<PAGE>

                                                                    EXHIBIT 10.6

                        INVESTMENT MANAGEMENT AGREEMENT

TO: HAMBLIN WATSA INVESTMENT COUNSEL LTD.
    95 Wellington Street West
    Suite 802
    Toronto, Ontario
    M5J 2N7
    Fax No.: (416) 366-3993

                                                           DATE: August 13, 1998

1.   We authorize you to manage on a continuous basis an investment account (the
     "Account") on our behalf on the terms and conditions set out in this
     agreement.

2.   You shall manage the Account in accordance with the investment objectives
     from time to time communicated in writing by us to you. Until mutually
     agreed otherwise with the consent of the Insurance Department of the State
     of Ohio (the "Department"), the investment guidelines shall be as set out
     in the investment guidelines attached hereto.

3.   Subject to Section 2 above, you shall manage the Account in our name and
     you are hereby authorized to take such action for the Account as you, in
     your sole discretion, may consider appropriate for the operation of the
     Account including, without limitation, the power to buy, sell and exchange
     and otherwise deal in all securities which may at any time form part of the
     Account and to invest, in securities selected by you, all funds contained
     in, paid to or derived from the operation of, the Account, except to the
     extent that you are otherwise instructed in writing by us.

4.   The securities and funds of the Account have been deposited with and shall
     be held by The Bank of New York at its principal custodian office in New
     York City (or with such other custodian in the State of New York as is
     chosen by you from time to time and is acceptable to the Department) (the
     "Custodian") pursuant to an agreement which we have entered into with the
     Custodian. We have instructed the Custodian to promptly follow your
     directions at all times and to provide you with all such information
     concerning the Account as you may from time to time require in connection
     with your management of the Account, including without limitation, copies
     of relevant monthly statements.

5.   Provided you have used reasonable care and diligence you shall not be
     responsible for any damage, loss, cost or other expense sustained in the
     operation of the Account or relating in any manner to the carrying out of
     your duties under this agreement. We agree that you shall be entitled to
     assume that any information communicated by us or the Custodian to you is
     accurate and complete, and that in making investment decisions you shall be
     entitled to rely on publicly available information or on information which
     you believe to have been provided to you in good faith, in both cases
     barring actual knowledge by you to the contrary.

6.   You shall be entitled to such fees, payable quarterly in arrears, for your
     management of the Account as you may specify from time to time. Attached
     hereto is a copy of your current fee schedule and you agree to give us
     thirty (30) days prior written notice of any change in such schedule, which
     change shall require the approval of the Department. Such fees shall be the
     exclusive fees and charges payable (excluding third party disbursements
     reasonably incurred) for your management of the Account. As regards third
     party services, you will charge us only the amount of your actual
     disbursements paid to arm's length third parties for such services, and you
     will select as agents, brokers or dealers executing orders or acting on the
     purchase or sale of portfolio securities only agents, brokers or dealers
     operating in the United States.

7.   You shall deliver in writing to us, as soon as practicable after
     implementation of an investment decision, your confirmation of such
     implementation to enable us to ascertain that such implementation has been
     effected pursuant to the guidelines and procedures of our Board of
     Directors or a duly authorized committee thereof. Otherwise, the nature and
     timing of your reporting to us on the status of the Account shall be at
     least quarterly, within 45 days after the end of each quarter.
<PAGE>

8.   We acknowledge receipt of a copy of policies that you have established to
     ensure that investment opportunities are allocated fairly among your
     discretionary investment accounts and we confirm that these policies, until
     revised by you, will apply to the account.

9.   Either party hereto may terminate this agreement without penalty by giving
     the other party at least thirty (30) days advance written notice of its
     desire to terminate the same. In the event that the day upon which this
     agreement is so terminated is a day other than the first day of a calendar
     quarter, the fees payable in accordance with paragraph 6 for such quarter
     shall be pro-rated and shall be determined having regard to the market
     value of the Account based upon the most recent financial report which has
     been delivered to you by the Custodian.

10. All notices and communications to either party to this agreement shall be in
    writing and shall be deemed to have been sufficiently given if signed by or
    on behalf of the party giving the notice and either delivered personally or
    sent by prepaid registered mail addressed to such party at the address of
    such party indicated herein. Any such notice or communication shall be
    deemed to have been received by any such party if delivered, on the date of
    delivery, or if sent by prepaid registered mail on the fourth business day
    following mailing thereof to the party to whom addressed. For such purpose,
    no day during which there shall be a strike or other occurrence interfering
    with normal mail service shall be considered a business day.

11. This agreement shall enure to the benefit of and shall be binding upon the
    parties hereto and their respective successors. This agreement may not be
    assigned by either party.

12. This agreement, when executed, shall replace all earlier agreements between
    us in connection with your management of our managed investment account on a
    discretionary basis, without prejudice to any action taken under any such
    agreements. We acknowledge that we have read and understood this agreement
    and that we have received a copy of the same. You and we each acknowledge
    that the terms of this agreement are the exclusive and conclusive terms of
    our mutual agreement with regard to the subject matter hereof.

13. This agreement may only be amended by written agreement signed by the
    parties and approved by the Department.

<Table>
<S>                                                <C>
                                                   CRUM & FORSTER UNDERWRITERS CO. OF OHIO
                                                   305 Madison Avenue
                                                   Morristown, New Jersey 07962
                                                   --------------------------------------------
                                                   Address
                                                   (973) 490-6617
                                                   --------------------------------------------
                                                   Fax No.

By:  /s/ VALERIE GASPARIK                          By: /s/ JAMES STARK
    ----------------------------------------       ----------------------------------------
    Witness                                            Authorized Signature
                                                       James Stark
                                                   ----------------------------------------
                                                       Name of Authorized Signatory
</Table>

                                        2
<PAGE>

     We accept the Account and the foregoing.

DATED AT TORONTO, as of the 13th

DAY OF August, 1998.

                                        HAMBLIN WATSA INVESTMENT COUNSEL LTD.

                                        By:  /s/ FRANCES BURKE
                                           -------------------------------------
                                            Authorized Officer
                                            Francis Burke
                                           -------------------------------------
                                            Name of Authorized Officer

                                        3
<PAGE>

                             INVESTMENT MANAGEMENT
                                  FEE SCHEDULE

     Investment management fees are comprised of two parts:

(A) The Base Fee Amount

     and

(B) The Incentive Fee Amount

(A) THE BASE FEE AMOUNT

     1)    As described in Part 6 on the Investment Management Agreement, fees
           will be payable quarterly in arrears.

     2)    After the end of each calendar quarter year, Hamblin Watsa Investment
           Counsel Ltd. shall submit its investment management charges in
           accordance with the schedule below.

     3)    The charges are on a calendar year basis. They will be calculated at
           the end of each calendar quarter year based upon the average of the
           market value of the funds at the close of business for the three (3)
           preceding months.

<Table>
<Caption>
                 MARKET VALUE                                               CHARGE
    4)           ------------                                               ------
    <S>          <C>                                                        <C>
                 On Total Market Value....................................  .10%
</Table>

(B) THE INCENTIVE FEE AMOUNT

     The incentive fee amount relates to the investment management of equity
securities only.

<Table>
         <S>                      <C>
         Annual Base Fee:         a) If performance equals or exceeds benchmark, base fee is
                                  unchanged from current fee.
                                  b) If performance is less than benchmark, base fee is 90% of
                                  current fee.
         Maximum Fee:             1.75% (including base).
         Benchmark:               S&P 500 + 200 basis points.
         Incentive Fee:           Continuous rate of 10 basis point for every 100 basis points
                                  of outperforming the benchmark. (Incentive fee is in
                                  addition to base fee).
         Basis of Calculation:    Payable annually based on calendar year results. Not earned
                                  or paid unless results since inception (net of all fees)
                                  exceed benchmark return.
         Inception Date:
</Table>

(C) MAXIMUM INVESTMENT MANAGEMENT FEE

     Notwithstanding the foregoing, the maximum investment management fee
payable in any calendar year will be .25% of the Total Market Value (as
calculated in (A) 4) above); provided that any investment management fee not
payable in any calendar year as a result of the restriction in the preceding
sentence will be carried over to a succeeding calendar year, but the total
investment management fee payable in any such calendar year, including any
carry-over payment, shall be limited as provided by the preceding sentence.
<PAGE>

HAMBLIN WATSA INVESTMENT COUNSEL LTD.

<Table>
<S>            <C>
Signature:     /s/ FRANCES BURKE
               ------------------------------------
Name & Title:  Frances Burke
               ------------------------------------
Dated as of:   August 13, 1990
               ------------------------------------
Accepted by:   Crum & Forster Underwriters Co. of
               Ohio
               ------------------------------------
Signature:     /s/
               ------------------------------------
Title:         President
               ------------------------------------
Dated as of:   August 26, 1998
               ------------------------------------
</Table>

                                        2
<PAGE>

INVESTMENT OBJECTIVES

1.   Invest for the long term always providing sufficient liquidity for the
     payment of claims and other policy obligations.

2.   Ensure preservation of invested capital for policy holder protection.

3.   Invest in accordance with insurance regulatory guidelines.

INVESTMENT GUIDELINES

1.   APPROACH

     All investments are to be made using the value approach by investing in
     companies at prices below their underlying long term values to protect
     capital from loss and earn income over time and provide operating income as
     needed.

     With regard to equities, no attempt is made to forecast the economy or the
     stock market. The manager will attempt to identify financially sound
     companies with good potential profitability which are selling at large
     discounts to their intrinsic value. Appropriate measures of low prices may
     consist of some or all of the following characteristics: low price earnings
     ratios, high dividend yields, significant discounts to book value, and free
     cash flow. Downside protection is obtained by seeking a margin of safety in
     terms of a sound financial position and a low price in relation to
     intrinsic value. Appropriate measures of financial integrity which are
     regularly monitored, include debt/equity ratios, financial leverage, asset
     turnover, profit margin, return on equity, and interest coverage.

     As a result of this bargain hunting approach, it is anticipated that
     purchases will be made when economic and issue-specific conditions are less
     than ideal and sentiment is uncertain or negative. Conversely, it is
     expected that gains will be realized when issue-specific factors are
     positive and sentiment is buoyant. The investment time horizon is one
     business cycle (approximately 3-5 years).

     As regards bonds, the approach is similar. No attempt is made to forecast
     the economy or interest rates. The manager will attempt to purchase
     attractively priced bonds offering yields better than Treasury bonds with
     maturities of 10 years or less that are of sound quality i.e. whose
     obligations are expected to be fully met as they come due. We do not regard
     rating services as being an unimpeachable source for assessing credit
     quality any more than we would regard a broker's recommendation on a stock
     as being necessarily correct. In any form of investment research and
     evaluation, there is no substitute for the reasoned judgement of the
     investment committee and its managers.

2.   LIQUIDITY

     An adequate cash flow should be maintained to ensure that claims and
     operating expenses are paid on a timely basis. An operating cash position
     is to be maintained at appropriate levels and will be managed by the
     insurance operating company in accordance with the approved list for
     investments as determined from time to time by the Investment Committee.
     These securities will be managed by the Insurance Company as part of the
     Treasury function and currently are restricted primarily to Treasury and
     Agency securities of the U.S. government.

3.   REGULATORY

     Insurance regulations will be complied with, specifically Article 14 of the
     State of New York Insurance Law.

4.   DIVERSIFICATION

     The portfolio is to be invested in a wide range of securities of different
     issuers operating in different industries and jurisdictions in order to
     minimize risk.
<PAGE>

5.   PRUDENT PERSON RULE

     Prudent investment standards are considered in the overall context of an
     investment portfolio and how a prudent person would invest another person's
     money without undue risk of loss or impairment and with a reasonable
     expectation of fair return.

STRATEGY

1.   MAINTAIN ADEQUATE LIQUIDITY

     A review of portfolio liquidity is undertaken on a monthly basis. This
     liquidity analysis determines how much of each portfolio can be converted
     to cash in a given time period. Each company determines its liquidity
     requirements and the liquidity of the portfolio must match the requirement.

2.   ASSET ALLOCATION

     The asset allocation will be determined by the Portfolio Manager and will
     include short term investments that will generate appropriate cash flows
     and long term investments in stocks, bonds, debentures and money market
     investments, both domestic and foreign. The allocation will be in
     compliance with regulatory guidelines and should meet policy liabilities.

3.   FOREIGN EXCHANGE RISK

     Any foreign currency investments and exposures would normally be hedged via
     the use of forward foreign exchange contracts and/or currency options or
     preferably by a natural hedge with foreign pay liabilities of the Insurance
     Company. Unhedged foreign investments will be limited to 10% of invested
     assets at cost if judged appropriate. Unhedged exposure above this amount
     must be approved by the Investment Committee.

4.   INTEREST RATE RISK

     Interest rate risk will be minimized primarily through investment in fixed
     income securities with maturities less than ten years. While there are no
     specific duration/maturity limits for convertible securities, these issues
     are included in the total fixed income duration/term measure. Maximum fixed
     income portfolio duration is limited to the equivalent of a ten year term
     to maturity Treasury security.

INVESTMENT POLICY MIX

     The Investment Committee has established the following exposure ranges for
various asset mix classes:

<Table>
<Caption>
                                                               RANGE
                                                               -----
<S>                                                           <C>
Equities....................................................     0-25%
Fixed Income................................................    0-100%
Cash........................................................  Residual
Total.......................................................      100%
</Table>

     Within the Fixed Income portfolio, the Taxable/Tax Exempt mix will be
determined relative to the consolidated tax position of the Insurance Company
and the relative investment attractiveness of available tax exempt securities.

     The Investment Committee will control the total asset mix and will give
performance objectives to the Investment Manager regarding the assets managed.

RETURN EXPECTATIONS

     Total asset mix policy is expected on an annual basis to result in returns
better than the Consumer Price Index plus 3% over a ten year period before the
disbursement of investment management fees. However, in any one year the annual
return may be significantly above or below this expectation.

                                        2
<PAGE>

INVESTMENT OBJECTIVES OF THE FUND MANAGER

     The Manager, subject to regulatory and company imposed constraints
mentioned elsewhere, expects to provide additional returns to those returns that
would be earned by the alternative of passively managing a surrogate market
index.

     Performance of the Fund Manager is expected to result in the following
returns:

<Table>
         <S>                                    <C>
         All Equities.........................  S&P 500 + 1% point
</Table>

        Fixed Income:

<Table>
         <S>                                    <C>
              Taxable Bonds...................  Merrill Lynch Intermediate Treasury Index + 0.25%
              Tax-Advantaged Bonds............  Lehman Brothers 3 & 5 Year State GO Indexes
</Table>

     Measured over four (4) year moving periods.

                                        3
<PAGE>

          AGGREGATE INVESTMENT LIMITS, PERMITTED INVESTMENT CATEGORIES
                        AND INDIVIDUAL INVESTMENT LIMITS

PERMITTED INVESTMENT CATEGORIES WITHIN ASSET CLASSES

CASH:               Cash on hand, demand deposits, treasury bills, short-term
                    notes and bankers' acceptances, term deposits and guaranteed
                    investment certificates.

EQUITY:             Common shares, rights and warrants.

FIXED INCOME:       Bonds, debentures, preferred shares, including those
                    convertible into common shares.

     All of the above may be either U.S. domestic, Canadian, or other foreign
investments.

     Convertible preferred securities will be classified as equities if the
preferred dividend is not being paid.

     Private placement issues in public companies are allowed.

INVESTMENT CONSTRAINTS

     All investments will be made in accordance with all applicable legislation.

INDIVIDUAL INVESTMENT LIMITS

     Any combination of investments in any one corporate issuer will be limited
to a maximum of 5% of admitted assets. Exposure beyond 5% will require approval
of the Investment Committee.

QUALITY CONSTRAINTS

     The Investment Manager may invest in the permitted investment categories
listed in the Investment Objectives and Policy Statement subject to the
following quality constraints:

     Investments in money market instruments (less than or equal to 1 year term)
     will be limited to the approved list. This list will include money market
     instruments of the U.S. Treasury, Agencies of the U.S. government, and as a
     minimum commercial paper rated A1 or higher by Moody's and rated P1 or
     higher by Standard & Poor's.

     Investments in bonds and preferreds will be limited by quality tier as
follows:

                  LIMITS AS A % OF THE FIXED INCOME PORTFOLIO

<Table>
<Caption>
BOND RATING                                                   % OF TOTAL    MIN./MAX.
-----------                                                   ----------    ---------
<S>                                                           <C>           <C>
A or better.................................................     65%          Min.
BBB.........................................................     35%          Max.
BB, B.......................................................     10%          Max.
C, D........................................................      0%
</Table>

     The above limits are subject to adjustment to conform with the regulatory
requirements of Article 14 of the New York State Insurance Law.

     Limits are determined on a cost basis and include convertible securities.

     Downgrades will be taken into account when making new investments but will
not necessarily result in the sale of existing positions.

     Securities un-rated by the public rating agencies must be rated by the
Investment Manager and included as part of the categories above for the purposes
of determining overall exposure by quality tier.

     Any exceptions to the above must be approved by the Investment Committee.

                                        4
<PAGE>

PROHIBITED INVESTMENTS

     No loans will be made in any of the investment portfolios.

     No Real Estate will be purchased without Investment Committee approval.

     No Mortgages on real estate will be purchased without Investment Committee
approval. The exceptions to this are obligations issued by an agency of the U.S.
Government, or by U.S. domiciled corporations that are issued as part of a
registered public offering that also meet the minimum quality tier requirements.

FOREIGN INVESTMENT LIMIT

     Foreign Securities may be purchased in compliance with established
regulatory guidelines and with the policy on foreign exchange risk outlined
herein.

     Foreign investments must be in the same kinds of securities and investments
as the Insurance Company is normally allowed.

OTHER

     Derivative securities may be purchased up to 2% of the portfolios cost at
book. Use of derivative investments is infrequent and for hedging purposes.
Derivative investments will be justified to the Investment Committee prior to
use.

                                        5