Most hobbyists are aware of the corrosive nature of the water on electronics equipment. There are some key things that a hobbyist should be aware of in creating electronics for their boat. You should read the US CFR's and USCG guidances as well as have some knowledge of
ABYC requirements.
1) A boat vibrates, shakes and shudders. Displays (LCD's) , laptops (Mine is a Panasonic toughbook CF-28), hard drives, and relays (as well as connectors and everything else) all get a serious pounding. While CarPC's (www.mp3.com) are common, boats generally need special motherboards and connectors to survive. If you build it, shock proof the case.
2) A boat often has explosive vapors. Electronics are sealed (and relays are explosive proofed) for a reason. You can buy cases and electronics that are made for this environment. Not every component requires this, but switches and relays should be proofed. For this reason (and for corrosion) , I don't automotive parts (especially battery chargers) in the bilge.
3) Corrosion. Keeping water and moisture out is hard. Use a NEMA4X case and .... silica gel packs for your hobby item. Make sure you can replace these packs (I wish I knew someone with a small regenerative breather.) Conformal coating (a plastic coating) is needed to protect wiring on the motherboard. BTW: there are new regs on Restriction of Hazardous Substances mean that solder is tin coated(good), but subject to the
tin whiskers problem. This affects boat electronics manufacturers as it puts a limit on product life.
4) Temperature - electronics come in different levels of quality. Industrial ranges are what is generally needed (-40 to 85C) . Most products will have a very limited life outside these ranges. Digikey, Jameco and Mouser all spec these items for these purposes. One thing I like about Parallax is that the Basic stamp modules can be purchased for industrial use. Bright LCD's 700+ nits that are not fan forced cooled are expensive.
5) Coding requirements for safety critical systems are a high barrier. For production productions this means a module (unit test), through code tracing with predictable execution paths, and full compliance testing. The discipline and testing for SC systems requires independent testing. A hobbyist who is not creating critical systems doesn't worry if his software fails, but a manufacturer must. This is the reason for the Level A and B NMEA 2000 certifications.
Oddly, boating electronics should be exempt from ROHS limits as most of it is safety critical. A radar that fails from tin whiskers in a storm is a safety critical issue. I use a lot of free software (like Seaclear) as an auxiliary navigation system.
So, Why does marine (boat) equipment cost so much? Rules and regs (see Federal Regulation CFR 46 Parts 159-165 and the marine environment
1) Coast Guard approval and testing requirements
a. Any modification must be resubmitted for testing
b. Lack of independent labs
c. Combined products (Carbon Monoxide +temp + heat + fire + gas, water in bilge) do not fit in the regs (so a bilge safety system is done with 3 or 4 systems (separate regs) even though cost effectively one module with multiple sensors could do all of that...)
d. Legally specified testing procedure in Regs, not in policy
2) Limited market
3) High priced tool chain and nautical specific message sets owned by organizations
a. Only recently did NMEA consider a message set similar to another industry
b. CANBUS licensing and stacks leave a high barrier to many small companies. Some will use stack modules that have a SPI or I2C bus for integration (like Sirf's GPS modules).
c. Reliable parts and systems that survive boats without sparking or corroding.
d. Test equipment and V&V capabilities for the marine environment are very expensive. (example Smart Scopes for CAN, simulators (e.g. Matlab), Test booths, special engineering skills in SC, documentation costs, and certifications)
4) Safety Critical liability
a. lawsuits and liability.
Unzinced ships sink at slips.
