Wall of force question

[Myth27]

So 4 npc are escaping on a boat, my player says “I cast wall of force TROUGH the boat, making the people crash and fall and stopping the boat”
I was thinking if you summon the wall on the boat it moves with the boat. If you summon it on a point in space can it go through objects? How would you rule it?

[Aimeryan]

So 4 npc are escaping on a boat, my player says “I cast wall of force TROUGH the boat, making the people crash and fall and stopping the boat”
I was thinking if you summon the wall on the boat it moves with the boat. If you summon it on a point in space can it go through objects? How would you rule it?

Ah, the old 'What is the anchor?' and 'Does momentum apply?'

There are no rules for this; it is up to the DM. Other scenarios you will find this crop up in often include illusions. One problem you will find if you rule that such things have zero velocity (as measured by kinetic energy) is that they would instantly wizz off/along/through the planet since it does have velocity - at lot of it.

I think most DMs rule (without realising) that spells are anchored with relative velocity to the caster, but that the cast happens as if the caster is not using their own movement to propel them - so boats, carts, etc., are fine as long as they carry on at the same velocity, but no running while casting to make a wall that sweeps along. Some DMs will rule that spells with ongoing effects are anchored to the planet - if you are on a boat, in a cart, etc., they fail to stay with such vehicles (and the caster). A few DMs allow anchoring to be completely subject to the caster - illusionary rings that stay with the finger they were placed on, etc.

[RickAllison]

I generally rule that they can be set in relation to (reasonable) surfaces. It’s easier to set up those things for solid-in-conception surfaces like the planet or a boat. They can be oriented to more complicated surfaces as well (say, riding a dragon), but it requires more arcane programming, which is why we have dedicated spells for it like Disguise Self or Seeming.

[Myth27]

I was more concerned about the possibility of it going through objects in this instance, what do you think about that?

[ad_hoc]

The boat gets pushed to one side of the wall, caster's choice.

[RickAllison]

I was more concerned about the possibility of it going through objects in this instance, what do you think about that?

I don't think you can set it to be through an object.

[Sigreid]

It can't pass through objects. Depending on the size of the boat you can put it right in front of the boat or even in a horseshoe around the front to stop it from going.

If it's a ship under full speed, a force wall right in front of it should do considerable damage.