Ships – Towing or pushing – Cable fairing
Patent
1984-09-26
1987-10-20
Basinger, Sherman D.
Ships
Towing or pushing
Cable fairing
B63B 2100
Patent
active
047006510
DESCRIPTION:
BRIEF SUMMARY
There is described in U.S. Pat. No. 3,611,976, issued Oct. 12, 1971, to HALE et al., a fairing for tow cables that has, since its inception, become very successful. The fairing has a low drag co-efficient, is relatively inexpensive to make, can be developed with ease and without damage by the crew of the towing vessel even when the vessel is moving at speed, and has only a small tendency to indulge in "kiting".
"Kiting" is the term used to describe the following phenomenon. The fairing includes a tail portion whose function is to streamline the flow of water that has been parted by the cable back together without inducing turbulence. The tail portion has the characteristic airfoil profile needed to achieve this. The tail portion ideally should trail absolutely symmetrically to the direction of motion of the cable, and indeed the tail portion is urged to do so: if it starts to deviate from the symmetrical, a restoring force arises to urge it back. However, even though the restoring force does arise, nevertheless there has been a tendency for the tail portion to deviate slightly from the truly symmetrical position. If this happens, the fairing behaves like a rudder, and carries the cable off to one side. The condition, when it happens, is called "kiting". Sometimes the condition is not stable, the cable kiting first to one side then the other. It is an objective of the present invention to reduce kiting.
Kiting is caused by friction. The tail portion of the fairing has to be divided into segments, so that the fairing can easily flex as the cable flexes, in order that the fairing can follow the path of the cable when they are wound together onto a winch or pulley or sheave or drum, or when the cable adopts its normal catenary curve during use. Not only has the tail portion been segmented, but the nose portion, encircling the cable, has also been segmented. The segments are prevented from travelling along the cable by means of abutments placed at intervals along the cable. Each abutment holds a section of segments in position.
It has been the practice to stack a number of segments together to make up a section of fairing, one segment resting on top of the other, the bottom-most segment of that section resting on the abutment (which typically comprises a collar secured to the cable).
BRIEF DESCRIPTION OF THE INVENTION
One way, in the above described fairing, in which friction can cause kiting is that a segment is kept from perfect alignment by the friction between itself and adjacent segments. Another way in which a segment is prevented from aligning itself is by friction between the segment and the cable.
It is recognized in the invention that friction between the segment and the cable can be alleviated by a large clearance hole. The fairing can in this case easily swivel without any binding or interference due to tightness. The hole, and the cable, need not be made so accurately if the clearance is large. Apart from that, the large clearance has another benefit. In use, the cable tends to lie as far forward in the large hole as it can. The cable actually touches the fairing only at the very leading edge of the cable. The important aspect that follows from the large clearance is that the fairing can rock or roll about this point as a pivot to a certain extent. Thus, in order to swivel in response to movement through the water, the fairing may rotate by rocking or rolling (which is a substantially frictionless operation) instead of the fairing having to rotate about the cable axis, which would involve the fairing sliding around the cable surface. The permitted angle for which the rotation is frictionless is only a small one, but only a small angle is needed: if the fairing were very far out of alignment, the restoring force would be large enough anyway to overcome the friction. Thus, for small angular movements, the movement is frictionless: for large angular movements, normal rotational frictions start to arise. The greater moment, and the reduced friction, combine to maximise the freedom that the fairing h
REFERENCES:
patent: 2435956 (1948-02-01), Craig
patent: 2859836 (1958-11-01), Wiener
patent: 2949090 (1960-08-01), Gerber
patent: 3092067 (1963-06-01), Armstrong
patent: 3224406 (1965-12-01), Clark
patent: 3343516 (1967-09-01), Nichols
patent: 3407777 (1968-10-01), Anastasio
patent: 3611976 (1971-10-01), Hale
patent: 4075967 (1978-02-01), Silvey
patent: 4567841 (1986-02-01), Hale
Basinger Sherman D.
Fathom Oceanology Limited
Hewson Donald E.
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