Appendage design

Abstract

Submarines usually have three groups of appendages: sail; forward control surfaces; and aft control surfaces. Appendages contribute a considerable increase in drag, and need to be considered carefully. There are two approaches to sail design: a foil type; and a blended type. The blended type of sail has a larger volume than the foil type, and is better faired into the hull. If the sail is at an angle of attack it will generate a side force high up resulting in a heel angle (particularly snap roll) and a force and moment in the vertical plane on the hull, resulting in a stern dipping tendency. The magnitude of the side force when manoeuvring will depend on the distance of the sail from the Pivot Point. The location of the sail will also affect the turning radius. The forward planes can be located in three different positions: midline; eyebrow; and sail. The pros and cons of each of these are discussed. The aft control surfaces may include fixed and movable surfaces, with the fixed surfaces increasing stability, and the movable surfaces used to change trim, and hence to make large depth changes, and to turn the submarine. Different aft control surface configurations include: cruciform; X-form; inverted Y; and pentaform. The pros and cons of these different configurations are discussed.