Area spells on boats?

[Dalin]

Would you all allow an area spell to be cast on the deck of a boat such that it moves with the boat?

I'm thinking of allowing it, but requiring that the area conform to the edge of the vessel. Thus to cover the entire deck of a 17-yard long (5-yard wide) Viking knarr would require a 9-hex casting; the extra hexes outside the area of the deck would not be covered. This would prevent weaponized area spells where you could force your enemies into the area just by sailing near them.

[rosignol]

Originally Posted by Dalin

Would you all allow an area spell to be cast on the deck of a boat such that it moves with the boat?

I don't have my books handy at the moment, but I seem to recall that this is specifically addressed somewhere, and the answer is yes.

[Balor Patch]

Putting a ring of fire around your ship and sailing near your enemies sounds frankly awesome.

[Dalin]

Originally Posted by Balor Patch

Putting a ring of fire around your ship and sailing near your enemies sounds frankly awesome.

Agreed! I love that image.

My group was specifically wondering about Mystic Mist. At a base cost of 1 with a 10-hour duration, it seems quite powerful if you could center it on your canoe while paddling through the Fens of Woe (or through the canals of Venice). And if you could do that, why not a wheelbarrow? Mystic Mist on the deck of a ship has great defensive value against boarders, but doesn’t seem like it would it would profoundly transform naval strategy.

[Balor Patch]

Sometimes awesome and excessive are closely coupled. Mystic Mist does seem far too powerful if it can be used that way, and the wheelbarrow trick is very exploitable.

I would still allow an area spell to be cast on a moving platform up to its edges and, from past discussions, believe that is RAW.

[ericbsmith]

I like the idea of allowing area spells to be cast on the deck of the ship, to the edges. If you want to cast it beyond tn and you'll soon sail out of it.

Originally Posted by Balor Patch

Putting a ring of fire around your ship and sailing near your enemies sounds frankly awesome.

Originally Posted by Dalin

Agreed! I love that image.

My group was specifically wondering about Mystic Mist.

And this is why I wouldn't allow it to be cast beyond the ship but centered and anchored to the ship. To easy to abuse. If you anchor it to the ship you can't extend the area beyond the ship. If you want it to go beyond the ship you need to anchor it to the local "geography."

[Kromm]

Area spells can be anchored to anything that has a surface large enough to contain the entire spell. Spell diameter is (2 × cost multiplier) - 1 yards, so the smallest dimension must be no smaller than this. Put another way, the cost multiplier cannot exceed (smallest dimension in yards + 1)/2.

Example: For a ship's deck that's 7 yards wide and 25 yards long, width is the smallest dimension, and thus the limiting factor. That's enough to fit an Area spell cast at (7 + 1)/2 = 4 times base cost. As the diagram on p. 12 of Spells shows, that gives exactly 7 yards of radius, which is small enough not to exceed width.

You cannot cast a larger spell to cover the entire vehicle area and "leave out" parts of the spell just because Area spells let you leave holes. To anchor a spell to a mobile surface, it must be theoretically possible to anchor the entire spell.

In the example, you couldn't cast at 13 times base cost to get 25 yards of radius and then just leave out everything beyond the width of the deck to encompass the entire deck from stem to stern.

Nor can you cast a larger spell to cover the entire vehicle area and not "leave out" anything, to enable a small vehicle to cart around a large Area spell. Again, the entire spell must fit atop the vehicle.

In the example, you couldn't cast at greater than 4 times base cost to get 9 or more yards of diameter, giving a portable area effect that extends beyond the deck to either side (and possibly ahead and astern).

I realize this is less fun for those seeking to exploit magic shamelessly, but it keeps things under control.

[Tom H.]

Thank you for the explanation and the discussion. It brought some welcomed insight.

Once I began considering the nuances of area spell rules, they became less intuitive to me.

I was initially disturbed by the fact that area spells don't seem to be contained by barriers, but I believe this is the accepted behavior.

There was a scenario I had considered in another thread a while back.

It especially recognizes that the default height of the area is four yards.

Consider a mage casting fire cloud in a crowded dungeon with low, irregular ceilings and multiple levels.

Which inhabitants and adventurers are getting burned on the level above the mage as the height of the default fire cloud extends into their "separate" space?

[Phil Masters]

Note the GURPS Vehicles: Transports of Fantasy has some notes on the topic of casting area spells on vehicles — mostly in the sense of turning your galley to Essential Wood or whatever.

[benz72]

Originally Posted by Kromm

Area spells can be anchored to anything that has a surface large enough to contain the entire spell. Spell diameter is (2 × cost multiplier) - 1 yards, so the smallest dimension must be no smaller than this. Put another way, the cost multiplier cannot exceed (smallest dimension in yards + 1)/2.

Example: For a ship's deck that's 7 yards wide and 25 yards long, width is the smallest dimension, and thus the limiting factor. That's enough to fit an Area spell cast at (7 + 1)/2 = 4 times base cost. As the diagram on p. 12 of Spells shows, that gives exactly 7 yards of radius, which is small enough not to exceed width.

You cannot cast a larger spell to cover the entire vehicle area and "leave out" parts of the spell just because Area spells let you leave holes. To anchor a spell to a mobile surface, it must be theoretically possible to anchor the entire spell.

In the example, you couldn't cast at 13 times base cost to get 25 yards of radius and then just leave out everything beyond the width of the deck to encompass the entire deck from stem to stern.

Nor can you cast a larger spell to cover the entire vehicle area and not "leave out" anything, to enable a small vehicle to cart around a large Area spell. Again, the entire spell must fit atop the vehicle.

In the example, you couldn't cast at greater than 4 times base cost to get 9 or more yards of diameter, giving a portable area effect that extends beyond the deck to either side (and possibly ahead and astern).

I realize this is less fun for those seeking to exploit magic shamelessly, but it keeps things under control.

Good Dr., If you have time and inclination could you please consider and rule on these (admittedly odd and somewhat Munchkiny) questions?

1) Does the orientation of gravity affect the validity of a surface of sufficient area to be the subject of a spell?
Can I cast Sunlight on a wall or slope instead of a floor? What about Rain of X? Does the effect remain normal to the surface? or come directly from overhead?

2) How rigid must a valid subject area be? Can the surface be intentionally flexible? If so, what happens to the spell effect when the surface changes shape? Can I cast Fog onto a tarp and roll it up then unroll it to let a non-mage surprise someone with a few hexes of fog?
2a) If a brittle surface breaks while the subject of spells, what happens to those spells?

3) How flat must a valid subject surface be? Can a 1 hex Grease be cast on a ~1' diameter shaft? Or a tree trunk?

4) Are surfaces that are 'discontinuous' within their own hex (e.g. stairs, a bed of nails, a hex with a small plinth in it) valid subjects for area spells? If so, do the effects follow some kind of 'best fit' covering over the surface or does the effect anchor at the lowest/nearest altitude and rise up/out from there?

Thank You Very Much