So, each rope only needs to be too strong for the individual worker to snap. Obviously, that’s pretty easy, even with the worst natural fiber cordage - fibers are strong. Then they meet in some way, and ultimately attach to the wooden sled. The exact math for that is not straightforward, and we don’t really know how they tied it off, but it’s not an unusual amount of load for a large wooden structure. Assuming the sled measured 100 meters2 (80 tons was a special block worthy of an oversize sled), that works out to less than a ton per square meter, and a tree with 1m2 cross section at the trunk can weigh several tons without even considering the wind load on the foliage, which will be larger yet for most species.
80 tons is a lot, but it’s not a lot a lot. Thousands of tons are pretty common if you’re talking about ships, for example. Even the wooden ones; honestly wood is an underrated material.
So, each rope only needs to be too strong for the individual worker to snap. Obviously, that’s pretty easy, even with the worst natural fiber cordage - fibers are strong. Then they meet in some way, and ultimately attach to the wooden sled. The exact math for that is not straightforward, and we don’t really know how they tied it off, but it’s not an unusual amount of load for a large wooden structure. Assuming the sled measured 100 meters2 (80 tons was a special block worthy of an oversize sled), that works out to less than a ton per square meter, and a tree with 1m2 cross section at the trunk can weigh several tons without even considering the wind load on the foliage, which will be larger yet for most species.
80 tons is a lot, but it’s not a lot a lot. Thousands of tons are pretty common if you’re talking about ships, for example. Even the wooden ones; honestly wood is an underrated material.