The manuscript “Multi-fidelity actuator line modelling of tandem floating offshore wind turbines” by Firpo et al. documents a numerical study on how flow simulation methods at different levels of fidelity (URANS, LES) impact the wake of a floating wind turbine modelled by actuator line methods. The impact of the wake on the loads of a second wind turbine placed downstream is also investigated. The paper confirms many known phenomena, such as that inflow turbulence reduces the difference between the wakes of a fixed and a floating wind turbine, and that LES is better than URANS when simulating wake dynamics. This manuscript could be considered for publication if the following comments are taken into account.

1. My main concern is about the title of the manuscript. Conventionally, “multi-fidelity” modelling refers to simulation methods that employ models at different levels of fidelity simultaneously and consider information exchange at the interfaces between these models. However, this work compares URANS and LES without coupling them together in the same simulation. This cannot be referred to as multi-fidelity.
2. My second concern is also about the title. The focus of the work is mostly on the wake of a single floating wind turbine. It is only in Section 6 that the second wind turbine is introduced; only one of seven sections concerns the tandem configuration, so I don’t think the title emphasizing tandem configuration is appropriate.
3. The reason why URANS cannot reproduce large coherent structures should be studied in more depth. In principle, these large structures should not be so difficult to predict. Please verify whether the same phenomenon still occurs if the URANS employs the same grid as LES.
4. It is found that the inflow triggers significant meandering in the wake. The spatial and temporal scales are very important to the receptivity of the wake. In Figure A1(b), the low-frequency peak of the experimental data and of the simulations differ considerably. Please try to see whether this discrepancy persists if a different inflow turbulence is employed.

Some point comments are:

1. Line 191, please specify how the Courant number is defined. If it is defined based on the flow velocity, then the rotor tip, traveling much faster than the local flow, could cross many grid cells in a single time step.
2. Figure 3, it is suggested to add a subplot for the LES_laminar case as well.
3. The captions of the figures are not self-contained. It is not clear what the light-colored curves represent.
4. Line 400, it is odd that a work published in 2024 is said to be confirmed by a work published in 2022.

Dear authors,

Interesting paper. Please see my comments attached.

Good luck with the revision,