<p>This study presents a design-oriented investigation of multi-cylinder horizontal tank assemblies as dual-purpose buoyant and liquid-storage elements for floating offshore wind turbine (FOWT) platforms. A hydrostatic-consistent geometry framework is established by coupling tank diameter and filling ratio so that all investigated configurations satisfy platform-level static equilibrium. Within this admissible design space, unbaffled and baffled two- and three-cylinder assemblies are analyzed using Reynolds-averaged Navier-Stokes simulations with a Volume-of-Fluid free-surface formulation. Prescribed pitch motions are imposed to isolate internal sloshing effects, and the resulting sloshing-induced forces and pitching moments are used to compare the dynamic characteristics of the candidate layouts. For unbaffled tanks, the response is governed mainly by filling ratio and excitation frequency. Intermediate filling ratios (<i>H</i>_<i>w</i>/<i>D</i> ≈ 0.6–0.7) providing the best compromise between storage capacity and load levels. However, geometry variation alone does not generate a meaningful phase offset, and the resulting sloshing response remains predominantly unfavorable under the prescribed excitation conditions considered. The introduction of transverse baffles substantially reduces RMS force and pitching-moment levels and also produces a noticeable phase shift in the sloshing-induced moment relative to the imposed motion. Among the configurations examined, a symmetric two-baffle arrangement provides the most balanced overall performance. Overall, the results indicate that multi-cylinder horizontal tanks can function not only as buoyant and storage components but also as tunable internal liquid systems within an early-stage design framework. The proposed methodology provides screening-level guidance for preliminary design and a basis for subsequent studies incorporating fully coupled wave-platform interactions and global response analysis.</p>