This paper addresses a very interesting topic, investigating the hydro-elastic coupling effects of a spar-type floating wind turbine. The study on the tower eigenfrequencies of the FOWT system with inclusion of floater flexibility and added mass is well presented, with a valuable comparison between numerical results—using beam and shell element modeling in Homer—and full scale in-situ sensor data. This contributes significant value for both academic and industry community.

The authors have also developed a coupled model in OpenFAST by largely tuning the tower stiffness while maintaining a rigid-body assumption for the floater. However, in my view, this model is insufficient to capture the hydro-elastic effects on the global dynamic response of the system. For the stated objectives of the study, Updating the OpenFAST model to explicitly incorporate floater flexibility is recommended.

In the following sections, I provide some remarks that the authors may consider during revision:

1. In the abstract, it is stated that incorporating floater flexibility and added mass reduces the error to 5%. However, Section 3.1 shows that the error decreases from 33% to 28% when added mass is considered, and further to 5% when floater flexibility is included. I would recommend to highlight this finding in the abstract.
2. In paragraph 6 of Section 1, the reference to Zhixin Zhao (2022) should be verified. The software used is not HAWC2, and the floater type discussed in that study is not a spar-type.
3. In Section 2.2.1, it is mentioned that the floater and tower are discretized using beam or shell elements. However, later sections refer to the model as using shell elements. Please clarify this to avoid confusion. Additionally, the structural model in Homer should be described in more detail—for example, specifying which components (e.g., tower, floater) are modeled with beam elements and which with shell elements.
4. In the final two paragraphs of Section 3, the displacements and moments at the tower are discussed, but the corresponding figures are missing. Please include the relevant figures and expand the discussion to thoughtfully interpret these results.
5. The reference formatting should be corrected to comply with the journal's guidelines: https://www.wind-energy-science.net/submission.html#references. Additionally, some references appear to be duplicated, please remove.

Here are some minor comments:

(1). There should be a space between a number and the unit. Please ensure consistent formatting throughout the manuscript.

(2). In Table 1, the decimal separator should be corrected: "8,3 m" should be written as "8.3 m".

(3). The figure order in the text should be reviewed and updated to improve readability. For instance, Figure 4 is introduced before Figure 3, and Figure 9 appears before Figure 8.

(4). The in-text citation formatting should be checked for consistency and compliance with the journal's style guide.

(5). A proofreading for grammar is recommended. Several sentences contain awkward phrasing or are missing grammatical elements such as subjects.

In the present paper the authors investigate the effects of the floater rigid hypothesis, the hydrodynamic added mass and the flexibility of the blades have on the global dynamic response of the spar-type floating wind turbine Zefyros. The floater rigid body assumption made so far is challenged. The authors are suggesting an 'engineer oriented' method to follow for accounting the elasticity of floater into the time domain analysis. The paper is interesting and can be accepted for publication but there are some issues that should be further highlighted in the paper.

Please provide some more information about how the values in Figure 3 are calculated (in 4-5 lines). Since you use those values you must report how you calculate them (eg using 1 day measurements ? 1 hour?  how you make the frequency calculations?). You are providing relevant references but this critical information should be included in this paper too.

The authors and in order to approximate the floater structure to the rigid hypothesis in the Homer model, the material Young modulus was increased from the steel value of 2.1E +11Pa to 1E +20Pa. How did you decided this increase? why not 1E+30Pa etc?  How reliable is this very stiff value and if is a realistic one. The rationality for this increase should be discussed. Or you must present a sensitivity analysis. Moreover, the authors should explian if this is a generic value that should be followed in all possible FOWTs or if this is just a value that is valid only for the purposes of the present paper.

Moreover the authors should provide more information about the manual trial and error tuning performed to fit the measured spectrum. Please provide the sensitivity analysis results and how you decide the suggested value. 

My main concern with the paper is that the trial and error methods are not methods with permanent scientific added value. Sometimes the trial and error methods result to completely unrealistic and unscientific results. Please expalin further the process and provide statements about the generality of the process as well as the advantages and disadvantages that the process has. If possible try to defend the suggested values with any possible mathematical or analytical method.

The authors should explain clearly the possible methods that researchers can use when dealing with hydroelasticity and how hydroelasticity is included in time domain calculations in connection with what they did. More references hould be added and more discussion about this in Introduction section.