Low price Catamarans

Discussion in 'Multihulls' started by SteveW, Mar 8, 2008.

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  1. khunian
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    khunian Junior Member


    Warren had this information posted on his site for a while - you just never bothered to read the information - preferring to criticise without the facts.

    The motor is not 3kW as you indicate - the numbers are there in the specs - which again it seems you did not read. At 48V and 200 amps peak the rating is 9.6kW with a maximum continuous load of 4.8kW. Interesting that you use the power of the outboard motor at its peak - whereas it is very rarely operated at peak rpm.

    There is another consideration. There are gearbox losses in the outboard, which need to be considered and the torque characteristics of an outboard mean that the prop is comparatively underpowered compared to that which can be used with a high torque electric motor.

    All of these factors are the reason for the favourable comparison and perhaps why Cunard power a cruise liner with electric motors!

    I agree that at this stage electric propulsion is not fully developed but Lagoon are producing an electric motor drive catamaran and other companies are evaluating the technology.

    Warren's point seemed to be that if you plan to sail mainly offshore and only use your motors in entering and leaving port then electric motors have attractions.
     
  2. khunian
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    khunian Junior Member

    Sailing with no Engines

    For Alik's benefit - perhaps he should read:

    http://landlpardey.com/

    Lin and Larry continue to sail around the world without auxiliary power - not the choice of most but still possible even today :)
     
  3. Alik
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    Alik Senior Member

    Do You think I have nothing to do to read Your blog??? :)

    Electrical motor - please read manufacturers specification on cruising, 40-60 amps with 48V. Multiply these numbers, get the result. I don't believe in miracles, in Santa Claus and in magic pills!
    Do You know why this model of motor is '3000'? Because it is 3kW=3000W motor!

    For Your info, continuous RPM for outboard motor is about 80% of max RPM. It is very close to peak, and for some engines it is peak of power. See power/RPM curves on manufacturers' sites.

    This is ********. Warren, study the basic propeller theory, don't talk about things You don't understand! It is absolutely impossible that 3kW or even 10kW(!) motor will give the performance of 20-25HP outboard.

    There is no comparison, there is a false statement in advertisement.

    Yes, attractions for those self-confident 'dilletantes', who believe in advertisements :)
     
  4. Alik
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    Alik Senior Member

  5. rasorinc
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    rasorinc Senior Member

    Hello Alik, I just learned something from you. I did not know that outboard engines rated HP that way. I am used to flywheel HP and shaft or ship hp. SO ARE OUTBOARDS SHAFT or ship hp? tHANKS MUCH, Stan PS I usually multiply flywheel or brake HP by .07 to get Ship HP. Am I right???
     
  6. Alik
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    Alik Senior Member

  7. rasorinc
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    rasorinc Senior Member

    Thank you Alik, I did not know that but I'm only 67 and still learning. Stan
     
  8. khunian
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    khunian Junior Member

  9. wait Also Concerned post again because you are going a little off of this thread with those electrical considerations....then RB can sell another boat....
     
  10. Alik
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    Alik Senior Member

    Good promotional reading! :)

    It is common knowledge that electrical motor gives more flexibility to choose operational mode of vessel because fixed pitch propeller is matching only one point at diesel/gasoline engine power curve. Diesel-electrical propulsion with generators and electrical motors is used for floating cranes, tugs, some trawlers where high propulsive manueverability is required. BUT this does not mean that electrical motor is more efficient, and this does not mean that 3kW motor can give same performance as 20-25HP diesel/outboard.

    Try Google again! Try to find a curve showing how the engine matches the propeller, then You can see want happens.
     
  11. Alik
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    Alik Senior Member

    This is exactly what I said - don't look at peak/max power, look at 'cruising' power recommended by supplier. Supplier rates this model as '3000' that is 3000W=3kW. So congratulations Warren - You've got 3kW motors, so can well perform 4-6kts... if there is not too much wind :)

    Also once You have burned the engine or any electronics - can not fix it in the sea, can not even get a service in marina - there is no service, only from supplier :)
    Honda, Yanaha or Suzuki outboard one can service in any marina.
     
  12. khunian
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    khunian Junior Member

    You still cannot read nor make logical comparisons. IT IS NOT A 3kW motor - comparing on the same basis that you rate the outboard i.e. peak power then it would be 9.6kW or about 13 hp. compared to a 20hp outboard. given the considerations of torque / power / prop sizing given in the previous reference indicates the basis for the equivalence statement.

    Lagoon actually uses either 10kW motors or 40hp diesels - but I guess that their designers and engineers are not as knowledgeable as you.

    By the way I am not Warren - again you make assumptions without reviewing the facts - which clearly demonstrates why Russians have a stereotype reputation as being pig-headed and arrogant - as well as rude.
     
  13. RB PowerSailing
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    RB PowerSailing Senior Member

    i found a photo of Also Concerned

    Cleaning the computer what i found just right now ?

    A photo of Also Concerned , the day of the delivery of his boat !!!

    and was an electric powered catamaran ! I don't know the power exactly , as we did not install the motors , but was running in calm waters at about 6 knts .
     

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  14. Alik
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    Alik Senior Member

    SPECIALLY FOR THOSE WHO CAN NOT READ:
    Outboard's power is rated at about 80% RPM that corresponds to continous power. You can drive the boat at this RPM for considerable time.

    Peak power of electrical motor is not continous power! You can not drive motor at this power excerpt for few seconds. Recommended power is 3kW - this is basis for any calculations.

    Don't tell me about prop size/torque/power - You are absolute ZERO in these matters, You are not marine engineer to argue about that. Have You ever did propeller calculations Yourself? I know the answer - NO.

    I don't care what is Lagoon doing, woud like to see the feedback (not promotional test drive from magazine) on real things.
     
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