NO341056B1 - Pivotally suspended lifeboat davit - Google Patents

Description

A davit with a pivotally suspended lifeboat cradle

The present invention relates to an aligning davit forfree-fall lifeboats.

When installing davits on structures, in particular floating structures such as vessels, ships and floating offshore installations, there is a risk that the floating structure floats at an angle. A list or heel is typically the result of some sort of damage to the structure, resulting in an "off design" angle on the davit. This angle may be both at a lengthwise and/or transversal direction of the floating structure. The result is a lifeboat directed at an unfavourable angle.

Free fall lifeboats must be designed to withstand a fall from a less than ideal angle of the davit and thus the lifeboat. Lifeboats are typically designed to withstand a fall at an angle of 17° off the ideal angle in all directions due to formal regulations. A fall that deviate 17° from the ideal angle imposes considerable stresses on the lifeboat and its passengers.

NO 20100750 shows a method and system for elevating and preparing a freefall lifeboat, including inclined skids and an opening between the skids, where the lifeboat is located below an elevating device for elevating the lifeboat. The elevating device is provided at a location allowing the lifeboat to be elevated through the opening of the skids with a vertical motion.

It is a purpose of the present invention to provide a solution to ensure that a lifeboat is dropped at the correct angle even if the structure the davit is attached to is inclined.

In the description below are "cylinders" intended to cover actuators for rotating a cradle of the davit to different angles. It should be noted that "cylinders" are intended to cover other actuators with the same purpose. Other actuators may include electric linear actuators, and electric or hydraulic rotational actuators in the pivot points.

The lifeboat davit may further include a boom element pivotally supporting the support structure in a first axis of rotation P1, pivotally supported in the foundation in a second axis of rotation P2 perpendicular to the first axis of rotation P1.

The lifeboat davit may further include a lifeboat launching and lifting winch attached to the support structure of the cradle.

The lifeboat launching and lifting winch may be attached to a free fall lifeboat in a single lifting point.

The lifeboat davit may further include a free fall lifeboat supported by the lifeboat carrier elements. A vertical axis through a centre of gravity (CG) of the lifeboat may coincide with a vertical axis through a centre of gravity (CG) of the lifeboat cradle when a longitudinal axis of the free fall lifeboat is inclined between 30° and 40°.

The lifeboat launching and lifting winch may include a winch wire extending through a centre of gravity (CG) of the lifeboat cradle.

The lifeboat davit may further include at least one cradle actuator controlling at least one angle of the pivotally suspended cradle and a control system for the cradle actuator.

The pivotally suspended cradle may turn 17° each way away from a centre position in pitch and/or roll.

The lifeboat carrier elements may include hinged runner beams with a first lifeboat holding position and a second lifeboat passing position.

The lifeboat davit may further include runner beam actuators adapted to shift the hinged runner beams between the first lifeboat holding position and the second lifeboat passing position.

Fig. 1 is a perspective view of a lifeboat davit according to an embodiment of the invention, holding a lifeboat; Fig. 2 corresponds to fig. 1, in a situation where a winch lifts or launches the lifeboat in a single lifting point; Fig. 3 shows the davit and the lifeboat from the side; Fig. 4 shows the davit and the lifeboat in a situation where a winch lifts or launches the lifeboat in a single lifting point; Fig. 5 shows the lifeboat cradle at an angle of 52° in relation to a vertical direction; fig. 6 show the lifeboat cradle at an angle of 18° in relation to a vertical direction;

Fig. 7 is a front view of the davit shown on the figures 1-6.

Fig. 8 is a front view of the davit of the figures 1 -7, including a lifeboat in the cradle; and Fig. 9 is a rear view of the davit with a lifeboat located and held between runner beams. Fig. 1 is a perspective view of a lifeboat davit according to an embodiment of the invention. A free fall lifeboat 7 is held in the davit for illustration purposes. The davit includes a foundation 5 above a cradle 6. The cradle 6 serves as a holding frame for two runner beams 8. Ordinary runner surfaces at each side of the lifeboat 7 are supported by the runner beams 8 and allow the lifeboat 7 to slide along the runner surfaces. The runner beams 8 are hinged to the cradle to allow the lifeboat to be lifted past the runner beams 8 and into the cradle from below.

The main purpose of the cradle is to provide a structure holding the runner beams 8, a winch 3 and to provide attachment points for a boom 1. The cradle 6 is hinged to the boom in two pivot points on top of the cradle 6, allowing the cradle to pivot in relation to the boom 1. The cradle 6 is allowed to pivot in relation to the boom 1 with an axis of rotation substantially parallel to a longitudinal axis of the lifeboat.

List or roll cylinders 2 are typically hydraulic cylinders located between the cradle 6 and the boom 1. The list cylinders are used to selectively lock or rotate the cradle 6 in relation to the boom 1.

The boom 1 is pivotally attached to the foundation 5, and a trim or pitch cylinder 4 is located between the boom 1 and the foundation 5. The trim cylinder 4 is typically a hydraulic cylinder and is used to selectively lock or rotate the boom 1 in relation to the foundation.

The winch 3 is provided to lift the lifeboat 7 into the cradle 6, and to launch the lifeboat 7 for training or in the event of ice on the water surface. Fig. 2 corresponds to fig. 1, but shows the davit and the lifeboat 7 in a situation where the winch 3 lifts or launches the lifeboat 7 in a single lifting point. The runner beams 8 are shown in a lifted position, allowing the lifeboat 7 to be lowered or launched by the winch 3. The single lifting point is located on the lifeboat at a location allowing the lifeboat to hang at an angle with a longitudinal axis substantially coinciding with the longitudinal axis of the runner beams 8. The angle is in the range 30° to 40°, typically 35°. This angle is the typical drop angle for a free fall drop. The cradle 6 includes a lifeboat access opening 11 allowing the lifeboat to be launched from - or lifted into the cradle 6. For launching, the winch 3 may lift the lifeboat 7 sufficiently to allow one or several actuators 15 to rotate the runner beams 8 upwards and out of the way for the lifeboat 7 in the runner beam hinges 14 before launching the lifeboat 7 by the winch 3 through the lifeboat access opening 11 between the runner beams 8. The runner beams 8 are hinged to lower cradle beams 12 forming a part of the cradle 6. The lower cradle beams 12 form the cradle along with the cradle support structure 13 forming a superstructure above the lower cradle beams 12. A first pivot P1 and a second pivot P2 enables the cradle to move with two degrees of freedom. The cradle 6 is accordingly suspended above the centre of gravity of the cradle 6 and of the combination of the cradle 6 and the lifeboat 7. Fig. 3 corresponds to fig. 1, but shows the davit and the lifeboat 7 from the side and that the centre of gravity 9 of the lifeboat 7 and the cradle is located on a vertical axis 10 below the pivotal attachment of the boom 1 to the foundation 5. The lifeboat 7 and cradle 6 combination is designed to hang at the correct angle due to gravity without input from the actuators in the form of the trim cylinder 4 and the list cylinders 2.

A winch wire of the winch 3 is also located along the vertical axis below the pivotal attachment of the boom 1. The winch wire may extend through a fairlead (not shown) to guide the wire and to keep the point of attack of the force from the winch wire within a certain area to maintain the balance of the cradle 6 and boat irrespective of the amount of wire on the winch 3. The angle of the lifeboat 7 when hanging from the winch wire should more or less coincide with the angle of the runner beams 8 when the actuators in the form of the trim cylinder 4 and the list cylinders 2 are unloaded.

Fig. 4 corresponds to fig. 1, but shows the davit and the lifeboat 7 in a situation

where the winch 3 lifts or launches the lifeboat 7 in a single lifting point. The winch wire follows the vertical axis extending through the pivot point of the boom 1 in the foundation 5 and the attachment point of the winch wire in the lifeboat 7. Again the angle of the longitudinal axis of the boat coincides with the angle of the longitudinal axis of the runner beams.

The figures 5 and 6 corresponds to fig. 3 apart from the lifeboat 7 missing from these figures. Fig. 5 shows the cradle at an angle of 52° in relation to a vertical direction. 52° is 17° steeper than the normal drop angle of 35° and represents an outer limit of motion of the cradle. The trim cylinder 4 is in an extended position, and the list cylinders 2 are in a neutral position. The boom 1 pivoting in the foundation 5 is at the outer limit of rotation.

Furthermore does fig. 6 show the cradle at an angle of 18° in relation to a vertical direction. 18° is 17° less steep than the normal drop angle of 35° and represents an outer limit of motion of the cradle. The trim cylinder 4 is in a retracted position, and the list cylinders 2 are in a neutral position. The boom 1 pivoting in the foundation 5 is at the outer limit of rotation.

Fig. 7 is a front view of the davit shown on the figures 1-6. Fig. 7 shows the cradle in a horizontal position in the middle. The figure to the left shows the cradle angled 17° to the left and the left list cylinder 2 is retracted while the right cylinder is extended.

The figure to the right shows the cradle angled 17° to the right and the right list cylinder 2 is retracted while the left cylinder is extended.

Fig. 7 also shows the pivot point marked with a cross where the boom 1 is pivotally attached to the cradle 6. The foundation 5 is made out of two foundation parts and the boom 1 is pivotally attached between these two foundation parts.

Proper alignment of the cradle 6 also prevents the lifting or launching wire from the winch 3 from accidently interfering with the cradle 6 or the runner beams 8. Interference between the lifting and launching wire from the winch 3 and the cradle 6 or the runner beams 8 may cause wear and abrasion on the lifting wire, ultimately causing breakage of the wire. The interference may also cause unwanted stresses and damage to the cradle 6 or runner beams 8, unpredictable and erratic motion of the lifeboat hanging from the wire, problems during lifting or launching past the runner beams 8, unpredictable stresses on the davit attachment and other problems. Fig. 8 is a front view of the davit of the figures 1 -7, including a lifeboat 6 in the cradle 6. The cradle 6 is pivotally attached to the boom 1 in pivoting point P1. There is a distance D between the upper part of the cradle 6 and the top of the lifeboat 7 to allow the lifeboat to be lifted sufficiently to allow the runner beams 8 to be folded out of the way to enable the boat to be lifted or launched through the lifeboat access opening on a bottom side of the cradle. Fig. 9 is a rear view of the davit with a lifeboat 7 located and held between the runner beams 8. A lifeboat access opening 11 is located on a bottom side of the cradle 6 between the runner beams 8, allowing the lifeboat to be lifted or launched into or from the cradle 8.

The foldable runner beams 8 are operated by actuators (actuators 15 on fig. 2) to enable the runner beams 8 to be folded away from the runners on the lifeboat 7 and to enable the lifeboat 7 to be launched straight down through the lifeboat access opening 11 at the bottom side of the cradle 6.

The list cylinders 2 and the trim cylinder 4 can be connected to a hydraulic system that includes a control system. The control system may be a system that monitors the angle of the lifeboat cradle and ensures that the lifeboat always is positioned in the correct position, i.e. with a horizontal transversal axis and a longitudinal axis of 35° in relation to a horizontal line. Alternatively may the lifeboat be in a locked position until the lifeboat is to be used.

The hydraulic system is included to ensure that the lifeboat is launched at the correct angle in spite of snow, ice, friction in the pivot points or anything else that could hold the cradle and lifeboat in the wrong position.

The hydraulic system is also used to prevent the cradle from moving when the lifeboat is launched and to prevent the lifeboat from swinging due to motion in the structure, strong winds etc. both during operation and storage.

The hydraulic system may also be manually operable eitherfrom inside the boat or from on-board the structure.

The system may also be dynamically controlled to accommodate for movement in the floating structure.

The boom 1 pivotally connected with the cradle 6 and the foundation 5 prevents the cradle from yaw rotation while allowing pitch and roll. The suspension of the cradle can be considered as universal- or gimbal joint. Furthermore is the term "cradle" used to describe the framework with the lower cradle beams 12 and the support structure 13 holding the lifeboat 7. The cradle 6 is a boat stand that in a way is inverted as the main structure is above the hull of the lifeboat 7.

Parts:

Claims (10)

1. A lifeboat davit including: a foundation (5) and a lifeboat cradle (6) with , lifeboat carrier elements and a lifeboat access opening (11) on a bottom sidecharacterized in: that the lifeboat cradle (6) further includes a support structure (13) on a top side, and at least one attachment point on the support structure, pivotally suspending the support structure (13) in the foundation (5), whereby the cradle (6) is pivotally suspended.

2. The lifeboat davit of claim 1, further including a boom element (1) pivotally supporting the support structure (13) in a first axis of rotation P1 and pivotally supported in the foundation (5) in a second axis of rotation P2 perpendicular to the first axis of rotation P1.

3. The lifeboat davit of claim 1, further including a lifeboat launching and lifting winch (3) attached to the support structure (13) of the lifeboat cradle (6).

4. The lifeboat davit of claim 3, wherein the lifeboat launching and lifting winch (3) is attached to a free fall lifeboat (7) in a single lifting point.

5. The lifeboat davit of claim 1, further including free fall lifeboat (7) supported by the lifeboat carrier elements and wherein a vertical axis (10) through a centre of gravity (CG) of the lifeboat coincides with a vertical axis (10) through a centre of gravity (CG) of the lifeboat cradle (6) when a longitudinal axis of the free fall lifeboat (7) is inclined between 30° and 40°.

6. The lifeboat davit of claim 3, wherein the lifeboat launching and lifting winch (3) includes a winch wire extending through a centre of gravity (CG) of the lifeboat cradle (6).

7. The lifeboat davit of any of the preceding claims further including at least one cradle actuator controlling at least one angle of the pivotally suspended cradle (6) and a control system for the cradle actuator.

8. The lifeboat davit of any of the preceding claims wherein the pivotally suspended cradle (6) can turn 17° each way away from a centre position in pitch and/or roll.

9. The lifeboat davit of any of the preceding claims wherein the lifeboat carrier elements include hinged runner beams (8) with a first lifeboat holding position and a second lifeboat passing position.

10. The lifeboat davit of claim 9, further including runner beam actuators (15) adapted to shift the hinged runner beams (8) between the first lifeboat holding position and the second lifeboat passing position.