Thickness of Ice.—Generally speaking, the ice is desired at an average thickness of fourteen inches; this being convenient for subsequent handling. In practice, the thickness of the ice, as it is stored or shipped from the water, varies with the exigencies of the season and the average thickness formed at the locality.
In the latitude of Central and Southern Ohio six-inch ice is often stored; in the vicinity of Chicago and Omaha, ten inch; in Maine, sixteen inch, and in Minnesota, twenty inch. Ice, thirty inches thick, has been cut and stored on Lake Superior, in Northern Wisconsin, where ice forms equal in purity and brilliancy to any found in this country. The ordinary printing on the pages of a Chicago newspaper has been easily read through a block of Lake Superior ice twenty-nine inches thick. At Winnipeg, Manitoba, ice is cut forty inches in thickness. Such thick ice keeps the year through.
FIG. 9. MARKER, WITH SWING GUIDE.
FIG. 10. FIELD PLOW.
FIG. 11. SWING GUIDE PLOWS.
Laying Out the Ice Field.—As the ice field is inspected and mapped out for plowing, all unsound places, air holes, or shallow places where rocks or sand bars approach near to the surface, are marked for avoidance. A convenient method is to bore holes at such places, and plant pieces of brush in them. Thin ice, formed where the ice has been removed during cutting, is also marked in this manner, to give warning of the danger of venturing upon it.
Like a good general, the ice harvester takes note of the physical advantages of his position. If he can so lay out the field that the current and prevailing winds are in his favor and assist to float the ice toward the house, his strategy is not without reward. Room for refuse ice is needed where it will not impede the ice floating toward the house. The lay of the shore line must not be overlooked, on streams where the current is strong, in calculating for support for the shore ice. The best ice in the field will always be secured as a prime consideration.