6m low power (10 hp) cat

Discussion in 'Boat Design' started by BrianPearson, Jun 24, 2016.

  1. Manfred.pech
    Joined: Apr 2010
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    Manfred.pech Senior Member

    I am not a naval architect nor a multihull designer. I am just fascinated by hydromechanics: hydrostatics and hydrodynamics since I sailed my first catamaran. I am only an amateur here.

    I have built my first CAT (6,25m x 3,25m, 22m² - my design) 1967-1968. It had a lot of failures but it sailed wonderful and I loved it together with the other mates of our club who were allowed to sail it too. The boat had nearly no rocker and sailed and tacked without difficulties.

    [​IMG]

    The pic shows the CAT september 1968 first time in the water. I took the photo.

    Since then I´ve built 36 boats, most of them small for members of our boatbuilding group as some members had problems with epoxy.

    Most of the boats had rocker as nearly all boats have rocker to be able to tack, to get more displacement, to be soft in a chop and so on.....

    Later on I had the possibility to watch tank and CFD tests of maderform hulls the underwater shape of which you can see above without the tradtional rocker. From this time I avoid tradtional rocker as I found out for me and my boats that it is absolutely not necessary. A good design does not need it.

    To answer your question, I cannot see any reason why I schould need rocker on a 6,5m to 9m power catamaran. Same opinion: http://www.boatdesign.net/forums/multihulls/look-ma-no-rocker-42608.html

    [​IMG]
     
    Last edited: Jul 17, 2016
  2. Manfred.pech
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    Manfred.pech Senior Member

    IPA6000 hull in profile: [​IMG]

    Both hulls are to be seen in profile and can be compared. Convex hull above and concave part in profile below.
     
  3. Manfred.pech
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    Manfred.pech Senior Member

  4. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

    Google translated

    The boat is a Werftbau with certification and built in 2012. It was once used for demonstration purposes. The boat has a super ride. The trawler goes up to 17Km / H then it goes very gently and not noticeable on the glide phase. The top speed is 25Km / H with 15 hp motor and you can drive any speed very loosely. There are no annoying Angleitphase and speeds that are not mobile. Up to 35PS are attachable. The length is 5.20m and the width of 2.40m, the weight is with the motor at an estimated 300KG. For weight shift laterally is nearly no roll recorded. The boat stand absolutely stable. The depth is about 20cm plus drive. Thus, it can be moved almost in a puddle.
    The engine is a Suzuki DF15ARL Lean Burn and currently has more factory warranty. He has installed an injection and thus runs absolutely comfortable. Started it can be starter, or even without battery with the cable. Of course, a steering wheel and remote control is installed. By the super directional stability, high hull speed, the stable tilting behavior and the low draft, it is perfect for anglers, canoeists, or to build a small houseboat. Especially the channel, and Havel speeds are driving quite loose and without jostling. Also, the slipping is a breeze. Here is a short video of the boat https://www.youtube.com/watch?v=PMdIVN-HPT4 If I have forgotten something, simply ask your questions!
     
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  5. ElGringo
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    ElGringo Senior Member

  6. schultzfactor
    Joined: Oct 2013
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    Location: Rotorua New Zealand

    schultzfactor Senior Member

    Concave Rocker

    Glad to see this concept is accepted and not a out there idea. My reasoning behind the slight concave rocker was to increase lift. Seems to be working with the skinny hulls getting on the plane quite well.
     

    Attached Files:

  7. Manfred.pech
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    Manfred.pech Senior Member

    Thank you for sharing your experience.
     
  8. bergwerk
    Joined: Jun 2016
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    Location: Florida

    bergwerk Junior Member

    On this website the links to "Contact" and "Home" go to blank pages. Does anybody know how to get in touch with him?

    He shows a ECO75 power cat on his website and I could be interested if this were a seaworthy design.
     
  9. ElGringo
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    ElGringo Senior Member

    I have talked to him by email about the ECO 75 and the possibility of using two motors. He sent me a picture of one that used two. I like the boat but am reaching the point where I am unable to do the work. I contacted him at bernd@ikarus342000.com
     
  10. Rurudyne
    Joined: Mar 2014
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    Rurudyne Senior Member

    There's a sample drawing of the ECO75 in PDF format that gives some indication of bridge deck clearance (important to prevent slamming), shows the use of added buoyancy to prevent slamming, and also gives some indications of the scantlings used.

    One of our resident NAs could ... heheheh ... okay in a minute ... might be able to tell you what they think of them.

    Now, about me laughing. At the exact moment I wrote "resident NAs" I imagined a video game where a naval architect was trying to flee amateur designer/builder zombies wanting confirmation that theirs are the best ideas ever seen. What can I say but ... I be silly.
     
  11. bergwerk
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    bergwerk Junior Member

    Many thanks. I'm also thinking small twins. What would your application be?

    Rurudyne, thanks as well.
     
  12. ElGringo
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    ElGringo Senior Member

    Bergwerk, My original plan was to build something here in the desert, haul it to Florida, put it together and spend a long time going south among the islands. I still like the idea but my back decided it didn't want to do the work. I thought about it some more and started looking at the Great American Loop. I would have twin 20hp motors and after reading about other people making the loop, a lot of fuel. I bought the study plans and the only thing I really didn't like was not having an easy way from the front to the back, you would have to go over the top. Depending on age that might be a very big problem while going through the locks with no help for the ropes and fenders. I think that a person would need some kind of lockable, very secure cabin while out sightseeing and that limited my choices.

    And then there was my list of wants, like float on damp pavement, go a hundred miles on a teaspoon of gas and things like that.
     
  13. bergwerk
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    bergwerk Junior Member

    El Gringo! I also Emailed Bernd and he responded with two photos of a 40hp twin, probably the same ones you have.
    For me the design fits my requirements in respect to low hp twins/ low fuel consumption/ long range. I live in Amelia Island and want to be able to follow the ICW from St.Marys inlet to Jupiter and then crossing to the islands.
    Good blue water behavior and going forward safely around the gunwales are my other requirements.
    I will ask Bernd about these issues and if he is willing to modify the design to fit my needs.
    I like boats out of female tooling but that is certainly not economical for a one-off.
    How would you build yours?
     
  14. bergwerk
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    bergwerk Junior Member


  15. ElGringo
    Joined: Mar 2014
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    ElGringo Senior Member

    Bergwerk, I would use plywood and glass. Hulls covered with two layers of 6oz. Everything topside as light as I could build it and enclosed in 4oz. glass. I don't think I would worry about the interior being slick and smooth, just sort of an industrial speckle paint. I would not do anything for just cosmetic appearance other than the hulls, I would want them slick.
     
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