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The third option is to use your boil kettle. At the 2015 National Homebrewer's Conference in San Diego, James Howat's presentation, ''Wild and Spontaneous Fermentation at Home'', brought up the issue of [https://en.wikipedia.org/wiki/Surface-area-to-volume_ratio surface area to volume ratio] <ref name="Howat">[http://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars/ ''Wild and Spontaneous Fermentation at Home''. Presentation by James Howat at 2015 NHC.]</ref>. The ''surface area to volume ratio'' of a hot liquid, directly affects the cooling rate of that liquid (it affects the cooling rate of all objects, not just liquids) <ref>[http://www.fmf.uni-lj.si/~planinsic/articles/Cheese%20cubes_EJP.pdf The surface-to-volume ratio in thermal physics: from cheese cube physics to animal metabolism. Gorazd Planinsic and Michael Vollmer. European Journal of Physics. 29 (2008) 369–384.]</ref>. In other words, the greater the surface area of a given volume of liquid, the faster it cools. For example, imagine 100 liters of hot liquid is in a very wide and flat container. It will cool much faster than if it was in a perfectly square container, and even faster still than if it was in a spherical container. See [http://wordpress.mrreid.org/2011/10/20/spherical-ice-cubes-and-surface-area-to-volume-ratio/ this article for another explanation of how surface area to volume ratio affects cooling].
<code>
::Dimensions of the example coolship: 10 ft x 10 ft x 1.5 ft.
::Wort volume = 1122 gallons = 150 cubic feet.
::Surface area of the top surface of the wort = 150 100 square feet.::Surface Area to Volume ratio = 150100/150 = '''10.67''' square feet per cubic foot.
:Example of a 10 gallon coolship:
::Dimensions of the example miniature "mini-coolship": 2.5 ft x 2.5 ft x 0.5 20 ft (6 2.4 inches).
::Wort volume: 9.35 gallons = 1.25 cubic feet.
::Surface area of the top surface of the wort = 36.125 25 square feet.::Surface Area to Volume ratio = 36.12525/1.25 = '''2.5''' square feet per cubic foot.
</code>
The above example shows that the surface area to volume ratio of the 36 bbl coolship is much less than the surface area to volume ratio of the 10 gallon coolship, thus it will cool slower. A typical boil kettle (math not provided due to it involving circles) has dimensions that provide a surface area to volume ratio that is closer to the 36 bbl coolship(estimated 1-2 square feet per cubic foot). Further insulation of the boil kettle may help obtain a cooling rate that is comparable to the 36 bbl coolship. Other factors that influence the cooling rate of wort are the temperature between the wort and its surroundings, and what the [https://en.wikipedia.org/wiki/Thermal_conductivity thermal conductivity] is of the material that the coolship is made out of.
Another factor that is affected by the surface area to volume ratio is the inoculation rate. The larger the surface area, the more microbes that are collected. However, it has been shown that the surface area to volume ratio of large commercial coolships is adequate for collecting microbes, so in theory this shouldn't be a concern for homebrewers <ref name="Howat"></ref>. For more information on the process of brewing with a coolship, see [[Spontaneous Fermentation]].