In 2010, PVS crew members under the guidance of Nainoa Thompson, began researching routes for Hōkūle‘a’s Worldwide Voyage. Below are some of the guidelines they used.
As much as possible, in her journey around the world, Hōkūle‘a will use non-carbon-based renewable energy, like wind and sunlight.
To take advantage of prevailing gentle-to-moderate easterly trade winds and warm temperatures, Hōkūle‘a will generally sail north-south and westward within the tropics. (The tropics are the area of the globe between the Tropic of Cancer at 23˚ 26′ N and the Tropic of Capricorn at 23˚ 26′ S.)
In the northern hemisphere tropics, the trade winds blow predominantly from the northeast; and in the southern hemisphere tropics, from the southeast. The winds are generated by two belts of high atmospheric pressure, one around 25°-30° N and the other around 25°-30° S.
For explanations of how wind is generated, see “Global Scale Circulation” in The Physical Envrionment and “Origin of Wind” in JetStream.
Hōkūle‘a will likely cross the equator four times during the voyage:
Tropical cyclones are the most serious weather risk to vessels sailing in the tropics. (See “View Lesson 14 – Hurricanes” for a NOAA video on tropical cylcones; see also “Tropical Cyclone Introduction.” Tropical cyclones are also called hurricanes and typhoons.)
There are seven areas in the tropics where tropical cyclones form, four in the northern hemisphere and three in the southern.
These powerful storms, with winds over 74 mph (64 knots), form during periods of hot weather, generally in summer and fall.
To avoid tropical cyclones, Hōkūle‘a will sail in the tropics in the winter and spring:
(For an explanation of why the seasons in the northern and southern hemispheres are opposite of each other, see “Seasons” in The Physical Envrionment.)
In the northern hemisphere Atlantic and Pacific Oceans, the tropical cyclone season begins in May-June and extends to October-November. In the Indian Ocean, the season is longer, beginning in April and extending to December. In the Northwestern Pacific there is no official season as tropical cyclones form throughout the year, but the main season is from July to November, with a peak in late August/early September.
In the southern hemisphere, the tropical cyclones form from November-December to April-May.
Contrary to what one might expect based on high equatorial temperatures, the area within 5° of latitude north and south of the equator is, with rare exceptions, free of cyclones.
In the chart below, the light colored tracks represent tracks of tropical cyclones. The dark blue band extending horizontally through the center of the map represents the equatorial belt (10˚ wide) where tropical cyclones generally do not form. (For a larger image, click on map below and zoom in.)
Around the equator, Coriolis Force is insufficient to circulate warm rising air masses into cyclones. (See Coriolis Force in The Physical Envrionment; also “Meteorology” under “Coriolis effect” in Wikipedia.)
The Maldives, in the Indian Ocean, an archipelago of atolls extending from 0° 40′ S to 7˚N southwest of India and Sri Lanka, could provide a safe haven as Hōkūle‘a waits for the northern summer-fall hurricane season to end before sailing north to and through the Red Sea in winter and spring.
Hōkūle‘a will travel to the subtropics (i.e., outside the tropics, north of the Tropic of Cancer or south of the Tropic of Capricorn) to get around the continent of Africa and to sail to Aotearoa. These subtropical excursions will take place in the spring, after subtropical winter storms subside.
Hōkūle‘a will remain in the cooler, safer subtropics during the summer-fall hurricane season before returning to the tropics in the following winter-spring.
Possible Subtropical Excursions
Hōkūle‘a has voyaged in the subtropics three times before:
Hōkūle‘a will avoid or take special preautions in areas known for maritime piracy, like the waters around Indonesia, particularly the Malacca Straits, and the Gulf of Aden and the Horn of Africa.
The U.S. State Department issues Travel Warnings, “when long-term, protracted conditions … make a country dangerous or unstable.” These warnings will be considered as PVS plans for the places Hōkūle‘a will visit.
The Worldwide Voyage will be segmented into sailing routes (legs) that will be designed to require not more than a month at sea. Crews will be selected to complete each leg of the voyage.
For each leg, the PVS navigation team will develop a course strategy and a sail plan, based on the sailing capabilities of Hōkūle‘a and the likely winds and weather conditions between the departure point and destination during the month that the route will be sailed. For best conditions for a successful sail within the time frames for each leg, routes should have at least a 75% average of favorable winds (winds from the beam or back of the canoe).
Basic data on winds are published in the Atlas of Pilot Charts:
Pilot Charts depict averages in prevailing winds and currents, air and sea temperatures, wave heights, ice limits, visibility, barometric pressure, and weather conditions at different times of the year. The information used to compile these averages was obtained from oceanographic and meteorologic observations over many decades during the late 18th and 19th centuries.
The charts are intended to aid the navigator in selecting the fastest and safest routes with regards to the expected weather and ocean conditions.
Links to digital versions of many of the charts are available online at website like sailnet.com. The following image is a section of the chart for the South Pacific in May, depicting average winds between Tahiti and the Cook Islands, using “wind roses” to present the data:
How to read a wind rose (the blue circles in the illustration above):
Also useful in sail planning is the 42-volume Sailing Directions (published by NGA), which describes features of coastlines, ports and harbors, and local winds, weather, currents, and tides (in 37 Enroute volumes); as well as “country-specific information such as firing areas, pilotage requirements, regulations, search and rescue information, ship reporting systems, and time zones” (in four Planning Guide volumes).
The open-ocean legs will be navigated without instruments.
The Worldwide Voyage is a real-world cultural and education project. PVS will continuously monitor data on global conditions that may pose a danger to the canoe and crew; plans will be made and modified, as needed, to reduce the risk of harm. Variations in global weather and other factors may necessitate changes in the sail plan during the four years of the Worldwide Voyage.
RT @kkbmanoa: Charting Our Ancestral Past http://t.co/30lveylzvS #WorldwideVoyage #Nainoa #Hokulea
Presentation by Chadd Onohi Paishon #pwo Waimea Middle School ‘Journey of Learning’ (May 22) http://t.co/L1RDermDTV
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