This is a comms system based on a pier-to-pier data transport layer - i.e. semaphore flags being waved at the end of a pier, passing messages to the next pier along the coast.-- hippo, Sep 24 2019 Clacks Towers https://discworld.fandom.com/wiki/Clacksnow with Docks Towers P2P add-on! [Sgt Teacup, Sep 24 2019] Semaphore Telegraph https://en.wikipedi...Semaphore_telegraphBeen there, done that. Superseded by electrical telegraph in the mid 19th century. [neutrinos_shadow, Sep 25 2019] Baked and WKTE... in Discworld <link>. Sounds like a coastal adjunct to the system, though, so [+]-- Sgt Teacup, Sep 24 2019 Yes indeed, semaphore systems used to be widespread and were used, e.g. during the Napoleonic wars to convey military communications around the country. But as you point out, this is an offshore coastal implementation, and I should also point out for fans of communications technology, that piers are natural waveguides.-- hippo, Sep 24 2019 Haha. We saw what you did there. There's a special place in Hell for people like you...-- 8th of 7, Sep 24 2019 random, halfbakery