There is no blanket answer that covers all cases. Just like designing for an office or a factory, it all comes down to the application and the
environment. There are bunches of conditions that you might have in the
marine environment:
- high humidity
-
salt spray in the air
- immersion in sea
water (boarding seas, device dropped overboard)
- mechanical shock (device falls off table,
boat falls off waves)
- varying roll/pitch/yaw
- "12 V" DC
power can be 10 to 16 volts and/or noisy/spikey
- AC
power with poor voltage and frequency regulation (e.g. from a generator)
- AC power with non-sinusoidal waveform (e.g. from inverter)
- high ambient temperatures (inside sealed
cabin in summer)
- low ambient temperatures (out on
deck in the winter)
- RF
noise in the environment (VHF
transmission, EMI from on-board electronics)
- user error brought on by fatigue
- user has wet hands /
clothing / whatever
There are probably others, but that list is all I thought of in a minute. Your question, then, is just how the environment is going to affect your application. For example, if your device has no user interaction, you probably don't need to worry about their wet jacket dripping on your device.
Standard components are fine, unless you need extended temperature range or something like that. For example, I have a box that uses a regular
commercial Rabbit processor module. I think it is only rated for operation down to 0 C, but that's ok because I am unlikely to be using it outside during the
winter.
b.t.w. I also built it on standard perfboard, and even though I take it in the
dinghy, it has holes in the case that
water could get through. I just don't let water spill on it. (If it fills up with water, I'll be very unhappy.) You can get away with compromises like that on things you build for yourself.
I've had pretty good success with consumer
electronics on board -- tv/dvd, vcr,
laptop computer, POTS
phone,
cell phone, toaster (with digital controller),
battery chargers (AA/C/D). This stuff all lives in the
cabin, which is heated/cooled so it is comfortable for me. I have much narrower environmental requirements than most of the
electronics.