You have a terrible investment track record and a good programming track record. Go with your strength. Since you have a short attention span, you should focus on short projects that you can ship quickly.
Bring maritime weather / charts to the iphone, I'd buy that :-)
You're right that chart plotter on the ipad would be pretty tops. As waterproofing.. you'd have to use a material that lets the capacitance of your finger through.
The other issue is connecting a GPS to the iPad if the internal GPS is not good enough. I don't know if it is yet, will take my iPad sailing this August.
Apple requires you to build external accessories specifically to work with iOS devices. I think that even requires a special chip. An external Bluetooth GPS would likely be power-hungry.
I think http://www.tacktick.com/ are an awesome example of low-power marine electronics. They designed and built their own low-power wireless network to connect their instruments and powered them with solar energy whenever possible.
Tacktick looks pretty awesome, i will check them out!
Regarding the connection of a GPS to the iPad, I don't have on hands the technical details of the iPad (or iPhone) GPS, but on open water, it will surely be better that in an urban canyon. It can see a lot of sky --> a lot of satellite. So, the internal GPS may be not so bad in your scenario.
But an external GPS with an active antenna will always be better (better GPS chip, better antenna and fewer electronics noise being far from the iPad radios). You can find kits build by Microchip and Cypress for the connection of external devices to the iPod/iPhone, but you first, must enroll in Apple’s Made for iPod licensing program, by completing the online application at http://developer.apple.com/programs/ipod/.
Here is the microchip kit: http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_P...
And here's the Cypress one: http://www.cypress.com/?rID=41030
Let me know if you need some advice on the GPS stuffs.
"High-sensitivity, -157dBm assisted acquisition sensitivity (with coarse time assistance) and -162dBm tracking sensitivity, enabling indoor and deep urban operation"
You can compare this with an usual SIRF Star III based GPS receiver (Leadtek 9101x), which is not assisted: http://www.leadtek.com/eng/gps/overview.asp?lineid=8&pro...
With a sensitivity of -159dB and a cold start time of 35s (worst case scenario).
I think that, on open water, with a good sky visibility, the GPS included in the iPad 3G and the iPhone 4 should be more than adequate for this kind of usage.
EDIT: I just tried wearing a Ziploc sandwich bad as a mitt and operating my iPad. There's apparently no degrading of the touch screen! I'll have to pick up some large Ziploc bags the next time I'm at the store.
Took two days for my shoes to dry.
The Ziplock bag around my Runkeepering iPhone didn't miss a trick. :)