Pressure Recovery in Overflow Piping due to Siphonic Effects


By: Anthony DeFilippo, P.E.

The purpose of this study is to determine if siphonic effects are able to induce a pressure recovery in ship tank overflow piping in favorable flow conditions. The study will go over key features and flow parameters that will likely produce the siphonic effects and the potential that this knowledge imparts for the design of tank overflow arrangements.

Overflow piping is necessary when filling tanks on a large scale since allowing a closed tank to fill past its capacity will likely exceed its design strength resulting in failure. Investigating if a pressure recovery credit can be taken to minimize or negate the effects of frictional losses can have a positive effect to optimize tank and piping design. An optimized design can reduce cost and weight.

The methods implemented in this study include the use of a Pressure Drop Worksheet which uses the Darcy-Weisbach equation for friction loss through a pipe, a computational fluid dynamics simulation program (Star-CCM+), and a fluid flow analysis and design modeling software (Pipe-Flo Professional). Using these three tools, the effects of siphons on pressure drop can be compared across different flowrates. A baseline will be established in order to ensure that each tool will provide a similar result in a simplified scenario. Star-CCM+ and Pipe-Flo Professional will be tested to ensure that a siphon can actually be modeled within the program. A pressure drop vs. flowrate comparison between the three tools will be established. Future work can be performed to determine how upstream and downstream conditions will affect the magnitude of the siphon.


Figure 16: CFD Volume Fraction at 200 GPM


To learn more about Pressure Recovery in Overflow Piping Due to Siphonic Effects please reach out to Anthony DeFilippo at

Reproduced with permission from the American Society of Naval Engineers.

CFD simulations for Scout Boats

Since the founding of DLBA, we have always said that the design of high-speed boats requires the combination of rigorous science and a little bit of art. While a great designer relies on experience to understand the impact of the artistic decisions on a design, CFD allows the impacts of those artistic decisions to be quantified to ensure that the best possible vessel is delivered to our clients.

DLBA is doing just that with CFD simulations on a new double stepped planing hull for Scout Boats. From hump to maximum speed, stepped planing hulls exhibit complex hydrodynamic relationships that traditional tools for unstepped hulls fail to capture. When traditional tools fall short, we utilize CFD to provide performance predictions across the operating regime. However, it goes much further than that. With CFD, we can see in detail what is happening as the hull interacts with the water around it allowing a better understanding of why a hull is performing the way it does and informing the best possible design choices for the craft.

With the enhanced visualization provided by CFD, DLBA has been able to recommend tangible design modifications to improve performance. In the hands of an experienced Naval Architect, CFD allows invaluable insights into high-speed craft hydrodynamics, leading to reliable, concrete, and actionable design recommendations supported by data. This analysis allows the mitigation of previously unforeseen problems at the design stage rather than after construction and testing of the first vessel.


Sea Force CC 410 under development

Charging into the new year, the DLBA and Sea Force teams are continuing to develop the new SeaForce 410 – the first in a new line which is changing the paradigm for what is possible with outboard powered boats. This program is truly a collaborative effort which continues to be both challenging and rewarding.

With the hull, structural grid, and interior liner tooling models already being released for manufacturing, DLBA’s effort has focused on the deck and console tooling. This is a time-consuming task, as many of you know, as it needs to be practical and user friendly while meeting all the client’s goals…and at the same time, it has to look fantastic. The deck part (which is actually the main deck and liner, and the cap deck) includes many details including hatches, drain details, windscreen landing, rod holders, and the list goes on and on…

An additional challenge of this project is the extremely aggressive schedule the client must meet with the goal of having the first boat at the 2021 Fort Lauderdale Boat Show. This boat will have a fit and finish normally reserved for larger yachts, and some new features not seen elsewhere in the market.

She’s really coming together and promises to be a head turner both at the dock and when she’s leaving folks in her wake running at a cool 65 mph with quad Mercury 450’s on the transom.

Developing the Maritime Industry

The maritime industry’s evolving technological trends provide ample opportunity to grow and invest strategically. At Gibbs & Cox, we invest in our people. We encourage all of our staff to be active participants and role models in the STEM community and share their insights with the next generation of maritime industry leaders. Our dedicated team enables G&C to continue innovating after more than nine decades, as we lead the maritime advancements of tomorrow.

As the largest independent naval architecture and marine engineering firm in the United States, we are proud to have the opportunity to present technical concepts, host round tables, publish articles, and work complex programs that give our employees the ability to work on a wide range of projects and travel the world. From naval architecture and marine engineering to program management and software development, we support our employees in exploring their interests and pursuing what drives them, including personal certifications such as PEs and PMPs.

The future of the maritime industry depends on the development and growth of those who have not yet begun their career, which is why we focus on and work with those who are still in the process of completing their education. As the sponsor of this year’s STEM event at ASNE’s Technology, Systems and Ships Symposium, on January 26, we look forward to connecting with all of you virtually.

Velocity 38m: Keeping It Simple Has Never Been So Fancy…

New on the drawings boards at DLBA for 2021 is the 38M semi-displacement yacht, VELOCITY. This 125-foot raised pilot house yacht is coined VELOCITY, not for her speed, but for her ease of use. This concept has evolved out of the old axiom “Keep It Simple Stupid (K.I.S.S.)” and is an attempt at lowering the barriers to entry into yacht ownership. Yachts are being packed with more features than ever before, and almost everything on the boats have wires connected to them. The end result of this evolution is a vessel that is more complex to operate and maintain than the vessels of year’s past. The concept here is to provide a contemporary yacht which provides some of the modern amenities found aboard superyachts, without being overly complicated. Additionally, by making some conscious decisions on certain items with respect to fit and finish, an attempt is made to keep build price under control as well. The net result is a feature-packed, reliable vessel that is perfect for owners stepping up in size, or jumping in head first into this size bracket.

VELOCITY is capable of a modest 20 knot cruise speed thanks to twin diesel engines driving fixed pitch propellers. The propeller tunnels are located in pockets to keep operational draft to a minimum. The electrical plant has twin generators which have the ability to switch over or parallel automatically, depending on the plant needs, to keep the lights onboard burning bright. Due to the smaller size of the vessel, all exterior components will be manually operable by the yacht’s crew – all doors and openings, the boarding ladder, swim ladder, etc. The machinery space is a little larger than normal on this vessel to allow more room in the machinery spaces for auxiliary equipment to provide better layouts and access for maintenance. The arrangement of the equipment, piping, and electrical systems was developed to allow intuitive arrangements of piping and components, with redundant components in many locations. This allows the crew to easily understand operation and perform maintenance of the fully independent systems onboard.

On the interior, automation and electrification is also kept to a minimum. Systems that have been historically unreliable or troublesome have been eliminated – such as raising TV platforms, electric blinds, and electrically opening windows. Instead these components are integrated in a way in which they keep with the styling of modern yachts, however the owner and guests can operate them by themselves one hundred percent of the time. She will be fitted with the latest lighting and entertainment systems, selected to follow the most popular land-based systems, for enhanced reliability and familiarity to guest operators. These are intended to be the most advanced/complex systems on the vessel, where all others are laid out akin to a commercial workboat, for increased reliability, maintainability, availability, and reduced cost. Keeping it simple has never been so fancy….

Introduction to Set-Based Design

Traditional design method, utilizing the classic design spiral, brainstorms a manageably sized set of competing concepts very early in the design process. In yacht design, this is often accomplished at the system level. The high level concepts are then analyzed and evaluated. These evaluations generate more detailed knowledge about each concept, and gradually the concepts are refined and re-evaluated until a final “best” design emerges. While this process works, it doesn’t always work well. By its very nature, this process is iterative in its approach, and inherently involves redesign throughout the process (excessive redesign = cost overruns + schedule slip). Additionally, because design decisions are being made early in the process while technical details are still evolving, late-stage integration problems tend to arise, where, for example, at the eleventh hour a piece of equipment in one system is found to be incompatible with a connected system.

DLBA has found Set-Based Design (SBD) can be a desirable alternative to traditional design for complex engineering design projects, such as yacht design. Based on advanced mathematical techniques, SBD is able to generate and evaluate a significantly larger number of concepts, and intentionally delays design decisions until adequate technical information is known. The end result is a small set of viable concepts, all of which meet regulations and customer-specific requirements that can then be further filtered to a desired parameter (e.g. fuel economy, seakeeping ability, etc.) or a set of parameters. Detailed design can then proceed with high assurance of integration success and minimal design rework, supporting our goal of on-time and on-budget deliveries.

Should every yacht be designed using SBD? Probably not. But is there a place for SBD in yacht design? Absolutely! SBD is well suited for large, complex designs, where there are numerous interconnected systems with possibly competing objectives. Its power is seen best in projects where the “design canvas” is blank. DLBA has the experience to determine whether a traditional design approach or Set-Based Design is right for your project, or whether a tailored hybrid design approach (e.g. traditional design with targeted elements of SBD) might be more advantageous.

The U.S. Navy Ship-to-Shore Connector program utilized Set-Based Design to generate and evaluate concepts for the next generation of the Landing Craft, Air Cushion (LCAC).

Image courtesy of Textron Systems.

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