That's good news. After a year we normally have no problems with people driving cars any more. Why should somebody have problems with you working on a boat? After two years you are safe: Regulations say for epilepsy: "Temporarily unfit category 3 until at least two years fit free and either off medication or on stable medication with good compliance"
I would try to pass the ENG1 and hope for another career for you. The requirements for the royal marine are much higher than those for ENG1, which is a very simple examination. Since you don't have an issue at time you have a good chance to passss. I wish you luck!
I would think that you would be completely on the safe side if you waited until you are two years without seizures. As I cited, according to the regulations they should let you pass then. If you are in a hurry, you can give it a try. If you don't pass, you can go again after the 2 years are completed. I can perfectly understand what you mean!