Which hitch is most appropriately used on rough-surfaced materials like logs and spars?

The timber hitch is the most appropriate choice for securing rough-surfaced materials like logs and spars due to its design, which allows it to grip these surfaces effectively. This hitch is specifically constructed to handle heavy loads and provides a reliable hold without slipping, making it ideal for securing large, heavy objects that may not have a smooth surface. The nature of the timber hitch enables it to apply pressure on the object it's wrapped around, which increases the friction and prevents movement.

It is important to note that while other types of hitches can serve various purposes, they may not perform as well on rough surfaces. For instance, the Spanish bowline is primarily used for creating loops and might not provide sufficient grip on logs. The mast head hitch is specifically designed for rigging purposes and won’t hold securely on rough materials as the timber hitch does. Similarly, the black wall hitch, while it also creates a secure hold, is not as effective on uneven surfaces as the timber hitch. Hence, for securing rough-surfaced materials, the timber hitch stands out as the most suitable option.