<PAGE>

                         SUPPLEMENTAL INDENTURE NO. 4

This SUPPLEMENTAL INDENTURE NO. 4, dated as of December 31, 1997, is by and
among MORAN TRANSPORTATION COMPANY, a Delaware corporation (the "Company"),
MORAN TOWING CORPORATION, a New York corporation ("Moran Towing"), the
Guarantors listed on Annex I hereto (collectively, the "Guarantors"), MORAN BULK
CORPORATION ("Moran Bulk"), a Delaware corporation, and FLEET NATIONAL BANK
(formerly known as Shawmut Bank Connecticut, National Association), as trustee
(the "Trustee").

                             W I T N E S S E T H:

      WHEREAS, the Company, the Trustee, the Guarantors and Moran Bulk are
parties to that certain Indenture dated July 11, 1994, as amended by
Supplemental Indentures No. 1, 2 and 3 (as so supplemented, the "Indenture"),
pertaining to the Company's 11-3/4% Series B First Preferred Ship Mortgage Notes
due 2004 issued under the Indenture (the "Notes");

      WHEREAS, after giving effect to the merger of Moran Bulk with and into
Moran Towing described below, the Guarantors listed on Annex I hereto will
constitute all of the Subsidiaries of the Company.

      1.    Moran Bulk Corporation Merger.

      WHEREAS, pursuant to a certain agreement and plan of merger, effective
December 31, 1997, Moran Bulk shall merge with and into Moran Towing with Moran
Towing being the survivor of such merger.

      2.    General

      WHEREAS, Section 6.03 of the Indenture provides that (a) a Qualified
Restricted Subsidiary shall have the right to merge with any other Qualified
Restricted Subsidiary provided that the Qualified Restricted Subsidiary which is
the surviving corporation shall execute a supplemental indenture (in a form
reasonably satisfactory to the Trustee) pursuant to which such surviving
corporation shall (i) expressly assume the obligations under the applicable
Guarantee of the merged Qualified Restricted Subsidiary which is not the
surviving corporation in such merger and (ii) confirm the due and punctual
performance of the Guarantee of such surviving corporation and every covenant in
the Indenture on the part of such surviving corporation to be performed or
observed; and that (b) a Restricted Subsidiary that is not a Qualified
Restricted Subsidiary shall have the right to merge with any other Restricted
Subsidiary which is not a Qualified Restricted Subsidiary provided that the
Restricted Subsidiary which is the surviving corporation shall (i) execute a
supplemental indenture (in a form reasonably satisfactory to the Trustee)
pursuant to which such surviving corporation shall (1) expressly assume the
obligations under the applicable Guarantee of the merged Restricted Subsidiary
which is not the surviving corporation in such merger and (2) confirm the due
and punctual performance of the Guarantee of such surviving corporation and
every covenant in the Indenture and the Collateral Documents on the part of such
surviving corporation to be performed or observed and (ii) execute any
instrument required by the Trustee pursuant to Section 3.4 of the applicable
Ship Mortgage(s);

      WHEREAS, Moran Bulk is a Qualified Restricted Subsidiary, and Moran Towing
is a
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Restricted Subsidiary which is not a Qualified Restricted Subsidiary;

      WHEREAS, notwithstanding Section 6.03 of the Indenture, which relates to
mergers of (i) Qualified Restricted Subsidiaries with other Qualified Restricted
Subsidiaries and (ii) Restricted Subsidiaries which are not Qualified Restricted
Subsidiaries with other Restricted Subsidiaries which are not Qualified
Restricted Subsidiaries, the Company and Moran Towing intend that the merger of
Moran Bulk with and into Moran Towing fulfill the requirements of the proviso to
Section 5.14 of the Indenture;

      WHEREAS, Section 5.14 of the Indenture provides that subject to Article 6
of the Indenture, the Company will do or cause to be done all things necessary
to preserve and keep in full force and effect (i) its corporate existence and
the corporate existence of each of its Restricted Subsidiaries, in accordance
with their respective organizational documents (as the same may be amended from
time to time) and (ii) its (and its Restricted Subsidiaries') rights (charter
and statutory), licenses and franchises; provided, however, that the Company
shall not be required to preserve any such right, license or franchise, or the
corporate existence of any Restricted Subsidiary, if the Board of Directors of
the Company shall determine that the preservation thereof is no longer desirable
in the conduct of the business of the Company and its Restricted Subsidiaries
taken as a whole and that the loss thereof is not adverse in any material
respect to the Holders;

      WHEREAS, Sections 10.01(g) and (h) of the Indenture provide that the
Trustee, the Company, the Guarantors and a Subsidiary, as applicable, may amend
or supplement the Indenture without the consent of any Holder to make any
changes that do not adversely affect the legal rights of any Holder or to
supplement the Indenture to provide for mergers of Restricted Subsidiaries
pursuant to Section 6.03, and

      WHEREAS, the Company, Moran Towing and the Guarantors intend that this
Supplemental Indenture No. 4 fulfill the requirements of Section 5.14, and that
Moran Towing assume the obligations of Moran Bulk under the Guarantee and the
Indenture.

      NOW THEREFORE, the parties agree as follows, for the benefit of each other
and for the equal and ratable benefit of the Holders of the Notes:

      Section 1.01 Defined Terms. Capitalized terms used in this Supplemental
Indenture but not defined herein shall have the meanings given such terms in the
Indenture.

      Section 2.01 Acceptance by Trustee. The Trustee accepts the modifications
of the Indenture hereby effected only upon the terms and conditions set forth in
the Indenture as supplemented by this Supplemental Indenture No. 4. Without
limiting the generality of the foregoing, the Trustee shall not be responsible
for the correctness of the recitals contained herein, which shall be taken as
statements of the Company, and the Trustee makes no representations and shall
have no responsibility for, or in respect of, the validity or sufficiency of
this Supplemental Indenture No. 4.


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      Section 2.02 Construction. This Supplemental Indenture No. 4 is executed
as and shall constitute an instrument supplemental to the Indenture and shall be
construed in connection with and as part of the Indenture.

      Section 2.03 Ratification. Except as modified and expressly amended by
this Supplemental Indenture No. 4, the Indenture is, in all respects, ratified
and confirmed and all the terms, provisions and conditions thereof shall be and
remain in full force and effect.

      Section 2.04 Moran Towing. Moran Towing hereby agrees as follows:

            (a) to assume the obligations of Moran Bulk under the Guarantee of
Moran Bulk; and

            (b) that Moran Towing confirms the due and punctual performance by
Moran Towing of the Guarantee and the Collateral Documents, to the extent
applicable, of Moran Towing and/or Moran Bulk and every covenant in the
Indenture and the Collateral Documents, to the extent applicable, to be
performed or observed by Moran Towing and/or Moran Bulk; and

      Section 2.05 Exhibit F. Effective as of the date of this Supplemental
Indenture No. 4, Exhibits F-1, F-2 and F-3 to the Indenture shall be replaced
with Annex I attached hereto.

      Section 2.10 Counterparts. This Supplemental Indenture No. 4 may be
executed in any number of counterparts; each signed copy shall be an original,
but all of them together represent the same agreement.

      Section 2.11 Governing law. This Supplemental Indenture No. 4 shall be
subject to the governing law and choice of forum provisions of Section 13.09 of
the Indenture.


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      IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture No. 4 to be duly executed as of the day and year first above written.


MORAN TRANSPORTATION COMPANY


By: /s/ Jeffrey J. McAulay
    --------------------------
Name: Jeffrey J. McAulay
Title: Vice President


MORAN TOWING CORPORATION


By: /s/ Jeffrey J. McAulay
    --------------------------
Name: Jeffrey J. McAulay
Title: Vice President


THE GUARANTORS LISTED ON ANNEX I HERETO


By: /s/ Alan Marchisotto
    --------------------------
Name: Alan Marchisotto
Title: Secretary As to each of the Guarantors
       listed in Annex I.


MORAN INSURANCE COMPANY LIMITED


By: /s/ Jeffrey J. McAulay
    --------------------------
Name: Jeffrey J. McAulay
Title: Vice President


MORAN BULK CORPORATION (to be merged as described above)


By: /s/ Alan Marchisotto
    --------------------------
Name: Alan Marchisotto
Title: Secretary


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FLEET NATIONAL BANK,
 as Trustee


By: /s/ Mark A. Forgetta
    --------------------------
Name:  Mark A. Forgetta
Title: Authorized Signatory


                                       S-2
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                                                                         ANNEX I
                                   GUARANTORS


          Guarantors after Giving Effect to the Merger Described Herein

A. Restricted Subsidiaries

      1. Restricted Subsidiaries which are Not Qualified Restricted Subsidiaries

Moran Towing Corporation
Petroleum Transport Corporation

      2. Qualified Restricted Subsidiaries

Florida Towing Company
Curtis Bay Towing Company of Pennsylvania
Curtis Bay Towing Company of Virginia
Moran Insurance Company Limited
Moran Towing of Texas, Inc.
Moran Shipyard Corporation
Jakobson Shipyard, Inc.
Moran Barge Corporation
Portsmouth Navigation Corporation
Hampton Roads Land Co., Inc.
Moran Services Corporation
Moran Towing of Delaware, Inc.
Seaboard Barge Corporation


B. Unrestricted Subsidiaries

None




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