BALLASTING AND TRIM SYSTEMS 



In addition to descending to the bottom, 

 ascending to the surface and running hither 

 and yon, submersibles must make small ad- 

 justments in buoyancy and trim when sub- 

 merged. Such changes serve the following 

 purposes: To follow a sloping bottom, to han- 

 dle additional weight in the form of water or 

 biological/geological samples, and to surface 

 with sufficient freeboard for safe transfer of 

 personnel and equipment. All of these func- 

 tions are performed by changes in the vehi- 

 cle's buoyancy or trim. The approaches to 

 buoyancy and trim control are many, and 

 most are successful. In some cases trim 

 changes are accomplished dynamically with 

 the vehicle's thrusters and dive planes. But 

 use of thrusters calls for electrical power 



which is limited, and attitude changes using 

 dive planes require that the submersible be 

 underway, a condition not always compatible 

 with the mission. 



The nature and capacity of a ballasting 

 system depend upon several factors, but the 

 total submerged displacement of the vehicle 

 and the desired payload assume primary im- 

 portance. Other considerations might include 

 desired reaction time of buoyancy changes 

 and the anticipated number of cycles such 

 changes may require on one dive. 



WEIGHT AND VOLUME 

 ESTIMATES 



As a first approximation, the designer may 



279 



