Please knock down stupid idea

Discussion in 'Boat Design' started by VT-tuna, Jul 4, 2006.

  1. VT-tuna
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    VT-tuna Junior Member

    Hi all,
    Been reading over this site for a short while now. I am an offshore fishing fanatic in the midatlantic (east coast of US). Long and rough rides to the fishing grounds are the norm.

    I have this silly idea that a boat (sportfishing) could be built for fast and comfortable ride out (yeah right). I have it in my mind that a light weight hull(thinking aluminum) could be built such that it actually rides on muliple jet-ski like sub hulls that perhaps are connected through a dampening device (i.e shocks). When on plane, primary hull would basically be out of the water and the sub (jet ski) hulls would be planing or even pushed through a wave. I picture this as each sub hull possessing a jet drive exhaust. I also see these as getting their water flow from one large diesel engine and pump that supplies the flow to each sub hull jet from a cental location in the main hull.

    Lift is acheived via planing subhulls, jet angle (fore and aft locations) and part of primary hull at aft for water intake.


    As an electrical engineer with controls and machinery background (and of course boat owner all my life), it just seems possible to build a light weight, basically fitted sportfishing boat with such a setup. 40 foot range with single 800 hp diesel with speeds of ..... well I want embarrass my self too much just yet.


    Please point out the basic boat design physics that insist this vessel will simply sink or at best push water to 5 knots.
     
  2. stonebreaker
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    stonebreaker Senior Member

  3. bntii
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    bntii Senior Member

  4. Ike
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    Ike Senior Member

    What you are describing sounds a lot like a SWATH. Small Waterplane Area Twin Hull. I know there have been quite a few ships built using this concept but I don't know if any small (under 100 feet) ones have been built. see http://www.solarnavigator.net/s_w_a_t_h.htm
     
  5. VT-tuna
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    VT-tuna Junior Member

    Swath technology is kind of what got me to thinking. My understanding of swath was that it basically was a set of submarine modules mounted to a cat hull with modules staying underwater. What I have read is remarkable for large boats with no info on smaller vessels.

    Hydrofoil example above is interesting and actually saw that on the tube. Guy set it up wit pc control system (the real trick). But not very exciting as far as results with weight and speed with an outdrive in the water.
     
  6. VT-tuna
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    VT-tuna Junior Member

    Okay,
    After reading a bit more and looking at the two hydrofoil links above, I feel foolish. Not an unusual feeling for me!


    SO, why don't we see more hydrofoil boats. I have never seen one in person and based on the Talaria data (especially the low cost), seems like they would be more visible.

    So here's some more questions (as I really like the hydrofoil idea now). Out drives simply disgust me in a saltwater enviroment. With speeds of more than 35kts, wouldn't the jet drive be the hot lick for this type of setup. I'm sure one of the biggest issues is pump intake but seems like that is very possible to deal with.

    Any good links to provide some more specific data on hydrofoils. This will be a lot of fun to learn about. Thanks for the links already posted.
     
  7. stonebreaker
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    stonebreaker Senior Member

  8. Ike
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    Ike Senior Member

    Many of the larger hydrofoils do have jet drives. Boeing had a jet hydrofoil they called Little Squirt that they used to do a lot of research that was used when they built the navy hydrofoils. The problem is the technology is bit complex. But is more efficient than a prop. Hydrofoils are usually fast enough that prop cavitation becomes a real problem. But it is easier to use a long shaft outdrive than have a jet pump pickup in your foils.
     
  9. mark424x
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    mark424x Junior Member

    I'm not sure if you've run across the hysucat or other variations of the hydofoil supported cat. It's a passive system, so it's much simpler. They use a wing betweenthe cat hulls, and trim tabs in the back. You don't get completely free from bouncing in the waves, but there are boats out there with it already. It's been picking up steam the last 10 years, a local ferry in so cal that goes out to the islands is using the system.

    http://www.allamericanmarine.com/cats/32_sportfisher.html
    http://www.morrellimelvin.com/powerboats/cruising/022-Corsair.html
    http://www.hydrospeed.co.za/index2.html
    http://www.hysucat.net/cms/index.php?id=1
    http://www.teknicraft.com/
     
  10. VT-tuna
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    VT-tuna Junior Member

    Guys, thanks so much for the info here. This started as a silly engineer trying to reinvent the wheel for a better ride to the fishing grounds. Been reading about this all day and just can't believe we don't see these hydrofoils designs here on the east coast (maybe I'm just not keeping the appropriate company). The foil assisted cat design seems to do exactly what I'm looking for and I don't have to invent it (which probably would never really happen anyway).

    I will continue to look into this. Seems I can find a hull (35 - 40 foot) and retrofit the foils. Still don't like the outdrive thing but I have some silly ideas there too.

    Thus far the only negative I have read on the foils is collision which to be honest is ALWAYS a serious issue even at 25 kts. Almost went in the drink myself 60 miles offshore once thanks to a mola-mola. The will be an exciting little adventure.
    Thanks.
     
  11. mark424x
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    mark424x Junior Member

    Let's here em, always like a good propulsion idea. Though I just sold my go fast boat and think I'll try to stay < 20 knots. Can't afford a boat big enough to go fast in the pacific rollers even with the foils.

    If you are can use your top speed that's great, my old boat could do 55 and it was propped for that, I hardly ever got over 30, so it was very inefficient. Here an interesting tid bit you might like. I wish they made outdrives and outboards that could take much larger props and you could change the gear ratio.
    http://www.ossapowerlite.com/tech_library/fuel_efficiency/fuel_efficiency.htm
     
  12. kach22i
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    kach22i Architect

  13. VT-tuna
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    VT-tuna Junior Member

    Thats just funny (day late, dollar short). Actually, it has been remarkably entertaining to read all the stuff people are working on. Kinda funny in hind site. After graduating from engineering school and getting a brief insite into graduate school, I remember coming to a very sober realization that for just about any simple, silly, crazy or outlandish concept, you can be sure that atleast one individual now or past tense, has devoted near life time brain power to the thought.
     
  14. marshmat
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    marshmat Senior Member

    An issue to consider with SWATH is the problem of payload capacity. A large SWATH can take on ballast when running light and dump ballast when loaded, and an individual person doesn't change the attitude much. A 25-30' SWATH of comparable geometry to the biggies, would sink and rise far too much as people got on and off, or moved around- with so little waterplane it takes a large vertical motion to get a significant increase in buoyant force.

    I think the hydrofoil concept is a good one for what's being discussed here. My concerns with foils are two-fold: the impact scenario mentioned above (hit mola, isocontainer, whatever and you're toast), and the cost. Also, to a lesser extent, the huge draught at idle speed. The draught problem can be overcome with retractable foils but that's expensive and trouble prone.

    As for the foil/cat thing: Take a look at Prout's Panther 64 for ideas here. The thing is reportedly quite a pig in its natural form, slow to accelerate and cubmersome once on plane. So Prout added a big foil between the hulls up front, and three little foils in the back. The 70,000 lb Panther now does 45 knots with ease, carves like a runabout and draws only 1'6" while cruising, all on twin 1150 hp diesel/waterjet units.
     

  15. VT-tuna
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    VT-tuna Junior Member

    I'd like two please.
     
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