choosing designer / naval architect

Discussion in 'Boat Design' started by ViennaYachtworx, Aug 25, 2010.

  1. ViennaYachtworx
    Joined: Oct 2009
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    ViennaYachtworx Junior Member

    We would like to build a 4,5-5m electric powered boat in GRP with a classic appearance. How do we find the right designer for the job? The underwater is bit more tricky as it may seam at first glance as we would like the boat to plane with merely 2kW.
     
  2. HJS
    Joined: Nov 2008
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    Location: 59 45 51 N 019 02 15 E

    HJS Member

    To plane with five-meter boat with 2 kW electric is probably quite difficult.
    A boat with a total weight including driver of 300 kg has a planing speed around 12 knots.
    And it is impossible to achieve that with 2 kW, especially if the boat has a classic look.

    I enclose a picture of a boat that I designed for a client. It has very good qualities thanks to its special bottom form adapted for small engines, electric power and rowing.

    Length over all 5,5 m
    Length in waterline 4,8 m
    Beam over all 1,6 m
    Beam in waterline 1,1 m
    Displacement on datum waterline 0,33 m3
    Weight 130 kg
    Weight with el. engine and lithium batteries 165 kg
    Weight with el. engine and lead batteries 210 kg
    Range with lead batteries 25 nm at 6 knots
    Range with lithium batteries 50 nm at 6 knots
    Speed with 8 hp outboard engine, 1 pers. 16 knots
    Speed with 3 kW electrical engine, 1 pers. 9 knots
     

    Attached Files:

  3. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    Until the batt set gets 10X to 50X the power density of what is aviliable today, most likely any "designer" you get to take this comission seriously will be a con artist.

    FF
     
  4. ViennaYachtworx
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    ViennaYachtworx Junior Member

    Dear Fast Fred. The battery set for a 2kW engine for a small lake boat is in LiFe under 20kg. reducing weight further is easier by putting the driver on a diet. ;-)

    By classic look we meant above the waterline.

    Can a 4kW outboard be enough for a 250-300kg boat (including driver) for planing?

    Thanks for all the answers!
     
  5. HJS
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    Location: 59 45 51 N 019 02 15 E

    HJS Member

    With 4 kW outboard of proper design (most are not) and the right propeller it CAN be done.

    js
     
  6. ViennaYachtworx
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    ViennaYachtworx Junior Member

    Dear HJS,

    What do you mean by "proper design" ? - We have a Torqeedo Cruise 4R in mind - is that proper enough for the task?
     
  7. HJS
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    HJS Member

    Just a sketch, there is a difference.
    Also check the prop, is it suitable for 12-13 knots? I doubt.

    js
     

    Attached Files:

  8. apex1

    apex1 Guest

    NO,
    the Torqueedo will not get any boat that size on plane.

    I fear you will have either to give up planing speed or el. propulsion.

    Regards
    Richard
     
  9. ViennaYachtworx
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    ViennaYachtworx Junior Member

    Dear HJs and apex,

    Took a few days to receive the numbers from the engineers but nevertheless.

    The Torqeedo Cruise 4.0 R develops roughly 350N at 12,5kn. A Testboat (from Torqeedo) with a total weight of 200some kg was measured at 27km/h. An Ultra highspeed Prop is also currently in development.

    They do however recommend us to stay below 250kg total weight.
     
  10. apex1

    apex1 Guest

    No surprise,

    planing speeds are NOT to achieve at these spec.s

    sorry.
    Richard
     
  11. ViennaYachtworx
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    ViennaYachtworx Junior Member

  12. HJS
    Joined: Nov 2008
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    HJS Member

    No, it is not planing. According to the second video is the boat traveling 15.9 km/h, that´s 8.5 knots. That is probable true with a 12" x !0" prop at 1250 rpm. That is the highest rpm according to the Torqeedo website. That gives a 17 % slip.

    js
     
  13. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    350 N @ 12.5 kts = 2250 W effective power.
    Not enough to push a 300+ kg planing hull at that speed. Besides, since the motor absorbs 4000 W, it means that the propulsive efficiency is roughly 0.55, not really a stunning value.
    With a better designed prop the overall efficency could hopefully be pushed to 0.80, which would give 3200 W effective power. In that case you would have something to start with.
     
  14. Wavewacker
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    Wavewacker Senior Member

    Will a hydrofoil design work? (Just a thought, I have no idea!)
     

  15. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    A classic appearance is required. ;)
     
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