Getting the antenna up and outside by installing some sort of booster will help with range.
But not bandwidth. You want to stream video. In my experience, very few free marina WiFi installations are sized for that sort of thing. Often they share one "business class" internet connection with the marina office. Two or three people streaming will drive the performance for everyone down the drain. Then even those who just want to check e-mail or view a web page or two will suffer.
For streaming, we've had far better luck with an unlimited data cell plan.