Another "revolutionary new" hull design

Discussion in 'Boat Design' started by DCockey, Oct 16, 2011.

  1. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Cutwater is a new brand of trailerable, cruising power boats. One of the design goals appear to be large interior volume within the constraints of being trailerable in North America.

    The hull design has assorted "features" which are claimed to improve high speed performance and ride with reduced drag by introducing air under the hull. Looks to me like they will increase resistance and fuel consumption at lower speeds.

    Image and text below is from their website: http://www.cutwaterboats.com/hull_design


    [​IMG]

    A radical departure from conventional deep-V hull geometry, the revolutionary new Cutwater Hull design incorporates a number of features that together deliver a smooth ride, straight tracking, agile, responsive performance, and maximum fuel economy. With all these advantages, each Cutwater model offers the range to expand everyoneís cruise horizons while providing exceptional comfort underway.

    1. Foremost among these features is the Keel Stepped Hull bottom with tapered intake tunnels to distribute an uninterrupted flow of air evenly across specifically designated segments of the running surface, while vectoring air away from the propeller.

    2. A keel pad runs the full length of the bottom to concentrate lift and adds directional stability. The entire tunnel-step-keel pad configuration employs a consistent distribution of air along the bottom to reduce drag for a measurable improvement in hull speed and fuel efficiency.

    3. A substantial skeg keel extends along the aftmost third of the hull, to improve straight-line tracking for efficient course-keeping, and to resist rolling for greater ride comfort. Additionally, this keel protects the propeller and running gear against damage from submerged hazards.

    4. Along either side of the keel where it meets the bottom is a rounded shoulder where the machinery compartment has been expanded to allow positioning the engine low in the hull. This in turn lowers the boatís center of gravity for greater stability, and allows lowering the main deck structure to provide greater interior headroom while preserving the boatís attractive exterior profile.

    5. Well forward, the raked stem curves downward near the waterline to a slender, near-vertical forefoot that cuts oncoming waves to ensure a smooth ride. This nuance also extends the waterline to improve fuel efficiency, and allows fuller sections throughout the forward hull sections for greater useable interior space. Together, these refinements enable the Cutwater hull to deliver an ultra-smooth ride and superior performance, plus an extra measure of comfort and convenience, adding up to unexcelled cruising enjoyment.
     
  2. messabout
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    messabout Senior Member

    Is this to be the next best thing? Call me a mean old curmudgeon because I am a wee bit skeptical.
     
  3. DCockey
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    DCockey Senior Member

    But you are probably not the target customer.
     
  4. daiquiri
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    daiquiri Engineering and Design

    I don't get items 2, 3 and 4. For the rest, it's - well, ok.
     
  5. DCockey
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    DCockey Senior Member

    The skeg adding directional stability, damping roll and protecting the propeller as claimed in 3 makes sense to me. But it does add substantial drag.

    The rounded shoulders between the skeg and hull allowing the engine to be lowered as claimed in 4 also makes sense to me. In Maine lobster boat terminology that would probably be "semi-built down" but this design doesn't have much to do with a lobster boat.

    Whether these are worthwhile trade-offs depends on the requirements and customers.

    It's interesting though that another builder is claiming "air along the bottom to reduce friction".
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Any customer that has no knowledge of boats, never been on a boat has no basic high school education (o-levels) and can't read (like books/journals/Internet) etc, oh and has a deep pockets...is the target audience :eek:

    Must be the season for it again... :eek:
     
  7. Willallison
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    Willallison Senior Member

    Oh... John... you are such a sceptic....;)

    Their website is predictably light on numbers to back up any claims of increased efficiency. I managed to track down one published "test". http://www.cutwaterboats.com/articles/Sea_Trail_2011.pdf

    Specs for the Cutwater 28:

    LOA molded 28' – 0" 8.5 m
    LOA rigged (with swim & pulpit) 32' – 4" 9.85 m
    Bridge clearance (with folded mast) 9' – 1" 2.76 m
    Beam 8' 6" 2.59 m
    Draft 28" .71 m
    Fuel capacity 100 U.S. Gal 378.5 L
    Water capacity 40 U.S. Gal 151.4 L
    Holding tank capacity 30 U.S. Gal 113.6 L
    Weight (Dry) 6,400 lbs 2,904 kg
    Engine Yanmar 6BY2 260 HP


    Which are remarkably similar specs to one of my own designs, Graphite http://imaginocean.net/contents/en-us/d8.html :

    Length Overall 9.9 metres
    Length Hull Only 8.8 metres
    Length Waterline 7.9 metres
    Maximum Beam 2.8 metres
    Draft (Hull) 0.3 metres
    Displacement 2,900 kilograms
    Fuel Capacity 525 litres
    Water Capacity 400 litres
    Power Yanmar 6BY-2 260Z with Bravo 3 Drive

    The Cutwater has a top speed of 24 knots vs Graphite's 32.
    At 15 Knots, The Cutwater manages 2.5 nmpg vs Graphite's 3.3 nm per US gal in full cruising condition (not the lightweight configuration that most 'tests' are carried out under). Moreover, that consumption is almost constant from around 12 to 22 knots. I suspect that as the speed increases with the Cutwater, so to would the consumprion as a reult of the increased drag from all those 'interuptions'.

    No "keel stepped hull" or other revolutionary contrivance. Just careful consideration to design fundamentals.

    Having said all that, I quite like the Cutwater. At least it's not a fat, heavy blob that looks like it just popped out of a jelly mold
     
  8. PAR
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    PAR Yacht Designer/Builder

    A bunch of preformance enhancements, yet burdened with all the extra area and drag. I don't get it . . . why bother.
     
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  9. viking north
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    viking north VINLAND

    Maybe it's nothing more than adding blade number 7, to that french sounding razor. If for nothing else creating "wool over the eyes" buying hype. Having said that, can you imagine the cost of developing that mold plus always the big question before popping one out, did I get the release in every nook and cranny before lay up :?: :eek:
     
  10. gonzo
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    gonzo Senior Member

    A boat with so much draft needs to be really heavy to float on her designed lines. How can you have economy with heavy displacement and a hodgepodge of appendages dragging in the water?
     
  11. Willallison
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    Willallison Senior Member

    I expect that the skeg makes up for a fair proportion of the draft....
     
  12. gonzo
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    gonzo Senior Member

    Look at the proportion of the designed waterline to length of hull. It is pretty deep even without counting the skeg.
     
  13. Willallison
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    Willallison Senior Member

  14. viking north
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    viking north VINLAND

    Calling it a skeg is pushing the enveloppe-- more like a keel containing the prop tube/shaft and bearing. Normally one thinks of a skeg as a loner sitting back there in many cases acting as an attachment point for the rudder. Basically this is a craft making use of modern lifting strakes incorporating a keel to accomidate the drive line rather than the more expensive and higher maintenance of inboard/outdrive systems.
     

  15. FAST FRED
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    FAST FRED Senior Member

    "Any customer that has no knowledge of boats, never been on a boat has no basic high school education (o-levels) and can't read (like books/journals/Internet) etc, oh and has a deep pockets...is the target audience "

    Sounds like the Tiawan market (sail and trawler) of decades ago.

    Those folks bought on internal volume and teak trim.

    FF
     
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