Weird as it sounds, that piece of wood is a ... radar detector :|
My boat is a piece of junk right now just because I started to play Open Horizons using the "silentotto" trick, so my boat is "naked" and I got 0 renown. But soon as I will make more renown points I will make me boat shine by installing all the weaponry and technology available at the end of the war. It will look awesome, just perfect for showoff in ports and attract the local chicks
The radar detector will be available around 1942 as a sensor upgrade.