Journal of The School of Marine Science and Technology,Vol.5 No.1
Basic Study of A Hull Form Restoration Method
―The Development of a Multi-Laser Projection System―
Shunsuke TANAKA and Hikaru YAGI
Abstract
Ships of all times and places have been playing an important role in transportation of cargoes and also the culture. When we study the maritime cross-cultural exchange in East Asia, the role of ship is outstanding. Recent years, ancient wrecked ships have been excavated in fairy good conditions from the sea in China and Korea, and intensive studies have been conducted from the stand point of archaeology and nautical archaeology.It is understood that engineering approach into such ships may contribute to make various historical events or incidents clear technically by confirming the historicity of documentary accounts and oral traditions. However, researches from engineering aspects are very limited especially in ship performances.One possible reason is that excavated ships are very limited in portion of the whole hull, and reconstruction of the exact whole hull shape is prevented. Another reason may be the difficulties in hull form conservation during excavation and reconstruction of wooden hull.In order to measure the hull form with the accuracy allowing us to draw hull lines,direct on-site measurement is preferable but difficult.On the other hand,recent technologies made it possible to measure various shapes without direct contact to the object.One typical application is ‘laser optical systems’used in civil engineering,architecture and archaeology and so on. This is basically triangular survey to each point of target, and requires fairly long time.
Another method is ‘stereo photo system’which requires no direct contact.But the optical color-signal detection
depends on the distinctiveness of color of the target point on the body,and such condition is often beyond our control.In the cases of wrecked wooden ships, it is usual that the hull is monotonic color of water-logged smooth surface.This makes it difficult to detect the exact three dimensional shape.
In this study, stereo photo method is investigated combined with a newly developed multi-laser projection
apparatus which makes it possible to mark multiple clear and distinctive targets on the body.
For the first step, a model ship is used to simulate a wrecked ship with smooth and monotonic color body.The
analysis of photographs and consecutive treatment of fairing technique are applied using a computer aided engineering
tool in ship design. The results indicated that the ship dimensions and fullness factors of the hull form can be
derived with reasonable accuracy within several percent.