Submersible, convertible, hydrofoil cat

Discussion in 'Boat Design' started by Infinitus, Oct 8, 2011.

  1. Infinitus
    Joined: Jul 2008
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    Infinitus Junior Member

    I’m intending to build a fast, long-range hydrofoil-catamaran. It will be a powered vessel and also have a collapsible mast for emergency sails. Primarily it will operate as a hydrofoil craft with folding hydrofoils, but will also be capable of normal catamaran operation.

    It will consist if three primary sections: a central section, which will contain living quarters, controls, engine, and so on; and two outer hulls, which will function as fuel tanks and ballast tanks for submersion. It will be possible to bring these three sections together to form a monhull in order to reduce the envelope of the craft as well as improving robustness in icy waters. It will also be possible to configure the craft as a trimaran.

    While submerged, either or both of the outer hulls can be ejected in case of failure of the ballast discharge system.

    I would like the boat to have a range of 13000 statute miles, and a cruise speed of around 40 knots (in hydrofoil mode). The boat will be constructed of aluminium with a double thickness hull. It will be designed to accommodate a crew of one.

    The principle reasons for its submersible capability are: protection from storms – a stronger more buoyant design which is inherently harder to sink. It will also be able to submerge below the worst of the weather for comfort during rough seas; pirate evasion – if approached by adversarial craft, the boat will be able to submerge to avoid trouble.

    I am a final-year mechanical engineering student (BEng (hons)) with no specific study in navel architecture or immediately related fields. This boat is intended for my personal use, not as part of my studies. I am posting this thread mainly to invite opinions on this project – although I have a feeling as to how many of them will be like – and also to request help with book recommendations and other sources of relevant information. I don’t intend to continue studying or working in the field of boat design; this boat will be a one-off. I would be very grateful for guidance towards specific texts which would get straight to the points I wish to reach concerning catamaran design, fast boat design, hydrofoil design, submarine design, sail design, and so on. I need to learn the fundamentals of design in all the relevant areas, and in an efficient way.

    Thanks in advance for any help.
     
  2. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    A couple of quick points

    The Russians have done a lot of work on ocean going, or at any rate large, hydrofoil boats. Maybe Alik can help more

    Then 13000 mile range sounds excessive. I doubt if many ships can make 4 Atlantic crossings without refuelling, why should they? 13000 miles will probably relate to 5000 gals fuel, being optimistic, or over 15ton of fuel. You'll need a big boat to carry that load.

    Remember that when not hydrofoiling it will be a very inefficient hull.

    You are in the UK. The Red Funnel ferry line to the Isle of Wight used hydrofoils for years. But had lots of problems with cavitation. They changed to fast cats.

    I suggest going for a regular catamaran or possibly an Ilan Voyager trimaran concept

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Ah, the exuberance of youth ! The budget for this one would likely impoverish an oil tycoon. Still, it is an interesting concept.
     
  4. Infinitus
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    Infinitus Junior Member


    I confess that, at this very early stage of the project, I am yet to calculate/estimate the various drags, and thus determine an accurate fuel consumption value. The 13000 miles range is simply based on an approximate longest distance form the UK to Australia. If I have to I could lower it.

    However, a quick not-even-back-of-envelope guestimation for fuel consumption was based on a rough idea of power needed and the efficiency of a good car diesel engine. (I intend to use such an engine as the budget would likely not permit a dedicated marine diesel. As car/truck engines are generally cheaper, I would have a spare engine onboard, or at least a full set of spare components.) My fuel estimation for that range came to around 2.5 tons, but as I wrote I am yet to make proper calculations.

    The idea for the catamaran is mainly based on stability while stationary and trying to sleep! I originally thought of including extendable struts on the outer hulls so that they could be partially filled with sea water and submerged so as to provide for SWATH configuration. If it doesn’t overly complicate the project (weight is very important) I may well still include them.

    Thanks for your post.
     
  5. Infinitus
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    Infinitus Junior Member


    I was wondering if you would notice this thread!
     
  6. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Infinitus,

    Nice to see a person sets themself a "challange".
    There are too many nay sayers on a forum, including me.
    There are also serious points raised even if the person seems negative.
    Hopefully you will just use the negatives as a check list to defeat (somehow) and will pay serious attention to people like Richard Woods.

    Good luck and have some amunition to fire back next time you post. People will see you are serious, not just dreaming.

    Good luck again.

    Marc

    PS Have you learned to weld aluminum yet? That would be a good start unless you have a lot of money.
    PPS Do you think you could outrun hijackers at 40kts instead of becoming a submersible. I was on a sub for a short time, you really cannot imagine the complexity, cost, and weight you are looking at. BTW, my sub was seriously affected by a Typhoon in the Pacific while we were 300Ft deep. Dont think just being 20 feet down will protect you from any storm you are afraid of.
     
  7. Dave Gudeman
    Joined: Nov 2009
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    Dave Gudeman Senior Member

    Can you explain how making it submersible makes it more buoyant? I would think that to make it submersible you have to make it less buoyant.
     
  8. Infinitus
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    Infinitus Junior Member


    I’m very happy to receive negative feedback, for the very reasons you stated. I’m aiming high with this project and, after running the calculations, am willing to reduce/alter the design where shown to be absolutely necessary.

    I’m really hoping to be gently nudged in the right direction, especially towards information which gets straight to the point and tells me that which I need to know without being overly abstract/convoluted/theoretical.

    I will learn to weld aluminium when it comes time to manufacture. I’m often told it’s very difficult, but I’m prepared for the challenge.

    I know that subs are still affected by rough seas even while submerged. But it depends on the depth and the severity of the weather. I’m sure where typhoons are concerned I would most likely have advanced warning sufficient to be able to be far from the danger zone – if I am unable to get away, at least the boat will be built strong enough to safely endure. I am also confident that the vessel I am planning will be capable of diving to a depth such as to leave it comfortably clear of the major effects of the bad weather I am most likely to encounter.

    As to the complexity of a typical sub: I’m not exactly intending to go into competition with BAE Systems! All I am after is a boat that can fill itself with water, sink, have some manoeuvrability while submerged (not enough to permit any real distance to be crossed), and be able to surface again, and be strong enough to endure the process. As for breathing, I’ll be happy enough wearing a sealed suit with pressurised oxygen supply.

    Another advantage of a submersible capacity is the ability to dive if capsized, in order to right itself before resurfacing.

    I want 40 kts to be the maximum cruise speed (it felt like a not too unrealistic limit). If it is, the engine would be running at around 75 % of maximum revs (I believe 75 % to be a rule of thumb value for maximum continuous running speed while allowing for good longevity), which would leave plenty of capacity to allow for a much greater speed during exigent times. Surface running would be the first option, I imagine, as I should first spot any pirates heading towards me at speed from quite some distance using radar. However, if that fails there would always be the submerge option. I could even release smoke and pretend to sink. It should take me out of the line of fire and give me good opportunity to hide, especially as the vessel will be decorated in a camouflage paintjob.
     
  9. Infinitus
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    Infinitus Junior Member


    Unlike a typical boat show vessel, my boat will be strong and fully enclosed; it will be designed to withstand bombardment from huge waves without fear of sinking, unlike the weak over-priced consumer products most boats are designed to be nothing more than. Most (small) boats are weak and flimsy; their crews need to call out rescue helicopters as soon as the wind picks up! My boat is not intended to be a commercial product to be sold to complacent people with no intention of even leaving the confines of a safe harbour – where they spend a few weeks of the year consuming highly-priced alcohol in the sun and talking nonsense with their like-minded peers.

    My boat will have three main components, each with multiple airtight compartments, strongly constructed in aluminium and will incorporate much redundancy. Its design will be inherently strong and much more resistant. Its buoyancy will be controllable but, when in surface mode, will be much greater than that of a standard patio-doored craft. I’m building a boat for self-reliance, which is what commercial boat makers should be doing, if they were not too busy pandering to dumbed-down market forces.
     
  10. upchurchmr
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    upchurchmr Senior Member

    How do you intend to run your motor while submerged? There probably will not be a pressurized suit for the engine.
     
  11. rasorinc
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    rasorinc Senior Member

    How many mates will you have and who is going to train them in all the systems you will have? The systems have to be redundent.
     
  12. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Dave, I think he means "unable to take on green water"

    How about pressurizing the hulls to 2 atmospheres at about that depth(64' down)?

    Have a snorkel keep pumping surface air and have a man-hatch on the underside of the hulls to let excess air escape, so the hulls wouldn't need to be strong.

    Sure, it might get dicey if you need to surface and you get the bends, but it would be a way to ride out even the worst storms in a lightweight hull.

    Sort of like how airliners fly for 100,000 of miles without any problems...nothing but clear air up there.

    I've always wondered why a military submarine wouldn't have that feature, even if it put the crew through some discomfort. Could add a few extra hundred feet of diving depth.
     
  13. CatBuilder

    CatBuilder Previous Member

    Other points aside, this one part of the idea is a no no.

    If other boats can't see you, they surely cant avoid you. Boats should never be camouflaged in any way.

    As for pirates while on the high seas (while not near land), you will only find those in a very few specific areas of the world, which you can easily avoid. You are getting too nervous about them. Criminals coming to your boat at anchor is far more likely.
     
  14. Tritonsubs
    Joined: Jun 2011
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    Tritonsubs Submarine design & build

    I would drop the submersible concept. A sub has to weigh as much as the water it displaces to be neutrally buoyant. Your craft would be too heavy to plane on reasonable size foils and you'll be able to outrun almost anything at 40 knots, anyway. You are much better off to carry a small sub you can launch and recover.

    BTW, I am the CEO of a series of companies that produce more civil submarines and submersibles than anyone in the world. I've been doing this for more than 25 years. I'm not saying some variation can't be done, but the cost, complexity and compromise would not be worthwhile.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    This thread surely is a wind-up. The er, specifications, are straight out of Boy's Adventure Annual.
     
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