Developing the next generation of climate modelling tools to increase throughput and ensure performance portability is crucial. The choice of an underlying grid for ocean modelling, an important climate compartment, is difficult. The almost fractal-like boundaries of ocean domains and quickly changing bathymetry often make unstructured triangular meshes the preferred choice. Their construction is simple and adaptability high. An alternative is Block-Structured Grids (BSG), an unstructured collection of blocks, each containing a topologically structured mesh. We present the performance impact of utilizing BSG on diverse hardware employing SYCL and the current state of BSG generation. Computation on unstructured grids is associated with suboptimal performance due to irregular memory access patterns, whereas structured grids enable near-optimal efficiency. Our shallow water equations solver UTBEST exploits the regular memory access pattern on a per-block basis provided by the BSGs to enable performance gains. This impact is studied with respect to the block size and the influence of unstructured blocks. As SYCL allows programming for heterogeneous parallel computing in C++ on CPU, GPUs (and FPGAS), two major SYCL implementations (oneAPI, AdaptiveCpp) with multiple backends CUDA, OpenMP, OpenCL are evaluated.