Page 393 - Practical Design Ships and Floating Structures

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potential advantages of FRP over other materials for small craft construction, such as the higher
strength, the lower maintenance and the lighter weight etc. (Edmunds, 1999) However construction of
the hull, deck or other structures of a ship usually necessitate a mould to mantain a desired shape by
supporting laminas until completely cures. The method is suitable for the mass production of identical
boats but even the minor variations in shapes to meet owner's requirements is not easy to achieve. To
construct a ship of different shape, new mould should be constructed again and resulting higher cost
and longer construction period.

The philosophy of using developable surfaces for ship hull construction has initially applied
towarships to reduce construction costs and times. Application of the same idea to the merchantship
has been carried out at Burmeister & Wain Shipyard recently. They reported 20% reduction in man-
hours required to produce a hull that implements developable surfaces in its design.(Norskov &
Lauritsen, 1985) It is well known that the use of a developable surface has several advantages over
conventional one including lower labor costs in construction, smaller capita investment in equipment,
ease of repair and simple tools for construction.(Calkins etc., 1989)
Applying the developable surface concept in steel ship, the hull surface can be formed.by simple
bending and welding of the developable plates. Using the same method in construction of a FRP ship
needs extra stacking of laminas to obtain an adequate strength. Unlike the traditional FRP
construction method using a mould, a new construction method using an adjustable mould is proposed
in the present paper. In the method, hull surfaces are developed onto several plane pieces and thin
FRP plates identical to the pieces are manufactured on a flat bed. The plates are simply bended along
the generation lines to form the three-dimensional hull shapewith help of an adjustable mould. The
construction of the ship is completed with additional stacking of FRP to obtain the required hull
strength. The present paper briefly introduces a newmethod for FRP boat constructions and an
adjustable mould including a newly designed jig system.

2 HULL DEVELOPMENT
A new effective and productive method for building small FRP fishing boats and planing boats is
proposed in this section. The new method is applied to the construction of a small FRP fishing boat of
3 ton class. Figure 1 shows a typical fishing boats and Figure 2 shows the new hull form consists of
developable surfaces. The box keel and the spray strips shown in the Figure 1 can be treated as
appendages, therefore and hence only the main hull is drawn in Figure 2. Modification of the parent
hull into the developable one, minor changes in the hull shapes are inevitable but the principal
characteristics of the parent ship are almost preserved as shown in Table 1. Model tests are carried out
at the speed of 15 knots to compare the resistance characteristics of the ships. It is found that the
resistances of the ships are almost identical.

I II
Figure 1 : 3 Ton class parent hull Figure 2: Lines of the developed hull