This thesis quantitatively assesses two energy efficiency retrofits fitted to two LNG carriers, LSA and PL: a silicone fouling-release coating and Propeller Boss Cap Fins (PBCF). Using ISO 19030 based comparison of pre- and post-retrofit data, each retrofit's effect on required power is measured across speed and loading condition, then converted into fuel-cost savings and investment metrics. Both retrofits show a measurable, positive improvement. The silicone coating reduces required power by 0.54% to 8.01%, larger in Ballast than Laden and at low speed than high speed. PBCF reduces required power by 10.42% (Laden) and -2.43% (Ballast) at real average speed, a small Ballast loss offset by Laden's larger gain, on a thinner data sample. Both retrofits recover their cost well within their economic life: the silicone coating returns an NPV of approximately EUR421,000, based on measured fuel consumption rather than power reduction (IRR 34.6%, payback 2.24 years), and PBCF returns an NPV of approximately EUR2.1 million (IRR over 490%, payback 74 days), reflecting its low capital cost. Neither retrofit's benefit is fixed: both vary meaningfully with loading condition and speed, showing that evaluating retrofits against a vessel's real operating profile gives a more defensible economic case than a single-point estimate.