Low price Catamarans

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

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  1. RB PowerSailing
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    RB PowerSailing Senior Member

    power requirement for Tiki 38

    About this i got a specific experience :

    We installed 2 x 9.9 Tohatsu 2 strokes outboard motors ;

    After sea trials i would recommend 2 x 15 hp Honda or Yamaha or similar , but 4 strokes ;

    The power of the 9.9 is may be enough but supplied at high RPM and with increased tendency to cavitate wioth waves ;

    The main issue with Wharram's cat outboards , is that if they sit properly high , always tend to cavitate . When sitting low , then the cavitation is reduced , but there is the big risk to get the motor badly submersed with waves ;

    A solution we offered , was to install Yanmar Diesel outboards 27 hp ; Excellent motors , fantastic choice . The motors we installed on the Island Breeze of Kenneth Stone , 42' RB cat .

    Unfortunately much heavier then a gas motor , but with a super torque at low RPM and then little tendency to cavitate .

    I think that 2 x15 hp 4 stroke outboards would be the best compromise ; but then probably need to redesign the tanks as the ones in the original plans supplied by Wharram ,are to small .
     
  2. RB PowerSailing
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    RB PowerSailing Senior Member

    my datas on Tiki 38 match


    With 2 x 9.9 hp Tohatsu , we reached 6.5 knts as top speed ,and with wind ( don't know wind speed but let's say about 7-8 knts ) speed dropped to 4 knts .

    3 persons aboard .

    Datas seems to match with your expectation . Electric motors should be ok for a Viking Funeral .
     
  3. Alik
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    Alik Senior Member

    Realistic, this means the boat is heavier than 4000kg (actually on Creed's boat volume by DWL corresponds to 4400kg), plus prop efficiency is lower that is likely to happen for standard outboard prop at displacement boat.
     
  4. RB PowerSailing
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    RB PowerSailing Senior Member

    one of our electric boats

    in attachment the Picnic 21' produced by RB in the 2003 and sold in Newport California .

    Electric powered with 3 KW motor , 48 V . 8 batteries x 6 V 225 amp .

    With 2 years of development and production , we thought to understand a little about electric motors .

    They are ideal for this boat , to be used on a lake or river , exactly as in Newport .

    RB repaired also electric motors on large oil tankers , for mayor oil Companies , operating in the Gulf of Siam .

    In my opinion , they are not suitable for the Tiki 38 , unless if the owner wants to play and spend some time with an experiment , and then would be ok .

    Anyway , even on the Picnic 21' , if pushed 'ful throttle' , the max power is lasting only for about 1 hour . Then we had a recovery system that cut automatically the power .
     
  5. RB PowerSailing
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    RB PowerSailing Senior Member

    forgot the attachment , sorry

    ok , the attachment should be here this time . Sorry
     

    Attached Files:

  6. RB PowerSailing
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    RB PowerSailing Senior Member

    again on electric motors

    We should calculate the weight of the wire too ; if a 35 mm section is required , for the 48 V motors , there would be a bit of wire involved , in a Tiki 38 .

    Considering a battery switch at the pod , batteries in 2 compartments ( the stores behind the beam ) and the position of the motors , well , i would say 30-40 mts of cable . 120 kgs ?

    Another interesting point is how to charge so many batteries . Huge , heavy battery charger and the problem of the splitter too to solve .

    Diesel genset and electric motor is a bit different ok . But i think that in this case the weight is even more , considering the extra fuel tank as well .

    Where and how to properly istall a genset into a Tiki 38 ??!! This is a mystery . Let's think a moment hot to do the exhaust ; the boat is a Deep V and hard to find the spac for the genset . Then the weight on only one side ...

    I agree with Warren that the electric motors never fail . But very often is the speed controller to burn or the microswitches of the forward and reverse to blow up .

    Try to see ; after 6 months the customer will be veeery expert ;)
     
  7. Alik
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    Alik Senior Member

    Another challenge could be installation of genset - if it is too high in deep-V hull, there should be problems with water cooling.
     
  8. la rochelle
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    la rochelle New Member

    About 'low cost boatbuidling ' : this is the exactly the market we are leaving ; if you can do better then us , there is a niche in the market :welcome .


    What luxury coracles that will float:D ?? That would be a new beginning indeed:!:
    No osmosis issues as skins are used. Ideal for some quick bucks;)
     
  9. aitch52
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    aitch52 Chris Harrell

    I am with the consensus here that electrical power has a limited future in the leisure marine industry, our present technology, advanced as it is, there is a long way to go.

    Ok, conventional submarines are diesel electric but with huge and heavy battery banks, the electric motors are very efficient and quiet, but need the diesels to charge the batteries and drive the boat at high speed.

    The Cunard Line Queen Mary has electrical motors driving the highly efficient and high tech propulsion pods but again heavy diesels and gas turbines are driving the electrical power generators which power the electric motors.

    The Stirling external combustion engine driving a generator could be the way to go, but as old as the design is, it is still probably in the experimental stage although great strides have been made.

    One of the most efficient forms of power generation could be the micro turbo via a constant speed drive unit reducing the high turbine speed, typically 44K RPM to a speed suitable to driving the generator and subsequently the engine/motor, but the CSDU would be by necessity very heavy and expensive also the micro gas turbine engines aren't exactly cheap.

    I applaud Warren for his innovative and lateral thinking and truly hope it is as successful as he hopes it will be, but having maintained advanced aircraft at sea for many years the achilles heel is usually the high tech electrical/electronic/avionics systems.

    The salt water environment as well as the sea herself demand the highest respect from us mere mortals as Warren has experience of 50 degrees South, he will know. I have spent time within the Arctic circle but on big ships, I used to watch the fishing trawlers in awe from my lofty perch on the flight deck and was comforted by the fact that after a long watch on deck, unlike the fishermen I had hot food and a comfortable warm bunk to climb into.

    To summarise then, I believe that electrical power on leisure craft will be affordable and efficient within my lifetime, but I don't think we are near yet, as ***** said in his earlier post, that if full throttle was selected an hours running time was good going for the Picnic 21 before the cut out activated. Resistance and power losses within the circuits are what it is all about here.

    Regards to all
     
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  10. Alik
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    Alik Senior Member

    For sailing cat, I would recommend to have minimum 4-6HP per 1 ton of displacement.
     
  11. Angélique
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    Angélique aka Angel (only by name)

    No dummies!

    100% agree!

    So this...

    ...can't be said without knowing all the spec's (or even better the results when the boat is ready). So lets not jump into conclusions about Warren's boat. Lets discus the fact's and spec's we know about.

    Angélique.
     
  12. Alik
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    Alik Senior Member

  13. Armchair
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    Armchair New Member

    Hmmm...Unsafe in a headwind? I thought that it was a sail boat that Warren was building? Wonder how mariners got on before motors were invented if it is unsafe to go to sea without one?
     
  14. Alik
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    Alik Senior Member

    For armchair info, even for offshore racing sailboats there are requirements for min speed/running time under power. These are top efficient sailing machines, can not be compared with Tiki with its not excellent windward performance.

    There could be different situations in the sea - loss of mast, man overboard (recommended procedure is to start engine in this situation), passing straits where use of sails is not allowed/not possible, approaching port, parking in marina, help to another boat, etc. etc. - any sailor (not armchair sailor!) knows. So 38' cat without reliable propulsion system is nonsence.
     

  15. aitch52
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    aitch52 Chris Harrell

    Hmm Armchair good handle, first saying in sailing; What if x goes wrong, breaks, tears, jams, picture yourself being blown and swept onto a lee shore, an engine with the power specified for the boat is going to be pretty useful. Before mariners had engines? The Cornish coast and others are littered with wrecks, if the the direction of the wind is where you need to go to avoid a hazard then an iron topsail will get you out of trouble.
     
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