The "Extremely Light Boat" or "Cowmaran"

Discussion in 'Boat Design' started by YotaTruck, Apr 6, 2016.

  1. YotaTruck
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    YotaTruck Junior Member

    Anyone ever see this? I searched for any reference on the forums and couldn't find one. Essentially it was an experiment to create a very fine hulled catamaran from the lightest materials possible. It is 27' LOA (not sure of the beam) and will do 12 kts with a 9.9, at a weight about 1200lbs:

    http://www.tropicalboating.com/2012/04/creating-the-extremely-light-boat

    The key to the whole design is the foam core construction of course, which I have neither the expertise nor the equipment nor the funds to utilize, but I wonder how much heavier the boat would be were it built in plywood? 27' is a bit long, so essentially I'd want to recreate the hulls at about 24'.
     
  2. Skyak
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    Skyak Senior Member

    I don't see what is accomplished, or even the objective. The hulls are extremely slender and lightly built so it's efficient at hull speed and light load. But it's tall so it has lots of wind drag and lower stability, and the large square footage deck is pointless because it can't carry much weight (if it does the efficiency drops).

    If you want extreme efficiency with ply construction keep the length of the main hull and have slender floats out on long arms for stability (like native trimaran designs). With a smaller amount of less exotic material you could carry more more efficiently.
     
  3. bpw
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    bpw Senior Member

    Doesn't seem that light, an Olson 25 (for example) sailboat only weighs 2900 lbs, and half of that is lead.
     
  4. tom28571
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    tom28571 Senior Member

    You might take at the Gougeon power cat called a Gougmaran. Innovative and may be a good base for what you want.
     
  5. YotaTruck
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    YotaTruck Junior Member

    They mention fuel economy and low wake a lot, which it does seem to achieve, but my goals are more inline with your next sentence:

    Bingo. I'm looking to be able to travel at hull speed (24' boat, 6-6.5kts) using the least amount of power possible.

    Interesting idea-I've toyed with the idea of a trimaran before but never really investigated it much. I've also never found much in the way of power trimaran plans either, except this one by Phil Bolger:

    http://grindercabinclamskifff.blogspot.com/

    Too heavy and requires too much power.

    I've drooled over that one many times, but I shudder to think how much those hulls cost. Way out of my league. I would love to hear more discussion of what a 24' power trimaran would look like.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Are we to assume you have a still-water, or sheltered waterway use in mind ? Because basically that is what this type of thing is restricted to. Ply construction won't be much different in weight, though the execution might be more difficult, depending on shape.
     
  7. Stumble
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    Stumble Senior Member

    Frankly it would be a shame to do...

    But picking up a Stilletto 23 and converting it from a sailing cat to a power cat would be trivially easy. It would also weigh less than the guesstimate of the cowmaran.

    It's a great project, and looks like a really good boat, but the end result is a boat that is severely overweight despite using high tech, and very expensive, materials.
     
  8. Corley
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    Corley epoxy coated

  9. YotaTruck
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    YotaTruck Junior Member

    This boat would only be used on small mountain lakes. Where I am located, there are many small lakes that only allow electric motors. As a result, these lakes are mostly utilized by kayakers and canoeists, or one or two fishermen in a small jon boat with a trolling motor, lots of batteries, and not much freeboard. I'd like to build something that can comfortably carry me, my wife and two small kids (and maybe the dog) for some leisurely cruising.

    Many of these lakes have great beaches and picnic spots along their shores, but with no trails to access them from land they are difficult if not impossible to get to without a boat. The electric requirement necessitates maximum efficiency as I'd like to be able to spend at least half a day on the lake. Granted, the boat would be sitting beached for a significant amount of time while the kids hunt rocks, eat lunch, and explore.

    I've been scouring Craigslist for a suitable "donor" sailing catamaran for a while but there just aren't any around, save for the 16' Hobie cats which just aren't enough for what I want to do. I live right between two large (2000 plus acre) lakes that are probably the biggest freshwater sailing spots in NJ because they are both 10HP max, but everybody seems to sail monohulls. I just looked up the Stiletto and indeed, it looks like it would be perfect. The Tornado is another that someone had suggested to me, but alas, none of those around either.

    I will indeed-looks promising-thanks!
     
  10. Skyak
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    Skyak Senior Member


    After a bit more thought I decided that the "Cowmaran" is for a guy that simply wants a BIG boat that is actually quite small in terms of capability. It has plenty of room and capacity to carry his ego.

    You want something more sensible, capacity and efficiency, so there are ancient hull forms for that purpose. An 'outrigger canoe' puts the material in the most efficient place for a displacement hull -length, at the expense of stability, then it tweeks the stability to the right levels (right natural frequency) with the most efficient form, light wave piercing floats placed wide. The floats don't drag much because they only displace water when 'righting' and very little righting is needed because cargo is kept low. In poor island nations outrigger canoes are the buses between islands -efficient and seaworthy.

    https://en.wikipedia.org/wiki/Outrigger_canoe#/media/File:Outrigger_Camiguin_Philippines.jpg

    I have a 20' kayak (17" beam) that I can paddle at 7kn for a 30 min workout -the point is you don't even need 24' for efficient 6.5kn. I have a design for a 2 sheet 19' canoe I have wanted to modify to have a small transom and 3 part nesting. It's 'fat' compared to typical OC but the point is that 2 sheets is all it takes even if want a heavy capacity. The floats could be from PVC pipe or even inflatable on an aluminum pipe backbone that swings out of the way at the dock.

    Long displacement hulls are the way to go for efficiency with heavy loads, but planing hulls go faster more efficiently for light loads -I have been wondering if an efficient displacement hull could carry some lifting foils to outperform planing hulls in light load -outperformance at all speeds and loads. Theoretically, foils provide more efficient lift, lower surface friction, and lower wave/induce drag so it can be done, but is there an attractive product?
     
  11. Skyak
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    Skyak Senior Member


    Beach cats are light and efficient but they have very little weight capacity. By the time you get one big enough to carry the family and batteries it is huge and a hassle to setup and launch. BTW Stiletto is launching a new 27' cat so the old ones might soon be 'available'.

    For electric on the protected waters you describe I would go with a freighter canoe. In England they have some real beauties they use to run around their canal system (6kn 40-60mile range common). If you use lead batteries placed low you will have so much stability you won't even need/want outriggers. If you go with lithium ion batteries an outrigger and solar might make sense.

    http://www.bing.com/images/search?q...A9A427D5E012F65CB5FC851DAF144F07D&FORM=IQFRBA
     
  12. Stumble
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    Stumble Senior Member

    The older Stiletto 27's are still available for about $20,000 or so. And would have plenty of load carrying.

    A Tornado just doesn't have enough load carrying capacity to make this work. They are high performance beach cats and would be swamped by the weight. Up to around 400lbs they are fine, past 500 and you will sink.

    There are plenty of good small cat designers that would all work well and be relatively easy to build. Richard Woods has a number of them.
     
  13. Village_Idiot
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    Village_Idiot Senior Member

    I would suggest a long, narrow flat-bottom Jon boat or garvey. They are best at carrying weight efficiently. However, you may have to have one custom-built (or build yourself), as they are generally not readily-available. The closest commercial d boats that I know of are aluminum boats mfd by Weldbilt or Weld-Craft, they offer boats up to 20 feet long with beams from 36" to 70".

    I myself run a 24-foot flat bottom with a 60-inch bottom width. It is custom-built, aluminum, and heavy, with a raised center console, a half-dozen storage hatches, and a 115hp for-stroke outboard. Many would think that it is underpowered, but it will jump up on plane in a boat length, and cruises at around 5-6mpg. It will also carry (literally) a ton of weight in a foot of water.

    Some will say the narrow beam is too unstable. That is mitigated by the length, and it is definitely more stable than a freighter canoe. The 2460 doesn't feel tippy at all. The only downside is that it is not very maneuverable in tight quarters.
     
  14. YotaTruck
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    YotaTruck Junior Member

    I appreciate your comments, but I'm looking for a boat that can achieve hull speed with a 3HP electric motor swinging a slow moving 9-10" prop.
     

  15. Village_Idiot
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    Village_Idiot Senior Member

    My recommendation remains the same if you are looking for carrying capacity for not a lot of money. The long slender hull will be efficient. Your next best bet would be a freighter canoe, but they may be harder to find and more expensive. To meet all of your objectives, you may have to build your own.
     
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