4.1 Preparation of Scale Models
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC/Circular.616 – Evaluation of Free-Fall Lifeboat Launch Performance – (22 June 1993) - Annex – Evaluation of Free-Fall Lifeboat Launch Performance - Section 4 - 4.1 Preparation of Scale Models

4.1 Preparation of Scale Models

  4.1.1 Model tests are conducted to develop an understanding of the velocity, acceleration, and trajectory of a free-fall lifeboat during launch. Such studies usually are not conducted to determine the structural behavior of the lifeboat. For a scale model to accurately and reliably predict the behavior of a prototype, the various parameters of the model must be in proper proportion with those same parameters in the prototype. However, not all parameters must be in the proper proportion for the model to serve a particular task. Some parameters are not relevant to the behavior being studied or have negligible effect on the behavior of the system. These parameters, therefore, can be neglected. In this sense, there are primarily two types of models that are of interest in engineering studies: true models and adequate models. A true model is one in which all significant parameters of the prototype are reproduced to scale (Murphy, 1950).

  4.1.2 An adequate model, on the other hand, accurately predicts one or more characteristics of the prototype but is not useful for predicting all characteristics of the prototype. Adequate models are often used if all parameters of the system cannot simultaneously scaled. This is particularly true in hydrodynamic modeling (Baker, 1973). In such models, the tests must be conducted in special, and often unavailable, fluids if all of the parameters are to be correctly scaled. Because the tests are usually conducted in water, it is impossible to satisfy both Froude's Number and Reynolds' Number unless full-scale models are used. One must decide if the phenomenon being studied is gravity-dominated in which case Froude scaling would be used or if it is drag-dominated in which case Reynolds' scaling would be used. In either instance, the model tests are limited in what they can predict but if the neglected phenomenon is insignificant, the model and test results are still adequate. Only from knowledge of the fundamental behavior of a system can insignificant parameters and the adequacy of a model for a particular task be determined.

Parent topic: Section 4
Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.