Several people have recently asked how the telescoping topmast worked. 8’4″ of the 58’3″ Sitka spruce topmast resided in the mast when fully erected. I have enclosed a sketch of how all this worked. A sheave at the butt of the topmast and sheave in the mast provided the mechanical advantage for the 330′ long 3/8″ diameter P.S. 19 steel topmast heel rope. The mast was fabricated from rolled steel plates riveted over rings and stringers. The top 24’8″ of the mast was tapered so the topmast was kept in place with lower and upper bearing rings. A fid resting on a ledge in the mast and kept the topmast in its erected position. Interestingly, the fid slot in the topmast was through the parabolic hollow section of the topmast, rather than through the solid portion. I wonder if this parabolic shape help better spread the load for the hollow topmast?

I also enclose pictures of the team shaping the topmast into its 13″ scale diameter. These pictures go with the earlier topmast posting and complete the basic construction of the topmast.

telescoping topmast operation

Getting ready to plane square topmast into octogon 1

Octogon shape marked out and being planed by Bill

Bill planes topmast to octogon shape

Topmast brought to round shape by planing edges and then sanding with long box

Topsail club after sanding