How do the tides work when the sun powers the moon to keep out evil?

Question

So I wanted to give the players a reason to eventually go to the moon. But this is a fantasy setting, so having the moon just be a big rock floating in space would just be so.... blasé. So I came up with a system where the moon is a giant battery storing up solar energy until it expends it on the night of the full moon to push back the forces of evil and keep them from entering our world for one more month. The moon's phases are pretty much a giant battery icon in the sky.

I've got a few plot points lined up where the bad guys do various things to mess with the cycle, culminating not just in visiting the moon to fix a leak, but going to the sun to... do something with sunspots that I haven't figured out yet. Whatever it is, the sunspots are a natural cycle that the bad guys have been preparing to exploit. The point is, everything lunar (and possibly solar as well) is a potential plot point.

Which brings me to the tides.

So far, what I've got is that there is a magical artifact (or possibly a pair of magical artifacts) under the sea that moves along a track to stay directly under the sun at day and the moon at night, alternately collecting and discharging energy to/from the sun/moon. While the artifact is under a region of the sea, the excess magical energy raises up that area of the sea, creating the tides. The first sign of something evil afoot is that there is a problem with the tides, probably that they are low or off-cycle, I haven't figure out what yet. And the way to fix it is to travel to the track under the sea and fix whatever is being done with the artifact.

The thing is, something feels off about this plan. Maybe it's the fact that I want the world to be a plane, I don't know. That seems to require a charge/discharge cycle instead of merely facilitating redirecting solar to the moon, which I would prefer because it would only require one artifact instead of a pair (though a pair might need repairs to be conducted at either high noon or midnight). Or maybe I feel like there's something better that I can't see right now. Whatever it is, I was wondering if anyone might have any ideas to help me polish this up a bit.

Answer 1

You're treating the tides as just a side effect of what the machine/moon are doing. But what if you went in a different direction, and made the tides themselves the important thing? It's not unheard of for the deep, dark, and mysterious ocean to be the source of evil. In which case it could be the machine/moon's job to dredge up that evil periodically to where it can be thinned out and destroyed, hence the tides. In other words, tides could be caused by the artifact receiving energy from the moon instead of the other way around. Sailors might begin to associate high tide as a period of danger, but what they don't know is that the alternative would be worse. If the underwater artifact stops creating tides, then evil forces would be able to fester and grow until they can attack the entire world.

Why does your lunar battery need something to redirect energy from the sun? Why not just absorb it directly? Even though your world is a plane, there are still plenty of configurations where the moon could do so easily (assuming the sun still radiates spherically). Maybe it stays suspended above the world and is just invisible or hard to see during the day. Maybe its 'orbit' is several factors slower than the sun's: the sun races past the moon repeatedly, giving it plenty of time to absorb more energy. Although maybe the moon needs more energy than it can absorb in a month, which would make redirecting artifacts necessary.

Answer 2

I would have thought the tides would be directly linked to the function of the moon.

Remember that while the tide is connected to the moon on Earth, it's not as simple as Full Moon = High tide. You need to provide two high tides and two low tides per day (more or less), with the biggest tides coinciding with the full moon and the new moon (spring tides), and the smallest tides being timed to the quarter moon (neap tides).

Now, your world is a plane, which is going to play all kinds of mischief, but from your description I get the feeling you'd like your world to mimic the behaviour of ours in at least some ways.

Lunar Phases

First, the description of the moon expending all its energy on the night of the full moon, and the phases that follow being a giant 'battery status' icon, doesn't match the phases our own moon follows. The full moon is followed by the waning moon, taking two weeks for the full face of the moon to retreat into shadow to become a new moon. In your scenario, that would make the most sense if it takes two weeks for the moon to discharge and push back evil - rather than a single burst at the full moon, you could have a full-power push at full moon, then two weeks of steadily weakening pushback, then deactivation until it charges up again.

Tides

So, we come back to the tides. We need two tides per day, a particularly strong high tide at the full moon, another at the new moon. We want whatever is causing the tide to be under the sea, so that the heroes can go there to fix it. So...

• There's a magic fortress on the sea bed that guards the portal of evil. Twice per day, patrols flood out of the fortress to search the whole seabed for any signs of evil, then return to the fortress. This causes the normal tides. During the full moon, the fortress itself swells, causing the spring tide. During the new moon, many more patrols emerge, using the last power of the moon cycle to prepare for the lean times ahead.
• The world is breathing. Twice per day, the world itself draws in breath and energy, which pulses throughout the world to keep evil at bay. When the moon is full, the earth takes a deeper breath than normal, providing more power to keep evil at bad. When the moon is new, the earth yawns, and begins to sleep, allowing evil to return. Beneath the sea, the veins of the earth are accessible, which allows your heroes to see the problem with the tides.
• There are two beasts under the sea, one evil and one good, and they strive with one another all the time. Their movement pushes the sea up and down as they fight. When good is weakest, evil tries to lift the sea off its back, causing a spring tide; the moon has to go to full power to push it back. Once the moon's glow is exhausted, at the new moon, evil tries again to lift the sea off its back, but good uses its remaining strength to pull evil back down.

Answer 3

How about having the tides be a side effect of the magical tether that keeps the moon from flying away or falling down. In one respect this is another way of saying what actually happens in the real world, gravity holding the moon in place also causes the tides to happen, but if the world is flat (like a plane?) then obviously the whole gravity things isn't going to work the same way.
So instead you have a magical force that ties the moon to the world, moving it around from place to place, and this magical tether also pulls on the water and causes it to mound up. This force could even be repulsive instead of attractive like gravity, so it is actually pushing up on the moon to keep it up in the sky.
This could also be a way for your characters to get to the moon, by attaching to this tether with some artifact or whatever and climbing it or riding the repulsive force, and remove the need for rockets or anything like that.

The sun could be on a similar tether, which could have an interesting effect where the the repulsive force could be greatly magnified during an eclipse as the force holding up the sun and the force holding up the moon join together...

The question then would be would the moon be pushed further out? Would the sun all the sudden come crashing down as the moon blocks the force pushing on it? Maybe both? Maybe this is what the forces of evil are waiting for/trying to make happen...