3015. A Methodology for Selecting Naval Ship Acquisition Margins

Paper

Abstract

Acquisition margins are included in a weight estimate to account for unknown or unanticipated growth in weight or KG which occur in future design phases. Weight and KG growth occurs for a variety of reasons during the course of a design. Some of these reasons are the following:
1. Errors carried over from previous design phases;
2. Requirement changes which result in equipment/system changes;
3. Ship arrangement/configuration changes;
4. Increased detail in design definition and weight calculations;
5. Material/equipment model changes during detail design and construction;
6. Deviation from construction drawings;
7. Shipyard unique design and construction techniques;
8. Increases in developmental systems? components.
Because it is a fact that weight and KG increases will happen, it is important to account for them from the beginning of the design. This is done by adding margins to the weight estimate at the start of the design that are equal to the anticipated growth. Once these margins are established and there is a single design concept, the margins are then depleted to offset the growth in weight and KG as it occurs. This allows the design to remain at a constant displacement and KG that facilitates the overall design effort. For example, without margins any growth in KG could jeopardize stability and could require a major configuration change in a later design phase that is disruptive and costly. With margins, the stability can be validated early in the design and as long as the growth does not exceed the margins, the stability will remain satisfactory throughout the course of design and construction. Ideally, the ship will be delivered at the original estimated displacement and KG with no margins remaining.