The tank top is a deck level formed by the inner-bottom of a double-bottomed vessel. Tank tops tend not to extend through aft of the aft peak bulkhead, or forward of the forepeak bulkhead, as hull curvature makes access difficult and limits utility. These spaces instead will favour open floors. Tank tops tend to be of limited height. Often, they will be lowered or discontinuous between engine girders, allowing the engines sump to be lower. The space between the tank top and hull is generally utilized for tankage.
Tank tops are not typically cambered. Generally, they run parallel to the baseline (as opposed to following the fairbody of the hull). Thick deck plate is often dictated by the requirement of the tank top to function as a tank crown. As a result, the tank top on double bottomed ship is a significant contributor to longitudinal strength.
Within the limits of classification and regulatory requirements, the tank top height can be varied as required to achieve adequate capacities of fluids or ballast. The height may also be taken a bit deeper to provide a buffer against damage in cases of grounding.