"Turn ships from the center!" Topic

You were asked – TMP link

When turning a ship – do you leave the bow as is and turn the stern so many degrees? Or leave stern and move the bow… or measure from center of ship… Talking model ships of several inches or more… And limited number of turns per game turn.

33% said "turn from center of ship"
22% said "leave stern, turn bow"
20% said "leave bow, turn stern"

Just a side note: real ships rotate around a point roughly 1/3 of the way back from the bow at the waterline. We all do it wrong.

The pivot point of a ship is dynamic, not fixed.

I have a set of AOP ship rules that use a reasonable representation of advance and transfer based on ship design, lading, sail state, rudder, heading, speed, wind velocity, and sea state/velocity. It's great fun if you're into that kind of thing, and not if you're not.

For simplicity I've always used a card turning circle to represent minimum radius steady turns, thus you turn around the centre of the circle; but allowed a 'slew' move, representing backing one side engines/oars or manipulating sails [not for single masted vessels]. This pivots the ship on it's centre but loses you a lot of speed; typically and arbitrarily I use 45 degrees and a third. It's not the dynamically accurate solution etotheipi's maths would give you but it seems to game OK.

For anyone who wants a much fuller explanation, this guy wrote it all down: link

In case you aren't willing to take ethotheipi at his word, a quick glance at this work should quickly illustrate why we all do it wrong, without befuddling you with the math.

@ Yellow admiral

your link appears to be for slow to stationary ships being maneuvered in harbours, I'm sure movement at speed in open water is even more complex; or maybe not. Bottom line like everything else we do in wargaming we make huge approximations that give us a game.

The turning discussion, as I think Etotheipi has implied above, becomes more complicated for a ship operating under sail. For example, a ship sailing on the Beam Reach or just off the wind with the intention of wearing (i.e. reversing course by turning away from the source of the wind, would often create an unbalanced by allowing her fore sails to fill while "shivering" her after sails (aligning the after yards with the wind in such a manner that they neither propel nor impede the ship's movement through the water. This technique would cause the ship to rotate her bow away from the wind. This rotation would produce an effective rate of turn greater than that achievable by use of the rudder alone.

As the source of the wind comes well astern, the utility of this scheme rapidly diminishes to the point when the rudder alone can contribute to the turn rate.

Devils and details.

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A really scary part of this discussion comes in the early 20th century when ships (particularly WW1 era DDs) built to exactly the same nominal production plans would display radically different turn performance, or even have a given ship exhibit radically different turning diameters when turned to port versus starboard.

See Edgar March's "British Destroyers" on this strange phenomenon.

B