Tsantanis updates 14.62% stake in United Maritime

Stamatios Tsantanis filed Amendment No. 3 to his Schedule 13D on United Maritime Corp, updating his ownership and recent equity awards.

Rhea-AI Filing Summary

Stamatios Tsantanis filed Amendment No. 3 to his Schedule 13D on United Maritime Corp, updating his ownership and recent equity awards. He reports beneficial ownership of 1,394,534 shares of common stock, representing approximately 14.62% of the outstanding class.

The percentage is based on 9,538,139 shares of common stock outstanding as of April 7, 2026. On March 9, 2026, Tsantanis, as an executive officer, was issued 200,000 shares under United Maritime’s 2022 Equity Incentive Plan, subject to vesting on specified dates through September 9, 2027.

Key Figures

Beneficial ownership: 1,394,534 shares Ownership percentage: 14.62% Shares outstanding: 9,538,139 shares +4 more

7 metrics

Beneficial ownership 1,394,534 shares Common stock beneficially owned by reporting person

Ownership percentage 14.62% Percent of United Maritime common stock class

Shares outstanding 9,538,139 shares Common stock outstanding as of April 7, 2026

Equity grant 200,000 shares Issued March 9, 2026 under 2022 Equity Incentive Plan

First vesting tranche 60,000 shares Vesting on September 9, 2026

Second vesting tranche 60,000 shares Vesting on April 9, 2027

Third vesting tranche 40,000 shares Vesting on September 9, 2027

Key Terms

beneficially owned, sole voting power, sole dispositive power, 2022 Equity Incentive Plan, +2 more

6 terms

beneficially owned financial

"Aggregate number and percentage of class beneficially owned: 1,394,534 shares"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

sole voting power financial

"Number of Shares Beneficially Owned ... Sole Voting Power 1,394,534.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

sole dispositive power financial

"Number of Shares Beneficially Owned ... Sole Dispositive Power 1,394,534.00"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

2022 Equity Incentive Plan financial

"shares of Common Stock in accordance with the Issuer's 2022 Equity Incentive Plan, as amended"

vesting provisions financial

"These shares of Common Stock are subject to vesting provisions, as follows"

Vesting provisions are the rules that determine when someone who receives equity—such as stock options, restricted shares, or other ownership-based pay—actually earns the right to keep or sell that equity. Like a savings plan that releases funds over time, these provisions set schedules, cliffs, and conditions (for example, continued employment or performance targets) that affect when shares become transferable. Investors care because vesting affects shareholder dilution timing, management incentives, and when insiders can sell shares.

Schedule 13D regulatory

"If the filing person has previously filed a statement on Schedule 13G"

A Schedule 13D is a legal document that investors file with regulators when they buy a large enough stake in a company to potentially influence its management or decisions. It provides details about the investor’s intention, ownership stake, and plans, helping other investors understand who is gaining control and what their motives might be.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What ownership stake in USEA does Stamatios Tsantanis report in this Schedule 13D/A?

Stamatios Tsantanis reports beneficial ownership of 1,394,534 shares of United Maritime Corp common stock, representing approximately 14.62% of the class, based on 9,538,139 shares outstanding as of April 7, 2026, according to information from the issuer.

How many United Maritime (USEA) shares were outstanding for this 14.62% stake?

The reported 14.62% ownership in United Maritime Corp is calculated using 9,538,139 shares of common stock outstanding as of April 7, 2026. This outstanding share count is based on information that the reporting person received from the issuer.

What new USEA shares did Tsantanis receive under the 2022 Equity Incentive Plan?

On March 9, 2026, Tsantanis was issued 200,000 shares of United Maritime common stock under the company’s 2022 Equity Incentive Plan, as amended. These shares are compensation-related awards granted in his capacity as an executive officer of the issuer.

What is the vesting schedule for Tsantanis’s new USEA share grant?

The 200,000-share grant to Tsantanis vests in tranches: 60,000 shares on September 9, 2026, 60,000 shares on April 9, 2027, and 40,000 shares on September 9, 2027. Each vesting date reflects when a portion of the award becomes fully earned.

Does anyone else share voting or dispositive power over Tsantanis’s USEA shares?

No. The filing states Tsantanis has sole voting power and sole dispositive power over 1,394,534 shares of United Maritime common stock. It reports zero shared voting power and zero shared dispositive power with any other person.

Has Tsantanis had any recent legal issues disclosed in this USEA Schedule 13D/A?

The filing states that during the last five years, Tsantanis has not been convicted in a criminal proceeding and has not been subject to civil judgments or final orders involving federal or state securities laws, other than disclosures already made in prior amendments.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 04/08/2026 - 04:51 PM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 3)

United Maritime Corp

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

Y92335101

(CUSIP Number)

Stamatios Tsantanis
154 Vouliagmenis Avenue,
Glyfada, J3, 166 74
0030 213 01 81 507

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

03/09/2026

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): Y92335101

1

Name of reporting person

Tsantanis Stamatios

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

GREECE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 1,394,534.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 1,394,534.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

1,394,534.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

14.62 %

14

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.0001 per share
(b)	Name of Issuer: United Maritime Corp
(c)	Address of Issuer's Principal Executive Offices: 154 Vouliagmenis Avenue, Glyfada, GREECE , 166 74.
Item 1 Comment: Explanatory Note: This Amendment No. 3 to Schedule 13D (this "Amendment No. 3") amends and supplements the Schedule 13D originally filed with the U.S. Securities and Exchange Commission (the "Commission") on January 6, 2023, as amended and supplemented by Amendment No. 1 to Schedule 13D filed with the Commission on November 26, 2024 and Amendment No. 2 to Schedule 13D filed with the Commission on April 10, 2025 ("Amendment No. 2", and as further amended and supplemented by this Amendment No. 3, the "Schedule 13D") by the Reporting Person (as defined in Item 2), to reflect an increase in the beneficial ownership of the Reporting Person of Common Stock (as defined in Item 1).
Item 2.	Identity and Background
(d)	The Reporting Person has not been convicted in a criminal proceeding during the last five years.
(e)	During the last five years, the Reporting Person has not been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws. Except as set forth in this Amendment No. 3, there are no material changes to this Item 2 from Amendment No. 2.
Item 3.	Source and Amount of Funds or Other Consideration
	The information set forth in Item 6 is incorporated herein by reference. Except as set forth in this Amendment No. 3, there are no material changes to this Item 3 from Amendment No. 2.
Item 5.	Interest in Securities of the Issuer
(a)	Aggregate number and percentage of class beneficially owned: 1,394,534 shares, or approximately 14.62% of the class, based on 9,538,139 shares of Common Stock outstanding as of April 7, 2026, based on information received from the Issuer.
(b)	The Reporting Person has the sole voting and investment power with respect to the Common Stock.
(c)	The information set forth in Item 3 above is hereby incorporated herein by reference. Except as described herein, no transactions in the Common Stock have been effected by the Reporting Person during the past 60 days.
(d)	No other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, any of the shares of Common Stock beneficially owned by the Reporting Person.
(e)	Not applicable.
Item 6.	Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer
	The first paragraph of Item 6 is hereby amended and restated in its entirety to read as follows: As described herein, the Reporting Person in his capacity as an executive officer of the Issuer, has been, and is expected in the future to be, granted shares of Common Stock in accordance with the Issuer's 2022 Equity Incentive Plan, as amended. On March 9, 2026, 200,000 shares of Common Stock were issued pursuant to the Issuer's 2022 Equity Incentive Plan, as amended, to the Reporting Person. These shares of Common Stock are subject to vesting provisions, as follows: 60,000 shares of Common Stock will vest on September 9, 2026, 60,000 shares of Common Stock will vest on April 9, 2027 and 40,000 shares of Common Stock will vest on September 9, 2027. Except as set forth in this Amendment No. 3, there are no material changes to this Item 6 from Amendment No. 2.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Tsantanis Stamatios

Signature:	/s/ Stamatios Tsantanis
Name/Title:	Stamatios Tsantanis
Date:	04/08/2026