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In my world, there are two countries constantly in cold or warm war with each other, and one of them has quite a lot of magi in their army. In my RPG campaign, the party is sailing one of the best-equipped ships of the other side. So I made some countermeasures against enemy magic. Would any of them be dangerous or make the ship slower or worse in some other way?

The easiest way to get rid of an enemy ship is to summon a strong water elemental and let it damage its rudder. So the ship has a system of pipes with some special oil inside, protecting the rudder. The oil itself repulses the elementals, and on the inner side there is the ship's kitchen, where the oil can be warmed up, so that it's even deadlier for the elementals. EDIT: the pipes make a cage around the rudder. They will be at least a meter from each other, so they wouldn't completely disturb the flows around the rudder. But especially when warmed up, they will affect them somehow; I don't know whether this will be important or not. They are made of bronze, with the parts regularly in contact with water silver-coated (yes, it was expensive).

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    $\begingroup$ 1) Where are the pipes? If they need to surround the rudder in the water, that would probably impair the functionality of the rudder by disrupting the water flow around it. Also, if they're immersed in the water, they'll have corrosion issues with the severity depending on the type of metal(s). $\endgroup$ – Adam Miller Sep 17 '14 at 21:29
  • $\begingroup$ @AdamMiller: thanks, you made me think again of how big is a galleon's rudder, so few pipes around it can't make a cage dense enough to protect from a swimming human saboteur (this would probably disturb the flows too much). I answered by an edit; this is a valid point, but I have no idea, how would this affect the ship. I hope some answer helps me with that :-) $\endgroup$ – Pavel V. Sep 17 '14 at 21:43
  • $\begingroup$ Also, it probably would have been better to split this up into three questions, possibly cross-referencing between them. You're asking for three different answers, and it's unlikely that they'd all be within the same submitted answer, so selecting one answer as the best answer would be difficult. $\endgroup$ – Adam Miller Sep 17 '14 at 22:05
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    $\begingroup$ +1 I have to say that I really like the way that you specified exactly what the magic you were protecting against was. We need more of that kind of description and detail in questions around here. $\endgroup$ – Mourdos Sep 17 '14 at 23:22
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    $\begingroup$ Why is the protection a cage around the rudder rather than just built into the rudder(i.e. run the pipes through the rudder itself. $\endgroup$ – Tim B Sep 18 '14 at 12:32
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The rudder is used to control the ship, so any form of disruption around it will affect the ships handling. A cage around the rudder, even if the pipes were space 1m apart, is likely to increase the ships turning circle and reduce its effectiveness in combat.

A solution to this would be to have the pipes formed to the shape of the rudder, effectively increasing its size and mass, or to replace the rudder entirely with one made of silver-coated bronze and have the pipes flow through it. The increased mass will make it harder to turn the rudder, so some form of assisted or power steering would be appropriate. If you're using a sailing ship (based on your other question I assume you are) then the ship already uses a pulley system to turn the rudder, you could just increase the number of pulleys to reduce the force needed to turn the wheel (although increasing the number of turns the wheel would need to make).

The difficulty with having the pipes turn is connecting them to the ship. A couple of solutions are available. 1 is to use a hose-like material if available, this allows the pipes to rotate and contract / expand freely. The other option is to use a ball joint, for a rudder that just turns from one direction to the other this should be sufficient, though may limit the maximum turning angle of the rudder.

If you were to heat up the pipes, thus heating the rudder this would only have a minor effect on the surrounding water, but it would reduce turning efficiency a bit. Warmer water would produce less flow over the rudder, reducing the force being imparted by the water. As the water passed over the warm rudder it heats up. But as long as the ship is moving, the warm water is constantly being replaced with cold water, so the effect would only be minimal, perhaps even negligible. The bigger problem I think would be keeping the rudder warm. You'd need to be constantly pumping hot water through the rudder to combat the cooling effects of the sea water.

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  • $\begingroup$ +1 - this should work better than the cage, so I redesign the ships in my world :-) $\endgroup$ – Pavel V. Sep 22 '14 at 11:17

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