Ships – Bulkheads and doors – Doors
Reexamination Certificate
1999-08-24
2001-04-03
Avila, Stephen (Department: 3617)
Ships
Bulkheads and doors
Doors
Reexamination Certificate
active
06209471
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a door structure, and more particularly to a door structure for ships with low Radar Cross Section requirements.
In order to make a ship invisible or nearly invisible to radar, a ship is build such, that when a radar beam irradiates the ship the reflection of said radar beam is directed away from the radar source, as a result of which the ship is not visible on the radar. However, radar is still further developed and smaller objects can be detected by radar. Traditional door structures, which are commonly used in such radar insensitive ships, still have protrusions and/or openings, which are particularly visible for radar,
Any opening or recess larger than approximately ¼ inch is especially visible for radar and therefore the connection of the conventional door to the bulkhead is visible.
SUMMARY OF THE INVENTION
An object of the invention is to provide a door structure, which is in contrast to traditional door structures less or not visible for radar.
This object is achieved by a door structure according to the invention, which door structure includes a door, a door opening in a bulkhead portion and a stiffening member extending peripherally in said door opening, wherein said door is hingedly attached to said bulkhead portion and is movable between a position substantially covering said opening and a position substantially freeing said opening and said door comprises a flat plate with peripheral edge zones, which extend to at least one of said stiffening member and the edge zones of said bulkhead portion bounding said opening, wherein the distance between said peripheral edge zones and at least one of said stiffening member and said edge zones of said bulkhead portion is smaller than ¼ inch.
As a result of the flat plate there are no protrusions on said door, which can reflect the radar beam in the direction of the radar receiver. As the flat plate also extends to the edge zones of the bulkhead portion bounding said opening, this door structure according to the invention does not have any openings which would reflect the radar beam in the direction of the radar receiver.
In a preferred embodiment, the peripheral edge zones comprise a bent portion, which is bent towards said bulkhead portion, such that a distance between said peripheral edge zones and said bulkhead portions is reduced. Because of the flat plate, the radar reflection of radar beams, which irradiate the door structure in a substantially perpendicular direction, is reduced.
Flat vertical surfaces will reflect horizontal radar beams horizontally back to the radar source and this makes these surfaces visible to the radar source. Surfaces placed under an angle with the vertical, will return horizontal radar beams not to the radar source, where they become visible, but will direct the radar beams upwards and avoid the beams from reflecting horizontally to the source. This is an effective means to make large surfaces less—or invisibly for radar. Any openings or protrusions in the flat surfaces may reflect beams horizontally, back to the radar source and thus make these openings and protrusions visible. The current state of technology makes openings and protrusions smaller than ⅛ inch not or barely visible for radar.
A curved bent portion will always have a part which reflects the radar beam directly to the radar source and receiver. It is therefore preferred that the bent portion is substantially flat. However, due to manufacturing conditions it may be preferred to provide the peripheral edge zones with a beaded edge.
The invention can also be applied to the vertical opening that is normally visible between the two leaves in the middle of a double door. The invention also provides for the cover of this vertical opening and protrusion.
According to the invention, there is also a door structure provided, including two door sections wherein the edge zones of the flat plates facing each other are bent in a direction substantially perpendicular to the direction of said flat plate.
In this case, preferably the edge zones of the flat plates facing each other are bent in a direction substantially perpendicular to the direction of said flat plate and the distance between the facing edge zones is smaller than ¼ inch.
When a door structure is formed by two door sections, which can open independently of each other, it is necessary to reduce or eliminate the gap between the door sections. This can be done as described above, or by constructing the door sections such, that one door section overlaps another.
REFERENCES:
patent: 6003461 (1999-12-01), Blanchette et al.
patent: 6009669 (2000-01-01), Jardine et al.
patent: 6059230 (2000-05-01), Leggett et al.
Avila Stephen
Mafo Holtkamp B.V.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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