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    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PropertyPlantAndEquipmentSalesPrice" xlink:label="PropertyPlantAndEquipmentSalesPrice" xlink:title="PropertyPlantAndEquipmentSalesPrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentLineItems" xlink:to="PropertyPlantAndEquipmentSalesPrice" xlink:title="definition: PropertyPlantAndEquipmentLineItems to PropertyPlantAndEquipmentSalesPrice" order="2.0" />
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    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="PropertyPlantAndEquipmentTypeDomain" xlink:to="DukeshipMember" xlink:title="definition: PropertyPlantAndEquipmentTypeDomain to DukeshipMember" order="2.0" />
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    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_UnitedMaritimeCorporationMember" xlink:label="UnitedMaritimeCorporationMember" xlink:title="UnitedMaritimeCorporationMember" />
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  <link:definitionLink xlink:type="extended" xlink:role="http://seanergymaritime.com/role/VesselsUnderConstructionDetails">
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    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_VesselCapacity" xlink:label="VesselCapacity" xlink:title="VesselCapacity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="VesselCapacity" xlink:title="definition: LongTermPurchaseCommitmentLineItems to VesselCapacity" order="2.0" />
    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PropertyPlantAndEquipmentPurchasePrice" xlink:label="PropertyPlantAndEquipmentPurchasePrice" xlink:title="PropertyPlantAndEquipmentPurchasePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="PropertyPlantAndEquipmentPurchasePrice" xlink:title="definition: LongTermPurchaseCommitmentLineItems to PropertyPlantAndEquipmentPurchasePrice" order="3.0" />
    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_NumberOfInstallmentPayments" xlink:label="NumberOfInstallmentPayments" xlink:title="NumberOfInstallmentPayments" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="NumberOfInstallmentPayments" xlink:title="definition: LongTermPurchaseCommitmentLineItems to NumberOfInstallmentPayments" order="4.0" />
    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PercentageOfPurchasePricePayableDuringFirstThirtyMonths" xlink:label="PercentageOfPurchasePricePayableDuringFirstThirtyMonths" xlink:title="PercentageOfPurchasePricePayableDuringFirstThirtyMonths" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="PercentageOfPurchasePricePayableDuringFirstThirtyMonths" xlink:title="definition: LongTermPurchaseCommitmentLineItems to PercentageOfPurchasePricePayableDuringFirstThirtyMonths" order="5.0" />
    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_TermForPaymentOfFortyPercentOfPurchasePrice" xlink:label="TermForPaymentOfFortyPercentOfPurchasePrice" xlink:title="TermForPaymentOfFortyPercentOfPurchasePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="TermForPaymentOfFortyPercentOfPurchasePrice" xlink:title="definition: LongTermPurchaseCommitmentLineItems to TermForPaymentOfFortyPercentOfPurchasePrice" order="6.0" />
    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PercentageOfPurchasePricePayableDuringFirstFifteenMonths" xlink:label="PercentageOfPurchasePricePayableDuringFirstFifteenMonths" xlink:title="PercentageOfPurchasePricePayableDuringFirstFifteenMonths" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="PercentageOfPurchasePricePayableDuringFirstFifteenMonths" xlink:title="definition: LongTermPurchaseCommitmentLineItems to PercentageOfPurchasePricePayableDuringFirstFifteenMonths" order="7.0" />
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    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PercentageOfPurchasePricePaidUponExecutionOfAgreement" xlink:label="PercentageOfPurchasePricePaidUponExecutionOfAgreement" xlink:title="PercentageOfPurchasePricePaidUponExecutionOfAgreement" />
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    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PercentageOfPurchasePricePayableUponDeliveryOfVessel" xlink:label="PercentageOfPurchasePricePayableUponDeliveryOfVessel" xlink:title="PercentageOfPurchasePricePayableUponDeliveryOfVessel" />
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    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PercentageOfVesselPurchasePricePaid" xlink:label="PercentageOfVesselPurchasePricePaid" xlink:title="PercentageOfVesselPurchasePricePaid" />
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    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_PeriodAfterSigningBareboatCharterAgreementToPayAdditionalDownPayment" xlink:label="PeriodAfterSigningBareboatCharterAgreementToPayAdditionalDownPayment" xlink:title="PeriodAfterSigningBareboatCharterAgreementToPayAdditionalDownPayment" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="PeriodAfterSigningBareboatCharterAgreementToPayAdditionalDownPayment" xlink:title="definition: LongTermPurchaseCommitmentLineItems to PeriodAfterSigningBareboatCharterAgreementToPayAdditionalDownPayment" order="15.0" />
    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_LesseeFinanceLeaseMonthlyBareboatRate" xlink:label="LesseeFinanceLeaseMonthlyBareboatRate" xlink:title="LesseeFinanceLeaseMonthlyBareboatRate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="LongTermPurchaseCommitmentLineItems" xlink:to="LesseeFinanceLeaseMonthlyBareboatRate" xlink:title="definition: LongTermPurchaseCommitmentLineItems to LesseeFinanceLeaseMonthlyBareboatRate" order="16.0" />
    <link:loc xlink:type="locator" xlink:href="ship-20260630.xsd#ship_LesseeFinanceLeasePurchasePrice" xlink:label="LesseeFinanceLeasePurchasePrice" xlink:title="LesseeFinanceLeasePurchasePrice" />
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