<PAGE>

                                                                   EXHIBIT 10.31


                             ELEVENTH AMENDMENT TO
                             ---------------------
                          LOAN AND SECURITY AGREEMENT
                          ---------------------------
                 AND AMENDMENT TO CERTAIN OTHER LOAN DOCUMENTS
                 ---------------------------------------------

          THIS ELEVENTH AMENDMENT TO LOAN AND SECURITY AGREEMENT AND AMENDMENT
TO CERTAIN OTHER LOAN DOCUMENTS (the "Amendment") is made and entered into on
                                      ---------
this 14 day of March, 2000, to be effective (unless otherwise specified herein)
as of the date of execution of this Amendment, by and among FLEET CAPITAL
CORPORATION, a Rhode Island corporation, successor in interest by merger to
FLEET CAPITAL CORPORATION, a Connecticut corporation, formerly known as SHAWMUT
CAPITAL CORPORATION, successor in interest by assignment to BARCLAYS BUSINESS
CREDIT, INC. ("Lender"), LOWRANCE ELECTRONICS, INC., a Delaware corporation
               ------
("Lowrance"), LEI EXTRAS, INC., a Delaware corporation ("LEI"), LOWRANCE
----------                                               ---
CONTRACTS, INC., a Delaware corporation ("Lowrance Contracts"), and SEA
                                          ------------------
ELECTRONICS, INC., an Oklahoma corporation ("Sea Electronics") (Lowrance, LEI,
                                             ---------------
Lowrance Contracts and Sea Electronics are herein individually and collectively
called "Borrower").
        --------

                                   RECITALS

          A.  Borrower, Lowrance Australia Pty Limited ("Lowrance Australia")
                                                         ------------------
and Lender have entered into that certain Loan and Security Agreement, dated
December 15, 1993, as amended by (i) that certain First Amendment to Loan and
Security Agreement, dated October 16, 1995, by and among Lender, Borrower and
Lowrance Australia, (ii) that certain Second Amendment to Loan and Security
Agreement, dated November 1, 1996 by and among Lender and Borrower, (iii) that
certain Third Amendment to Loan and Security Agreement, dated December 30, 1996,
by and among Lender and Borrower, (iv) that certain Fourth Amendment to Loan and
Security Agreement, entered into effective as of April 1, 1997, by and among
Lender and Borrower, (v) that certain Fifth Amendment to Loan and Security
Agreement, entered into effective as of August 25, 1997, by and between Lender
and Borrower ("Fifth Amendment"), (vi) that certain Sixth Amendment to Loan and
               ---------------
Security Agreement and Certain Other Loan Documents, entered into effective as
of August 28, 1997, by and between Lender and Borrower, (vii) that certain
Seventh Amendment to Loan and Security Agreement, entered into effective as of
November 1, 1996, by and between Lender and Borrower, (viii) that certain Eighth
Amendment to Loan and Security Agreement, made and entered into as of December
9, 1997, by and between Lender and Borrower, (ix) that certain Ninth Amendment
to Loan and Security Agreement made and entered into as of September 14, 1998,
by and between Lender and Borrower, and (x) that certain Tenth Amendment to Loan
and Security Agreement and Amendment to Certain Other Loan Documents, executed
in November of 1998, by Lender and Borrower (as amended, the "Loan Agreement").
                                                              --------------

          B.  Borrower and Lender desire to amend the Loan Agreement and certain
of the other Loan Documents as hereinafter set forth.

          NOW, THEREFORE, in consideration of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties, intending to be legally bound, agree as
follows:

                                       1
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                                   ARTICLE I
                                  Definitions
                                 ------------

          1.01  Capitalized terms used in this Amendment are defined in the Loan
Agreement, as amended hereby, unless otherwise stated.

                                  ARTICLE II
                                  Amendments
                                  ----------

          2.01  Amendment to Section 1.1 of the Loan Agreement; Addition of
                -----------------------------------------------------------
Certain Definition.  Effective as of the date of execution of this Amendment,
------------------
Section 1.1 of the Loan Agreement is hereby amended by adding the following
-----------
definition thereto in alphabetical order:

               "Eleventh Amendment Agreement - the Eleventh Amendment to Loan
                ----------------------------
     and Security Agreement and Amendment to Certain Other Loan Documents,
     executed in February of 2000 by Lender and Borrower."

          2.02  Amendment to Section 3.1(A) of the Loan Agreement.  Effective
                -------------------------------------------------
as of the Effective Date, Section 3.1(A) of the Loan Agreement is amended as
                          --------------
follows:

               (a) Each reference to "1.50%" is hereby deleted and substituted
     therefor is a reference to "0.50%."

               (b) The last sentence of Section 3.1(A) is amended and restated
                                        --------------
     to read in its entirety as follows:

          "Notwithstanding anything contained herein to the contrary, Lender and
          Borrower agree that if at any time after execution of the Eleventh
          Amendment Agreement Borrower fails to maintain a Fixed Charge Ratio of
          not less than the ratio specified in Section 9.3(C) of this Agreement,
                                               --------------
          the Applicable Annual Rate relating to the Term Loans, the Equipment
          Loans and the Revolving Credit Loans shall thereafter be permanently
          increased to 1.00% above the Base Rate."

          2.03  Amendment to Section 3.2 of the Loan Agreement.  Effective as
                ----------------------------------------------
of the Effective Date, Section 3.2 of the Loan Agreement is amended as follows:
                       -----------

               (a) The reference to the date "December 31, 2000" is deleted and
     substituted therefor is the date "December 31, 2002."

               (b) The reference to the date "December 31, 2001" is deleted and
     substituted therefor is the date "December 31, 2003."

          2.04  Amendment to Section 3.3(A) of the Loan Agreement.  Effective
                -------------------------------------------------
as of the Effective Date, the last sentence of Section 3.3(A) of the Loan
                                               --------------
Agreement is deleted and substituted therefor is the following sentence:

                                       2
<PAGE>

               "At the effective date of any such termination of the Revolving
     Credit Commitment and this Agreement, Borrower shall pay to Lender (in
     addition to the then outstanding principal, accrued interest and other
     charges owing under the terms of this Agreement and any of the other Loan
     Documents), as liquidated damages for the loss of the bargain and not as a
     penalty, an amount equal to (i) 0.75% of the Termination Amount if such
     termination occurs during the period from the date of execution of the
     Eleventh Amendment Agreement through December 31, 2000; and (ii) 0.50% of
     the Termination Amount if such termination occurs during the period from
     January 1, 2001 through December 31, 2001.  If termination occurs after
     December 31, 2001, no termination charge shall be payable."

          2.05  Amendment to Section 9.2(X) of the Loan Agreement.  Effective as
                -------------------------------------------------
of the date of execution of this Amendment, Section 9.2(X) of the Loan Agreement
                                            --------------
is amended and restated to read in its entirety as follows:

               "(X)  Leases.  Become a lessee under any operating lease (other
                     ------
     than a lease under which Borrower is a lessor) of Property if the aggregate
     Rentals payable during any fiscal year of Borrower, beginning with fiscal
     year 2000, under the lease in question and all other leases under which the
     Borrower is then lessee would exceed $2,500,000.00.  The term `Rentals'
                                                                    -------
     means, as of the date of determination, all payments which the lessee is
     required to make by the terms of any lease."

     2.06  Amendments to Section 9.3 of the Loan Agreement.  Effective as of the
           -----------------------------------------------
date of execution of this Amendment, Section 9.3 of the Loan Agreement is
                                     -----------
amended as follows:

          (a) Section 9.3(A)  Minimum Tangible Net Worth is amended and restated
              --------------  --------------------------
     to read in its entirety as follows:

               "(A)  Minimum Tangible Net Worth.  Maintain a Consolidated
                     --------------------------
          Tangible Net Worth of not less than the amount indicated below on the
          last day of each calendar month during the period corresponding
          thereto:

<TABLE>
<CAPTION>
                                    Period                                               Amount
                                    ------                                               ------
                       <S>                                        <C>
          (a)          January, 2000 through December,            (a)          $7,000,000
                       2000
          (b)          Thereafter                                 (b)          the sum of (i) $7,000,000,
                                                                               plus (ii) 80% of the positive
                                                                               Adjusted Net Earnings From
                                                                               Operations for Borrower for
                                                                               the fiscal year of Borrower
                                                                               ending closest to July 31,
                                                                               2000"
</TABLE>

                                       3
<PAGE>

           (b) Section 9.3(B) Maximum Leverage Ratio is amended and restated
               -------------------------------------
     to read in its entirety as follows:

                   "(B) Maximum Leverage Ratio. Maintain, on a Consolidated
                        ----------------------
           basis as of the last day of each calendar month, beginning with the
           calendar month ending February 29, 2000, a ratio of (i) total
           Indebtedness to (ii) Tangible Net Worth of not more than 4.0 to 1.0."

     2.07  Amendment to Section 12.10 of the Loan Agreement.  Effective as of
           ------------------------------------------------
the Effective Date, Section 12.10 of the Loan Agreement is amended such that (i)
                    -------------
any notice to Lender shall hereafter be addressed as follows:

           "(A)  If to Lender:   Fleet Capital Corporation
                                 5950 Sherry Lane, Suite 300
                                 Dallas, Texas  75225
                                 Attn:  Loan Administration Manager

                 with a copy to: Patton Boggs LLP
                                 2001 Ross Avenue, Suite 3000
                                 Dallas, Texas  75201
                                 Attn:  Larry A. Makel, Esq."

and (ii) any notice to Borrower shall hereafter be addressed as follows:

           "(B)  if to Borrower: Lowrance Electronics, Inc.
                                 12000 East Skelly Drive
                                 Tulsa, Oklahoma  74123
                                 Attn:  Douglas J. Townsdin

                 with a copy to: Doerner, Saunders, Daniel & Anderson, L.L.P.
                                 320 South Boston Avenue, Suite 500
                                 Tulsa, Oklahoma  74103
                                 Attn:  H. Wayne Cooper"

     2.08  Amendment to Revolving Credit Notes.  Effective as of the Effective
           -----------------------------------
Date, each Revolving Credit Note is amended by deleting therefrom the date
"December 31, 2000 and substituting therefor the date "December 31, 2002."

                                  ARTICLE III
                             Conditions Precedent
                             --------------------

     3.01  Conditions Precedent.  The effectiveness of this Amendment is
           --------------------
subject to the satisfaction of the following conditions precedent, unless
specifically waived in writing by Lender:

                                       4
<PAGE>

           (a) Lender shall have received each of the following, each in
     form and substance satisfactory to Lender: (i) this Amendment, duly
     executed by Borrower; (ii) Fifth Amendment to Mortgage, Security Agreement,
     Financing Statement and Assignment of Rents, duly executed by Lowrance
     regarding the existing Mortgage in favor of Lender, covering Lowrance's
     Tulsa, Oklahoma real property; and (iii) such additional documents,
     instruments and information as Lender or its legal counsel may request;

           (b) The representations and warranties contained herein, in the
     Loan Agreement and in the other Loan Documents, as each is amended hereby,
     shall be true and correct as of the date hereof, as if made on the date
     hereof;

           (c) After giving effect to this Amendment, no Default or Event of
     Default shall have occurred and be continuing, unless such Default or Event
     of Default has been specifically waived in writing by Lender; and

           (d) All corporate proceedings taken in connection with the
     transactions contemplated by this Amendment and all documents, instruments
     and other legal matters incident thereto shall be satisfactory to Lender
     and its legal counsel.

                                  ARTICLE IV
                                   No Waiver
                                   ---------

     Nothing contained in this Amendment shall be construed as a waiver by
Lender of any covenant or provision of the Loan Agreement, the other Loan
Documents, this Amendment, or of any other contract or instrument between
Borrower and Lender, and the failure of Lender at any time or times hereafter to
require strict performance by Borrower of any provision thereof shall not waive,
affect or diminish any right of Lender to thereafter demand strict compliance
therewith.  Lender hereby reserves all rights granted under the Loan Agreement,
the other Loan Documents, this Amendment and any other contract or instrument
between Borrower and Lender.

                                   ARTICLE V
                 Ratifications, Representations and Warranties
                 ---------------------------------------------

     5.01  Ratifications.  The terms and provisions set forth in this
           -------------
Amendment shall modify and supersede all inconsistent terms and provisions set
forth in the Loan Agreement and the other Loan Documents, and, except as
expressly modified and superseded by this Amendment, the terms and provisions of
the Loan Agreement and the other Loan Documents are ratified and confirmed and
shall continue in full force and effect.  Borrower and Lender agree that the
Loan Agreement and the other Loan Documents, as amended hereby, shall continue
to be legal, valid, binding and enforceable in accordance with their respective
terms.

     5.02  Representations and Warranties.  Borrower hereby represents and
           ------------------------------
warrants to Lender that (a) the execution, delivery and performance of this
Amendment and any and all other Loan Documents executed and/or delivered in
connection herewith have been authorized by all requisite corporate action on
the part of Borrower and will not violate the Certificate of Incorporation or
Bylaws of Borrower; (b) the representations and warranties contained in the Loan

                                       5
<PAGE>

Agreement, as amended hereby, and any other Loan Documents are true and correct
on and as of the date hereof and on and as of the date of execution hereof as
though made on and as of each such date; (c) no Default or Event of Default
under the Loan Agreement, as amended hereby, has occurred and is continuing; (d)
Borrower is in full compliance with all covenants and agreements contained in
the Loan Agreement and the other Loan Documents, as amended hereby; (e) the
Borrower's Certificate of Incorporation and Bylaws are in full force and effect
on and as of the date hereof without modification or amendment in any respect
since November 1, 1996; (f) as of the date hereof, (i) Borrower is in existence
and in corporate and tax good standing in the State of its organization, (ii)
the Borrower is qualified to do business as a foreign corporation and is in
corporate and tax good standing in each jurisdiction where Borrower is doing
business and is required to be so qualified, (iii) Borrower does not owe
franchise taxes or other taxes required to maintain its corporate existence and
no franchise tax reports are due, and (iv) no proceedings are pending for
forfeiture of the Borrower's charter or for its dissolution either voluntarily
or involuntarily; and (g) the officer of Borrower executing this Amendment has
been duly elected and is, at present, qualified and acting in the office
indicated below such officer's name and is duly authorized to execute this
Amendment on behalf of Borrower.

                                  ARTICLE VI
                           Miscellaneous Provisions
                           ------------------------

     6.01  Survival of Representations and Warranties.  All representations
           ------------------------------------------
and warranties made in the Loan Agreement or any other Loan Document, including,
without limitation, any document furnished in connection with this Amendment,
shall survive the execution and delivery of this Amendment and the other Loan
Documents, and no investigation by Lender or any closing shall affect the
representations and warranties or the right of Lender to rely upon them.

     6.02  Reference to Loan Agreement.  Each of the Loan Agreement and the
           ---------------------------
other Loan Documents, and any and all other agreements, documents or instruments
now or hereafter executed and delivered pursuant to the terms hereof or pursuant
to the terms of the Loan Agreement, as amended hereby, are hereby amended so
that any reference in the Loan Agreement and such other Loan Documents to the
Loan Agreement shall mean a reference to the Loan Agreement, as amended hereby.

     6.03  Expenses of Lender.  As provided in the Loan Agreement, Borrower
           ------------------
agrees to pay on demand all costs and expenses incurred by Lender in connection
with the preparation, negotiation and execution of this Amendment and the other
Loan Documents executed pursuant hereto and any and all amendments,
modifications, and supplements thereto, including, without limitation, the costs
and fees of Lender's legal counsel, and all costs and expenses incurred by
Lender in connection with the enforcement or preservation of any rights under
the Loan Agreement, as amended hereby, or any other Loan Documents, including,
without, limitation, the costs and fees of Lender's legal counsel.

     6.04  Severability.  Any provision of this Amendment held by a court of
           ------------
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

                                       6
<PAGE>

     6.05  Successors and Assigns.  This Amendment is binding upon and shall
           ----------------------
inure to the benefit of Lender and Borrower and their respective successors and
assigns, except that Borrower may not assign or transfer any of its rights or
obligations hereunder without the prior written consent of Lender.

     6.06  Counterparts.  This Amendment may be executed in one or more
           ------------
counterparts, each of which when so executed shall be deemed to be an original,
but all of which when taken together shall constitute one and the same
instrument.

     6.07  Effect of Waiver.  No consent or waiver, express or implied, by
           ----------------
Lender to or for any breach of or deviation from any covenant or condition by
Borrower shall be deemed a consent to or waiver of any other breach of the same
or any other covenant, condition or duty.

     6.08  Headings.  The headings, captions, and arrangements used in this
           --------
Amendment are for convenience only and shall not affect the interpretation of
this Amendment.

     6.09  Applicable Law.  THIS AMENDMENT AND ALL OTHER LOAN DOCUMENTS
           --------------
EXECUTED PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND TO BE PERFORMABLE
IN AND SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
STATE OF TEXAS.

     6.10  Final Agreement.  THE LOAN AGREEMENT AND THE OTHER LOAN DOCUMENTS,
           ---------------
EACH AS AMENDED HEREBY, REPRESENT THE ENTIRE EXPRESSION OF THE PARTIES WITH
RESPECT TO THE SUBJECT MATTER HEREOF ON THE DATE THIS AMENDMENT IS EXECUTED. THE
LOAN AGREEMENT AND THE OTHER LOAN DOCUMENTS, AS AMENDED HEREBY, MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS
OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. NO
MODIFICATION, RESCISSION, WAIVER, RELEASE OR AMENDMENT OF ANY PROVISION OF THIS
AMENDMENT SHALL BE MADE, EXCEPT BY A WRITTEN AGREEMENT SIGNED BY BORROWER AND
LENDER.

     6.11  Release.  BORROWER HEREBY ACKNOWLEDGES THAT IT HAS NO DEFENSE,
           -------
COUNTERCLAIM, OFFSET, CROSS-COMPLAINT, CLAIM OR DEMAND OF ANY KIND OR NATURE
WHATSOEVER THAT CAN BE ASSERTED TO REDUCE OR ELIMINATE ALL OR ANY PART OF ITS
LIABILITY TO REPAY THE "OBLIGATIONS" OR TO SEEK AFFIRMATIVE RELIEF OR DAMAGES OF
ANY KIND OR NATURE FROM LENDER.  BORROWER HEREBY VOLUNTARILY AND KNOWINGLY
RELEASES AND FOREVER DISCHARGES LENDER, ITS PREDECESSORS, OFFICERS, DIRECTORS,
AGENTS, EMPLOYEES, SUCCESSORS AND ASSIGNS, FROM ALL POSSIBLE CLAIMS, DEMANDS,
ACTIONS, CAUSES OF ACTION, DAMAGES, COSTS, EXPENSES, AND LIABILITIES WHATSOEVER,
KNOWN OR UNKNOWN, ANTICIPATED OR UNANTICIPATED, SUSPECTED OR UNSUSPECTED, FIXED,
CONTINGENT, OR CONDITIONAL, AT LAW OR IN EQUITY, ORIGINATING IN WHOLE OR IN PART
ON OR BEFORE THE DATE THIS AMENDMENT IS EXECUTED, WHICH THE BORROWER MAY NOW OR
HEREAFTER HAVE AGAINST LENDER, ITS PREDECESSORS, OFFICERS,

                                       7
<PAGE>

DIRECTORS, AGENTS, EMPLOYEES, SUCCESSORS AND ASSIGNS, IF ANY, AND IRRESPECTIVE
OF WHETHER ANY SUCH CLAIMS ARISE OUT OF CONTRACT, TORT, VIOLATION OF LAW OR
REGULATIONS, OR OTHERWISE, AND ARISING FROM ANY "LOANS", INCLUDING, WITHOUT
LIMITATION, ANY CONTRACTING FOR, CHARGING, TAKING, RESERVING, COLLECTING OR
RECEIVING INTEREST IN EXCESS OF THE HIGHEST LAWFUL RATE APPLICABLE, THE EXERCISE
OF ANY RIGHTS AND REMEDIES UNDER THE LOAN AGREEMENT OR OTHER LOAN DOCUMENTS, AND
THE NEGOTIATION OF AND EXECUTION OF THIS AMENDMENT.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       8
<PAGE>

     IN WITNESS WHEREOF, this Amendment has been executed and is effective as of
the date first above-written.

                                 "LENDER"

                                 FLEET CAPITAL CORPORATION

                                 By:  /s/ Hance VanBeber
                                     ------------------------------------------
                                 Name:    Hance VanBeber
                                       ----------------------------------------
                                 Title:   Vice President
                                        ---------------------------------------

                                 "BORROWER"

                                 LOWRANCE ELECTRONICS, INC.

                                 By:  /s/ Darrell J. Lowrance
                                     ------------------------------------------
                                 Name:    Darrell J. Lowrance
                                       ----------------------------------------
                                 Title:   President
                                        ---------------------------------------

                                 LEI EXTRAS, INC.

                                 By:  /s/ Jane M. Kaiser
                                     ------------------------------------------
                                 Name:    Jane M. Kaiser
                                       ----------------------------------------
                                 Title:   President
                                        ---------------------------------------

                                 LOWRANCE CONTRACTS, INC.

                                 By:  /s/ Ronald G. Weber
                                     ------------------------------------------
                                 Name:    Ronald G. Weber
                                       ----------------------------------------
                                 Title:   President
                                        ---------------------------------------

                                 SEA ELECTRONICS, INC.

                                 By:  /s/ Mark C. McQuown
                                     ------------------------------------------
                                 Name:    Mark C. McQuown
                                       ----------------------------------------
                                 Title:   President
                                        ---------------------------------------

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