We have a U-Line icemaker model ULN-5598-03. (just happen to have our survey on the table for an insurance application) The ice maker is one of those things that we never knew we needed. Now that we have it, I don't think I would ever want to be without it again. Runs on 110V. The ice bucket inside makes a ton of ice, we've never used it all, and its as cold as your freezer at at home. We set up its own 3 gallon reservoir, which we fill with bottled water.
The trick is to leave the dock with it completely full so the temp doesn't decline too much during the day. It will obviously be off all day long. If we run the genset an hour at night and in the morning, it all refreezes fine. Because the ice just skins over with a little water, the cubes freeze together, but are very easy to break back up with the scoop. If you only run the genset once during each day, it will melt a bit on the bottom and after a few days, you need to dump it and start over. If you return the dock each night, you'll go weeks before enough melts to notice.
We just thought of this trick which we will try this summer. Bury some Ben and Jerry's ice cream under all the ice. At the dock, its a huge freezer. The ice should keep it in reasonable shape for the day and the quick runup in the evening should put us back in the ice cream business for dessert. Probably the biggest thing my wife misses on the boat.