Your eggs not hatching is independent of your mode of transit. This means that whether you are on a boat or not does not affect your eggs hatching. What does affect distance being recorded is connection to the internet, travel speed, and being soft banned.
Connection to the internet - when you visit a lake, often you are going to remote places with no wifi and poor cell coverage. Thus, if the app cannot accurately track your location and connect to Niantic servers, you distance will not be tracked for your eggs. Check your available networks and reassure that you still have ample data coverage on your boat.
Travel speed - it is now confirmed by a large number of players that traveling too fast can affect egg hatching. It is a general consensus among players that the maximum speed for hatching eggs is ~10-12mph (15km/h is about 9.3mph), so perhaps consider slowing down, as you are traveling at just about the maximum speed for tracking egg hatching distance. You can reference this question for more about speed: How fast can I travel?
Soft ban - if you have been recorded for cheating via GPS spoofing or any other form of cheating, you will likely be soft-banned (or banned for a short amount of time). When you are soft banned, you cannot catch Pokemon (they all run away), some distances don't track, and you can't get items from PokeStops. Refer to this question for more about soft bans: Why can't I catch Pokemon in Pokemon Go anymore?
In addition, if it worked yesterday and doesn't work today, it might just be a server issue with Niantic, and will resolve itself in time. It's a bit hard to conclude anything with only 24 hours of evidence, but wait a little longer and try again. If your distance is still not tracking, consider one of the above prognoses.
Yes, walking distance will count even if you are capturing a Pokemon.
Egg progress will also be made in the following scenarios (credit to this Reddit post from theSilphRoad:
- Having a pokestop selected on your screen
- Having a different egg hatch mid walk. I'm referring to the screen with a picture of an egg that says "Oh?"
- Having your menu open while walking. I was on the egg selection screen for testing. What is interesting is that the distance values don't actually update until you close the screen and reopen it, but the distance logged was correct.
- CATCHING A POKEMON. I'm very excited to report this as it's been speculated for a long time that catching a pokemon while walking won't log your location correctly. That is wrong. I entered a battle/cutscene whatever you want to call it prior to walking. Didn't interact with it for the entire 1 km. At the end I caught 2 of the pokemon and ran from the other two. All four attempts gave me full distance logging.
From observation, egg and buddy distance progress are calculated the same way (delta vector calculated each minute), so buddy distance should be unaffected by these actions as well, so long as you are walking less than 10.5 km/h.
Best Answer
For mega/primal raids, it depends on the specific mega. Only the legendary Megas - Latias, Latios, Kyogre, and Groudon being the four to be released so far - count towards the Battle Legend medal. All other Mega raids so far have counted towards the Champion medal. In addition to this distinction, the legendary Mega raids are a Tier 6 difficulty raid, versus the regular Tier 4 mega raids.
EX Raids no longer exist, but they counted towards the Battle Legend medal while they were available. The feature that replaced them, Elite Raids, also count towards the Battle Legend medal.