Flexible boom and its sail system-FBSS

Abstract

 Flexible Boom and its Sail System consisting of a rigid frame sail boom system encompassing the major part of a vertically rigid but horisontally flexible - at varying camber - airfoil shaped boom. With the utilisation of attached extension string cables, its contour is controlled by one or more lateral expansion rods. These rods are driven by hydraulic, threaded carrier or similar mechanism. Depending on apparent wind parameters the rods serve to ensure that the appropriate camber is attained and stabilised for a close linear wind flow around the sail in its entirety, boom included.As an option, a detachable flexible modular skirt, with inversed T profile, can be attached to the underside of the boom. In larger vessels, the camber of the boom is determined by a computerised control system adjusting the position of the rods in accordance with the apparent wind parameters for the attainment of linear air flow.

Description

[0001] The invention consists of a lateral (horizontally) rigid frame sail boom system of string cable lines, enclosing the major part of a vertically rigid but laterally flexible airfoil shaped adjustable boom and its sail. As an option, a detachable flexible modular skirt, with inversed T profile, can be attached to the underside of the boom that would increase the effective sail area and minimise the turbulence cause by the pressure differential on the two sides of the sail and the boom. The camber is controlled by one or more laterally expanding rods driven by hydraulic, threaded carrier - or similar-mechanism.

[0002] In addition, in its complete form, primarily although not exclusively for sizable vessels, it includes a computerised control system that determines and positions the rods according to apparent wind parameters so that the appropriate airfoil camber is attained and maintained by the boom and its sail.

[0003] The aim is to achieve, under given apparent wind parameters, an airfoil shape of the total surface area of the sail including the boom itself thus maximising propulsive force.

[0004] Optimum efficiency is attained through the use of modern carbon fiber matrix mix and impregnation materials in a high profile rectangular cross section design for the boom with a progressive variation of mass rate of its section in order to achieve near perfect airfoil shape when deflected by the rod(s). The use of such materials also aims at minimizing residual elasticity latency and fatigue ensuring long life. In-mast or boom reefing are compatible. Boom reefing allows for battens that enhance the sail stability for linear airflow. In-boom reefing is possible without the utilisation of battens. In-mast reefing provides a simpler and thus more trouble free option.

[0005] With the flexible boom determining its optimum operating form as an airfoil, the required sail has a practically flat shape.

[0006] As a simple package, the system can easily be installed on existing vessels. In this form, the invention requires no modifications to the remaining sail propulsion systems and will result in significant gains in sail power. FBSS requires negligible electrical power and stored energy and none in case of manual handling.

Prior Art

[0007] An example illustrates how sails are typically arranged on an average sailing boat with one mast. The design shown consists of sails attached to the mast, located ahead of amidships (Drawing 1). A triangular head sail ahead of the mast is raised or prehoisted along a forestay which is braced approximately from the bow to near the mast tip. The clew as the free end of the leech and foot of the sail is hauled tightly by means of a jib sheet so that the sail can adopt the most favorable possible aerodynamic profiled shape to take advantage of the apparent wind.

[0008] The draft of this head sail also energetically intensifies the lee flow of the subsequently positioned mainsail. This ensures the most extensive possible wind deflection without the lee flow becoming separated from the mainsail, and thus minimises the risk of creation of complex wake turbulence, which would result in an important loss of sail driving force.

[0009] For increased efficiency, the mainsail usually has battens attached to it. These allow for the formation of the most aerodynamically favorable sail profile providing stability and allowing an increase in the sail surface compared to a more traditional sail propulsion system utilising a mast of the same length

[0010] The characteristic configuration of the sail profile and its angle of attack is crucial for the specific propulsion power per square meter of sail area. Utilising current practices and current sail, mast and boom technology, the maximum production of driving force is achieved in the upper part of the sail. In the area near the boom, the propulsion-bringing flow profile is increasingly deflected - and ultimately interrupted - by the turbulence produced by the boom.

[0011] Neither the angle of attack in the luff zone of a well-positioned main sail, that is close to the incoming wind direction, nor the outflow angle at the leech following the forward-driving flow deflection inside the sail are similarly directed to the angle of attack of the boom. Thus, appreciable power losses occur in the transition zones from the sail, even when profiled as correctly as possible, in the upper region, to the straight connected boom.

[0012] Modern sails design has reached its limit in remedying this deficiency. The barrier of a rigid boom remains insurmountable using existing technology and design.

[0013] This problem is accentuated as the otherwise usable downdraft of the head sail does not meet an ordered lee flow on the rear side of the main sail.

[0014] In conclusion, when the main sail is attached to a standard profiled rigid boom head, some wake turbulence is formed along the foot of the sail, caused by the exchange of air from the luff-side (positive pressure zone) to the lee side (negative pressure zone). The flow turbulence this produces however is combined with the more important aforementioned turbulence losses resulting from the straight boom and results in an important expense of drive energy and should be prevented (figure 1).

[0015] Wind tunnel research confirms this situation. An example reference can be found at http://www.wb-sails.fi/Portals/209338/news/470StreamAnim/index.htm;

[0016] In commercial vessels equipped with successive masts hoisting sails equipped with booms a similar set of deficiencies occur due to the rigidity of their booms.

Description of the invention

[0017] The invention, described hereinafter as the Flexible Boom and its Sail System (FBSS), is designed to address and minimise the effect of the aforementioned disadvantages (Drawing 1). The generic concept is demonstrated in Drawing 2.

[0018] The boom is attached to the mast in an articulated manner on all sides by means of a gooseneck, held in an approximately horizontal position by means of a mast support and hauled tightly with a sheet. On the upper side of the boom the foot of the sail is held in a conventional manner, e.g. pulled in a boom groove or bound by means of marlines in multiple locations. As an option, a flexible modular skirt can be attached to the boom (more details below).

[0019] The Flexible Boom and its Sail System (FBSS) consists of a vertically rigid but laterally flexible high profile adjustable airfoil boom and its near flat shaped sail. It is framed by string cables tensioned in a controlled manner by a mechanism of an expanding rod (Drawing 4). In this description the rod is driven either by a single hydraulic cylinder or a "threaded carrier". It rotates inside an expansion carriage (drawing 6) around the boom and locks and expands in opposite sides as shown in drawings 7, 8 and 9. Any other appropriate mechanism can be used to drive the expansion mechanism (EM). As an option, a detachable flexible modular skirt, with inversed T profile, can be attached to the underside of the boom (drawing 10) that would increase the effective sails area and minimise the turbulence cause by the pressure differential on the two sides of the sail.

[0020] In addition, in its complete form, mainly for sizable boats and commercial vessels, the invention includes a computerized control system that automatically positions rods according to apparent wind parameters to attain a near linear wind flow.

[0021] In operation, the luff string cable running along the length of the boom is pushed away by the rod (Drawing 4). This forces the boom to bend thus providing the appropriate airfoil camber for a linear wind flow around the sail in its entirety including the boom itself whilst maintaining rigidity laterally at any chosen position.

[0022] In more detail, a hydraulic EM is described first. A threaded carrier expansion mechanism (EM) is shown as a complement. The concept can easily be extended for larger vessels to multicarriage packages, depending on the bending force required and distribution along the boom.

[0023] Amidships the lateral rigidity of the system is ensured by the boom being under no bending load. The string cables frame attached to it is under no tension (Dr. 3).

[0024] In any other position, with the hydraulic cylinder swung on the luff side (Figure 8), the lateral (horizontal) rigidity is ensured by a lateral frame under tension that includes the boom itself under camber, the rod extended on the luff side and the luff side string cable under tension. Notice that the lee side cable is at rest. In simplistic terms the system resembles a drawn bow with the rod as the arrow positioned off center towards the bows and the hydraulic carriage attached firmly on the boom. (Dr. 4)

[0025] The string cables on each side of the boom are attached ahead as near to the gooseneck as possible. On the rear they are attached after the point of attachment of the boom sheet - the exact position depending on the material used for the boom extrusion and its cross section profile. The aim is to ensure near perfect airfoil shape under load and thus maximum linearity of airflow with minimum swinging tendencies of the system on the lateral (horizontal) plane. (Dr. 5)

[0026] Technical details of an expansion carriage are shown in Figure 6. The hydraulic EM is shown in drawing 7 (not expanded) and drawing 8 (expanded). Similar details of a threaded carrier EM are shown in figure 9. The length of the expanding rods is determined by the maximum desired camber.

[0027] The expansion carriage is attached to the boom at approximately a quarter of the boom length from the gooseneck (drawing 5). In aiming at near perfect airfoil shape of the sail, its exact position is determined by the material to be used for the boom extrusion and its cross section profile as well as the arrangements for the kicking strap.

[0028] The whale shaped base of the carriage, where the boom sits in, had hard elastic airfoil shaped pads so that with increasing camber the pressure on the boom is distributed evenly across its surface to ensure minimum contour irregularity and smooth distribution of load. Due to their elastic properties, the integration of these flanks to the rest of the carriage and its shape provide for minimum local wind turbulence.

[0029] At each change of course, the crew manages the position of the EM and its driving rod in order to modify the amplitude of the boom camber ensuring near linear wind flow of the system. When the boat is facing the wind with the boom amidships the EM drops amidships and no lateral force is exercised on the boom.

[0030] The sail required is a simple design and nearly flat, as the boom to which it is attached serves as a guide allowing it to naturally take a smooth airfoil shape for its entire height including the boom itself when energised by the wind. As an option, a flexible modular skirt can be attached to the boom that would minimise pressure differencial turbulence and increase the effective sails area.

[0031] As the boom camber is adjusted according to the apparent wind parameters, the sail itself, following this camber, will provide maximum possible propulsive power whilst lowering its center of effort, resulting in to significant increase in performance. At the chosen camber, stability is attained by absorbing the variation in intensity and direction of the wind, through the lateral rigidity of the system under the control of the carriage base pinned on the boom. This arrangement absorbs volatility vibrations ensuring minimum stress fatigue on the boom and greater airfoil stability for it and its sail.

[0032] Most of the operational details described above are also applicable to the system using a threaded carrier (drawing 9) or other expansion mechanism.

[0033] The above description broadly reproduces the more important features of the present disclosure.

[0034] As the proposed system is a package attachment, it does not require other modifications to a vessel's propulsion arrangements

[0035] Given the generic basis of this proposition, the embodiments of the disclosure are not restricted to this description and the outline of the construction which are arranged in the following description and the drawings. Other embodiments can also be implemented within the scope of the invention and executed in different ways. In addition, it is understood that the phraseology and terminology used is only used for the description and not as a restriction as it does not demostrate finer details of the system's design deemed uneccessary for the purposes of this application.

[0036] Exemplary embodiments of the invention are explained in more detail with reference to the drawings.

List of drawings

[0037] 

Drawing 1 shows the wake turbulence along the foot of the sail.

Drawing 2 shows the generic concept of the invention

Drawing 3 shows the boom amidships

Drawing 4 shows the boom under camber

Drawing 5 shows the points of attachment of the tension string cables

Drawing 6 shows an expansion mechanism (EM) carriage

Drawing 7 shows states of the expansion mechanism

Drawing. 8 shows an expansion rod extended.

Drawing 9 shows a threaded carrier EM

Drawing 10 shows a modular element of a flexible skirt

Description of the drawings

[0038] Drawing 1 shows the distribution of wind flow around a boat in wind tunnel tests. When the main sail is attached to the boom head, e.g. with a freely tensioned, therefore profile-able foot of the sail, the formation of some wake turbulence along the foot of the sail, caused by exchange of air from the luff-side (positive pressure zone) to the lee side (negative pressure zone) is quite evident. The tow turbulence this produces coupled with the significant turbulence generated by the straight boom (not adapted to the direction of flow) are at the expense of the drive energy. The proposed system greatly reduces this obstacle.

[0039] Drawing 2 shows the generic concept of the invention. It is applicable in all cases of sail booms and their sails as used by various kinds of recreational and professional sailing boats as well for commercial vessels of all sizes carrying boom suppported sails. The accurate location of the extending rods carriage and the extension string cables attachment points along the boom length is critical for the attainment of a near perfect airfoil and maximum effectiveness of the sails driving capacity. The location of the rear attachment, very close to the rear end of the boom, moderates the required load for the attainment of certain camber. This however needs to be balanced with the need to minimise swinging tendencies created by the position of the boom sheet attachment. The risk of additional turbulence at the straight part of the boom at its tail after the rear attachment point is considered negligible.

[0040] Drawing 3 shows a boom amidships with its carriage (6). It is attached to the mast (1) in an articulated manner on all sides in the conventional manner by means of an appropriately modified gooseneck (2), held in an approximately horizontal position by means of a mast support and hauled tightly with a sheet. On the upper side of the boom the foot of the sail is held in a conventional manner. A rod carriage (3) is attached to the boom with safety pin, as shown in drawing 6 below. Extension cable springs (4) are attached to the fore and aft (5), as discussed further.

[0041] Drawing 4 shows a boom under camber with a starboard wind and a hydraulic EM carriage. The boom has swung around the mast (1) via its gooseneck (2) in a favorable angle to the oncoming apparent wind. The EM carriage is lifted laterally and the expansion rod has been activated (3) pushing the luff side string (4) giving the boom an airfoil shape in order to achieve optimal shape of the total surface of the sail and the boom itself. It is thus producing maximum propulsive power under the prevailing wind conditions. The lee spring is not under tension.

[0042] Drawing 5 shows the points of attachment of the tension strings on the boom. The front attachment (3) is located as forward as possible by the mast (1) and its gooseneck (2). The rear attachment point (5) is located aft near the point of attachment of the boom sheet. The EM carriage is located around a quarter of the boom length from the gooseneck. The exact position for both depends on the material used for the boom extrusion and its cross section profile the aim being to ensure maximum linearity of airflow with a minimum boom bending and swinging forces. Note that these string attachments arrangements apply irrespective of the extension mechanism (EM) used.

[0043] Drawing 6 shows a typical expansion mechanism (EM) carriage. The boom and its sail are retained by the expanding pads of the EM carriage via an attachment pin. The carriage has two slots where the expansion strings rest when not under tension. The EM auxiliary lifting hydraulic cylinders are positioned on the edges of the carriage to ensure their free movement when they raise the EM on either side. When the EM is raised, supporting blades ensure its stability in operation. A turbulence limiting hood minimises local wind flow disturbance.

[0044] Drawing 7 shows the expansion carriage and its hydraulic EM in two phases. At rest the lifting cylinders are inactive and the EM rests amidships. Both expansion strings rest in their slots under no tension. When the system is activated, in the second phase, the EM is raised in an almost horisontal lateral position on the luff side but the expansion rod is still inactive and the luff expansion string is also at rest.

[0045] Drawing 8 shows the expansion carriage and its EM in operation. The EM is secured laterally on the luff side and the main expansion rod is extended to a position for attainment of the desired camber, taking the extension string with it. The bow shaped rigid frame is formed and the boom is bent.

[0046] Drawing 9 shows details of a threaded carrier EM that can easily replace the hydraulic cylinder EM shown in the description above. A small electric motor is located at its rear side. The threaded rod is guided by a rectangular blade sliding in a slot of the controlling bloc to be attached to the EM carriage. In such an arrangement alternative for manual operation can br arranged.

[0047] Finally, Drawing 10 shows a modular element of a flexible skirt that can be added to the system as an option. The interlocking elements are introduced to a groove fixed to the underside of the boom, enabling the skirt to assume the camber. As a result the surface of the sail is augmented whilst, due to the inversed T profile of the skirt, the turbulence created due to the pressure differential of the two sides of the sail is minimised. The material used for the skirt is transparent. The actual height of the skirt depends on the space available on deck and the need for an adequate visibility forward for navigation safety purposes.

Claims

1. Principal claim: A Flexible Boom and its Sail System (FBSS), as presented in the description file, provides for a vertically rigid but laterally (horizontally) varying camber airfoil shaped flexible boom. This is bent and stabilised at any desired camber by a laterally rigid frame consisting of the boom itself, a cable string attached to its ends and an expansion rod. An attached sail of simple straightforward design complements the system. As an option, a detachable flexible modular skirt, with inversed T profile, can be attached to the underside of the boom that would increase the effective sail area and minimise the turbulence caused by the pressure differential on the two sides of the sail. In its complete form, primarily - although not exclusively-for sizable vessels, it includes a computerised control system that determines and sets the boom camber according to apparent wind parameters.
The proposed system delivers a significant reduction of wake turbulence compared to a straight boom (which is unable to adapt to the direction of air flow). This feature of the invention provides a significant increase in the effective surface of the sail, including the boom itself. It results in an increase in propulsive power and lowering of the sail's center of effort by converting most of the wake turbulence along the foot of the sail and the boom into a linear wind flow.
Consequent subservient interrelated claims, when compared to a vessel equipped with a more classical rigging plan, and for the same sail area; the invention will allow important benefits from new and improved characteristics:

2. Boat righting couple reduction due to lower sail center of effort.

3. Sharper tacking behavior, due to an increase of the surface of the sail under linear air flow.

4. Smaller ballast due to reduction of righting couple requirement.

5. Lesser heeling due to smaller righting couple.

6. Lighter boat due to need for smaller ballast.

7. Faster vessel due to increase of propulsive power, reduced weight and drag

8. Safer boat due to smaller relative righting couple.

9. Diminished pressure differencial turbulance with optional boom skirt

Amended claims

Amended claims in accordance with Rule 137(2) EPC.

1. A Flexible Boom and its Sail System (FBSS), characterised by, an integral, vertically rigid but horizontally varying camber flexible boom that is designed to achieve close to linear flow on the whole surface of the sail and the boom itself. The boom is bent and stabilised at any desired camber by expansion rod(s) positioned appropriately, inside a laterally rigid frame consisting of the boom itself and cable string lines attached to its ends. The expansion rods convey the bending force produced by hydraulic or electromechanical power source attached to the boom. A boom sail of straightforward flat design is an equally essential part of the system. Given the underline principles of an expansion rod controlling the boom spar camber, and a flat sail we claim that the proposal is new according EPO Article 54.
Dependent claim 1a: An additional option, to the FBSS system is characterised by a detachable flexible modular segments skirt, in inversed open T profile of varying height, attached to the underside of the boom that would increase the effective sail area and minimise the turbulence caused by the pressure differential on the two sides of the sail. This is a useful addition to the sail surface in specific wind conditions. Given the properties of this skirt we claim that the proposal is new according EPO Article 54.
Dependent claim 1b: In its complete form, primarily - although not exclusively - for sizable vessels, the FBSS system includes a computerised control system characterised in that it determines through its sensors along the leech of the sail the expansion rods position that set the boom camber according to apparent wind conditions thus achieving near perfect flow around the sail.. We claim that these features of control package are new according EPO Article 54.

Drawing