His not owning a boat is irrelevant: unless he is violating local zoning in some way, he may build anything he likes on his property, whether or not it impacts the views of neighbors; that is an intrinsic risk of buying property for a view, when there is someone who owns land between you and the view. As long as he complies with local zoning, building, etc. laws, he can build anything he likes on his land, whether it is useful or not--i.e. he could build a stable for non-existant horses, a lighthouse to guide steamships that don't exist safe to shore, etc.