Bow wave cancelation

Discussion in 'Boat Design' started by Boston, May 17, 2009.

  1. Boston

    Boston Previous Member

  2. Ad Hoc
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    Ad Hoc Naval Architect

    It is just a "variation on a theme", nothing revolutionary.
    Trouble is, all these 'lifting surfaces' require forward velocity to obtain some benefit of sorts.
    Would love to see those foils after a few thousands hours of service!!!!
     
  3. Ilan Voyager
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    Ilan Voyager Senior Member

    Very interesting paper with nothing very new. Plenty of money, truly too much money for a civilian work, so probably military sugaring funds, with results judged not interesting enough for the Navy, if it was funding it, to keep them secret (the ratio HP/displacement/speed of the 70 feet has nothing remarkable).
    Probably with all these (expensive) controls the boat must be very sea kind so would interest rich ferries companies. Not applicable to displacement hulls.

    As the word lifting implies, there is a need of speed to get lift...so it becomes not very interesting on a displacement hull with speeds to low to get a useful lift: the ratio drag/lift is simply too bad.

    In a displacement boat with rather low speeds; a weight reduction, slimier hull and repartition of volumes, low hull drag with an "aerodynamic" work and an optimization of displacement/length/habitability ratio will pay more.

    Amusing note; the lifting forward body is the twin brother of the lifting bodies studies by the NASA in the fifties. I'm sure that none of the engineers would imagine in 1950 some, that the design will be used on a boat.
     
  4. Ilan Voyager
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    Ilan Voyager Senior Member

    Foils are like propellers, if there is not cavitation they will a have good life span. The problem is to never have cavitation...so staying in safe side (under about 35-40 knots) so going to the air injected foils...oh la la Boeing had headaches with that.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    I.V.

    I'm more interested in the construction quality of the foils. I know what happened on the first SLICE that was built, despite endless millions thrown at it. Concepts are only worth investing in, if the 'thing' can be built and built with quality fabricators; which comes down to good detail design coupled with proper QA on the shopfloor.
     
  6. Boston

    Boston Previous Member

    Ilan are you referring to the boundary layer effect that Boeing tried to counteract with an air pressure ( exhaust ) relief system

    idea being that the boundary layer could be interrupted and so friction reduced with an alteration of the pressure of the near surface interface
    IE the exaust of the engines run over the wing surface

    I also read about a system that releases exhaust from a boats engines into an step under the hull of a high speed hydroplane
    reduced the density of the water at the surface boundary of the hull and so reduces friction for a faster ride
    I think it was Bently who did it for the Royal Navy

    Ad
    what happened to the first slice
    am curious
    I take it it didnt work out to well ?
    B
     
  7. daiquiri
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    daiquiri Engineering and Design

    I was really wondering how could that submerged lifting body possibly work at 30+ kts - with all the lift generated it will "scream" to jump out of the water...

    Then I found the paragraph about "Ride control system", which reads this:
    - custom designed microcontroller-based electronics
    - bow height is measured with a microwave-radar
    - this height is controlled by the two large winglets on the outside of the bow lifting body
    - they are moved in unison by a pair of large hydraulic rams that are fed by a hydraulic servo-valve
    - pitch and roll are measured with a motion reference unit mounted in the aft portion of the boat, and are controlled via the pair of T-foils mounted on the transom
    - the T-foil incidence angles are adjusted by hydraulic rams driven by servo-valves which are controlled by the second of the two custom single-board controllers
    - hydraulic power for the control system is provided by a pair of piston pumps driven by mechanical power take-offs on the main engines
    - rudder position is electronically fed back through the ride control system for operator display
    - information about ship attitude, speed, and control surface deflections are available to the operator through a pair of LCD screens.

    So it is not just that little spaceship in front of the bow that makes the system... Every single line of text above is 10^x dollars (or euros) added to ship's construction and service cost and is a potential candidate for a failure which would disable the functionality of the whole system.
    I'm for simplicity, and share Ilan's opinion that the similar advantages can be obtained through a careful hull optimization.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Boston

    The first SLICE had to turn back on her delivery voyage after a few miles out from Hawaii, leaking! Got sorted in the end, but at great expense. Simply becasue too much effort went into those very expensive and fancy looking systems, as noted above by daiquiri, and little into the actual detail design and manufacturing.
     
  9. Ilan Voyager
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    Ilan Voyager Senior Member

    It's 6:47 AM and I'm drinking my coffee. I'll try to answer without having to write War and Peace...

    - As Ad Hoc said Slice was plagued with structural problems. It's very bad in boat design to have bits and pieces everywhere. Big Surface, heavy weight and lack of rigidity (inertia varies at the third power of the section...) nothing good structurally.

    Add the use of aluminum, a metal with big problems of fatigue, plus a structure like the four legged Slice with the four small torpedoes trying to have their independent life because of the waves, and you'll get vibrations and maybe resonances on a structure surely calculated with very little margin. The twisting torques are enormous.

    In my opinion the most astonishing would be that a such structure lasts more than a few hours...I think that the boat is now scrapped, but I have no information.

    Yes Daiquiri, you put the finger on the thing. It's not just only the lifting body, it's a very complicated device. Fancy electronics are good on planes not submitted to corrosion, and always troublesome on boats. I have remarked the price and big cost maintenance (plus redundancy systems) needed on war ships. This project smells the techno-military funding. Getting mid thirty knots and 23.5 knots cruising with 1400 HP on a 70 feet 28 metric tons boat is not a very good result...that explains why we find the paper in Internet.

    I remember an article in the french press about a trial of all computer controlled US warship in the nineties which ended with all the system failed (Windows NT...thus the joke; "happily Microsoft did not exist in 1942, we would lost the war") and the boat was totally crippled. Fighters have computers but THREE computers comparing each other, and sometimes that gives trouble.

    - Foils. Too much hope has been placed on very fast foiled boats, a lot of wild claims. Always the same problem with the waves and the orbital movement of the water that makes deep foils difficult to use. Add the problems of ventilation and cavitation and you have a nightmare. Plus structural problems. Plus powering problems (engines in the flying hull, propellers away in the water) Boeing made a high speed patrol foiler (70 knots) that exploded all the funding budgets to get the boat working. Finally it worked with a maintenance schedule similar to a Formula One, and the complexity of a rocket. All the boats have been scrapped. I would remark that a catamaran ferry (the Juan Patricio) goes every day at about 60 knots on the Mar de Plata between Buenos Aires and Montevideo without any of these complexities except a small "deployable" foil near the bow used when it becomes too choppy in a pampero wind...
    Cavitation occurs always on foils beyond about 40 knots. You can design profiles that delay the problem but the Cz (lift coefficient) is low, you can add flaps and other devices. A lot of mechanics, so the Murphy's principle applies totally. You can ventilate them injecting air (the lift goes down but at least the foils won't be destroyed by the cavitation. Not known material can resist to cavitation which erodes a propeller or a foil in a few hours) that's was used by Boeing.
    I do not know if they used the exhaust gases (that are very dirty, it doesn't seem good for a foil) or clean air. And to end foils are fragile. A good log, a lost container and you imagine what happens.

    The Russian have a very pragmatic approach to foils (in the similar way that they solved the problem of hand writing in the space: they used lead pencils. The NASA after a painful and costly research invented a nitrogen pressurized ball point pen able to write in any position...) and kept them under 45 knots with no computers. So a lot of ferry foilers designed in the sixties and later are running on the russian rivers. The foils are used also only on rather small boats, and made in stainless steel for the old ones and titanium for the new ones. MIG has a small activity of foils fabrication, using the same tooling as used for the plane undercarriages. Always pragmatic...

    You can have remarkable small foilers; a little group of russian engineers I met when the sovietic empire was crumbling down, tried to survive by designing a 11m monohull foiler, very simple and straight in aluminum with foils in titanium. The boat was autostable and did not need any device to control the lift. Very soft ride and absolutely remarkable performances; with 250 HP (an out of box diesel Volvo Penta with sterndrive) the foiler (weighting around 3.5 metric tons) was able of 42 knots in flat water and 38 knots in 1 meter waves. Surely all of you will apreciate...it's far better efficiency than any planing boat, or even the so called lifting body.
    The ambient conservatism plus the protectionism of some, killed the project. I have been told (true? false?) that the russian authorities did not like to see this piece of clever engineering in occidental hands. It's true that the Russian export only the most obsolete foilers, never the advanced ones.
    I did like this project because it was made with very little means but with a lot of brain juice. All was in the profiles (I never saw so strange ones), the twist and the controlled ventilation. Brief the result of years of improvement and practical know how. Nothing you will find in calculations.
    At my knowledge two boats were built during the post sovietic chaos. I have lost sight of this group very sympathetic but impossible to follow when they started the piroshki, blinis and vodka. You need weekly training since adolescence to survive such hard drinking.

    - I wrote a post some years ago about air lubricated boat. I have been told by the russians engineers I met that big bubbles have not use; small ones are needed, rolling like ball bearings injected in the laminar layer. I see a big problem of superficial tension of the bubbles to solve. The Russian again have a neat advantage in this technology. It's a fact that they have big patrol boats going at 55 knots using only the power to get 45 knots. All those who have tried to give 5 knots more to a fast big boat without adding huge amounts of power will appreciate.

    I have been told that the hulls are very peculiar and system of air injection very sophisticated. I think that we won't see any data or drawing of the genuine working system. As the Russian Navy seems to master the system or are making us believe that they master it, I do not see the Russian giving the technology away, specially in times when the russian are reaffirming their geopolitical power. The Russian are reconstituting and modernizing their navy at forced pace, the launching of several new atomic submarines is the proof and other surface ships will follow. It is the logical answer to the foreign politics of the former US government.

    So that we see in Internet are crude representations accompanied of wild claims like using 5% of the power for compressing air you'll get 50% more speed... It looks like it is the simplified system of the genuine system: a big air pocket in a hollow hull. For me it's creating a new free surface with all the problems attached to other wave systems, plus perturbations of the flow under the boat and tutti quanti.
    As it's out of my domain of knowledge I'll stay in simple guessings. Always very difficult to see where is the truth hidden by all the toxic information. The Russian are masters of the desinformation. It's seems also that the other navies have tried the technology without extraordinary results, but what exactly they have tried?

    You have to read the offered information with caution. An example; go the French Navy internet site, read the characteristics given about the air carrier Charles de Gaulle. Compare the length, speed, displacement and the power announced, take a small calculator, torture some ciphers and tell me what you think.

    I've written a post longer than the Karamazov brothers. Duty is calling me. Have a nice day.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    I.V.
    It was a matter of hours, for the first SLICE.!..it is not scrapped just awaiting "something to do".

    The second SLICE is considerably different and better designed. I can send you a paper on it if you like.
     
  11. Ilan Voyager
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    Ilan Voyager Senior Member

    Thanks for the kind offer. I appreciate it highly. Use the email I have with my profile, if some problem send me a private messsage.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    I.V.

    Hope you enjoy the read :)
     
  13. Ol-Paint
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    Ol-Paint Junior Member

    While there is no doubt that there is a great deal of innovation in Russia & the countries of the former Soviet Union and their design solutions may differ from western practice, the space pen story is incorrect. The pressurized ballpoint pens were developed by a private venture and eventually used by both Russian and US space programs.

    http://www.snopes.com/business/genius/spacepen.asp As the article points out, there are actually good reasons why pencils are less than ideal for use aboard spacecraft.

    As for the lifting bodies, they have their advantages, but they suffer many of the disadvantages shared by other unusual appendages. Skimming the paper (i.e. looking at the pictures and reading the summary) in the original post, my first big question would be the structural weight penalty due to the slamming loads as compared to a conventional bulbous bow, given the lifting body shapes shown in the analysis. Then, there's the draft penalty as well as the maneuvering characteristics of a hull with that much projected area concentrated so far forward (in the case of the BLB-160). Not what I'd consider insurmountable issues, but it would be interesting to see the total life-cycle costs & operator opinions as compared to other designs, conventional or not.

    Douglas
     
    Last edited: May 18, 2009
  14. Ilan Voyager
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    Ilan Voyager Senior Member

    Oh yes!!!! :D
     

  15. Ilan Voyager
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    Ilan Voyager Senior Member

    Many thanks for the precision about pencils. Good to learn something so I'll have to forget that was finally a "urban legend" among some engineers, and common people also. I'll read the link.

    I agree with you with the analysis. I do not say no but I'm not fully convinced at first sight by lifting bodies.

    Maybe because I'm used to the "normal" shapes and I'm not familiar with the new ones, so an intellectual effort is needed to understand fully the theory and purpose of these extensions.

    That means that maybe I'm becoming obsolete...;)

    That does not forbid to make constructive critics.
     
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