Powercat speed

Discussion in 'Boat Design' started by Sailcy, Oct 21, 2016.

  1. Sailcy
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    Sailcy Junior Member

    I've come across an Bernd Kohler design of 7.5 Eco Powercat.

    http://www.ikarus342000.com/ECO75page.htm

    The description - "Speed with a 25 HP engine will be around 25 knots full power and 18 knots at half power" sound to me a bit optimistic. Could anyone to comment, please regarding the speed prediction using just such a small engine?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I cannot see any boat that weight hitting 25 knots with twice that hp. And the problems with a centrally mounted motor are sometimes vexing.
     
  3. Richard Woods
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    Richard Woods Woods Designs

    That does indeed seem optimistic, even if the boat was very light and had just one crew on board

    Although they are very inefficient hull shapes, pontoon boats make a good starting point, lots of them around and lots of manufacturer data to prove speeds. Like this one, about the same length and weight as the Eco7.5

    http://yamahaoutboards.com/sites/de...thrust_d-t_hmp_2485_t60tlr_2010-10-14_pnt.pdf

    with a 60hp speed is under 9 knots at half throttle and under 17 WOT (speeds are given in statute miles in the Yamaha data, not knots)

    So that would imply that if the pontoon boat was fitted with a 25hp not a 60hp top speed would be around 10 knots

    here is a video of my Skoota 24 powercat doing 15 knots with 8 men (so 600kgs loading say) on board and using a 50hp outboard

    https://www.youtube.com/watch?v=TrScTmbERrE&index=21&list=PLT7PbPvOm8lyeFTNim_D88IrEuPNyb-qI

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  4. kerosene
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    kerosene Senior Member

  5. Richard Woods
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    Richard Woods Woods Designs

    sorry!! edited to 15 now

    RW
     
  6. messabout
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    messabout Senior Member

    Chances are that the 25 knot claim with 25 HP is an invention of the advertising department, not the result of actual sea trials.
     
  7. Richard Woods
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    Richard Woods Woods Designs

    Trouble is the unknowing will believe the advertising department. As always, false claims hurt everyone

    RW
     
  8. Sailcy
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    Sailcy Junior Member

    Keeping in mind there could be just a text error in the boat description I've contacted Bernd directly with similar question-
    ...speaking about the Eco 7.5 powercat....25 knots with 25hp for boat this size sound a bit to optimistic to me, please correct me if I'm
    wrong, are those guys who already builded the boat have a real figures for the speed and motor they used. On the pictures they
    have 2 outboards installed. Would be very interesting to know about the consumption and distance range.

    He reply-
    Making the right desition is never easy...
    The ECO power boat shown is very heafy and has to transport till 14 persons for day charter work. This is the reason why he needs this engines. If the boat is build to plan and keept as ligth as possible the speed prediction is correct.
     
  9. tom28571
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    tom28571 Senior Member

    Well, that clears it all up.
     
  10. mydauphin
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    mydauphin Senior Member

    Figure 115-125hp to get a 25-foot pontoon boat to 25 mph with 8 people, if you can do it at all with that many people. They better be on the skinny side. Also remember it is likely to have a nice big sun shade that makes it so aerodynamic... like a brick.
    I see an 18kt boat with 60hp, and 4 to 6 people.
     
  11. Sailcy
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    Sailcy Junior Member

    Hmm... I still remain on the pessimistic side, even after the designer's explanation. Are there any Eco 7.5 Powercat builders around wanting to share their experience?
    Or perhaps boat owners to whom those weight / HP / speed figures seems realistically achievable
     
  12. Richard Woods
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    Richard Woods Woods Designs

    I see the empty weight is given at 800kgs which seems reasonable. The CWL (DWL?) is 1400kgs again reasonable. Makes one wonder where the builders added extra weight (apart from the second engine/fueltank/controls etc)

    of course an open deck charter boat has no cabin and no interior fitout, nor cruising stores. So that weight saving offsets the extra crew weight

    Adding a bimini to my Skoota 20 and then 28 didn't noticeably affect performance, but then I only cruise at 12knots so windage is less of a problem.

    Maybe contact the builder of the charter cat version direct and ask what speed/hp he needs and how fast the boat goes with one on board

    RW
     
  13. garydierking
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    garydierking Senior Member

    [​IMG]

    My converted Tornado catamaran has a maximum speed of 13.8 knots with a 9.9 hp Honda outboard.

    [​IMG]
     
  14. mydauphin
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    mydauphin Senior Member

    NIce little boat Gary, have thought of building something like it for years. Does it plane?
     

  15. Richard Woods
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    Richard Woods Woods Designs

    Russell Brown has also built one, fast and seaworthy, seen here in the Juan de Fuca so maybe 20 miles from land. A regular US-Canada commuter. He is building another

    Richard Woods
     

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