raising and lowering of the lift 42. To this end, the carriage 44 has, along each side thereof, a pair of fore-andaft. spaced-apart, downwardly extending struts 48 having bearing units 50 at their lower ends for journaling a shaft 52 which projects from the proximal end of a pontoon 46, thus rotatably supporting the pontoon 46.

EAch pontoon 46 is of elongated, generally tubular configuration having hemispherical end closures 54 and a continuous peripheral wall 56 which defines an air or water chamber 58 within the body of pontoon 46. The rearmost of the end closures 54 of each pontoon 46 is completely closed at its junction with the shaft 52, but the forward closure 54 is provided with an air inlet 60 therein disposed in concentric relationship to the proximal shaft 52 and adapted for coupling with a supply line 62 associated with the bearing 50 which leads to an air pump (not shown). As illustrated, each pontoon 46 is mounted for rotation about its longitudinal axis, such axis coinciding with that of the shafts 52, inlet 60 and bearings 50.

Each pontoon 46 is also provided with a pair of inletoutlet tubes'64 and 66 which are secured to the outside of wall 56 in communication with chamber 58 for the passage of air and water into and out of chamber 58 during floating and sinking operations of the lift 42. The tube 64 is of larger capacity than tube 66 and projects radially from pontoon 46 for protrusion downwardly into the water when the pontoon 46 is in the position of FIGS. 5, 6 and 8. On the other hand, the tube 66 is slender and is circumferentially spaced from tube 64 so that when pontoon 46 is rotated in the direction illustrated in FIG. 7, tube 66 leads tube 64 and breaks the surface of the water before the pontoon 46 has been rotated a full 90. Tube 66 extends generally in parallelism with tube 64 for projection with the latter downwardly into the water when the pontoon 46 is in the position of FIGS. 5, 6 and 8.

A pair of air pockets 68 are disposed in diametrically opposed positions on each pontoon 46. The pockets 68 are located on the outside of pontoons 46 and are sealed from the chambers 58 of the latter by the walls 56 of the pontoons 46. As hereinafter explained, pockets 68 serve the purpose of returning the pontoons 46 to their normal float positions from their sink positions approximately 45 beyond the rotative position illustrated in FIG. 7.

Rotation of the pontoons 46 in unison is effected by a cable arrangement which includes a pair of side-byside, individually rotatable pulleys 70 (FIG. 7) mounted beneath carriage 44, each of the pulleys 70 having a cable 72 from a corresponding pontoon 46 entrained therearound. An off-center lug 74 on each pontoon 46 secures one end of the corresponding cable 72 to the pontoon 46, and a conduit 76 receives the two cables 72 after entrainment around the pulleys 70 for guiding cables 72 during actuation thereof and for 10- cating their opposite ends at convenient location above carriage 44 for actuation by a person located within boat 12. Preferably, the actuatable ends of the cables 72 are joined to a common gripping element (not shown) which not only facilitates manipulation of cables 72, but also precludes accidental release of the cable 72 through conduit 76.

A third pontoon 78 is located adjacent the front of carriage 44 and extends transversely across the latter to form the apex of an imaginary triangle defined by the two rear pontoons 46 and the front pontoon 78. Pontoon 78 is similar in general construction to pontoons 46, but it is not rotatable and'has a constant supply of air trapped therein for remaining in a continuously floating condition. Thus. as illustrated in FIG. 5, pontoon 78 serves as a pivot for the remainder of lift 42 during operation thereof. One or more rings 80 may be provided at the forwardmost end of carriage 44 for use in securing the lift 42 to a dock or like structure.

The operation of lift 42 may best be illustrated by assuming that the lift 42 is initially in its raised position supporting the boat 12 out of the water as illustrated by solid lines in FIG. 5 and also in FIG. 6. Normally, the forward end of the lift 42 will be loosely secured to a dock through rings 80 to permit actuation of the lift 42 to the broken line position of FIG. 5.

When the lift 42 is in its raised condition, the pontoons 46 thereof are disposed with their inlet-

outlet tubes

64 and 66 pointed downwardly into the body of water. Therefore, air that is pumped into the chamber 58 of each pontoon 46 by its supply line 62, is trapped by the water which surrounds and seeks to enter

tubes

64 and 66. So long as pressure of sufficient magnitude is supplied through line 62, air within each chamber 58 cannot escape therefrom back through inlet 60 and, accordingly, the lift 42 floats.

To operate lift 42, it is but necessary for a person situated within the boat 12 to grasp the cables 72 conveniently located at the proper height by conduit 76 anad exert a sufficient pull to rotate the pontoons 46 in opposite directions about their longitudinal axes beyond the intermediate rotative position of FIG. 7 until just less than a full 90 rotation has been effected. In this respect, suitable stop means (not shown) could be provided to prevent a full 90 rotation and beyond so that the pockets 68 of each pontoon 46 are never in a true vertical relationship with one another.

Movement of the pontoons 46 in this manner exposes the slender tubes 66 thereof to the atmosphere and allows the air previously trapped therein to escape while water floods the chambers 58 through tubes 64. Initially. because of the location of each tube 64 on its pontoon 46, both air and water simultaneously pass through the tube 64, the water flowing into chamber 58 and the air rushing outwardly therefrom. However, it will be appreciated that this action is brief and that air is exhausted primarily through each tube 66 and water is received primarily through each tube 64.

Flooding of the chambers 58 of pontoons 46 causes the lift 42 to gradually submerge to its broken line position of FIG. 5 as the carriage 44 pivots about the front pontoon 78. Thus. as soon as carriage 44 is submerged sufficiently. the boat 12 is released by lift 42 and allowed to float on its own.

Once the pontoons 46 have become sufficiently flooded to lower the lift 42, the operator may release cables 72 and the lift 42 will continue sinking until reaching its fully lowered position. Such release of cables 72 causes the pontoons 46 to be automatically returned to their float positions in which the

tubes

64 and 66 project downwardly by virtue of the return pockets 68 located on opposite sides of each pontoon 46. It will be appreciated that because of the existence of the pockets 68, wwhich are always provided with a supply of trapped air, the pontoons 46 tend to seek an orientation in which both pockets 68 of each pontoon 46 are at the same level. Thus. (using the pontoon 46 of FIG. 7 as an example) with one pocket 68 in an approximately 7 oclock position and the other in an approximately 1 Oclock position when a pontoon 46 is in its sink position to exhaust air and receive water, the pockets 68 force their pontoon 46 to rotate clockwise when cable 72 is slackened until equalization is once again established. Because the pocket 68 at 7 oclock on pontoon 46 is submerged more deeply than the opposing pocket 68 and yet is the same density and volume, a buoyancy force differential is created that causes the pockets 68 to seek an equalized condition.

And because the lower pocket 68 is not in a true vertical relationship with the opposing pocket 68, its buoyancy force is not divided into equal and oppositely projecting forces from a vertical line that would result in a static condition. Moreover, it will be appreciated that the presence of pockets 68 stabilizes the pontoons 46 when they are in their float positions, such stabilization being especially important when the boat 12 is supported out of the water so that pontoons 46 are prevented from accidentally rotating during rough water to flood their chambers 58 and submerge the lift 42.

The projection of

tubes

64 and 66 of each pontoon 46 for a substantial distance beyond the wall 56 thereof is important inasmuch as the outer ends of the

tubes

64 and 66 are thus not exposed to the atmosphere. even in rough water conditions. In this manner, the pontoons .46 may thus be bounced completely out of water for short distances to expose portions of the undersides thereof without water entering chambers 58 to accidentally sink the lift 42 and hence float boat 12.

When it is desired to remove the boat 12 from the water it is but necessary to sink the lift 42 in the manner above described and bring the boat into overlying relationship with the submerged carriage 44.

Air is then pumped into the pontoons 46 to exhaust the water from chambers 58 through

tubes

64 and 66 until such time as a flotation condition is reached, thereupon the lift 42 will swing upwardly to engage the hull of boat 12 and raise the same completely out of the water. With the pontoons 46 in their float positions during exhaustion of the water from chambers 58, it is assured that the air pumped into pontoons 46 will remain trapped therein when the lift 42 has reached its fully raised condition.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

l. A boat lift comprising:

a carriage;

a tubular, essentially closed, elongated pontoon having a continuous outer wall defining a chamber within the pontoon and provided with inlet means and outlet means; and

means rotatably mounting said pontoon on the carriage for rotation of the pontoon about its longitudinal axis between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter.

2. A boat lift as claimed in claim I, wherein said outlet means includes a tube projecting outwardly from said wall for protrusion downwardly into the water when the pontoon is in its float position.

3. A boat lift as claimed in claim 2, wherein said tube both exhausts air and receives water when the pontoon is initially rotated to its sink position.

4. A boat lift as claimed in claim 1, wherein said outlet means includes a pair of tubes projecting outwardly from said wall. one for primarily receiving water and the other for primarily discharging air when the pontoon is rotated to its sink position.

5. A boat lift comprising:

a carriage;

a tubular, essentially closed pontoon having a continuous outer wall defining a chamber within the pontoon and provided with inlet means and outlet means; and

I means mounting said pontoon on the carriage for movement of the pontoon between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter,

said outlet means including a pair of tubes projecting outwardly from said wall. one for primarily receiving water and the other for primarily discharging air when the pontoon is moved to its sink position,

said pontoon being mounted on said carriage for rotation between said positions, said other tube being spaced from said one tube along the path of rotation of the pontoon to project out of the water when the pontoon is rotated to its sink position,

6. A boat lift comprising:

a carriage;

a tubular, essentially closed. elongated pontoon having a continuous outer wall defining a chamber within the pontoon and provided with inlet means and outlet means; and

means rotatably mounting said pontoon on the carriage for movement of the pontoon between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter,

said pontoon being mounted for rotation about its longitudinal axis between said positions and being provided with means for automatically returning the same from its sink position to its float position.

7. A boat lift as cliamed in claim 6, wherein said return means comprises a pair of diametrically opposed air pockets on the outside of said pontoon sealed from said chamber 8. A boat lift comprising:

a carriage;

a tubular. essentially closed pontoon having a continuous outer wall defining a chamber withinthe pontoon and provided with inlet means and outlet means; and

means mounting said pontoon on the carriage for movement of the pontoon between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter,

said pontoon being elongated and being mounted for rotation between said positions about its longitudinal axis, said outlet means being spaced laterally from said axis of the pontoon.

9. A boat lift as claimed in claim 8, wherein said inlet is located at one end of said pontoon in association with said mounting means.

10. A boat lift claimed in claim I, wherein'said carriage is provided with a second rotatably mounted pontoon spaced from said first-mentioned pontoon, said carriage further being provided with means for operating the pontoons simultaneously.

11. A boat lift as claimed in claim 10, wherein said operating means includes cable means operable from a boat overlying said carriage.

Claims

1. A boat lift comprising: a carriage; a tubular, essentially closed, elongated pontoon having a continuous outer wall defining a chamber within the pontoon and provided with inlet means and outlet means; and means rotatably mounting said pontoon on the carriage for rotation of the pontoon about its longitudinal axis between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter.

2. A boat lift as claimed in claim 1, wherein said outlet means includes a tube projecting outwardly from said wall for protrusion downwardly into the water when the pontoon is in its float position.

4. A boat lift as claimed in claim 1, wherein said outlet means includes a pair of tubes projecting outwardly from said wall, one for primarily receiving water and the other for primarily discharging air when the pontoon is rotated to its sink position.

5. A boat lift comprising: a carriage; a tubular, essentially closed pontoon having a continuous outer wall defining a chamber within the pontoon and provided with inlet means and outlet means; and means mounting said pontoon on the carriage for movement of the pontoon between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter, said outlet means including a pair of tubes projecting outwardly from said wall, one for primarily receiving water and the other for primarily discharging air when the pontoon is moved to its sink position, said pontoon being mounted on said carriage for rotation between said positions, said other tube being spaced from said one tube along the path of rotation of the pontoon to project out of the water when the pontoon is rotated to its sink position.

6. A boat lift comprising: a carriage; a tubular, essentially closed, elongated pontoon having a contInuous outer wall defining a chamber within the pontoon and provided with inlet means and outlet means; and means rotatably mounting said pontoon on the carriage for movement of the pontoon between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter, said pontoon being mounted for rotation about its longitudinal axis between said positions and being provided with means for automatically returning the same from its sink position to its float position.

7. A boat lift as cliamed in claim 6, wherein said return means comprises a pair of diametrically opposed air pockets on the outside of said pontoon sealed from said chamber.

8. A boat lift comprising: a carriage; a tubular, essentially closed pontoon having a continuous outer wall defining a chamber within the pontoon and provided with inlet means and outlet means; and means mounting said pontoon on the carriage for movement of the pontoon between a float position wherein said outlet means is submerged for trapping air within the chamber supplied through said inlet means and a sink position wherein said outlet means is open to the atmosphere for exhausting air from the chamber for entry of water into the latter, said pontoon being elongated and being mounted for rotation between said positions about its longitudinal axis, said outlet means being spaced laterally from said axis of the pontoon.

10. A boat lift as claimed in claim 1, wherein said carriage is provided with a second rotatably mounted pontoon spaced from said first-mentioned pontoon, said carriage further being provided with means for operating the pontoons simultaneously.