6m low power (10 hp) cat

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

  1. Manfred.pech
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    Manfred.pech Senior Member

    It is a really nice bow and I like the shape. But it might be a stagnation point and the water might rise and increase the wetted area to create undesirable skin friction ... and start the bow wave ??? It is just a question. Suggestions ???

    [​IMG]
     
  2. Wavewacker
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    Wavewacker Senior Member

    A few years ago I had the same idea of doing the loop with a motorcycle on board a catamaran, you should have seen the responses I got, LOL.

    I was going to take a 650 Honda Transalp, a dual sport, 320 pounds or my cruiser at 700 pounds.

    Cats aren't good for load carrying abilities, the cabin is probably where the bike should be as to the CG.

    I was told I'd need about a 40 footer with fat hulls and there goes that efficiency I wanted.

    Motoring a cat is best with 2 motors, efficiently so that cost doubles.

    Along the loop it's pretty muddy, not many ideal places to off load a bike.

    Loading you'll need a ramp or a crane rig, that helps to get you past the muddy banks, if you just lift a bike off and set it aside, you're either setting it in water or mud.

    You're then looking for boat ramps and paying fees I'd suspect. How many are there and where did you want to go on the bike?

    Off load at a dock, chances are you'll have steps to go up before getting to the street. Where there are ramps, they are intended for pedestrians pulling a wagon or cart, they may tell you to get your motorcycle off the sidewalk!

    Some went so far as to claim the salt air would rust my bike pretty fast, not an issue really, the paint is pretty good, so is the chrome and alloy, but whatever. Coat it with WD40.

    Dock space, by the foot and beam, cats cost more to spend the night.

    On the cat subject of this thread would have the bow in the air with a bike on the back and crew aft of the CG, not good in open waters.

    Anyway, my quest for that arrangement ended quickly taking under consideration a monohull landing craft. After more investigation of where to load and unload, the bike idea was dropped.

    Now, if you mean a bicycle with a small weed eater motor, well, okay. But a motor cycle worthy of touring, it's going to be a big boat.

    The loop will take you a good 3 months at displacement speeds and that is rushing it. That means lots of gear, water/food and fuel. I can see a foot locker full of seasonal clothes, boots and shoes for 2 people.

    I have no doubt that our cat build here could do the loop, but it won't carry a lot of weight and keep its sea keeping attributes. The idea of operating in the shallows will probably mean in knee deep water.

    So, from what I've found is that to have an economical, efficient, stable looper with much load capacity, that defaults to a mono that is long and narrow. Can't get around that. For every additional foot in beam there will be a cost in all of these areas. The most efficient and stable boat will have a flat bottom, the trade of is your teeth falling out in the chop, it's a trade off.

    Another craft that fits the bill might be a trimaran over a cat, might check those out.

    I think someone has already mentioned a "Strawler" sailboat converted to a trawler, also a great option for the loop on a budget.

    Seems too that the USCG has regulations that kick in at 26 feet, with a home built wood boat you may want to stay below that length. That will be a minimal cruiser, IMO, for the loop that offers the comfort required by most of us mature folks.

    Now, I really like this BK cat, I'm watching for the finish and a splash. But I think one week on that boat and I'd be wanting to head home. :D
     
  3. ElGringo
    Joined: Mar 2014
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    ElGringo Senior Member

    Hi Wave, I am talking about a common bicycle with an 80cc motor mounted on it. One of the kind where you pedal then put it in gear, engage the clutch or whatever. Probably 50 to 60 pounds total including the bicycle.

    Do you know where I can find the USCG regulations that start at 26 feet?
     
  4. Wavewacker
    Joined: Aug 2010
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    Location: Springfield, Mo.

    Wavewacker Senior Member

    Go to the USCG site, http://www.uscgboating.org/regulations/boatbuilders-handbook.php

    Also try here http://www.uscgboating.org/images/420.PDF

    There is also the boater's guide book, gives requirements for lighting vessels, safety, registration, etc.

    80cc? That thing should fly at 60 mph, as a kid I had a Schwinn Stingray with a 40 cc and that was faster than you'd want to try it. Hope you have good hospitalization insurance......be careful!

    Back to boats!
     
  5. ElGringo
    Joined: Mar 2014
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    Location: Amarillo Texas

    ElGringo Senior Member

    Hi Guys, if this question was answered, I missed it and I would still like to know
     
  6. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    Just some extra drag. How much? I don't know, but 1/2" would probably not be noticeable at a guess.
     
  7. Manfred.pech
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    Manfred.pech Senior Member

    NO COMMENT

    [​IMG]

    [​IMG]
     
  8. ElGringo
    Joined: Mar 2014
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    Location: Amarillo Texas

    ElGringo Senior Member

    Manfred, I have links to Bernd's Facebook page, his website for selling plans, and the "Duck" website But, I can't find where you got the pictures in the above post. Do you have a link that you could share?

    With the exception of not having two motor wells, it is almost what I want.
     
  9. Manfred.pech
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    Manfred.pech Senior Member

    Here it is: https://www.facebook.com/groups/duckworks/photos/ . Please scroll down. Kind regards, Manfred
     
  10. Manfred.pech
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    Manfred.pech Senior Member

    Nice. Again some progress and near to hit the water.

    [​IMG]

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    Interesting Nacelle for the motor.
     
  11. garydierking
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    garydierking Senior Member

  12. ElGringo
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    ElGringo Senior Member

    Gary, do you think that it was a better arrangement than mounting the motor to the aft cross beam?
     
  13. garydierking
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    garydierking Senior Member

    The Tornado doesn't have much buoyancy aft, so I mounted the motor as far forward as I could while still maintaining good steering.
     
  14. Manfred.pech
    Joined: Apr 2010
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    Manfred.pech Senior Member

    Good advice! And there is another reason for it.
    The total resistance of a catamaran is not simply the sum of the individual resistances of each hull. The catamarans resistance is twice the individual hull resistance plus the added induced drag due to the interference waves of the hulls with each other.
    The worst place for the motor is the spot where the half whorls of the bows meet unter the bridge deck at working speed. To accellerate the flow it is possible to use asymmetrical hulls to change the distance between the hulls or to design a bulb to reduce the bow wave.

    [​IMG]


    To mount the motor as far as possible forward is the best method in my opinion.

    [​IMG] Koen Geurts https://www.researchgate.net/profile/Koen_Geurts
     

  15. ElGringo
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    ElGringo Senior Member

    Manfred, if you drew a line down the centerline of each hull and removed anything on the inboard side, leaving them as a straight line, What would the wave flow in the picture above be changed to?
     
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