Stay supported membrane planing seal

A planing seal for a vehicle having a hull with downward extending sidewalls. The seal comprises a plurality of juxtaposed supporting stays positioned parallel to and between the extended hull sidewalls. These supporting stays are connected to the hull at their forward end and remain free at their rearward end. A plurality of forming cables are attached to the hull at one of their ends and at least one of the plurality of cables attach to at least one of the supporting stays intermediate its ends. The cables have a length selected to provide a curvilinear form to the supporting member which allows independent freedom of movement of the stays toward the hull cable attach point. A flexible, non-permeable membrane extends the width of the hull between the sidewall extensions. The membrane has a spaced-apart sealed attachment to the hull fore and aft. The combination of the extended sidewalls and membrane hull attachments provide a pressurizable plenum chamber with seals supported by the stays.

BACKGROUND OF THE INVENTION 
The invention herein described was made in the course of or under a 
contract or subcontract thereunder, with the Navy Department. 
The present invention relates to a planing seal for a gas cushion vehicle. 
In particular, this invention relates to apparatus for providing a 
flexible skirt, that in concert with the vehicles body or hull provides a 
plenum chamber for the containment of the gaseous fluid cushion. 
Air cushion vehicles may have flexible skirt assemblies, made from suitable 
flexible impermeable material, to act as barriers to the escape of the air 
cushion. One of the difficulties encountered with state of the art 
flexible skirt assemblies is that when the vehicle traverses the support 
surface, the assemblies encounter considerable wear resulting in the 
constant cost of replacement and vehicle down time. 
Another difficulty encountered is the lack of sufficient skirt flexibility 
to maintain a minimum clearance above the surface when the vehicle 
develops heave, pitch and roll motions during high forward speeds. 
These and other disadvantages have not been successfully overcome until the 
emergence of the instant invention. 
SUMMARY OF THE INVENTION 
The planing seal of the instant invention comprises a flexible membrane 
constructed of conventional material and supported in part and separated 
from the supporting surface by a plurality of juxtaposed elongated 
supporting stays positioned parallel to the sides of the vehicle body or 
hull. The stays are attached to the ship at their forward end surface with 
their rearmost end free for independent and separate movement. Each stay 
is further attached to the hull intermediate its ends through a cable or 
forming member. 
This manner of construction provides a surface that when exposed to the 
surface being traversed, exhibits a planing action and high resistance to 
wear and abrasion. 
The membrane supported in this manner does not come into physical contact 
with the traversed surface in order to sustain cushion pressure. The 
combined membrane and stay flexibility manifests itself not only in 
response to deflections in the direction and plane of forward motion to 
compensate for heave and pitch displacement, but also in the crosswise or 
lateral direction to accommodate rolling motion. 
To this end the invention disclosed herein proposes several distinct and 
novel features for providing the necessary compliance, by aerodynamic 
properties, and wear resistant qualities disclosed. 
The above and other features of the invention will be readily apparent as 
the description continues while being read in conjunction with the 
appended drawings.

DETAILED DESCRIPTION OF THE FIRST EMBODIMENT 
The structure herein described is not limited in use to a vehicle 
traversing over a body of water, but can also be used by any other type 
vehicle or traversing surface. It is merely desired to form this invention 
in a representative environment for ease of explanation. 
Throughout the drawings and specifications, the same numerals are used in 
the various figures to indicate the identical element or part. 
Referring now to FIG. 1, a surface effect ship 10 has sidewalls 12 
extending downward from the deck 14 for engagement with the supporting 
water surface. A bow planing seal 16 with supporting stays 18 is shown. 
FIG. 2 is a showing of stern of ship 10 including the deck portion 14, the 
sidewalls 12 and the seal 16. The seal 16 is constructed of a plurality of 
side by side flexible stays 18 (see FIG. 3). The stays are of small width 
in comparison to their lengths, tapered in thickness or varied in width or 
both to vary stiffness along its length so that they have a forward and 
rearward flexible portions, 23, 26 respectively with a stiff portion 19 
positioned therebetween. The stiff intermediate portion 19 as well as the 
flexible rearward portion 26 act as a planar surface for riding over the 
surface discontinuities, i.e., waves in the same manner as a water ski. In 
accomplishing this function, the planar section 19, 26 will experience 
forward and aft forces as drag is developed during wave encounter. In 
order to isolate the resulting motion generated by the planar section 
reaction to those forces from the vehicle 10, the planer section ideally 
would be suspended by the flexible means such that the planer would be 
able to react to induced drag loads by deflection fore and aft. This 
method of mounting is, of course, not in equilibrium; to effect the 
required equilibrium, a force must be applied to the upper surface of the 
planer section to maintain the planer portion and support the vehicle. 
This is provided by membrane 28, hereinafter discussed, which is provided 
with an internal gas pressure that is induced between the vessel's lower 
hull (wet deck) 14 and the planer section. This pressure must be contained 
in the forward and aft extremities of the vessel. This is accomplished by 
providing a rear and forward seal from membrane 28 as hereinafter 
explained. The internal pressure will billow out the forward membrane, the 
planer is free to move forward, aft, and vertically in response to the 
wave action without transmitting any motion to the vessel. A feature of 
this stay configuration is its ability to deflect forward or aft in 
response to the planer motion. The stays may be constructed of any 
suitable material that exhibits sufficient elasticity to flex in infinite 
number of times without breaking. An example of such material that may be 
utilized is, but not limited to, metal, fibreglass resin, GRP systems and 
the like. The stays are supported at their forward end 20 by a hinge type 
attachment 22 to the vehicle hull 14. A former cable 24 is attached to the 
hull some distance aft of the hinge 22 and secured at its other end to the 
lower end of the stay 18 some distance from its free or unattached end 26. 
The cable length is selected so as to effect a curved shape to the stay 
when subjected to a positive gaseous pressure differential on its upper or 
hull side, leaving the free end capable of deflection within the cable 
length independent of the restrained portion of the stay 18. The former 
cables may be constructed of any suitable material having sufficient 
strength to support the required load and may be in the shape of cables, 
straps, etc. Additional stays are secured and formed in the same manner 
across the width of the vehicle terminating at each side against the 
vehicle sidewalls 12 which, as shown, extend down and are fully submerged 
in the water. The stays may be connected laterally to one another by 
flexible membrane 28 or may be free between their ends and support the 
membrane 28 on their upper surfaces. The membrane may be fabricated from a 
flexible resilient impervious material such as, but not limited to, 
reinforced, rubber, neoprene and the like. In either manner, the stays and 
membrane effect a continuous skirt consisting of the membrane supported to 
a controlled contour by stays. The relative spacing of the stays 18, the 
amount of stay area occupied by the membrane and the ratio of stay width 
and thickness to spacings are dependent variables inherent in the 
implementation of the design. Inasmuch as stay and membrane data are 
variable within the constraints of the design, so too are the number and 
location of the former cables 24. 
The aft portion of membrane 28 is gathered to form a plurality of 
convolutes 30. The convolutes are held in place by additional cables 25 
constructed as cables 24. The number of convolutes gathered in this manner 
is a function of the amount of unsupported span required or allowed within 
the constraints of the aforementioned variables, which include gas 
pressure differential, membrane strength and geometric limitation inherent 
in the design implementation, and as such constitutes a dependent 
variable. This apparatus yields a plenum chamber 32 of a three sided 
cross-section bounded at its top by the vehicle hull 14, at its forward 
extremity by a curved stay stiffened membrane assembly and at its aft 
extremity by a convoluted flexible membrane. The two ends of this plenum 
being closed off by submerged side hull structure. The internal portions 
of the membrane constitute load balancing members only, capable of holding 
the convoluted shape of the flexible membrane portion in its predetermined 
contour relationship and as such they offer little or no resistance to 
free gaseous motion within the plenum chamber created by this total 
assembly. The internal portion of the membranes, therefore, will be vented 
or tapered in such a manner as to efficiently perform their load carrying 
in a lateral plane and their internal venting function see FIG. 5. 
DETAILED DESCRIPTION OF THE SECOND PREFERRED EMBODIMENT 
In the aforementioned description, no consideration has been made relative 
to the position of the main cushion or lift pressure as described in the 
planing seal of the first embodiment which could apply to both fore and 
aft position, however, consideration of the position of the cushion area 
pressure will allow for certain changes resulting in a less complex 
structure. 
If the cushion area pressure is considered as existing aft of the free 
edge, i.e., the seal is being utilized as a forward seal, pressure 
sufficient to provide a downward force on the stay or planer surface 
exists within the cushion area, it no longer becomes necessary to provide 
the convoluted portion 30 of flexible membrane 28, see FIGS. 2 and 4, as 
would be required in an aft application due to the existence of ambient 
pressure aft of this flexible membrane. Variations in pressure along the 
planing surface may be obtained, and thereby variable flexibility or 
stiffness of the seal system, by removing the aft convoluted portion 30 of 
this membrane 28 and relocating the aft membrane hull connection forward 
of the former cables 24 attachment. 
Referring now specifically to FIGS. 6 and 7, a stay supported membrane 
planing apparatus is mounted as hereinbefore discussed. The flexible 
membrane 28 is attached at the upper stay 18 attachment position on hull 
14 and terminated aft of this point in such a manner as to effect a curved 
shape of predetermined contour when subjected to a pressure rise 
originating from the hull side. Additional forming cables 27 are installed 
to provide restraint and contour control to the planer section. The 
necessity for aft containment of the plenum chamber 32, is no longer 
required, therefore, membrane 28 will not be attached to the planer stays, 
but will function as a separately inflated unit, i.e., separate from the 
planer pressure system. The membrane 28 may also be provided with bleed 
holes 34 that allow for free flow of air from it to the main cushion area 
36 aft of the bow seal and thereby by the size, location and quantity of 
holes 34 provide a controlled compression or deflation rate when subjected 
to upward deflection of the planer action. 
OPERATION OF THE PREFERRED EMBODIMENTS 
Gas pressure is introduced from the hull side of the plenum chamber 32 at 
location 33, see FIG. 4, to create a pressurized chamber, that when 
balanced by controllable ducting systems (not shown) to the area forward 
or aft of this plenum chamber, effects a cushion area reaction against the 
water surface and the vehicle hull and a seal area exhibiting the 
properties of a spring. The stiff, curved surface of the stay supported 
membrane assembly, functions as a planing member when subjected to the 
surface of the water being traversed. During traversing, encounters with 
nominally even water surfaces, the stay supported membrane assembly 
element of the seal component will be balanced by the seal and cushion 
pressure ratios to assume a partially submerged position such that this 
element will be subjected to a planing action due to the hydrodynamic 
forces encountered, thereby decreasing the drag component that would 
otherwise be induced by a submerged or contact type seal element and 
providing a lift component to augment the main cushion lift requirements. 
The controlled shape, the materials of construction available for the 
design of members having the properties of flexibility of the stays 18, 
and their multiplicity of occurrence as a total portion of the entire 
element area, contribute to an increase in the design life predictability 
of such a seal element in comparison with a membrane only type of 
assembly, without sacrificing lateral flexibility. During encounters with 
water conditions conducive to the initiation of heave or pitching motion 
to the vehicle via the water contacting elements, the planing element of 
the seal will be deflected aft due the increased drag induced by the 
hydrodynamic action imposed upon it by the force of the increased volume 
of water to which it is exposed. 
The low inertia of the seal system as opposed to the large inertia of the 
vehicle to which it is attached will effect a decrease in the volume of 
the seal area plenum chamber caused by the rotation of the stay supported 
membrane assembly about its forward attachment point. This action brings 
about a change in the contour of the stay supported membrane assembly to 
one of decreased curvature. This change in contour performs the function 
of allowing the planer surface to lay flat against the vehicle under hull 
when fully deflected, thus facilitating stowing when the system is 
inoperative and as a stiffened member does not tend to lose its smooth 
planing surface contour due to local, unbalanced pressure gradients as 
could an unstiffened member. Therefore, the stay supported membrane 
assembly functions as a smooth, variable contour planing surface. In 
conjunction with the aft deflection of the seal element system by rotation 
of the stay supported membrane assembly, the decrease in volume of the 
seal area plenum chamber causes a rise in the gaseous pressure of this 
chamber which increases its relative stiffness and at a predetermined rise 
in this chamber pressure a transfer of gas occurs from the plenum through 
its supply port, at location 33 of FIG. 4, into the main cushion area. The 
cumulative results of the energy absorption properties of the stay 
supported membrane assembly, the chamber pressure rise and subsequent 
transfer of gas through the supply port to the main cushion area bring 
about a condition of controlled deflection of the seal components to the 
action of rising water conditions allowing the seal elements to maintain 
their function as cushion seal and planing devices without transmitting 
the effects of these water conditions to the vehicle that they support. 
During encounters with water conditions that would tend to bring about seal 
element deflection up to and including full seal height, compliance will 
be maintained by contact with and immersion into the surface traversed by 
the highly flexible element 26 of the stay supported membrane that extends 
beyond the attachment point of the former cables 24 and the aft convoluted 
membrane portion 30. During these encounters, planing action will have 
ceased due to the seal element deflections out of and away from the water 
surface, but the flexible free end will continue to provide the required 
main cushion sealing function without inducing heaving or vibration motion 
to the main seal element, and will allow a smooth transition from and to 
the planing efforts of main seal element immersion. 
During high speed encounters with relatively smooth water surfaces, the 
planing element of the seal will deflect aft to a position dependent upon 
the resultant force generated by the drag and hydrodynamic forces 
manifested by this encounter. As velocity increases, these forces produce 
a condition that decreases the total wetted area of the stay supported 
membrane assembly, placing dependence of seal function maintenance upon 
the flexible free edge of the seal assembly. Its high flexibility enables 
it to function in this capacity to maintain seal system efficiency by 
deflecting under the action of local surface discontinuities and vehicle 
pitching. 
The variations of the second embodiment would provide yet another measure 
of stiffness control to total deflection spectrum of seal operation. 
Functioning as a flexible member subject to variations in surface 
irregularities up to those sufficient to produce planing section 
deflection to the limit of membrane position, the restraining or dampening 
force exerted by the planer-cushions pressure system will provide a higher 
measure of compliance or flexibility than would a system employing a 
higher seal pressure containment system. When deflection of seal element 
exceeds a value determined by craft design criteria, the planer section 
would encounter an increasing stiffer reaction to deflection due to the 
restraint provided by the higher pressure of the membrane element during 
compression of this member. The overall effect of this feature would be to 
provide a much stiffer or dampening effect when unrestrained planer motion 
or accelerations become unduly excessive. 
While maintaining compliance to longitudinal variations encountered while 
traversing over a wide range of conditions, the lateral compliance 
inherent in the concepts of the stay supported membrane assembly, provides 
the necessary flexibility to successfully contour surface irregularities 
and vehicle motions that occur as rotation about the vehicle longitudinal 
axis. 
The embodiments outlined above will serve to produce a flexible seal that 
can be applied to both fore and aft sealing of cushion area, fore and aft 
being understood as being indicative of the seals position relative to the 
forward motion of the vehicle over the surface traverse. 
Many changes may be made in the details of the instant invention, in the 
method and materials of fabrication, in the configuration and assemblage 
of the constituent elements, without departing from the spirit and scope 
of the appended claims, which changes are intended to be embraced 
therewithin.