Project 1266 - Rubin - Zheleznyakov - Fleet Minesweeper
The project was developed in 1972. The main task of the ship was considered to fight against deep mines. The final tactical and technical requirements for the design was issued in 1979. Features: deep-pin trawl complex, new mine-detector CEO, STPA, the installation of small stroke and bow thruster. Planned construction of a series of 12 units in 1983-1985. Three ships were laid. During construction, it revealed the difficulty of construction of such a large [222.4 feet LOA] glass reinforced plastic [GRP] hull ship. The Mid-Nevsky SZ series was limited to two units (building a third ship was pulled on the metal).
Current ship hulls are normally made of steel which is magnetic and thus entails the well-known disadvantages thereof, especially during war-time conditions. Several studies have indicated that for hulls longer than about 200 feet, even carbon fiber composites do not provide the necessary stiffness and strength required for the hull. Furthermore, the cost of carbon fiber composites which is currently $12-18 per pound of carbon fiber as compared to $0.45-$0.50 per pound for high strength steel [US prices], would be prohibitive for ships of this size. Low cost, high performance composite materials such as glass fiber composites (GRP) using resin transfer molding processes which are presently used in patrol boats, Corvettes and mine hunters, do not offer the stiffness nor the in-plane strength required for long hulls of combatant ships or other large commercial ships.
Boat hulls are usually made from the outside-in by applying the gel coat to a waxed mold and then adding the layers of glass reinforcement and polyester to complete the hull. The gel coat, the pigmented and filled polyester, is used to hide the underlying glass composite structure, to color the hull, to produce a flexible surface which acts as a shock absorber and to help keep water from diffusing into the composite. Once the gel coat has become tacky to the touch, laminating resin is sprayed onto the gel coat and a reinforcing mat is applied with serrated rollers. This is done to squeeze out entrapped air, to obtain thorough wetting of the glass by the resin and to keep high glass to resin ratio.
Decked GRP hulls are conventionally made in two sections which are subsequently bonded together. The top edge of the lower hull moulding is rolled outward to give a narrow flange to which the deck is attached. This flange, which is often protected by a rubber rubbing strip, must be narrow and represents a line of weakness. The "rolling mould" approach to the manufacture described above allows the top edge of the hull moulding to be rolled inward:--the mould for the hull section is made with a removable top. This allows the flange for attaching the deck section to be made much wider than normal, so the attachment is much more secure. It also allows the gunwales to be reinforced to accommodate attachments for the central bridge section and also stanchion sockets for a grab line. Each hull becomes, in effect, a closed tube, and is therefore very strong in relation to its weight.
The load-carrying mechanism for long ships is by axial tension and compression in the hogging and sagging mode between waves. The technology of composite sandwich construction, which is common in smaller ship lengths or boats, does not satisfy the carrying capability for sea loads in longer ship hulls. The in-plane strength of the composite material is therefore critical. Moreover, for small ships and boats, the bending strength of the composite material is critical. The present technology of composite sandwich construction which is common in smaller ship lengths or in boats would not add to the carrying capability for sea loads in long ship hulls.
Many boats are designed to use GRP either as a hull material or for the super-structure and while small craft can generally be over-designed to resist rough handling and to have a high degree of compound curvature to provide additional strength and stiffness, as vessel size increases structural problems can arise. This is because it is uneconomic to provide the same degree of over-design in larger craft, and in such craft areas of flat panelling also become larger. The same situation arises in high speed craft which encounter severe operational conditions and require relatively flat planing surfaces. Large areas of flat panelling are also found in super-structures and deck-houses on ships and in modules on offshore rigs and platforms.
Glass reinforced polyester (GRP) composites, the structural material of many boats, are subject to a degradation phenomenon known as blistering. The surface blister is a bump that appears on the hull surface, usually under the water line. It grows because a pocket of acidic fluid developes within the hull. Blisters range in size from a few millimeters to several inches in diameter and normally occur near the gel coat-laminate interface but have been observed deeper in the hull.
Stresses are produced during boat use. Peak stress is produced by wave action, rigging stresses, impact stresses and bouyancy stress. Internal cracks produce stress concentration sites at the crack tips which can lead to further cracking or accelerated chemical attack. Strictly speaking, the crack does not produce a new stress but intensifies the stresses. Cracks can magnify a stress by hundreds of times.
With GRP panels high stress levels and large areas of flat panelling tend to lead to greater deflection of the panel under load. It has been found that the panels are then subject to shell surface cracking and even, because of the lack of reinforcement extending through the laminated structure, to inter-laminar debonding. Where panels are formed by building-up one layer upon another, e.g. in a GRP panel, the use of thinner panels reduces the time needed for construction and thus the labor costs. These consideration have tended to limit the use of such materials.
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