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                    UNITED STATES TRUST COMPANY OF NEW YORK,
                               as Collateral Agent


                                       and


                         NAVIGATOR GAS (IOM I-D) LIMITED




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                             ISSUE OF ONE DEBENTURE

                           Dated as of August 1, 1997


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         This Issue of One Debenture, dated as of August l, 1997 (the
"Debenture"), from Navigator Gas (IOM I-D) Limited, a private limited company
organized under the laws of the Isle of Man (the "Owner") to United States Trust
Company of New York, as collateral agent, a bank and trust company organized
under the New York Banking Law (the "Collateral Agent").

                              PRELIMINARY STATEMENT

         On the Issue Date, Navigator Gas Transport PLC (the "Issuer") issued
Notes in connection with the financing of the construction of the Vessels. The
net proceeds of such issuance were deposited into the Pre-Funding Account.
Pursuant to the Intercreditor Agreement, the Allocated Principal Amount of the
Notes for the Vessel has been used, INTER ALIA, to make the installments due
under the Building Contract for the Vessel. The Notes are guaranteed jointly and
severally by the Owner and the other Owners pursuant to the Guarantees. As
collateral for the Notes and to provide working capital for the Owners, Credit
Suisse First Boston, acting through its London branch as funding bank and
administrating bank for the participating banks party to the Letter of Credit
Reimbursement Agreement (as defined below) (the "Letter of Credit Issuer") is
issuing a letter of credit (the "Letter of Credit"). As further collateral for
the Notes and the obligations under the Letter of Credit Reimbursement
Agreement, the Trustees, the Letter of Credit Issuer, Holdings, the Issuer and
the Owners have entered into a Collateral Agency and Intercreditor Agreement
(the "Intercreditor Agreement"), dated as of August 1, 1997. The Issuer's
obligation to reimburse the Letter of Credit Issuer for draws made under the
Letter of Credit, the Owners guaranty thereof and Holdings' pledge in respect
thereto is set forth in the Letter of Credit Reimbursement Agreement and
Guaranty (the "Letter of Credit Reimbursement Agreement"), dated as of August 7,
1997, among the Letter of Credit Issuer, the participating banks from time to
time party thereto, the Issuer, Holdings and the Owners. The Vessel will be
managed by Navigator Gas Management Limited (the "Manager") pursuant to the
Management Agreement, dated as of the date hereof, among Holdings, the Owners
and the Manager. As collateral security for its obligations under the
Indentures, the Letter of Credit Reimbursement Agreement and the other Security
Agreements, the Owner has and will assign, pledge, mortgage and grant the
Collateral Agent a security interest in, INTER ALIA, the Vessel, the earnings
and insurances of the Vessel and will grant this debenture in favor of the
Collateral Agent.

         NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained and of other valuable consideration, receipt of which is hereby
acknowledged, the Owner and the Collateral Agent hereby agree as follows:

                                    ARTICLE I
                                   DEFINITIONS

         Unless otherwise defined in Schedule 1 to this Debenture, capitalized
terms used in this Debenture shall have the meanings assigned to such terms in
the Intercreditor Agreement or in the Indentures.







                                       -2-



                                   ARTICLE II
                                 COVENANT TO PAY

         Section 2.1. COVENANT TO PAY. The Owner hereby covenants and agrees to
pay and discharge each sum owing under the Obligations as and when the same
shall fall due, whether at maturity, by acceleration or otherwise.

                                   ARTICLE III
                         MORTGAGE, CHARGE AND ASSIGNMENT

          Section 3.1. CHARGE. As continuing security for the Obligations, the
Owner hereby:

         (a)      conveys, transfers and assigns absolutely to and unto the
                  Collateral Agent, for the benefit of the Letter of Credit
                  Issuer, the Participating Banks, the First Priority Trustee
                  and the Second Priority Trustee, all rights of the Owner in
                  and to the Current Receivables by way of fixed charge;

         (b)      mortgages, charges and assigns, and agrees to mortgage, charge
                  and assign to the Collateral Agent, for the benefit of the
                  Letter of Credit Issuer, the Participating Banks, the First
                  Priority Trustee and the Second Priority Trustee, all present
                  and future rights of the Owner in and to all freehold or
                  leasehold property of the Owner and all other estates or
                  interests therein together with all trade fixtures and fixed
                  plant and machinery now and for the time being thereon, by way
                  of a fixed charge;

         (c)      mortgages, charges and assigns, and agrees to mortgage, charge
                  and assign, to the Collateral Agent, for the benefit of the
                  Letter of Credit Issuer, the Participating Banks, the First
                  Priority Trustee and the Second Priority Trustee, all rights
                  now owned or hereafter acquired in and to the goodwill,
                  franchises, patent rights, copyrights, trademarks and other
                  intangible Assets of the Owner by way of fixed charge;

         (d)      mortgages, charges and assigns, and agrees to mortgage, charge
                  and assign, to the Collateral Agent, for the benefit of the
                  Letter of Credit Issuer, the Participating Banks, the First
                  Priority Trustee and the Second Priority Trustee, all rights
                  relating to the aforesaid property specified in Sections
                  3.1(a), (b) and (c) including, INTER ALIA, negotiable
                  instruments, legal and equitable charges, reservations of
                  property rights, rights of action, collection, recovery or
                  security, rights of tracing and unpaid vendor's






                                       -3-

                  liens and similar and associated rights, by way of fixed legal
                  mortgage and charge; and

         (e)      mortgages and charges in favor of the Collateral Agent, for
                  the benefit of the Letter of Credit Issuer, the
                  Participating Banks, the First Priority Trustee and the
                  Second Priority Trustee, all rights of the Owner now owned
                  or hereafter acquired in and to all other Security Assets
                  for the time being of the Owner not subject to the fixed
                  securities created by Sections 3. l(a), (b), (c) and (d)
                  wheresoever situate (including, INTER ALIA, all undertakings
                  and businesses of the Owner) by way of a floating charge and
                  the Owner shall not be at liberty to create any mortgage or
                  charge on any of the securities created by this Section
                  3.1(e) and no Encumbrance shall in any case or in any manner
                  arise on or affect any part of the said securities in
                  priority to or PARI PASSU with all charges hereby created,
                  it being the intention that the Owner shall have no power,
                  without the written consent of the Collateral Agent, to part
                  with or dispose of any part of the said securities except by
                  way of sale in the ordinary course of its business;

         PROVIDED, HOWEVER, that upon the unconditional payment and satisfaction
         of the Obligations the rights of the Collateral Agent hereunder will
         terminate and the Collateral Agent will at the direction, cost and
         expense of the Owner release or reassign to the Owner all remaining
         rights of the Collateral Agent in and to the balance of the Security
         Assets.

         Section 3.2. LEGAL SECURITIES. The Owner will forthwith at the request
of the Collateral Agent execute a legal mortgage, charge or assignment over all
or any of the Security Assets subject to or intended to be subject to any fixed
security hereby created in favor of the Collateral Agent in such form as the
Collateral Agent may reasonably require.

         Section 3.3. CONVERSION OF FLOATING CHARGE. The Collateral Agent may at
any time by notice to the Owner convert the floating charge hereby created into
a fixed charge as regards any Assets specified in the notice which the
Collateral Agent shall consider to be in danger of being seized or sold under
any form of distress, attachment, execution or other legal process or to be
otherwise in jeopardy and (whether or not this security has become enforceable)
may at any time appoint a Receiver (as defined in Section 7.1 hereof) thereof.

         Section 3.4. NEGATIVE PLEDGE. Except as otherwise provided in the
Owner's Mortgage of its Vessel or the Indentures, the Letter of Credit
Reimbursement Agreement, the Intercreditor Agreement and the other Security
Agreements, the Owner shall not, without the prior written consent of the
Collateral Agent, permit the sale, transfer, assignment lease or other
disposition of any Security Asset, or any Encumbrance or other right in or over
any Security Asset to subsist, arise or be created, other than such Encumbrance
as is created by this Debenture.







                                       -4-

         Section 3.5. NEW ACCOUNTS. If the Collateral Agent receives or is
deemed to be affected by notice whether actual or constructive of any subsequent
Encumbrance or other interest affecting any Security Asset or the proceeds of
sale thereof, the Collateral Agent may open a new account or accounts for the
Owner. If the Collateral Agent does not open a new account it shall nevertheless
be treated as if it had done so at the time when it received or was deemed to
have received notice and as from that time all payments made to the Collateral
Agent shall be credited or be treated as having been credited to the new account
and shall not operate to reduce the amount for which this Debenture is security.

                                   ARTICLE IV
                            PRESERVATION OF SECURITY

         Section 4.1. CONTINUING SECURITY. The security constituted by this
Debenture shall be a continuing security and shall not be satisfied by any
intermediate payment or satisfaction of the Obligations but shall secure the
ultimate balance of the Obligations. The security hereby given shall be in
addition to and shall not be discharged, released, prejudiced or otherwise
affected by any other security or Encumbrance now or hereafter held by the
Collateral Agent for the Obligations.

         Section 4.2. WAIVER OF DEFENSES. The obligations of the Owner under
this Debenture and this security shall not be discharged, released, prejudiced
or otherwise affected by any act, omission or circumstance which but for this
provision might so operate or otherwise release or discharge the Owner from the
Obligations, or the security created under this Debenture including without
limitation and whether or not known to or discoverable by the Owner or the
Collateral Agent:

         (a)      any time, indulgence, waiver, consent or other relief granted
                  to or composition with the Owner or any other Person;

         (b)      the taking, variation, extension, compromise, renewal or
                  release of, or refusal or neglect to perfect or enforce, any
                  rights under the Indentures, the Letter of Credit
                  Reimbursement Agreement, the Intercreditor Agreement, this
                  Debenture, any other Security Agreement or any other
                  guarantee, agreement or obligation or any right against, or
                  any security granted by, the Owner or any other Person;

         (c)      any irregularity, invalidity or unenforceability of any
                  obligation of the Owner under the Indentures, the Letter of
                  Credit Reimbursement Agreement, the Intercreditor Agreement,
                  this Debenture, any other Security Agreement or any other
                  guarantee, of any government or authority (whether of right or
                  in fact) purporting to reduce or otherwise affect any such
                  obligation to the extent that such obligation and this
                  security shall remain in full force and this Debenture shall
                  be construed accordingly as if there were no such
                  irregularity, unenforceability, invalidity, law or order;







                                                        -5-

         (d)      any legal limitation, disability, incapacity or other 
                  circumstance relating to the Owner, any guarantor or any other
                  Person;

         (e)      any defect in or invalidity or inadequacy of the constitution
                  or incorporation or borrowing powers of the Owner or of its
                  board of directors, executive committee or other equivalent or
                  analogous body or in the authorization, execution or delivery
                  of the Indentures, the Letter of Credit Reimbursement
                  Agreement, the Intercreditor Agreement, this Debenture, any
                  other Security Agreement, or any other guarantee, agreement or
                  obligation; or

         (f)      any supplement, amendment or modification to the terms of the
                  Indentures, the Letter of Credit Reimbursement Agreement, the
                  Intercreditor Agreement, this Debenture, any Security 
                  Agreement or any other guarantee.  agreement or obligation.

         Section 4.3. IMMEDIATE RECOURSE. The Owner waives any right it may have
of first requiring the Collateral Agent to proceed against or claim payment from
the Owner or enforce the Indentures, the Letter of Credit Reimbursement
Agreement, the Intercreditor Agreement, any other Security Agreement or other
guarantee, agreement or obligation before enforcing this Debenture.

         Section 4.4.  PRESERVATION OF RIGHTS.  Until the Obligations have been
irrevocably paid and discharged in full, the Collateral Agent may:

         (a)      refrain from applying or enforcing any other security, money
                  or right held or received by the Collateral Agent in respect
                  of the Obligations or apply and enforce the same in such
                  manner and order as the Collateral Agent sees fit; and

         (b)      hold in a suspense account (without liability to pay interest
                  thereon) any moneys received or on account of this Debenture
                  by way of a partial payment.

         Section 4.5.  ADDITIONAL SECURITY.  This Debenture shall be in addition
to and shall not in any way be prejudiced by any other security now or hereafter
held by the Collateral Agent.

         Section 4.6. CERTIFICATE. A certificate of the Collateral Agent setting
forth the amount due from the Owner in respect of the Obligations shall, in the
absence of manifest error, be prima FACIE evidence of such amount.

         Section 4.7. DISCHARGE. Where any discharge (whether in respect of the
Indentures, the Letter of Credit Reimbursement Agreement, the Obligations, this
Debenture, or any other guarantee, agreement, obligation or security or
otherwise) is made in whole or in part or any arrangement is made on the faith
of any payment, security or other disposition which is avoided or must be repaid
on bankruptcy, liquidation, winding-up, dissolution or otherwise, this security
and the obligations






                                       -6-

of the Owner under this Debenture shall continue as if there had been no such
discharge or arrangement.

         Section 4.8. REGISTRATION. The Owner hereby agrees to arrange for this
Debenture, any Security Asset or any agreement, document or instrument relating
thereto to be registered with or notified to any Person to preserve or perfect
the Collateral Agent's security in any Security Asset.

         Section 4.9. COLLATERAL AGENT'S POWERS WITH RESPECT TO SECURITY ASSETS.
The Collateral Agent may without demand or notice to the Owner being required at
any time after this security becomes enforceable exercise at its discretion (in
the name of the Owner or otherwise) and without any further consent or authority
by the Owner, any right which may be exercised by the Person in whose name any
Security Asset is registered or who is the holder thereof under the terms
thereof or otherwise including, but without limitation, all the powers given to
trustees by statute in respect of securities or property subject to a trust;
PROVIDED, HOWEVER, that until the security hereby constituted becomes
enforceable, the Collateral Agent shall procure that the rights attached to each
such Security Asset are exercised in such manner as the Owner shall direct so
long as the same is not inconsistent with any term of the Intercreditor
Agreement, this Debenture or any other Security Agreement and account to the
Owner for any sum or other distribution paid in respect of such Security Asset.

         Section 4.10. CALLS. The Owner will for so long as the Obligations
remain outstanding pay all sums which may become due in respect of the Security
Assets and in the event of default the Collateral Agent may if it thinks fit
make such payments on behalf of the Owner. Any sums so paid by the Collateral
Agent shall be immediately due and payable by the Owner to the Collateral Agent
without demand or notice being required.

         Section 4.11. DELEGATION BY COLLATERAL AGENT. The Collateral Agent may
at any time and from time to time delegate by power of attorney or in any other
manner to any Person or Persons all or any of the rights and discretions which
are for the time being exercisable by the Collateral Agent under this Debenture
in relation to any Security Asset. Any such delegation may be made upon such
terms (including power to sub-delegate) and subject to such regulations as the
Collateral Agent may think fit. The Collateral Agent shall not be in any way
liable or responsible to the Owner for any loss or damage arising from any act,
default, omission or misconduct on the part of any such delegate or
sub-delegate.

         Section 4.12. FURTHER ASSURANCES. The Owner shall at its own expense
execute and deliver all such agreements, documents and instruments and do all
such assurances, acts and things as the Collateral Agent may require for
perfecting or protecting this security over any Security Asset or for
facilitating the realization of such property and in the exercise of all rights
vested in the Collateral Agent or in any sub-delegate as aforesaid. The Owner
shall in particular execute all transfers, conveyances, assignments and
assurances of such property whether to the Collateral Agent or its nominees and
give all notices, orders and directions which the Collateral Agent may think
expedient






                                       -7-

and, for the purposes of this Section, a certificate in writing by the
Collateral Agent to the effect that any particular assurance, act or thing
required by it is reasonably required shall be conclusive evidence of such fact
in favor of all third parties.

         Section 4.13. REDEMPTION OF PRIOR MORTGAGES. The Collateral Agent may
at any time after the security hereby constituted has become enforceable redeem
any prior Encumbrances against any Security Asset or procure the transfer
thereof to itself and may settle and pass the accounts of the prior
Encumbrances. Any accounts so settled and passed shall be conclusive and binding
on the Owner. All principal moneys, interest, costs, charges and expenses of and
incidental to such redemption and transfer shall be immediately due by the Owner
to the Collateral Agent without notice or demand being required.

         Section 4.14. POWER OF ATTORNEY. (a) The Owner hereby by way of
security irrevocably nominates, constitutes and appoints the Collateral Agent
and every Receiver of any Security Asset appointed hereunder and every such
delegate or sub-delegate as aforesaid, each of them acting alone or jointly with
any other of them, to be its attorney (the "Attorney") and on its behalf and in
its name or otherwise to sign under seal or otherwise and deliver all such
agreements, documents and instruments and do all such assurances, acts and
things which the Owner ought to do but fails to do under the covenants and
provisions contained in the Indentures, the Letter of Credit Reimbursement
Agreement, the Intercreditor Agreement, this Debenture or any other Security
Agreement (including without prejudice to the generality of the foregoing to
make any demand upon or give any notice or receipt to any Person owing moneys to
the Owner and to execute and deliver any charges, legal and equitable generally
in its name and on its behalf to exercise all or any of the rights conferred by
or pursuant to this Debenture or by statute on the Attorney and (without
prejudice to the generality of the foregoing) to sign under seal or otherwise
and deliver and otherwise perfect any assurance, agreement, instrument or act
which the Attorney may deem proper in or for the purpose of exercising any of
such rights).

         (b)      The Owner hereby ratifies and confirms and agrees to ratify
                  and confirm any such Attorney described in Section 4.14(a).

         Section 4.15. AVOIDANCE OF PAYMENTS. No assurance, security or payment
which may be avoided under any enactment relating to bankruptcy, and no release,
settlement or discharge given or made by the Collateral Agent on the faith of
any such assurance, security or payment, shall prejudice or affect the right of
the Collateral Agent to enforce the security created by or pursuant to this
Debenture in respect of the full extent of the moneys thereby secured. The
Collateral Agent shall be at liberty at its absolute discretion to retain the
security so created as security for the Obligations for a period of seven months
in the case of fixed security and thirteen months in the case of floating
security after the Obligations shall have been paid in full, notwithstanding any
release, settlement, discharge or arrangement given or made by the Collateral
Agent on or as a consequence of, such termination of liability. If at any time
within the period of six months in the case of fixed






                                       -8-

security and twelve months in the case of floating security after such
termination a petition shall be presented to a competent court for an order for
the winding up of the Owner or the Owner shall commence to be wound up
voluntarily, the Collateral Agent shall be at liberty, notwithstanding as
aforementioned, to continue to retain such security or any part thereof for and
during such further period as the Collateral Agent in its absolute discretion
shall determine. The Owner agrees that such security shall be deemed to have
been and to have remained held by the Collateral Agent as and by way of security
for the payment to the Collateral Agent of all or any sums which are now or may
become due and owing to the Collateral Agent under the Indentures, the Letter of
Credit Reimbursement Agreement, the Intercreditor Agreement and the rest of the
Security Agreements.

         Section 4.16. POWERS TO LEND. The Collateral Agent may advance money on
the security of any Security Asset for the purpose of defraying any costs,
charges, losses and expenses which shall be paid or incurred by it in relation
to this Debenture (including the remuneration of any Receiver (as hereinafter
defined)) or which the Collateral Agent anticipates may be paid or incurred in
the exercise of the rights vested in it or for all other purposes of this
Debenture or any of them and the Collateral Agent may advance such moneys at
such rates of interest and generally on such terms and conditions as it shall
think fit.

                                    ARTICLE V
                          DEALINGS WITH SECURITY ASSETS

         Section 5.1. CHARGED ACCOUNTS. The Owner shall cause all sums hereafter
received or recovered by or for it in respect of any Current Receivable to be
directly credited to a separate and distinct account as the Collateral Agent may
from time to time designate and, if called upon to do so by notice in writing
from the Collateral Agent, shall execute an absolute assignment of any such
Current Receivable in favor of the Collateral Agent, all at the cost of the
Owner. Until the security hereby constituted is fully discharged in accordance
with the terms hereof, the Owner shall not be entitled to withdraw any sum
standing to the credit of any such account established as aforesaid without the
prior written consent of the Collateral Agent.

         Section 5.2. DEPOSIT OF PROPRIETARY RIGHTS. The Owner shall, if the
Collateral Agent so requires, deposit with the Collateral Agent all certificates
and other documents of title or evidence of ownership in relation to the patents
and rights referred to in Section 3.1(c).

         Section 5.3. LIABILITY TO PERFORM. Notwithstanding any other provision
herein contained to the contrary, the Owner shall remain liable to observe and
perform all of the respective conditions and obligations assumed by it in
respect of each Security Asset and the Collateral Agent shall be under no
obligation by reason of this Debenture, nor shall the Collateral Agent be
required in any manner, to perform or fulfill any obligation of the Owner in
respect of any Security Asset or to make any payment or make any enquiry as to
the maturity, amount, nature or sufficiency of any rental, interest, proceeds,
payments or receipts received by it or them or the Owner or to present or file
any






                                       -9-

claim or take any other action or give any notice to collect, exercise or
enforce the payment of any amount or the taking up of any rights or property to
which the Owner may have been or to which it may be now or hereafter entitled
thereunder at any time.

                                   ARTICLE VI
                                   ENFORCEMENT

         Section 6.1. WHEN SECURITY BECOMES ENFORCEABLE. The security hereby
conferred shall become immediately enforceable and the floating charge created
by this Debenture shall be deemed to have crystallized and an unrestricted power
of sale together with any powers conferred by statute as varied or amended or
granted by this Debenture shall be immediately exercisable by the Collateral
Agent (i) if the Owner fails to meet the Obligations in the manner specified in
Section 2.1 or (ii) upon and after the occurrence of any Event of Default. After
this security has become enforceable, the Collateral Agent may in its discretion
enforce all or any part of this security, and exercise all or any rights of
enforcement hereby granted, in such manner as the Collateral Agent sees fit.

         Section 6.2. ENFORCEMENT OF SECURITY. For the purposes of all powers
implied by statute the Obligations shall be deemed to have become due and
payable on the date hereof and any statutory restrictions on the power of sale
and restrictions on the right of consolidation shall not apply to this security.

         Section 6.3. REMEDIES, WAIVERS AND CONSENTS. No delay or omission of
the Collateral Agent in exercising any right under this Debenture shall impair
or be construed as a waiver of such right nor shall any single or partial
exercise of any such right preclude any further exercise thereof or the exercise
of any other right. The rights provided in this Debenture are cumulative and not
exclusive of any rights provided by law, agreement or otherwise. Any waiver and
any consent by the Collateral Agent under this Debenture must be in writing and
may be given subject to any conditions thought fit by the Collateral Agent. Any
waiver or consent shall be effective only in the instance and for the purpose
for which it is given.

         Section 6.4. EXERCISE OF POWERS. All or any of the powers conferred on
a receiver by Article VII hereof may be exercised by the Collateral Agent
without first appointing a Receiver or notwithstanding the appointment of a
Receiver.

                                   ARTICLE VII
                                    RECEIVER

         Section 7.1. APPOINTMENT AND POWERS OF RECEIVER. At any time after this
security becomes enforceable the Collateral Agent may without further notice
appoint in writing under the hand of its duly authorized officer any one or more
Person(s) to be a receiver or receiver and manager (hereinafter each called "a
Receiver") as the Collateral Agent at its sole discretion may see fit of any






                                      -10-

Security Asset in like manner in every respect as if the Collateral Agent had
become entitled under this Debenture and/or under statute to exercise the power
of sale thereby conferred. Every Receiver so appointed shall, in addition to any
powers conferred by statute or common law, have and be entitled to exercise all
rights to do any or all of the following things:

         (a)      TAKE POSSESSION.  Enter upon and take immediate possession of,
                  get in and collect any Security Asset and undertake any
                  works of demolition, building, reconstruction, repair or
                  decoration thereon;

         (b)      SELL ASSETS.  Subject to any necessary consent or approval of
                  any judicial, administrative, governmental or other
                  regulatory body, office or agency, sell, convert into money
                  and realize any Security Asset by public auction or private
                  contract, dispose of, grant options and other rights in
                  respect of and exercise all other rights conferred on an
                  owner under any statute, at common law or otherwise, in
                  respect of any Security Asset and generally in such manner
                  and on such terms (which may consist wholly or partly of
                  shares or securities of any company or body corporate) as
                  the Receiver shall think fit and transfer, convey, assign or
                  grant an assurance of the same in the name and on behalf of
                  the Owner. Without prejudice to the generality of the
                  foregoing, the Receiver may do any of these things for a
                  consideration consisting of cash, debentures or other
                  obligations, shares or other valuable consideration in cash
                  or in any other form whatsoever and any such consideration
                  may be payable in a lump sum or by installments spread over
                  such period as the Receiver may think fit;

         (c)      COMPROMISE.  Settle, adjust, refer to arbitration, compromise
                  and arrange any claims, accounts, disputes, questions and
                  demands with or by any Person who is or claims to be a
                  creditor of the Owner or relating in any way to any Security
                  Asset;

         (d)      Borrow and Create Security. Borrow or raise money and secure
                  the repayment thereof and interest thereon by mortgaging,
                  sub-mortgaging or otherwise charging any Security Asset or
                  this Debenture (whether or not in priority to the sums and
                  obligations secured by this Debenture) in such manner and on
                  such terms as the Receiver shall think fit; PROVIDED, HOWEVER,
                  that:

                  (i)      no Receiver shall exercise such right without first
                           obtaining the written consent of the Person
                           appointing him and the Collateral Agent shall not
                           incur any responsibility to the Owner or any other
                           Person by reason of giving or refusing its consent,
                           whether directly or subject to any limitation or
                           condition; and







                                      -11-

                  (ii)     no Person lending such money shall be concerned to
                           enquire as to the existence of such consent or the
                           terms thereof or as to the propriety or purpose of
                           the exercise thereof or to see to the application of
                           any money so borrowed or raised;

         (e)      EMPLOY AGENTS.  Employ solicitors, managers, agents and others
                  as the Receiver shall deem necessary;

         (f)      RECEIPTS.  Give valid receipts and discharges for all moneys
                  and claims and execute all assurances and things which may
                  be proper or desirable for realizing any Security Assets;

         (g)      CONSIDERATION. Receive or pay any consideration in cash or
                  other valuable consideration and so that the same may be
                  receivable or payable either immediately or at a later time
                  and in a lump sum or by installments spread over such period
                  as the Receiver shall think fit;

         (h)      DEALINGS.  Generally to deal with and effect any transaction
                  or arrangement of any kind whatsoever in respect of any
                  Security Asset;

         (i)      LEGAL PROCEEDINGS.  Settle, arrange, compromise and submit to 
                  arbitration any accounts, claims, questions or disputes
                  whatsoever which may arise in connection with any Security
                  Asset or in any way relating to the security constituted by
                  this Debenture, to bring, take, defend, compromise, submit
                  to and discontinue any actions, suits, arbitration or
                  proceedings whatsoever whether civil or criminal in relation
                  to the matters aforesaid, to enter into, complete, disclaim,
                  abandon or disregard, determine or rectify all or any of the
                  outstanding agreements or arrangements of the Owner in any
                  way relating to or affecting the Security Assets or any part
                  thereof and to allow time for payment of any debts either
                  with or without security as the Receiver shall think
                  expedient;

         (j)      IN OWNER'S NAME.  Generally at his option to use the name of
                  the Owner in the exercise of all or any of the rights hereby
                  conferred;

         (k)      EXERCISE OF RIGHTS. Exercise, or permit the Owner or any
                  nominee of the Owner to exercise, any rights incident to the
                  ownership of any Security Asset in such manner as the Receiver
                  may think fit and in particular (as regards shares, stock and
                  securities) any voting rights conferred by the same and (as
                  regards securities) any rights of enforcing the same by
                  foreclosure, sale or otherwise;







                                      -12-

         (l)      CORPORATE TRANSFERS.  Transfer any Security Asset to any other
                  company or body corporate, whether or not formed or acquired
                  for the purpose;

         (m)      CARRY ON BUSINESS.  Generally manage and carry on and conduct
                  any of the undertakings and businesses of the Owner;

         (n)      CALLS. Make calls, conditionally or unconditionally, on the
                  members of the Owner in respect of all or any part of its
                  uncalled capital with such and the same rights of enforcement
                  as are conferred by the Memorandum of Association and Articles
                  of Association of the Owner upon its directors in this
                  respect;

         (o)      GENERAL POWERS. Sign under seal or otherwise and deliver all
                  such agreements, documents and instruments and do all such
                  other acts and things as the Receiver may consider desirable
                  or necessary for realizing any Security Asset or incidental or
                  conducive to any of the matters or rights conferred on a
                  Receiver under or by virtue of this Debenture and to exercise
                  in relation to any Security Asset all such rights as the
                  Receiver should be capable of exercising if the Receiver were
                  the beneficial owner of the same; and

         (p)      MONEYS RECEIVED BV RECEIVER. All moneys received by a Receiver
                  shall after providing for the matters specified by any law be
                  applied by him in or towards satisfaction of this Debenture
                  and thereafter of any other Encumbrance of which he shall have
                  notice and thereafter the Receiver shall pay the residue of
                  the moneys received by him to the Owner.

         Section 7.2. COMPLY WITH INSTRUCTIONS. Any Receiver shall in the
exercise of the Receiver's rights conform to any regulations and directions from
time to time made and given by the Collateral Agent as appointed but so that no
Person dealing with the Collateral Agent or any Receiver shall be concerned to
enquire whether the Receiver has so conformed to any such regulations or
directions.

         Section 7.3. REMOVAL AND REMUNERATION. The Collateral Agent may from
time to time by writing under its hand remove any Receiver appointed by it and
may whenever it may deem it expedient appoint a new Receiver in the place of any
Receiver whose appointment may for any reason have terminated and may from time
to time fix the remuneration of any Receiver appointed by it.

         Section 7.4. COLLATERAL AGENT MAY EXERCISE RECEIVER'S POWERS. All or
any of the rights which are conferred by this Debenture (either expressly or
impliedly) upon a Receiver of any Security Asset may be exercised after the
security hereby created becomes enforceable by the Collateral Agent in relation
to any Security Asset without first appointing a Receiver of the same or
notwithstanding the appointment of a Receiver of the same.






                                      -13-

         Section 7.5. NO LIABILITY FOR ENTERING INTO POSSESSION. The Collateral
Agent shall not nor shall any Receiver appointed as aforesaid by reason of the
Collateral Agent or the Receiver entering into possession of any Security Asset
be liable to account for such entry into possession or be liable for any loss or
realization or for any fault or omission for which such acts may have made them
liable. Every Receiver duly appointed by the Collateral Agent shall be deemed to
be the agent of the Owner for all purposes and shall as such agent be deemed to
be in the same position as a Receiver duly appointed under this Debenture. The
Owner alone shall be responsible for its agreements, obligations, acts,
omissions, defaults and losses and the Collateral Agent shall not incur any
responsibility therefor (either to the Owner or to any other Person whatsoever)
by reason of appointing such Receiver or for any other reason whatsoever. Every
such Receiver and the Collateral Agent shall be entitled to all the rights,
privileges and immunities by statute conferred on receivers when such receivers
have been duly appointed.

         Section 7.6. PROTECTION OF THIRD PARTIES. No purchaser, mortgagee or
other Person dealing with the Collateral Agent or the Receiver or the agents of
the Collateral Agent or the Receiver shall be concerned to enquire whether any
of the Obligations are due or owing, the right which the Collateral Agent or the
Receiver is purporting to exercise has become exercisable or any money remains
due under this Debenture, as to the propriety or regularity of the actions of
the Collateral Agent or such Receiver, or to see to the application of any money
paid to the Collateral Agent or to such Receiver.

         Section 7.7. EXPENSES. All costs, charges and expenses incurred and all
payments made by the Collateral Agent or any Receiver appointed hereunder in the
exercise in good faith of any right hereby conferred whether or not occasioned
by any act, neglect or default of the Collateral Agent or such Receiver shall
bear interest from the date of the same being incurred or becoming due at the
rate at which interest accrues on the Second Priority Notes. The amount of all
such costs, charges, expenses and payments and all interest thereon and all
remuneration payable hereunder shall be payable by the Owner on demand. All such
costs, charges, expenses and payments shall be paid and charged as between the
Collateral Agent and the Owner on the basis of a full indemnity and not on the
basis of party and party or any other kind of taxation.

         Section 7.8. INDEMNITY. Each of the Collateral Agent, the Letter of
Credit Issuer, the Participating Banks, the First Priority Trustee, the Second
Priority Trustee and every Receiver, attorney, manager, agent or other Person
appointed by the Collateral Agent hereunder shall be entitled to be indemnified
out of the Security Assets in respect of all obligations, costs, charges and
expenses incurred and payments made by such Person in good faith in the
execution or purported execution of any right vested in such Person pursuant
hereto and against all actions, proceedings, obligations, costs, claims and
demands in respect of any matter or thing done or omitted in anyway relating to
any Security Asset and the Collateral Agent, the Letter of Credit Issuer, the
Participating Banks, the First Priority Trustee, the Second Priority Trustee and
any such Receiver may retain and pay all sums in respect of the same out of any
moneys received under the rights hereby conferred.






                                      -14-

                                  ARTICLE VIII
                             APPLICATION OF PROCEEDS

         Section 8.1. ORDER OF APPLICATION. Any moneys received by the
Collateral Agent pursuant to this Debenture or under the powers hereby conferred
shall after the security hereby constituted shall have become enforceable but
subject to the payment of any claims having priority to this security be applied
for the purposes and in the order of priority indicated in the Intercreditor
Agreement.

         Section 8.2. SUSPENSE ACCOUNTS. Any moneys received under the rights
hereby conferred may, at the discretion of the Collateral Agent, be placed in a
suspense account and kept there for so long as the Collateral Agent thinks fit.

                                   ARTICLE IX
                            MISCELLANEOUS PROVISIONS

         Section 9.1.  AMENDMENT.  This Debenture may be amended from time to
time by written agreement signed by the parties hereto.

         Section 9.2. SEVERABILITY. If any provision of this Debenture is held
to be in conflict with any applicable statute or rule of law or is otherwise
held to be unenforceable for any reason whatsoever, such circumstances shall not
have the effect of rendering the provision in question inoperative or
unenforceable in any other case or circumstance, or of rendering any other
provision or provisions herein contained invalid, inoperative, or unenforceable
to any extent whatsoever. The invalidity of any one or more phrases, sentences,
clauses or Sections of this Debenture contained, shall not affect the remaining
portions of this Debenture, or any part thereof.

         Section 9.3. NOTICES. All demands, notices and communications hereunder
shall be in writing, personally delivered or mailed by certified mail-return
receipt requested, and shall be deemed to have been duly given upon receipt (a)
in the case of the Collateral Agent, at the following address: 114 West 47th
Street, New York, New York 10036, Attention: Corporate Trust Department, (b) in
the case of the Owner, at the following address: 15-19 Athol Street, Douglas,
Isle of Man, or at other such address as shall be designated by such party in a
written notice to the other parties.

         Section 9.4. CONSENT TO JURISDICTION. Any legal suit, action or
proceeding against the Owner arising out of or relating to this Debenture, or
any transaction contemplated hereby, may be instituted in any federal or state
court in The City of New York, State of New York and the Owner hereby
irrevocably and unconditionally waives any objection which it may now or
hereafter have to the laying of venue of any such suit, action or proceeding,
and the Owner hereby irrevocably submits to the jurisdiction of any such court
in any such suit, action or proceeding. To the extent the Owner has or hereafter
may acquire any immunity from jurisdiction of any court or from any legal
process






                                      -15-

(whether through service of notice, attachment prior to judgment, attachment in
aid of execution, execution or otherwise) with respect to itself or its
property, it hereby irrevocably waives such immunity in this Agreement to the
extent permitted by law. The Owner hereby irrevocably appoints and designates
Cambridge Partners, L.L.C., having an address at 535 Madison Avenue, New York,
New York, its true and lawful attorney-in-fact and duly authorized agent for the
limited purpose of accepting servicing of legal process and the Owner agrees
that service of process upon such party shall constitute personal service of
such process on the Owner. The Owner shall maintain the designation and
appointment of such authorized agent until all amounts payable under this
Debenture shall have been paid in full. If such agent shall cease to so act, the
Owner shall immediately designate and appoint another such agent satisfactory to
the Collateral Agent and shall promptly deliver to the Collateral Agent evidence
in writing of such other agent's acceptance of such appointment. The Owner
further agrees to take any and all actions, including the execution and filing
of any and all such documents and instruments, as may be necessary to continue
such designation and appointment in full force and effect so long as this
Debenture shall remain in full force and effect.

         Section 9.5.  CAPTIONS.  The captions or headings in this Debenture are
for convenience only and in no way define, limit or describe the scope or intent
of any provisions or sections of this Debenture.

         Section 9.6.  GOVERNING LAW.  This Debenture shall be governed by and 
interpreted in accordance with the laws of the Isle of Man, without giving
effect to the principles of conflicts of law.

         Section 9.7. NO PARTNERSHIP. Nothing herein contained shall be deemed
or construed to create a partnership or joint venture among the parties hereto
and the services of each party shall be rendered as an independent contractor
and not as agent for any other party.

         Section 9.8.  COUNTERPARTS.  This Debenture may be executed in any
number of counterparts and by different parties hereto on separate counterpart,
each of which shall be deemed to be an original. Such counterparts shall
constitute one and the same agreement.

         Section 9.9. SURVIVAL. The representations, covenants and agreements
contained in or made pursuant to this Debenture in respect of either party
hereto shall survive the execution and delivery of this Debenture and shall
continue in effect so long as such party's obligations hereunder remain
outstanding.

         Section 9.10. INTEGRATION. This Debenture and the Schedule hereto, the
Indentures, the Letter of Credit Reimbursement Agreement, the Intercreditor
Agreement and the other Security Agreements constitute the entire agreement and
understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior agreements, understandings or






                                      -16-

representations pertaining to the subject matter hereof, whether oral or
written. There are no warranties, representations or other agreements between
the parties in connection with the subject matter hereof except as specifically
set forth or incorporated herein.

         Section 9.11. REPRODUCTION OF DOCUMENTS. This Debenture and all
documents relating hereto, including, without limitation, (a) consents, waivers
and modifications which may hereafter be executed, (b) documents received by any
party at the closing, and (c) financial statements, certificates and other
information previously or hereafter furnished, may be reproduced by any
photographic, photostatic, microfilm, micro-card, miniature photographic or
other similar process. The parties agree that any such reproduction shall be
admissible in evidence as the original itself in any judicial or administrative
proceeding (whether or not the original is in existence and whether or not such
reproduction was made in the regular course of business) and that any
enlargement, facsimile or further reproduction of such reproduction shall
likewise be admissible in evidence.

         Section 9.12. SUCCESSORS AND ASSIGNS; ASSIGNMENT. This Debenture shall
be binding upon and inure to the benefit of the Owner and the Collateral Agent
and their respective successors and assigns. The Owner shall not have the right
to assign its rights hereunder or any interest herein without the prior written
consent of the Collateral Agent. The Collateral Agent, at its sole option, shall
have the right to assign this Debenture and any of its rights and interest
hereunder and thereunder.

         Section 9.13.  GENERAL INTERPRETIVE PRINCIPLES.  For purposes of this
Debenture except as otherwise expressly provided or unless the context otherwise
requires:

         (a)      the defined terms in this Debenture shall include the plural
as well as the singular, and the use of any gender herein shall be deemed to
include any other gender;

         (b) accounting terms not otherwise defined herein have the meanings
assigned to them in accordance with generally accepted accounting principles as
in effect on the date hereof;

         (c) references herein to "Articles ", "Sections", " Subsections",
"paragraphs ", and other subdivisions without reference to a document are to
designated Articles, Sections, Subsections, paragraphs and other subdivisions of
this Debenture;

         (d) a reference to a Subsection without further reference to a Section
is a reference to such Subsection as contained in the same Section in which the
reference appears, and this rule shall also apply to paragraphs and other
subdivisions;

         (e) the words "herein", "hereof", "hereunder" and other words of
similar import refer to this Debenture as a whole and not to any particular
provision; and







                                      -17-

         (f) the term "include" or "including" shall mean without limitation by
reason of enumeration.







         IN WITNESS WHEREOF this Debenture has been executed by the Owner the
day and year first above written.


SIGNED, SEALED and DELIVERED                 )
as a Deed and Debenture                      )
by                                           )  Richard Klapow
for and on behalf of                         )  Director
Navigator Gas (IOM I-E) Limited              )  Geoffrey Richardson
in the presence:-                            )


SIGNED by                                    )
for and on behalf of                         )  Christine C. Collins
United States Trust Company of New York         Adam Levine
as Collateral Agent                          )
in the presence of:-                         )








                                   SCHEDULE 1
                       Defined Terms Used in the Debenture

         "ASSETS" means, in relation to any person, the whole or any part of its
business, undertaking, property and assets and includes, without limitation, any
right to receive revenues.

         "CURRENT RECEIVABLES" means (a) all obligations of the trade debtors of
the Owner due or owing to the Owner on account of the prevailing debit balances
of the present book debts of the Owner and (b) all rights relating to the
aforesaid property specified in clause (a), including, INTER ALIA, negotiable
instruments, legal and equitable charges, reservations of property rights,
rights of action, collection, recovery or security, rights of tracing an unpaid
vendor's liens and similar and associated rights (and each reference to a
"Current Receivable" shall be construed as a reference to the whole or any part
of any one or more of them).

         "ENCUMBRANCE" means any encumbrance and includes any mortgage, charge
(whether fixed or floating, pledge, lien, hypothecation, title retention or
other security agreement or security interest of any kind whatsoever and
howsoever arising and any equivalent or analogous interest to any of the
foregoing.

         "PERSON" means an individual, a partnership, a corporation, a joint
venture, unincorporated association, a joint stock company, a trust or any other
entity or a Governmental Authority.

         "SECURITY ASSETS" means all of the present and future Assets of the
Owner, including, INTER ALIA, the Current Receivables (and each reference to a
"Security Asset" shall be construed as a reference to the whole or any part of
any one or more of them).











                                TABLE OF CONTENTS

                                                                                                                   Page
                                                                                                                   ----
                                                                                                                

                                        PRELIMINARY STATEMENT ....................................................    2

                                    ARTICLE I
                                   DEFINITIONS ...................................................................    2

                                   ARTICLE II
                                 COVENANT TO PAY .................................................................    2

        Section 2.1.   COVENANT TO PAY............................................................................    2

ARTICLE III
                                    MORTGAGE, CHARGE AND ASSIGNMENT...............................................    2

         Section 3.1.  CHARGE.....................................................................................    2
         Section 3.2.  LEGAL SECURITIES...........................................................................    3
         Section 3.3.  CONVERSION OF FLOATING CHARGE..............................................................    3
         Section 3.4.  NEGATIVE PLEDGE............................................................................    3
         Section 3.5.  NEW ACCOUNTS...............................................................................    3

ARTICLE IV
                                             PRESERVATION OF SECURITY.............................................    4
         Section 4.1.  CONTINUING SECURITY........................................................................    4
         Section 4.2.  WAIVER OF DEFENSES.........................................................................    4
         Section 4.3.  IMMEDIATE RECOURSE.........................................................................    5
         Section 4.4.  PRESERVATION OF RIGHTS.....................................................................    5
         Section 4.5.  ADDITIONAL SECURITY........................................................................    5
         Section 4.6.  CERTIFICATE................................................................................    5
         Section 4.7.  DISCHARGE..................................................................................    5
         Section 4.8.  REGISTRATION...............................................................................    6
         Section 4.9.  COLLATERAL AGENT'S POWERS WITH RESPECT TO SECURITY ASSETS..................................    6
         Section 4.10.  CALLS.....................................................................................    6
         Section 4.11.  DELEGATION BY COLLATERAL AGENT............................................................    6
         Section 4.12.  FURTHER ASSURANCES........................................................................    6
         Section 4.13.  REDEMPTION OF PRIOR MORTGAGES.............................................................    7
         Section 4.14.  POWER OF ATTORNEY.........................................................................    7
         Section 4.15.  AVOIDANCE OF PAYMENTS.....................................................................    7
         Section 4.16.  POWERS TO LEND............................................................................    8

                                    ARTICLE V
                                           DEALINGS WITH SECURITY ASSETS..........................................    8
         Section 5.1.  CHARGED ACCOUNTS...........................................................................    8



                                       -i-







                                                                                                                
         Section 5.2.  DEPOSIT OF PROPRIETARY RIGHTS..............................................................    8
         Section 5.3.  LIABILITY TO PERFORM.......................................................................    8

                                   ARTICLE VI
                                                    ENFORCEMENT...................................................    9
         Section 6.1.  WHEN SECURITY BECOMES ENFORCEABLE..........................................................    9
         Section 6.2.  ENFORCEMENT OF SECURITY....................................................................    9
         Section 6.3.  REMEDIES, WAIVERS AND CONSENTS.............................................................    9
         Section 6.4.  EXERCISE OF POWERS.........................................................................    9

ARTICLE VII
                                                     RECEIVER.....................................................    9
         Section 7.1.  APPOINTMENT AND POWERS OF RECEIVER.........................................................    9
         Section 7.2.  COMPLY WITH INSTRUCTIONS..................................................................    12
         Section 7.3.  REMOVAL AND REMUNERATION..................................................................    12
         Section 7.4.  COLLATERAL AGENT MAY EXERCISE RECEIVER'S POWERS...........................................    12
         Section 7.5.  NO LIABILITY FOR ENTERING INTO POSSESSION.................................................    12
         Section 7.6.  PROTECTION OF THIRD PARTIES...............................................................    13
         Section 7.7.  EXPENSES..................................................................................    13
         Section 7.8.  INDEMNITY.................................................................................    13

                                  ARTICLE VIII
                                              APPLICATION OF PROCEEDS............................................    14
         Section 8.1.  ORDER OF APPLICATION......................................................................    14
         Section 8.2.  SUSPENSE ACCOUNTS.........................................................................    14

                                   ARTICLE IX
                                             MISCELLANEOUS PROVISIONS............................................    14
         Section 9.1.  AMENDMENT.................................................................................    14
         Section 9.2.  SEVERABILITY..............................................................................    14
         Section 9.3.  NOTICES..................................................................................     14
         Section 9.4.  CONSENT TO JURISDICTION...................................................................    14
         Section 9.5.  CAPTIONS..................................................................................    15
         Section 9.6.  GOVERNING LAW.............................................................................    15
         Section 9.7.  NO PARTNERSHIP............................................................................    15
         Section 9.8.  COUNTERPARTS..............................................................................    15
         Section 9.9.  SURVIVAL..................................................................................    15
         Section 9.10.  INTEGRATION..............................................................................    15
         Section 9.11.  REPRODUCTION OF DOCUMENTS................................................................    16
         Section 9.12.  SUCCESSORS AND ASSIGNS; ASSIGNMENT.......................................................    16
         Section 9.13.  GENERAL INTERPRETIVE PRINCIPLES..........................................................    16




                                      -ii-




                                   SCHEDULE 1
                       Defined Terms Used in the Debenture






                                      -iii-