Thanks for the quick reply.
The problem is localized to the galley area under the sink. From what I can describe, our boat has the interior floor boards that are made of teak and holly (I think). These are in good shape throughout. However, in the galley area, the underlayment has been wet and has swelled in some places. From what we can tell the underlayment is some type of coated plywood. The coating is white and is similar to the white material in the original picture of this post. We have addressed the source of the leak we inherited from the PO and want to replace the underlayment boards before anything gets worse. As a result, we are looking for a material that we can replace that underlayment with.
Thanks again