"Article on turning circles." Topic

Today I bumped into a nice paper about calculating tactical diameter: link

It was even written by a wargamer and aimed at other wargamers! Very nice.

- Ix

That is a fantastic resource, thanks very much for posting!

Years back, I came across a picture of the Yamato, taken from above, of a full speed turn. My friend, a former frigate/destroyer OOD, could not believe the tight circle the Yamato was making. He said his former ships would be way outside the huge battleships turn radius.

Calculating the minimum turning circle of a ship is heinously complex. The basic factors like length, beam and draft aren't enough. You also have to look at hull shape, rudder description, propellers, current displacement, and on and on. Even the depth of water under the keel can make a difference – I read once about a freighter accident somewhere in the Persian Gulf caused by a ship over a shallow bottom not turning as tightly as expected, so it swung wide and went *CRUNCH*!

I suspect the article confines the data to the 1910-1945 period because in that era warships tended to have similar underwater lines based on the role envisioned for the hull (e.g., DD, BB, CV, etc.). Until 1910, many ships were still built with "ram" bows, and before 1900 there was a lot of experimentation with underwater shapes. I read once that the Jeanne d'Arc (armored cruiser) had a tactical diameter of about 2000m. I don't know how they ever got that thing into a harbor… And then there are suggestive nicknames like "The Wobbly Eight". <ahem>

Years ago when I started researching this topic, my primary takeaway was that each ship is a unique combination of factors and length or size are not reliable indicators of turning radius. I was particularly impressed that DDs are not necessarily nimble little boats that turn on a dime as some games portray them, but might even have had a longer turning circle than the capital ships they served alongside. However, I never had the patience to hunt down, collect and analyze tactical diameter data and derive my own "correct" turning templates, so I'm pretty happy to have found this article.

- Ix

IIRC, the tactical diameter of a Fletcher Class DD (approx. 1,000 yds) was greater than that of an Iowa Class BB. Edgar March's book on British DDs states that many of the early British DDs had inexplicable peculiarities with respect to tactical diameter, such as dramatically different turn diameters when turning to port and starboard.

B

Thanks for sharing

I was once a qualified OOD Underway on a Forrestal class aircraft carrier. During the three years I was on that ship I can remember only one time in which we had an opportunity to conduct man overboard maneuvers without any aircraft onboard. We had great fun, and we were amazed at how fast we could turn the ship without having worry about dumping aircraft over the side. For us, it dispelled a lot of myths about how long it takes to turn a carrier. I wish I could remember the turning rates we were achieving that day.

HMS Dreadnought had a TD of 466 yards at 21 knots and 443 yards at 12 knots, but what gets lost is the fact that though the TD was wider at full speed the ship actually turned faster, taking 60 seconds to turn 90 degrees at full speed but 81 seconds at 12 knots.

As for the Fletcher's poor turning circle, they only had one rudder. This was much improved in the following Allen M. Sumner class by going to two rudders. Something that gets lost in comparing the Fletcher and the Iowa is the extra speed lost by the battleship and the longer time it takes to regain it. All ships slow to some degree when turning, and the better the horsepower/weight ration the faster the acceleration.

I've been working on my own rules for all this for a couple of decades now. It's not easy, and of course no one wants to play something that complicated anyway.

I guess I might add that ships built to the same design sometimes wind up mysteriously performing quite differently in both speed and maneuvering characteristics. As in many other things, the devil is in the details. Once in awhile the cause is obvious, such as a launching accident or a ship running aground at some point in her career.

IIRC we had the turn radius at various speeds on a table on the bulkhead of the bridge. It was based on actual measurement.

When I was a navigator one of the crucial tools for maneuvering in pilotage waters was the advance and transfer table. This gives the distance along the original course (advance) and the offset (transfer) for rudder angles at 5 degree intervals and speeds at 5 knot intervals. Though for most alterations of less than 90 degrees at 10 knots of less applying the wheel about 1 cable before the new course was about right.

I agree that as wargamers we tend to use turning circles that are much larger than reality. Remember that at the sinking of HMS Victoria the tactical diameter was 4 cables, less than half a mile.