[MA] Weapon Question: Rope Kusari?

[DemiBenson]

Originally Posted by DemiBenson

I realize that, but the worked-out weighted rope earlier in the thread has considerably less weight than a chain kusari, and since each chain is an elongated torus with more surface area than a cylinder of the same length, the rope probably has comparable surface area despite being less strong and weighing 1/7th as much per yard.

... unless a kusari's chain is much smaller/thinner than I'm imaging, but then you'd need to include its breaking ST because trying to entangle with a jewelry-weight chain is asking for trouble.

Because I was curious, I actually decided to calculate what the relative surface areas are for a chain kusari and a 3/8 inch rope, per 1 foot-long section.

Start with Kusari-fundo on wikipedia, follow the link for the long pic with the ruler. Copy that to a handy image editor that can determine lengths, and find pixel lengths for 1 inch on the ruler, the width and length of a whole link, the wire width of a link (is there a word for that?), and the number of links per 1 foot length.

The fine details (I picked a link around the 9 inch mark, since it looked as face-on as possible):

1 inch on the ruler: 202 pixel
Wire width: 21 pixel, ~0.10 inches
Link width: 112 pixel, ~0.55 inches
Link length: 319 pixel, ~1.58 inches
Start-to-start length of a link: 253 pixel, ~1.25 inches, or about 9.58 links per foot (actual number of slack links per foot ~9.8)

Surface Area, assuming links are roughly squarish = (1.58 * 0.55 - 1.38 * 0.35) * 2 + (0.35 * 0.1 * 2) + (0.55 * 0.1 * 2) + (1.58 * 0.1 * 2) + (1.38 * 0.1 * 2) = ~1.54 inch^2
Chain drag per foot (taking 9.7 links per foot) = ~15.0 in^2
(If anyone wants to correct me with better math, be my guest.)

If the link end-cap shapes were perfect semi-circles, Sketchup tells me that's ~1.24 inch^2 per link, which gives ~12 inch^2 per foot length. So the actual value would be somewhere between 12 and 15 sq inches, and closer to the high side since the links are much more square-ended than round-ended.

3/8in rope drag per foot = 3/8 * pi * 12 = ~14.1 in^2


Even though the calculation for the chain is approximate, it's very close to the surface area of the 3/8 inch rope. That's leaving out the increased drag effects of having interlocking square-edged links.

So the chain kusari and the weighted rope would have roughly the same drag along their lengths. The weight and strength of each would be different, but that was not in question.