Do you mean MDF? Not the best material as it can fall apart if wet, but as a quick fix, yes, probably.

I assume that is MDF. As long as you do not intend to start the prop and it is several inches above the waterline then, probably. I fear MDF is likely to absorb water and go soggy, but as long as it stays more or less dry and only for a few days then it is likely to do.