Where are you using it? Are you trying to reach your marina's wifi from the end of the dock or a mooring? Are you cruising the FLA coast and trying to hit open wifi connections from anchor?
I had played around with re-configuring a router as a repeater and using a larger antenna with mixed results (this was two years ago)
I ended up getting a MiFi unit that uses the cellular network. Basically I can get online anywhere I can get a cell signal. When I first got it speed was good enough to stream NetFlix to my 12v TV when anchored out. But Comcast started making an orphan out of these units and throughput fell through the floor - Comcast assures me this is a coincidence.
They're also going to stop supporting them in August. I hate Comcast
I'm going to get a new SIM card and convert it over to the Sprint network. If that doesn't work I'll pick one up from Verizon. Current cost is $40 a month, but it's reliable anywhere I can pick up a cell signal. It's a third smaller than a Blackberry. Best of all up to five people can share the connection. So far I've never even come close to the 5GB monthly limit.
YMMV depending on where you're cruising.