Seems like most boat builders stick in automotive speakers to save cost. They do not stand up to the humidity. I've seen many blown speakers and were replaced by water resistance i.e. 'waterproof' speakers. Speakers will be something I would replace personally. I can pick my own speakers and they are very easy to install.
As for speedometer, if you have a smartphone with GPS, you can use it as a speedometer.
https://www.cnet.com/how-to/turn-you...an%20analog%20