Tom, that's a good question...and altho' something many men wonder about, I've never seen posted before.
I've exclusively used an electric shaver, this time for the last 6 years while cruising. I keep the shaver in a ziplock if it doesn't have it's own case, and I find I have to change the blade no more often than when ashore in order to get a good shave. Being a rechargeable, I only have to plug it into the installed inverter once every 3 or 4 days, which means I can do that while motoring somewhere without an electrical price to pay.
If you go this route, consider getting a small spray can of lubricant intended for use with shavers. It's a non-residue type. To see why I recommend this, turn on your shaver and - with it running - give a short blast of spray to the shaver head. You'll be surprised at how much the rpm picks up due to that very small amount of lubrication.