(a) In addition to, and concurrently with, the basic pilotage rate described in Section 1190, a charge shall be levied for pilotage services at a rate necessary to provide the benefits to be paid out pursuant to the pension plan. The additional rate shall be determined as follows:

1. (1) On March 1, June 1, September 1, and December 1 of each year, the number of persons eligible to receive benefits under the plan, their identities, the calculated amount each shall be entitled to receive, and the total amount to be paid out to all of those persons during each month of the next three-month period shall be determined by the fiduciary agent or agents.
2. (2) After the total amount to be paid out monthly under the plan has been determined, the rate necessary to provide that amount each month shall be calculated by the fiduciary agent or agents. The rate shall be based upon the volume of shipping, in gross registered tons, handled by pilots licensed under this division for the 12-month periods ending the previous September 30 for benefit periods commencing the following January 1, ending the previous December 31 for benefit periods commencing the following April 1, ending the previous March 31 for benefit periods commencing the following July 1, and ending the previous June 30 for benefit periods commencing the following October 1, respectively. The rate shall be expressed as mills per gross registered ton and shall be calculated to the nearest one-hundredth of a mill.
3. (3) The estimated cost of the services of the fiduciary agent or agents to administer the pension plan shall be calculated by the fiduciary agent or agents for the benefit periods described in paragraph (2), shall be expressed as mills per gross registered ton, and shall be calculated to the nearest one-hundredth of a mill.