I meant for a mine. Why would a mine that is expected to have a smaller chance to hit have a smaller yield than one with a near guaranteed projected
In that case it depends entirely on the fuse.
Generally bigger the boat the easier it is to hit. The size of the mine is irrelevant other than yield and visibility.
I must have misunderstood then. I thought "breaking the back" of a ship was about where you target it and that the advancement would be about making a remote controlled (or in WHF magically triggered) mine that waits till the ship is above it instead of just touching it.
hit chance?
Breaking the back of a ship with a torpedo requires an explosive to detonate within a narrow window of time such that the explosive force is placed upon a ship's geometric load bearing center with enough force to overwhelm its engineered maximum, which usually involves the application of high explosives. Doing so with the means available would be similar to shooting the tyres off a car using a musket, you're probably not going to hit, and if you hit you probably wouldn't be looking at enough penetration to burst the tyre rather than tear it a bit..
Also remote control is hard, yes, even with magic. We checked, you need a continuous signal carrier, so its possible to wire trigger if you had a Gold Wizard, but the flowing water would be disrupting it with Ghyran otherwise.
First I must admit that I know nothing of explosion related engineering. So I trusted Vebyast in his assessment of how much yield is needed and how difficult it is to place such a mine in a river.
Regarding the trigger though, to my knowledge it should be as cheap as 0.5 CF per bomb fuze from a Gold Magister, or the equivalent in whatever currency a Marienburg Chamon Mage accepts. All you need is a delayed "Stoke the Forge" X seconds after whatever thing with a very large Chamon presence floats into detection range. And the delay can also be done chemically or mechanically if using just magic is too complex. Sure, a bomb where just the fuze costs ~50gp isn't cheap, but it would be an okay investment if the mission is deemed important enough.
Enchantments are neither cheap, easy, nor consistent, especially when you're trying to accomplish an effect(detect metal of particular quantity) that no established spell has and then use that to trigger a second spell.
This is very solidly in the realm of One Off Wonder, which doesn't make sense to be used here. Its beyond the cost of "I paid some dudes to get some attacks done", and closer to "someone high in a council of a nationstate funded a research project to produce ONE bomb".
The level of investment is irrational - its a lot to spend on an attack which would only piss off the Karaz Ankor beyond reason, specifically targeting them,
while not materially harming their warmaking or canal building capabilities. If you're spending this much effort on the attack it doesn't make sense to slack off on picking a target.
Hell, by picking off the leading vessel of the convoy, it ensures the whole river convoy has to stop and remain in position.
This attack, in other words, is done solely to hurt the Karaz Ankor on a strategic scale.
It makes sense if you're trying to weaken them on a scale of centuries, or if you were counting on it to bring them into a selfdestructive war.
It does not make sense if you're a human polity.
