We have used SeaClear II for the the past two ... I loaded the program onto the cheapest netbook Walmart had to offer and added a puck GPS from Amazon...
The netbook turned out to be pretty durable. Once in Nassau the backpack with the netbook went to the bottom of the dingy. Salt water poured from the netbook when we got to shore. We rinsed it in fresh water, let it dry out, and I'm using it now...
That sounds good. I went a different route, bought a used Dell Latitude and changed out the HD for a solid state drive (faster, less battery power). Updated the bios, and installed W7 and drivers. I got a plastic shield specifically formed for the keyboard which protects it fairly well from wet hands, coffee, and cocktails, all except the two lower extra mouse buttons. I also installed a lighted keyboard and extra RAM, all ebay items, so cheap. This allowed me to buy several heavy duty batteries which will fit my business Latitude as well, also inexpensive on ebay but good Dell batteries. So I can run the laptop for probably 36-48 hours straight on batteries alone. I can also recharge from my solar powered house battery.
In the dinghy, I set the laptop pack up on a square flotation cushion, which kept it out of the water.
I did not use free software, however. I paid $17 for an older DeLorme "TOPO" program, and for $29 was able (with the patience of Job) to download all east coast charts, harbor charts, offshore charts, etc. from N.E. Maine to around the Fla Keys and the Gulf. These are the same charts I have on my paper copies, only lots more of them. With a cheap older GPS usb puck it worked very well. Except that visibility in bright sunshine with Polaroids on was not good, really needed the shelter of the companionway to see clearly.
Incidentally, the TOPO was a useless program for the land, only useful for the sea. It would take a full time workforce to download any large area, they have a terrible system and should just sell you DVDs. A comparison of the same map between TOPO and National Geographic's NE topographic software showed that the Delorme product was blurry and low contrast, the Nat Geo maps were very sharp and clear, and you got discs covering a huge area with no downloads.