8. (5 points) There are 7 cylindrical logs, each with a diameter of 5 decimeters. Now, ropes are used to tie them together at two places, as shown in the figure. Then, at least $\qquad$ decimeters of rope are needed (the rope used for the knots is not counted, $\pi$ is taken as 3.14)


【Solution】Solution: According to the analysis of the problem, the total length of a rope is the sum of 6 segments and 6 arc lengths; the central angle corresponding to each arc length is: $60^{\circ}$, then the sum of the six arc lengths is exactly the circumference of a circle. The total length of the rope is:
$$
\begin{aligned}
& (6 \times 5+3.14 \times 5) \times 2, \\
= & (30+15.7) \times 2, \\
= & 45.7 \times 2, \\
= & 91.4 \text { (decimeters) },
\end{aligned}
$$

Answer: The total length of the rope is 91.4 decimeters.
Therefore, the answer is: 91.4.