Electric Pocket Cruiser 17'

Discussion in 'Boat Design' started by zacjupiter, Jun 24, 2010.

  1. zacjupiter
    Joined: Jun 2010
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    Location: Australia

    zacjupiter New Member

    I have just finished building a 12 foot classic style (full length shallow keel) sailboat from Scruffie Marine – epoxy and ply

    http://www.scruffie.com/the-boats-in-detail/timber-kit-boats/shimmy-12.html

    I discovered that I like building boats and I am already thinking of my next boat to build. However I would start in 2 years or so.

    I can’t find an existing design that would satisfy the following requirements

    - Displacement electric pocket cruiser about 5.2m long (17 feet)
    - Maximum space and comfort – two berths and some space for porta-potty
    - Reasonably efficient – to get at least 6 hours at 4.5-5knots out of 100kg led batteries (~3kWh)
    - I would use Torqeedo electric outboard
    - Some space for solar panels
    - As light as possible to tow ~700kg on trailer
    - To be good for bay boating and could handle 2m waves
    - Unusually I would like to have a short stayless mast ~4m right at the front and a simple triangular sail (something like spinnaker) that I could use on downwind +/- 60 degrees course. The main requirement is not to complicate life on the boat but to provide an extended range and alternative propulsion system.

    I liked Redwing18 but it does not look like 2m waves boat and it is a bit big.
    http://www.cmdboats.com/rw18.htm

    I am considering my own design. I work as structural engineer , I can use AutoCAD and I owned a few boats. I tried FreeShip the other day and it does not look like impossible task to learn to use. If I decide to design I would spend the next two years designing and building models. Am I nuts?

    I am open to comments and suggestions
     

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    Last edited: Jun 24, 2010
  2. Guest625101138

    Guest625101138 Previous Member

    The set of requirements look achievable.

    Your proposed approach should get you along the learning curve.

    I can help with performance prediction and some of the nuances of Freeship/Defltship. The main thing to remember is that it is a surface modeller not a solid modeller or a line drawing like 2D CAD. Autocad will likely be better for dimensioning.
     
  3. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

    I question the lead acid batteries.

    3kwh of Lead batt. will give you practical charge of 1.5-2 kwh (they really can't take deep discharge well and will go bad very quickly if discharged way below 50%).

    2 kwh for 6 hours is 333W. Less than half a hp.

    Options are way more weight or way more money for lifepo4 batteries. Getting real range out of e-boat is hard.

    I would calculate the total price of the e-system very carefully.
     
  4. zacjupiter
    Joined: Jun 2010
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    Location: Australia

    zacjupiter New Member

    Thank you for your input.
    It is hard to say if one can trust Torqeedo data but they claim that their 1000W motor is equivalent, in propulsion terms, to 3HP petrol engine, so 500W should push the boat at about 4.5 knots.
    The recommended and quite expensive led batteries are Optima deep cycle and they tolerate discharge down to 10% (one would not like to do this too often).
    If one takes six 12V 55Ah batteries = 3.96kWh (120kg weight) and count on 80% of that = 3.17kWh
    I hope that by the time I have that boat ready for water, in approximately 4 years, the technology becomes better and more affordable. I may be able then to use lithium batteries instead.
    I will be buying Torqeedo Base Travel 801 engine and two 12V 55Ah batteries soon for my little 12 feet boat. I hope that it will give me enough experience to determine if the above plan is feasible.
     
  5. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

    the e-motor sales pitch of electric hp being more than gasoline is not very factual. There are some advantages to electric motors but in the end 1000w at the shaft is 1000w at the shaft whether its spun by 4 men, batteries or gasoline engine.

    I think that the trolling motors have such props that at very low speeds they produce more thrust than small gasoline outboard. It doesn't mean that somehow the motor would be more powerful. still hp=hp.

    700kg boat traveling 5 knots at 500-1000w still seems really optimistic but other might be more qualified. Especially if 2 meter (6'5") waves are to be handled we are not talking about glorified kayaks.

    lithium batteries are already becoming more reasonable - in 4 years 3kwh might cost less than 1500 us$.
     

  6. zacjupiter
    Joined: Jun 2010
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    Location: Australia

    zacjupiter New Member

    Thank you for your thoughts.

    There seem to be a very few displacement motorboat designs (pocket cruisers) in particular in 16-18 foot range.

    Any good web sites with such designs?
     
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