Page 153 - Practical Design Ships and Floating Structures

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1 INTRODUCTION

It is well known that there is a greater demand of data and acceptable techniques for the preliminary
design of fast ships. In the same time there is an increase of interest for trimaran ships design, due to
the business that they offer for bigger spaces and higher speeds.

Actually intensive researches concern the minimization of the total resistance by the optimization of
the main hull and outriggers form, of the longitudinal and transversal outrigger positions, of the ratio
between the main hull and the outrigger displacement. The peculiarities of trimaran vessel furnish two
main applications: the first one in the military field, like polyvalent frigates, and the second one in the
commercial and tourist fields, like ferries or passengers ships in service on brief routs.

As far as the naval field is concerned, the presence of a great deck area consents to amplify, the active
defense component, with all the advantages for efficiency and operational flexibility. It also allows, the
installation of more efficient weapon systems of modular type and a better disposition of operational
and life spaces (figure 1).
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Figure 1 : General Layouts of 160 m trimaran frigate

The conformation of the hull assures an elevated stability, a good seakeeping behavior and
consequently a greater efficiency of the weapon systems. The lateral hulls also assure a protection of
the main hull.

2 PRELIMINARY DESIGN OF TRIMARAN SHIP: AUTONOMY, GENERAL LAYOUT,
FORMS AND GEOMETRY OF THE HULLS
According to a different comfort request and, consequently, a different voyage tolerable time on board
of a fast ship, by a passenger and a driver, the following upper limits of autonomy can be assumed, for
a transfer velocity of about 40 Knots:
- 250 nautical miles for the tourist application;
- 400 nautical miles, for commercial application.
As far as the naval field is concerned, elevated autonomy is required for carrying out long distance
missions.

In the commercial and tourist fields, the following ranges can be estimated from the market trend:
length between 85 m and 150 m; velocity between 36 to 45 knots and with medium load capacity of
about 1000 passengers and 250 cars.

General layout study and preliminary choice of the arrangements for tourist and commercial
application can be carried by the following criteria: -Minimum area available for each passenger; -
Area of the car decks according to the load capacity; -Shipping from stern on the main deck garage; -
Height of deck garage of 5m at least, for bus or T.I.R..