OK, so he actually co-authored the book. The primary authors were H.A. Van Foreest and R.E.J. Weber. Frank Fox was a consultant to Dr. Weber, and helped him resolve some issues with English ships. Why the book is so useful for me, are the Dutch and English ship lists for the Four Days Battle. Frank Fox has very good summary lists, but the lists in this book include much more detail than Frank could fit into his book on the Four Days Battle. the archival sources mentioned should be very helpful, if they can be found.
I put the statement that way, because just because someone found something in the archives 20 years ago does not mean it can be found today (sadly). I say that from experience with having someone else look for manuscripts for me in the archives.
An example of what can be found in the book is the listing for the Amsterdam frigate, the Asperen. The Asperen was built in 1656 at Amsterdam. Her dimensions were: 117ft x 29ft x 11ft. She carried 34 guns, at the Four Days Battle, which consisted of 6-12pdr and 12-8pdr on the lower tier and 12-6pdr on the upper tier. There were also 4-2pdr "voor de hut" (in the cabin), presumably on the quarterdeck, aft. Her intended crew was 120 sailors and 20 soldiers, but at the Four Days Battle, she only carried 110 sailors and 20 soldiers. She lost 1 killed and 5 wounded in the battle.