Elliptical Submarine Hulls

Discussion in 'Boat Design' started by Asleep Helmsman, Jan 16, 2010.

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Asleep HelmsmanSenior Member

Theoretical starting point:

A symmetrical hull form with elliptical curves from bow to stern. Each section is also an ellipse creating a hull that is narrower in water lines than it is in longitudinal sections.

The ratio of length to maximum vertical beam is in the range of narrow hulls, say 8 to 1.

The length to maximum horizontal beam ratio is going to be approximately 4 to 1.

The bow will be allowed to come to a natural 3D parabola ending in a theoretical horizontal line.

So far all is well.

If the design criteria determine that the curves located exactly at horizontal remain equivalent to the vertical ones, then the bow and the stern would need to be exaggerated in the horizontal plane. Leaving the bow and the stern elongated horizontally.

I have repeated myself in order to clarify the conditions.

As stated earlier the bow will come to a natural termination, no problem there; the bow of a totally immersed hull does well in a continuous curve.

Stern trailing edges need to come to a point. The problem with a horizontal line at the trailing edge has the adverse effect on changing dive angles. As the boat attempts to change the angle of attack, turbulence will be intensified as the flow become imbalanced.

Any suggestions? I can print some simple PDFs of a basic hull diagram if this will help clarify this problem.

Thanks Guys.

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gonzoSenior Member

If your stern comes to a point, where does the propeller shaft come out of? Also, you need to design for control planes, etc.

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Asleep HelmsmanSenior Member

Good morning Gonzo,

That is where it gets a little tricky. I was leaving that part out until we got a little further down the road.

Following the center line aft, the stern will have a longitudinal cylindrical bulge, ending in a cylindrical point that will be the hub of the prop.

Control planes will have to be appendages.

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haruJunior Member

I don't quite get about the horizontal beam bit. IMHO viewing from the front it doesn't matter how it looks, because resistance depends on the overall area.
That is if physics applies the same as air, which should be very likely.
For a surface ship the bow is made narrow in order to cut waves, for a sub this doesn't matter.

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Asleep HelmsmanSenior Member

You are correct; round works on the submarine bows, but sub bows are round for other reasons besides reducing drag.

If you are referring to the trailing edge or stern, a thin trailing edge reduces turbulence.

Have you ever watched a round piling in a current.

I see your point about the cross section not mattering but in a cylindrical hulls shape the flow will be constant around the perimeter. relative to any point along the axis of the hull.

In a hull with elliptical cross sections the flow will either take a longer path around the elongated curves, or as it flows it will encounter an area in the stern where the hull angle becomes great enough to induce additional turbulence and a side flow. Similar to what happens at the end of an airplane wing.

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SamSamSenior Member

Yes, do that.

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mydauphinSenior Member

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haruJunior Member

I read surface viscosity is important for multihulls this would also apply to a sub. An elliptic one would have more surface hence have more viscous resistance.

It seems you meant different flow as a means to suppress wake turbulence.
I don't know but isn't this counter to the thought of equal waves cancelling each other?
Also a difference may result in the lower pressure part to suck the other in and enhance the turbulence?

A simple idea to get rid of the turbulence is to design the stern the same as the bow. Or enhence that by streching it out further. Or spike it out.

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SamSamSenior Member

If the trailing edge isn't active like in an airplane's flaps and rudders or ailerons, and actively controlling dive angles, maybe if they were passive and flexible, like rubber or something, that would conform to the turbulence and smooth the flow or maybe conform to the flow and smooth the turbulence, whichever it might be. Vaguely like a tail on a kite, with no drag. A damper of sorts.

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Asleep HelmsmanSenior Member

Good Morning All,
Sorry for not responding sooner.

I have been busy all weekend (when I wasn’t watching the Cowboys get sent home) creating the shape that I have decided to build.

I think I have minimized the effect of the trailing edge will have on changes to the dive plane.

I’m going to refrain from posting any images for a while, I have been searching the world for images of UUVs and I am reasonably convinced that my design is fairly unique and solves a lot of the problems that others have encountered. (Everyone thinks that, but it’s a healthy thought process.)

I’m using the loft function in AutoCAD to create the shape. I just had a failed design but it brings it one more closer, to one that will work.

I’ll check back soon with the images.

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Asleep HelmsmanSenior Member

Either way it would seem to work. Active or flexible. Thanks for the sugestion.

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gonzoSenior Member

You also have to take into account the difference in pressure between the upper and lower parts of the hull. The water flow will never be even if the hull is a rotated solid shape.

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haruJunior Member

If this is like a american football, then you waste using the frontal 'shadow' to increase volume for use.
http://www.heiszwolf.com/subs/plans/plans.html see George Garrett's

As to stern turbulence the best design researcher found are ...surprise!...wave forms like fish fins. Also having them shaking reduces some more.

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Leo LazauskasSenior Member

Thank you for the link to a very beautiful set of drawings.

Leo.

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Asleep HelmsmanSenior Member

Nice post.

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