Hull speed

Some time back, I initiated a thread on the following question: has anyone else developed a displacement hull form that is not subject to the limitation of hull speed?

I have posed the question in this form because I believe I have solved the problem. I filed a utility patent application and PCT (international) filings a little over a year ago, and nothing remotely similar to my work has popped up (to my knowledge) so I'm ready to disclose my solution to the naval architecture and marine engineering community. I've already done some disclosure on LinkedIn, so its time to disclose to the maritime community.

Here's the short, short version:

For purpose of the discussion, I'm limiting the thread to displacement monohull forms and related developments. I do so because, with relatively few exceptions, multihull forms are not practical working vessels, and those that are typically operate at high speed. My focus is efficiency, not brute force.

I'm limiting the thread to powered monohulls, although it is obvious that the invention is equally applicable to motorsailers.

When a displacement monohull is examined from a system perspective, taken together with the environment in which it operates, and the effect that the operating monohull has on the surrounding environment, the system is dynamically open and energetically dissipative: the creation of the bow wave requires the application of energy which, upon generation, escapes into the open system, and is lost.

I asked myself if the system could be closed (at least asymptotically, in the mathematical sense), and what kind of hull form would emerge if you could do so?

The solution required a complete reinvention of the displacement hull form. It also required the recognition that, from a historical context, the powered version of the displacement hull form needs to be viewed separately from the sailing vessel upon which it is originally based.

Early steamships were simply sailing vessels with mechanical propulsion driven by steam engines patched on in a more or less orderly fashion. This is unsurprising, since the mathematical understanding required to develop a clean sheet design did not even exist until the development of chaos theory and the ability to model nonlinear systems in digital computers.

However, this excuse no longer exists.

So here's the payoff: my hull form completely integrates the propulsion system with control of system flow, with an aim toward asymptotic closure of the system: instead of viewing the system mathematically as a potentially infinite plane surface (as good a model as any), I have redefined the system as restricted to the course of the vessel under weigh, limited beamwise to attached flow.

This view logically dictates the positioning of the propulsion system at midships, port and starboard. Closure is accomplished both physically and dynamically, with physical closure limited to the immediate vicinity of the propulsion elements. Viewed from above, the dynamic model resembles a turbine engine.

More details will follow if anyone is interested.

 

Short answer: yes, many. However, "Hull speed" is not a particularly good
starting point for this sort of discussion. Maybe you should couch your ideas in
more scientific terms so it is amenable to analysis. Otherwise it just sounds like
another crackpot idea from somebody who knows nothing about hydrodynamics.

 

What is the "limitation of hull speed"? Do you mean the relative rapid rise in resistance for many hull forms as the speed approaches a Froude number of 0.3? Many narrow, light displacement hull forms do not a rapid rise in resistance as Froude number approaches 0.3.

Have you built a prototype and systematically tested it? If so what have you compared it to?

Or have you done numerical modelling? If so what type of modeling and what have you compared your concept to?

Or is this currently just a concept which you've thought about?

 

Sadly i fear the later

 

OK, please reveal all.

 

C'mon Robert, the suspense is killing me !

 

reply to Mr. Efficiency

I just finished my post 2 minutes ago.

 

There is nothing for anyone to form an opinion about, until you spell it out, if you fear somemone will steal it, no point in initiating a discussion. All I see so far is gobbledegook.

 

Is the hull rigid or does it have soft sections?
Details, please.

 

Mmmm I do not agree that ALL the energy of a bow wave is lost. My understanding is along the lines of trying to use and recover some of that energy is pertinent to efficiency. Where a designer chooses to displace that bow wave matters, underneath, sideways or wherever. I suspect that any vessel operating in water and air (real world) cannot have 100% efficiency ie no lost energy by the nature of the problem, so the trade off is one dense fluid against a less dense one. Closing the 'system' loop as you suggest would give a figure closer to 100%.

Most decent fully submerged foils recover most of the energy....

I have drawings of mid engined non propellor craft from the 1930s'....and even jetskis are roughly along that line but faster.

If the Patent is filed, we could look it up either in the US or Espace. Perhaps you could give up the number?

 

Robert is intent on hiding his light under a bushel, seemingly. He either has a new idea, or no idea, best way to settle that is for the drums to roll, then........voilà !

 

I posted a long explanation last night, but for some reason it did not upload. This time, I'm keeping a copy as a txt. file just in case.

This is not going to be a short note. Everyone is forewarned.

Respecting the patent, the public disclosure is not scheduled until some time in July: US filing 13/742,278, January 15, 2013, PCT US/742,278. There is presently no way to obtain it from public sources.

Back to the exposition:

My model of the hull speed limitation in displacement monohulls is this: the wavelength of the bow wave couples with the waterline length. When you try to exceed this, the wave decouples, and the hull pitches upward. This is the onset of planing (the "hump"). In typical hulls, the generation of the bow wave consumes a little more than half of the energy of propulsion.

The germ of the invention has its roots in the recognition that, as a system including the medium in which they operate, displacement hulls are dynamically open and dissipative. I asked the question: what results obtain when you try to close the system instead?

An asymptotically closed and regenerative system turns out to be a more compact system than an open one. Generalizing from an open system as occupying the plane out to infinity, the closed system is restricted to the course of the vessel under weigh, and limited in width to the width of the hull plus attached flow.

Next item up for discussion is the issue of the mathematics involved. It is a given that the equations of fluid dynamics describe a nonlinear system. Under certain conditions, turbulence results. The system is therefore mathematically chaotic, and behaves fractally. Anyone not familiar with fractal mathematics will have to either accept the math or learn the subject.

In addition to fractal math and applied chaos theory, there are the mathematics of self organizing nonlinear dynamic systems. Some of this work is my own, and it is proprietary. I will not be sharing it.

Shortening the math discussion, fractal systems have three essential characteristics: they are infinite, recursive and self similar under scaling (the typical reference is to the Mandlebrot set). It is necessary to understand why this is important, as it gives rise to the next issue: when you are designing a nonlinear system that is mathematically fractal, where do you start? (This is a trick question.)

The answer to the question is: the middle. In an infinite system, you're always in the middle, mathematically speaking. While this may seem unimportant, it is critical, in that it focuses the design process: you have to start in the middle and work outwards. You cannot pick the origin of the system coordinates at random.

So where is the middle of a powered displacement hull? I take the position that it is the propulsion system. Understanding this also leads to the need to integrate the propulsion system and the hull form as a single entity. Conventional designs are patchwork. This is due to the historical development of powered watercraft, which were originally sailing vessels with steam engines and mechanical propulsion added on utilizing the technology available at the time. This set in motion a design pathway which, in retrospect, is erroneous, and must be reconsidered.

My thesis leads to the conclusion that the propulsion system needs to be located port and starboard midships, rather than at the stern. At this point, in addition to propulsion, the system can be utilized to obtain asymptotically closed flow. The propulsion elements have the advantage of being located in "clean" flow. They also have the advantage of being closed at the blade tips, and it is relatively simple to eliminate vortices.

Add thrusters at the bow and the stern, and a conventional rudder is unnecessary.

All design details emerge from the repositioning of the propulsion system. For instance, both a bulbous bow below the waterline and a clipper bow above the waterline are natural design elements. Astern, the hull has a form resembling the tail of a fish, less the fins. The design is essentially a double ender. One of the ways to conceptualize the design (allowing for the asymmetry due to nonlinearities) is that the hull aft of the propulsion resembles a time reversed version of the forward half of the hull. Another conceptualization is a water breathing ram jet.

I have also incorporated a solution for dealing with sea states.

The first testing is under way. I have built two models: the experimental scale prototype and a conventional displacement hull of equivalent waterline and displacement.

There are predicted performance advantages associated with my design. It promises to be considerably more energy efficient, more stable in pitch, roll and yaw, more maneuverable, and more responsive to control inputs.

I will post results when I have conducted a statistically sufficient number of tests. After the testing if the scale models is complete, I will be building a full scale prototype.

 

Hulls with a high beam/length ratio do not trim up by the bow as the speed increases. They sink uniformly while maintaining a fairly even trim. Also, they maintain or increase waterline length.

 

Re: hull speed solution

Try this on for size. It's oversimplified, but will do for a first approximation. Assume smooth water for the first approximation.

Start with a venturi (you are familiar with Bernoulli, I hope). If you put one directly through the middle of a displacement hull, there would be no bow wave, and the wake would be next to non-existent. However, the interior volume would be next to useless. There are also other problems not germane to this thread.

So instead of one venturi you start with two venturis, and perform a relatively minor topological transform (yes, more mathematics). The transform consists of remapping the central axis of the venturi into an arc so that the outer wall of the venturi is remapped from either a paraboloid or a hyperboloid of revolution into a surface bounded by the bottom of the hull and the beam of the vessel. The central axis of the venturi is now curved, rather than straight. The result is a pair of venturis which wrap themselves quite nicely around a displacement monohull form.

Next, put the propulsion system in the middle. The optimal configuration is paired, contra-rotating, variable pitch propellors. Choice of power plant is irrelevant.

Next, you cut away ever part of both of the venturis which are not necessary to physically constrain the flow at design cruise speed, forming a more or less conventional bow and stern.

Add lateral thrusters at the bow and stern, and add a system for stabilizing flow into the propellors according to the mission of the vessel in question, and you're done.

Anyone who understands the physics will see that it is going to work.

 

Ahh, you mean like this



I see what you mean now