If you liked Riddle of The Sands, any Sam Llewellyn novels etc, then try this.
It just came out in Feb.
I bought it for less than £3 on Amazon Kindle.
Set pre-WWII, some sailing, some mystery, some spying, bit like Riddle of The Sands (and the author mentions the book a few times in his own story).
Not as good as Riddle of The Sands, but towards the end I couldn't put it down.
Mark's novel (Wrecker, I think) was great too.
I am now moving onto his non-fiction sailing stuff.
He writes well; entices the reader and holds their attention.
I hope he writes more because I have read all of Sam's stuff I think.