Sounds like you need a Coast Guard Lifeboat.
I suppose the boat is all up to you. however I can give you some insight into the line drop.
If all you do is have an extra loop of line, or the loop of the hook locked into a slotted brass tube,
When you pull the rod out of the tube using a servo, the line will drop.
The rod is filed to a half round where it crosses the slot. So there is a small space left to hook the loop, or the hook. The weight, of your sinkers should cause it to drop off.
Or, if you wanted to mount this above the deck, you could then just pull it out using the fishing rod once the servo has opened the latch.
The biggest problem I see occuring in the ocean, is that a wave will roll the boat, or push the boat back over the fishing line, and cause it to tangle in the propeller, or around the boat.
Good luck.
The image below is a Mine anchor release for my combat ship.