Catamaran Hull Squat

Discussion in 'Hydrodynamics and Aerodynamics' started by francotripepi, Feb 28, 2019.

  1. francotripepi
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    francotripepi Junior Member




    Ad Hoc, I knew there was a Design reason for the squatting, and it’s probably laying between lines, proportions and weight distribution

    Albeit all planning hulls squat to some degree
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Homo sapiens is the main cause of longitudinal trim changes on small, slender hulled cats.
     
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  3. Ad Hoc
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    Ad Hoc Naval Architect

    You need to differentiate between squat and trim then.
     
  4. francotripepi
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    francotripepi Junior Member

    Mind you guys,

    My whole discussion on “squatting” is referenced to the boat stance at anchor, not under way

    If you observe the pictures I’ve posted, the Beachcat is still, and in this position it squats alot, I am guessing that 60% of the transom is submerged

    As any planning hull, forward motion will produce an additional dip....until you accelerate on plane.....then its trim nature is to run bow up.....that’s expected

    What I am looking to figure out, is why does this particular hull squats so much standing still, based on what you know about hull design
     
  5. JamesG123
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    JamesG123 Senior Member

    That heavy chunk of outboard bolted to the transom probably has something to do with it. Monohulls without equal weight distribution will do the same thing. I don't understand your fixation with cats.
     
  6. francotripepi
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    francotripepi Junior Member


    That sure has something to do with it, but I believe it is more related to the Hull Volume vs Outboard Weight, a monohull will usually have more hull volume in the transom, hence supports higher loads....

    It's a personal thing, I love the motion and fluidity of a cat ride, its stability at anchor, its deck size, etc......I have owned a Wellcraft V20 CC, a Robalo 23, a 24 Aquasport SeaHunter (best intrerior deck design ever imo) a 22 Aquasport Sandpiper (deep V) an I am now at my second 1973 Grady White 191 Sportsman (floats and idles on 10" of water...) which I am redoing its interior to mimic the Aquasport SeaHunter....but my heart is on a Catamaran of around 24 ft where I could camp on for the weekends in the Keys Flats....
     
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  7. francotripepi
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    francotripepi Junior Member


    Ad Hoc, I read some of your interventions on other postings (wave piercing hulls) and like and appreciate your technical knowledge.....don't you think that this hull that I will show you now, perhaps captures better my desires considering the waters I navigate and the specific conditions? It has a veeeery fine entry and it flattens (overall, even thou you see ribs that I guess are to soften impact and help it go straight) after the first 1/3 of its length.

    If you see their videos you see that it does not squat like the Beachcat when at rest and look at when it accelerates, it stays almost true to horizon....perhaps a Catamaran version of this boat would give the benefits and ride characteristic I am looking for.....please take two minutes to look at pictures and maybe some of the video...and give me your opinion...... Mr Efficiency, your opinion too, please


    X3.jpg

    X3 A.jpg

    X3 C.jpg


    X3 G.jpg


    X3 E.jpeg


    X3 B.jpg


    X3 H.jpg
     
  8. francotripepi
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    francotripepi Junior Member

    Or perhaps those ridges on the bottom sides are to entrap air and make it go smoother and faster and facilitate lift...........
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    It is not clear to me, what characteristics you are seeking?

    Look at 2:15
     
  10. francotripepi
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    francotripepi Junior Member

    I am looking for a catamaran hull form, that allows me to navigate shallow water, but also bay, that could carry some load (not just a Sushi Roll), that does not squat alot (otherwise we hit bottom in shallow water), and that can perform with less horsepower and give me around 18 to 20 knots.....a 24 footer that can get to that speed with a 115 hp outboard, probably with a 4 blade prop with larger diameter.

    Biscayne Bay and the Shallows in the Fla Keys, have mostly short chop at short intervals, but most importantly, is that a navigable draft should be around 8 to 10" max, so that I could reach those gorgeous and isolated spots.

    Reality Check: I could care less of having a boat that can handle Sea Force 7 (by the way, almost all of those boat buyers I never see out at sea when sea conditions are more than 3 ft, regardless if their Contender or SeaVee can be shot at close range and take it, the reality is that they CAN"T), most of the time here is calm waters, I want to camp out for one or two nights, hence should carry basic items without compromising its draft and handling....I prefer a steady speed and good motion that can hurry but do it in comfort.....see some sketches I played with.....



    Cat.jpg


    Cat B.jpg


    Cat C.jpg

    As you can plainly see, my ideas look like a scaled version of those Displacement Catamarans I mentioned at the beginning, but the Hulls can be configured to be Planning or Semi-Planning or like the X3 Shallow Draft boat I showed you before......overall dimensions around 24 ft Length to 9 ft Beam............originally I wanted to use small 4 stroke outboards 10 to 20 hp each....but could be a single with 90 to 115 hp

    I look for lightness and nimbleness......
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Then all you need is simply a hull form/design that has a high length to displacement ratio.

    We have designed 45m catamarans that run in 2m of water at 25knots carrying 500pax. A high LD ratio design will allow you to do that.
    Simple!
     
  12. francotripepi
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    francotripepi Junior Member


    LMAO...simple for you.....any visualization of that type of hull? wetted surface?
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Do you understand what I mean by a high LD ratio hull ?
     
  14. francotripepi
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    francotripepi Junior Member


    Yes, but I do not necessarily know what form to use to achieve that....
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    If you do understand (totally its implications)...then you'll understand your comment makes no sense!
     
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