<PAGE>


                                                                    EXHIBIT 4.13


                                 AMENDMENT NO. 4
                                       TO
                                CREDIT AGREEMENT


         THIS AMENDMENT NO. 4, dated as of December 15, 2004 (this "Amendment
No. 4"), to that certain Credit Agreement, dated as of August 16, 2000, as
amended by Amendment No. 1 thereto, dated as of January 25, 2002 ("Amendment No.
1"); Amendment No. 2 thereto, dated as of November 15, 2002 ("Amendment No. 2");
and Amendment No. 3 thereto dated as of July 31, 2003 ("Amendment No. 3") (as so
amended, the "Credit Agreement"), is made by and among CAL DIVE I-TITLE XI,
INC., a Texas corporation (the "Shipowner"), GOVCO INCORPORATED, a Delaware
corporation (the "Primary Lender"), CITIBANK, N.A., a national banking
association (the "Alternate Lender"), CITIBANK INTERNATIONAL PLC, a bank
organized and existing under the laws of England, as facility agent for both the
Primary Lender and the Alternate Lender (and their respective successors and
assigns) with respect to the Floating Rate Note, and its permitted successors
and assigns (in such capacity, the "Facility Agent"), and CITICORP NORTH
AMERICA, INC., a Delaware corporation, as administrative agent for the Primary
Lender and the commercial paper holders of the Primary Lender (and their
respective successors and assigns) (in such capacity, together with its
permitted successors and assigns, the "Administrative Agent," and together with
the Facility Agent, the "Agents").

         WHEREAS, the Secretary has redetermined the estimated Actual Cost of
the Vessel, and the Shipowner has received its final total disbursements under
the Credit Agreement in the amount of $143,446,092 (which is not in excess of
87.5 percent (87.5%) of such redetermined estimated Actual Cost);

         WHEREAS, the Shipowner is required to revise the mandatory sinking fund
payments for the Floating Rate Note to take into account the changes referred to
in the first WHEREAS clause hereof by substituting the Third Revised
Amortization Schedule for the existing Second Revised Amortization Schedule,
which Third Revised Amortization Schedule has been approved by the Secretary and
is attached as Attachment 1 to Supplement No. 3 to Trust Indenture dated as of
the date hereof; and

         WHEREAS, the Parties wish to amend the Credit Agreement pursuant to
which the Lenders will agree to revise the mandatory sinking fund payments for
the Floating Rate Note.

         NOW THEREFORE, in consideration of the mutual rights and obligations
set forth herein and of other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows:



<PAGE>


         SECTION 1.01. CONCERNING EXHIBIT 1 TO THE CREDIT AGREEMENT. Exhibit 1
to the Credit Agreement is hereby further amended by adding thereto the
following definition:

               "Amendment No. 4 to Credit Agreement" means the Amendment No. 4
               to Credit Agreement, dated as of December 15, 2004, among the
               Shipowner, the Lenders and the Agents."

         SECTION 1.02. CONCERNING SECTION 4.01 TO THE CREDIT AGREEMENT. Section
4.01 of the Credit Agreement, as amended by Amendment No. 1 and Amendment No. 2
thereto, is further amended by deleting the Section in its entirety and
substituting the following therefor:

                    "4.01 Principal Repayment. The Shipowner shall repay the
                    Outstanding Principal of the Floating Rate Note as follows:

                          (1) In installments in the principal amounts set forth
                          in the Third Revised Amortization Schedule, Attachment
                          1 to Supplement No. 3 to Trust Indenture (which
                          replaces all prior changes to Attachment 1 to Trust
                          Indenture in Supplements No. 1 and No. 2 to Trust
                          Indenture), as the same may be further revised in
                          accordance with the Indenture on each Payment Date
                          commencing August 1, 2002, and continuing until
                          February 1, 2012; and

                          (2) The full amount of the remaining Outstanding
                          Principal, on the earlier of (x) February 1, 2012, or
                          (y) the date upon which the Trigger Event shall
                           occur."

         SECTION 1.03.  MISCELLANEOUS.

         (a) All capitalized terms used herein and not defined shall have the
meanings set forth in Exhibit 1 to the Credit Agreement.

         (b) Except as amended, the provisions of the Credit Agreement shall
apply to and govern this Amendment No. 4.

         (c) This Amendment No. 4 may be executed in several counterparts, each
of which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

                            (SIGNATURE PAGE FOLLOWS)



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<PAGE>


         IN WITNESS WHEREOF, this Amendment No. 4 to Credit Agreement has been
duly executed and delivered by the parties hereto as of the day and year first
above written.

<TABLE>
<CAPTION>

<S>                                                     <C>
CAL DIVE I-TITLE XI, INC.,                              GOVCO INCORPORATED,
           as the Shipowner                                    as the Primary Lender, by Citicorp
                                                               North America, Inc., its
                                                               attorney-in-fact

By  /s/ A. WADE PURSELL                                 By  /s/ PATRICK A. BOTTICELLI
    Name:  A. Wade Pursell                                  Name:    Patrick A. Botticelli
    Title: Vice President                                   Title:   Vice President

CITIBANK INTERNATIONAL PLC,                             CITIBANK, N.A.,
            as the Facility Agent                              as the Alternate Lender

By  /s/ PATRICK A. BOTTICELLI                           By  /s/ AE KYONG CHUNG
    Name:  Patrick A. Botticelli                            Name:    Ae Kyong Chung
    Title: Vice President                                   Title:   Vice President


CITICORP NORTH AMERICA, INC.,
           as the Administrative Agent

By  /s/ PATRICK A. BOTTICELLI
    Name:  Patrick A. Botticelli
    Title: Vice President
</TABLE>


                            CONSENT OF THE SECRETARY
                                       TO
                       AMENDMENT NO. 4 TO CREDIT AGREEMENT

         Pursuant to Section 11.08 of the Credit Agreement, the Secretary hereby
consents to this Amendment No. 4 to Credit Agreement and confirms the continued
Guarantee of the Obligation by the United States of America pursuant to Title XI
of the Merchant Marine Act, 1936, as amended.


                                            UNITED STATES OF AMERICA,
                                            SECRETARY OF TRANSPORTATION

ATTEST:                                     BY:  MARITIME ADMINISTRATOR

By /s/ SARAH J. WASHINGTON                  By /s/ JOEL C. RICHARD
    Assistant Secretary                        Secretary
    Maritime Administration                    Maritime Administration





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