Nausikaa described very succintly that we do not travel by direct or even great circle routes. We travel by winds and currents. Ever wonder why Columbus discovered the Caribbean first and not North America even though he departed from a latitude near to Washington, D.C.?
For long distance or even medium distance cruising (anything over 24 hours) we look at winds and currents. For the Pacific you can download for free the Pilot Charts for the South Pacific -
select "publications" in left column
select <menu options:> Atlas of Pilot Charts
then the region of the world you are interested in.
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Then you page through the Pilot charts for the months of the year to determine the best historical months for heading in the direction you want. Turns out for the Cocunut run from Panama to Polnesia via the Galapagos the magic months are March / April for departing Panama. Other months, as shown on the pilot charts have major adverse winds and seas. Also you can see the historical ocean current values for each area. By choosing a routing with the most favorable winds (or least adverse winds) and favorable currents you get the standard routing that hundreds if not thousands have used over the years. Panama to the Galapagos then west to the Marquesas in the March/April months. Generally the run from the Galapagos to the Marquesas is in very light winds, but with the favorable current, you can make good miles per day. Some opt to head southwest to pick up the tradewinds and then turn back towards the Marquesas. 6 to one, 1/2 dozen the other as to which is better.
But in any Pacific adventure be sure to download "Penniped's Waypoints"
These are waypoints for all the points of interest to cruisers in the Pacific - - but most important of all are the Atlas Bouy waypoints and some of those bouys just so happen to be right on the rhumb line between the Galapagos and the Marquesas. A few cruisers in the dead of nights in the middle on "nowhere" have collided with these monsterous metal obstacles. So pay heed to the ones which are on or near your route. Also there are a lot of reefs and other obstacles in the listing that it seems are not shown on any nautical charts. Reason, no commercial ships or Captain Cook every went that way so they were never reported or entered into any "official charts."
Cruise the websites of others who have gone before you and you can graze on some good ideas and suggestions on how to proceed with minimal grief and unpleasant surprises.