I have been meaning to start a thread on this, and the recent WiFi thread spurred me to finally do so. On our boat, we have weak wifi at our marina. Sometimes works fine in our slip, others not so much. Rather than start with an expensive marine WiFi extender, we decided to try one of these about a year ago:
It has a better antenna than our TV or Roku, and has worked great so far for our purposes. Also, I can place it in the pilot house, while the TV is in the Saloon, so I'm sure that also helps with the signal. It has a 110 AC plug, but also works with USB power. We usually power it through a USB adapter that is plugged into one of the cigarette lighter outlets in the pilot house.
In addition to boosting the WiFi signal, it also has a built in router. Because it creates our own network on the boat, it also allows us to cast things from our phones and laptop to the TV. Cost for the Netgear is under $40. Now on to the video part.
We have both Netflix and Amazon Prime, but on the hook, or if the marina WiFi isn't working, we can't stream video without eating up cell data. Well, about two weeks ago, Amazon decided to start allowing Prime members to download some video (TV and movies) for free, so as to be able to watch later when offline. Now, we can download video at home onto our laptop or Phone.
Once on the boat, to get the media to the TV, we use a Chromecast that is plugged into the TV. This great little device not only allows one to stream video when a signal is available, but also allows you to cast whatever is on your phone direct to the TV over your WiFi network. It sends both video and sound! Cost for the Chromcast is about $29.
In sum, if anyone wants an inexpensive way to have some media to enjoy while at anchor without using up cell data, this is a system that has worked great for us, since we already had Prime. Another thing that is nice with the Chromecast and our boat WiFi is that we can also cast photos from our phone to the TV. Much better than trying to show people pictures on the little phone screen.