The Department of Defense, specifically the Navy, is seeking innovative designs for toroidal propellers intended for the MK54 Lightweight Torpedo (LWT) and Unmanned Underwater Vehicles (UUV). The primary objective is to develop a propeller that enhances top speed, fuel efficiency, and reduces noise, thereby improving overall performance compared to existing designs. This initiative is crucial for advancing naval capabilities, as the new propeller design must meet stringent requirements for speed, efficiency, and operational stealth. Interested parties should note that the solicitation is set to open on January 8, 2025, with proposals due by February 5, 2025, and further details can be found at the provided source link.

## Description

A toroidal propeller design consists of a hub supporting multiple elongated elements. The novelty lies in the tips of these elements curving to contact with one another to form a closed structure. This design encloses the huge open space usually seen in conventional propellers, increasing the stiffness of the entire propeller, and providing enhanced strength. The configuration of the propeller also reduces the noise that these mechanical devices usually generate, translating to a reduced acoustic signature. This technology is differentiated by these two innovative aspects: increased stiffness and reduced acoustic signature, unlike conventional propeller designs whose open structure both for aeronautical and marine environments makes them less rigid and noisier. This propeller design offers a unique adaptation that makes the propeller tougher, quieter, and more effective.The Mk54 LWT Design of Record (DOR) utilizes a torque balanced inner/outer shaft design to propel the torpedo with a set of counter rotating propellers. These propellers operate at similar RPM with the forwards propeller operating at an RPM of ~0.5-3% greater than the aft propeller.Any newly designed propeller set will need to meet the current system capabilities in fuel efficiency, top speed, and transmission of noise to environment. Ideally this upgraded design would be able to improve upon all aspects of the system and provide a better all-around propeller for the LWT. The Navy priorities for design, in order are: top speed, fuel efficiency, cavitation mitigation. These three topics will be the primary benchmarks for modeling and will be compared against the current system abilities. The secondary goals will be to look at maneuverability, system quieting, and survivability due to damage.The LWT torpedo is a long cylindrical body that tapers in a streamline fashion in the aft section. This section contains the control fins and the two rotors. The rotors maintain the streamline taper for the hub designs and then uses specifically designed blades for minimizing noise and increasing the thrust capability of the device.As can be seen in Figure 1 (https://navysbir.com/n25_1/N251-043-Figures-1-and-2.pdf), the system normally uses two counter-rotating shafts on an inner/outer installation. The overall streamline dimensions for the shape are detailed in Figures 1 and 2.A closer look at an Initial Capabilities Document (ICD) of the Mk54 torpedo shows the dimensions allowed for creation of a new set of propellers. The internal design is a spline, which is detailed in Figure 4, while the dimensions of the available space for propeller design is detailed in Figure 3.The LWT operates from the surface down to LWT Depth and from RPM’s from 600 to 3000 RPM. This produces a torque balanced system with the two propellers balancing each other’s torque load. The Forwards propeller operates at a maximum of 3% less RPM at 600 RPM and 0.5% less at 3000 RPM. The speed range is between Low and High operation; with RPM Forwards being 300 and 2500, RPM Aft being 315 and 2690 low/high respectively. Associated Speeds and Depths are classified and may be shared after award.Only direct drop in replacement designs will be considered. There is no design envelop for hardware modifications to the LWT. RPM ranges for different operating modes can be modified. The propeller hardware may be designed with any material and any manufacturing process so long as the design can conform to current DOR shock and vibration requirements. The Navy is seeking +10% improvement on top speed and fuel efficiency, meaningful noise reduction, and significant acquisition cost savings. Current DOR LWT propellers are approximately $22K per set.The awardee will demonstrate new propeller design performance in a representative environment. The prototype design should provide no less than 8% improvement to top speed and fuel efficiency, and reduced cavitation compared to the DOR. The awardee will deliver a minimum of five of these prototypes to the Navy for evaluation. The awardee will perform detailed analysis to ensure materials are rugged and appropriate for Navy application. The proposer will provide a manufacturability and cost analysis in support of Navy Business Case Analysis for upgrading to the new propeller design. Environmental, shock, and vibration analysis will also be performed.The awardee will conduct computational fluid dynamics (CFD) analysis of the design, which the Navy will measure against the current DOR propellers. The proof of design analysis will inform as to the anticipated improvements to the priority topics of top speed, fuel efficiency, and cavitation. The awardee will also include a projected manufacturability and cost analysis.Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. owned and operated with no foreign influence as defined by 32 U.S.C. § 2004.20 et seq., National Industrial Security Program Executive Agent and Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence and Security Agency (DCSA) formerly Defense Security Service (DSS). The selected contractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances. This will allow contractor personnel to perform on advanced phases of this project as set forth by DCSA and NAVSEA in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material during the advanced phases of this contract IAW the National Industrial Security Program Operating Manual (NISPOM), which can be found at Title 32, Part 2004.20 of the Code of Federal Regulations.

## Objective

Design toroidal propellers for the MK54 Lightweight Torpedo (LWT) with focus on the metrics of speed, efficiency, and quieting.

## Phase I

Develop a concept to meet the needs for an innovative propeller design. Design a proof-of-concept propeller set for the MK54 LWT using the provided design parameters in the Description. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype solution in Phase II.

## Phase II

Develop and deliver Phase II prototypes for evaluation. The prototype will be evaluated to determine its capability in meeting the performance goals defined in the Phase II Statement of Work (SoW) and the Navy&rsquo;s need for improved top speed, fuel efficiency, and cavitation mitigation. It is probable that portions of the work under this effort will be classified under Phase II (see the Description section for details).

## Phase III: Dual Use Applications

Apply the knowledge gained in Phase II to refine and finalize the propeller design and characterize performance as defined by Navy requirements. Working with the Navy and applicable industry partners, demonstrate the final propeller design with a series of in-water runs equipped on a MK54 LWT. Support the Navy for test and validation to certify and qualify the system for Navy use. Explore the potential to transfer the propeller design to other military and commercial systems (e.g., other torpedoes, UUVs). Market research and analysis shall identify the most promising technology areas and develop manufacturing plans to facilitate a smooth transition to the Navy.

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Development of Toroidal Propellers for Torpedo and Unmanned Underwater Vehicles (UUV) Applications

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