The marine industry is currently aiming to eliminate its carbon footprint while adapting to evolving environmental legislation. To meet these demands, innovative energy systems need to be adopted. An attractive solution to accelerate the transition towards decarbonization is the adoption of alternative fuels, such as ammonia. Ammonia-fuelled engines are expected to be soon commercially available, contributing to a zero-carbon fleet. However, effective storage of ammonia, whether at low temperature and atmospheric pressure or at ambient temperature under elevated pressure, poses design challenges concerning containment system design and geometry, and the respective auxiliary equipment. Type C tanks are typically cylindrical pressure vessels with heads of varying shapes at their ends. A special category is the trilobe design, which incorporates three interconnected lobes, resulting to increased volume capacity, compared to the single-lobe case. The compact arrangement can assist optimizing the available volume on board, especially to vessels with space availability restrictions. The objective of this research is to assess the influence of different tank geometries, heat insulation characteristics, and storage conditions on the tank holding time (duration until activation of the relief system). A thermodynamic vapour-liquid dynamic equilibrium tank model is employed to simulate the behaviour of ammonia during storage under varying geometrical parameters, storage conditions (liquid volume as a function of level) and insulation specifications. Comparative results of a single-lobe and a tri-lobe configuration are given, including pressure, density, and phase diagrams over time, providing insights into tank performance and ammonia handling.