Utility Power Cat Design Study

Discussion in 'Boat Design' started by Chris Ostlind, Mar 6, 2009.

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  1. Chris Ostlind

    Chris Ostlind Previous Member

    I've just put up an article regarding a design study I have been working with for a high fuel efficiency power catamaran for a wide range of use applications.

    The article is on my site here: http://www.lunadadesign.com/largo.html#more-241

    If you guys could take the time to read the piece, take a look at the renderings and make some comments, I'd be grateful.

    Attached Files:

  2. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    Nice design Chris,i think its a very good concept.
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Hate to ask the obvious..what makes it fuel efficient?..and how much more efficient is it compared to "the alternative".?
  4. Chris Ostlind

    Chris Ostlind Previous Member

    10-1 L/B easily driven hulls
    low profile roof line with clean, aero surfaces
    small engines for typical boats of this size
    12 knot cruise at partial throttle setting

    Estimated to get 1/3 better fuel mileage than typical power cat of 21' LOA running at 12 knots cruise
  5. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    High L/B ratios help with the length displacement ratio. Most of the cat's Ive designed range in the 10~18 L/B ratio. So much better than low L/B ratios, for endless reasons...

    Not sure how a low profile will have much affect at a max speed of 10~12knots!

    The use of outboards for engine has been used before and is a good idea.

    I'm only looking to see what is "novel" or new about it, that's all..you're just using existing knowledge packaged in a different way. Good luck..
  6. Chris Ostlind

    Chris Ostlind Previous Member

    Yep, not an atom bomb on a napkin project. Just good solid problem solving with materials and technology that will not scare off the homebuilder guys. Put it all together in a nice looking package that is not too out there and the boat speaks for itself.

    I've got several freakazoid styling and tech designs in the portfolio, but they are mostly for eye/mind candy scenarios and have little bearing on the process of getting plans completed that someone will actually buy... and then build for their personal use.

    It is possible to push the envelope every once in awhile, but if it's done too many times without the meat and potatoes stuff, then the public gets kinda put-off and they will look elsewhere.
  7. northerncat
    Joined: Jan 2007
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    northerncat Senior Member

    so what holds the hulls together in rough water? i cant see any transom or supporting bulkheads?, also what about options for larger motors, i would be interested in something that would at cruise speeds use max 10l an hour top out at 22/24 knots and cruise at 18, would say twin 30s do this on yours
  8. Alik
    Joined: Jul 2003
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    Alik Senior Member

    My feeling that car concept does not really work for a cat.
    - how to get out on the bow deck?
    - how to get into the boat if moored alongside?
    - is the aft ramp watertight enough to comply with freeboard requirements?
  9. Chris Ostlind

    Chris Ostlind Previous Member

    It's not really meant for nasty rough water, but the Largo would have structure to stiffen and unitize the hull. I don't take the time to show everything in a design study.

    Cruising at 18 knots and operating in big time rough water with much bigger engines is a different boat. That design envelope is not what I'm going for with this study.
  10. Chris Ostlind

    Chris Ostlind Previous Member

    There are several things about the Largo that will change as the design process moves along. You mention bow deck access, Alik, as have others who have responded in different ways. You also mention the side-to docking potential. Those issues are being addressed in the next iteration, which is underway right now.

    Putting this study out in front of the gang here naturally invites a wide range of commentary from differing sources, each with their own personal preferences and perceived needs. I wanted to hear all these comments because this forum represents a real source of marine oriented thinking and it is an exciting environment in which ideas can be presented.

    When the next version of the Largo is pulled together, I'll bring that one here as well. There has been a fairly strong response at this point. Individuals have been making comments directly to me via email, as well as through my website and there is a lot of stuff to kick around for possible incorporation.

    As I indicated in the first post, I am looking for comments on the design study. I know that there will be positive, as well as negative, points to be made and frankly, the whole thing excites me. I'm a relatively new designer, I don't exactly live in a hotbed of marine activity and reaching out like this, on the Internet, has given me a chance to regularly interact with other design oriented people, as well as boat builders and enthusiasts. I know that my design thinking has gotten more focused as a result and look forward to more of your contributions.
  11. northerncat
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    northerncat Senior Member

    my other comment is that it looks like a station wagon :cool:
  12. Chris Ostlind

    Chris Ostlind Previous Member

    That's good, actually. I was going for a plywood morph of sorts between a Honda Element and a Toyota Venza with shapes that could be harnessed by the average guy.

    Styling and function cues are all around us. I think it's perfectly suitable to snag concepts from the automotive industry when they can work well with the overall design.
  13. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    One of the applications that I see for the boat is as a utility and supply boat for island cottages. I mean cottages on islands on inland lakes or otherwise inaccessible or difficult by land. There are a lot of those and how many boats can haul a small tractor, building supplies or other outsized materials? Then the same boat tows skiers or rides the family and guests around in style on Sunday afternoons. The access problem has to be addressed but does not look too difficult.
  14. erik818
    Joined: Feb 2007
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    erik818 Senior Member


    Nice design. It doesn't look like a boat ought to, so it takes some time getting used to the looks.

    When I approach a jetty at an island cottage, or a shore without a prepared landing, I want to come with the bow first. I really can't see many situations when I would be able to load/unload from the rear. At best a boat might be loaded/unloaded over the side.

    Instead of a rear hatch, it would be nice to have a bow hatch and to be able to lower the bow to be used as a ramp as on a landing craft. I don't see why it can't be done with your design.

    12 knots would be an acceptable cruising speed when used as a workboat, but with only a couple of persons on board a higher top speed would be nice.


  15. patiras
    Joined: Jan 2007
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    patiras Junior Member

    I've just finished a similar project, and this was my solution

    30 foot LWL, about 1 tonne all up, 2* 8Hp high thrust Yamaha's. 13 knots top speed, 8-9 knots with no problem. A bit over 2 miles per litre of gas running at a decent speed. Windage is not really an issue, unless you are trying to push into a 30 knot headwind, in which case the speed drops a knot or so.

    Please excuse me for being lazy and just pasting in an answer I gave to someone possibly interested in building one.

    Designed very specifically for the use intended; namely that it is used to ferry up to about 12 people and/or stuff (1000kg's) 2 miles across an estuary. The ability to run it up a beach dictated that the bow had an upturn to allow it to run up so people could disembark over the bow without getting their feet wet. I didn't want to get into the complication of boarding ramps, although a small boarding step would be quite a feasible addition. The fact that the carrying capacity was almost equal to the displacement of the boat also lead to a compromise on the L/B ratio (15/1) of the hulls keeping them slightly wider than ideal to stop it sinking too much when loaded. The use of a displacement stern under section also makes for a very specific operating speed window. ie. at up to hull speed (11/12 knots) it runs very efficiently, above this speed, the stern would tend to squat dragging the transom. If a higher operating speed is envisaged, then a semi-displacement hull form aft would be more appropriate. All these compromises are at the expense of top speed, but give a benefit of manoeuverability, a general usability and a ease of running at moderate speeds. Ease and speed of construction were also important to me, and a flat panel design makes for an easily assembled boat; the trade off being perhaps half a knot of so, one that I was happy to accept. My final design criteria (but one of the most important) was for fuel economy, and this cat is pushed along at 9 knots quite happily with a pair of 8 Hp outboards (12/13 knots top speed), with a barely noticeable drop in speed fully loaded. The cabin was consciously designed with a lack of aesthetic; flat panels make the best use of space and are the easiest to construct. The hull/deck sides round the forward part of the boat were again designed with the intended usage (minimal but usable seating area for maximun loading space) and the envisaged weather conditions in mind. Similarly, the bridgedeck height was kept to a minimum with the envisaged wave height in mind.


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