Boxy, simple ~8 m electric powercat

Discussion in 'Multihulls' started by ASM, Apr 16, 2009.

  1. ASM
    Joined: Sep 2005
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    Location: The Netherlands

    ASM Senior Member

    I have been looking into this forum every now and then, but did not yet come across a type of powercat (~8 x 4 m ?) to my likings. Basically, I would like to have a stable platform (for the misses and kids), usable space in hulls (beds/toilet/shower), large recreation space on deck (partly covered), solar panelled roof and electric propulsion. Touring area would be inland, main canals and occasionally (when wheather is fine) coastal for a few kilometers. A simple design which struck me was HOT CHILI (see attached pics), though it needs some streamlining, enlarging spaces and better design above waterline.

    Q1: Would the flat outerhulls sides also work inside out, so the flat parts on the inside ?
    Q2: Would a very simple canoe shape, pointy in both stern and bow (wavepiercing) be a good alternative ?
    Q3: Could a concept equal to be suitable for a displacement cat configuration, so only one electric propulsion unit necessary ?

    As you can see, I am not yet bound to one design, looking for a simple and cheap (Yes I am a Dutchman) design, yet roomy and efficient, knowing that this means simple lines and no fancy curvatures.

    Attached Files:

  2. Guest625101138

    Guest625101138 Previous Member

    I keep refining the tri concept. I am trying to get the package affordable and suitable for a trailer.

    My latest variation is down to 8m. It has to be built light to achieve the design power. I believe it is quite easy to achieve the weight target with carbon fibre composite but not certain with glass composite.

    As shown it has total displacement of 500kg. This is bare boat with motor lithium batteries and one person. It will achieve 7.8kts with 580W on the hull so with inefficiencies something around 800W at the battery or panels. I have not gone through all the losses yet.

    The cabin top will take 4 Sunpower 230W panels. So peak collection on a good day is 920W.

    The hull is capable of 6kts with 250W so around 400W at the batteries.

    There is room in the bow for two bunks. The cabin is quite large with full head height above the central passage.

    The hull panels are all simply developable although I have not checked if the panels could all be pre-formed both sides.

    Rick W

    Attached Files:

  3. ASM
    Joined: Sep 2005
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    ASM Senior Member

    Good to see you have taken the faux-tri further ! I wanted to start, but knowing me, my time and budget and space, the early design would not be easily build. Your evolution up till now looks good, comes close to what I have in mind. The step to a cat would be the larger roof surfce,more stability, and hopefully 2 (very) simple hull forms.

    But the faux tri is also still in my mind (see attached pic).

    Features I really love is a straight fwd bow, and would it be possible to go wider if trailerble is not needed, and thus just enlarging the gap between main driver and the outer hulls ?


    Attached Files:

  4. bad dog
    Joined: Apr 2009
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    Location: Broken Bay, Australia

    bad dog bad dog

    About 20 years ago West System Epoxy ran a design competition, which I entered and won some place or other - to long ago to remember, I've had 3 kids since then, struggle to remember yesterday now.

    But I DO remember the details of the boat, even though it way pre-dated electronic design (thus no soft copy).

    It was designed to be a clean, low energy, low wake vessel for exploring south west Tasmania's wild and pristine rivers. It was a 6m x 2.5m cat - a bit smaller than your idea, but trailable. It had semi-submersible hulls, basically torpedos, with in line motor-shaft-enclosed prop with semi-balanced rudder, and long keel for safe grounding.

    Reserve bouyancy was provided through slender flaring blades connecting lower torpedo hull with elevated deck platform. The hulls were (as I recall) 600 or 700mm Ø, and to float at a depth of 200mm (draft 800-900mm). The diameter needs to be adjusted to account for mass, largely dependent upon battery mass, which has dropped with recent tech advances.

    The deck platform stopped short 750mm of the ends of the hulls, to allow a bit of reserve bouyancy in the longitudal axis. It sits 600 above waterline, allowing a safe crossing of Macquarie Harbour in most conditions (local knowledge may call for this vary too). The connecting blades flare out sharply above waterline to provide immediate extra bouyancy, which would only come into play in rough conditions when the 'no wake' requirement is irrelevant.

    The solar panels are mounted on an open roof frame, and overhung the deck, being the full 6m x 2.5m to get as many of them little zappies into the batteries as possible. Sunshine in Oz is not really something you want to stand around in for too long anyway.

    Having since developed a solar powered trimaran to the International Solar Class Rule, which is the reigning Australian champion (come on guys - build something to take us on! - 7 years without loss gets a bit boring!), and having seen Solar Sailor do so well as a commercial charter boat (, I know what you are proposing is practical, and for the future, essential!

    So - go for it, any advice I can give on electronics (I have learnt a lot from our team guru, Solar Sailor, and the ATA, but may know who to refer you to) or hull form (more my area, given early career in naval architecture, and subsequent years as a slave to multihull mistresses of various kinds) I will be thrilled to give.

    Bad Dog (good cat)
  5. ASM
    Joined: Sep 2005
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    Location: The Netherlands

    ASM Senior Member

    Bad Dog
    Thank you for you reply and the assistance offered ! I am a non naval architect, fond of thinking and designing, work in luxury yacht acoustics, but always wondering why we all do not benefit more from efficiency of hulls and utilizing solar power. Most designs up till now are 'not tempting', to say it friendly , and therefor the mass will never focus on such vessels. Also, since my (and a lot of us) budget is close to 0, time and space limited, skills average, I feel there is a need for an electric powered, multihulled vessel, simple yet attractive, easy and cheap to build. It's like adding all things up, engineering skills like yours and from Rick W, having an average bloke like me with no real skills and knowledge to try and keep things in monkey proof style, it should work.

    As a first step, what would you say to be better to pursuit:

    Catamaran, which could be less complicated, larger deck area but 2 propulsion units or, (faux) trimaran, single propulsion, less space but also less berthing area needed ?
  6. Guest625101138

    Guest625101138 Previous Member

    A cat is a less efficient hull form than a trimaran if you are not severely length constrained. The cat would require something like 40% more power if the same weight and it would be difficult to achieve similar accommodation without it being heavier.

    My personal preference is for a boat to be self-righting rather than having high form stability. Going too wide increases the likelihood it will be stable upside down.

    I think you would find an 2.4m wide faux-tri would have adequate stability. The KMt rapidly increases to 2m once an outrigger is immersed. The KMt for a conventional monohull of 2.4m beam is around 1m. So the tri offers some real benefit in stability.

    Having a boat wider than trailerable width would severely limits its utility from my perspective.

    Rick W
  7. Guest625101138

    Guest625101138 Previous Member

    The attached is the linesplan so you can better appreciate the beam.

    Rick W

    Attached Files:

  8. ASM
    Joined: Sep 2005
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    ASM Senior Member


    Thanks, point taken, that knowledge is beyond my basics. Simply thinking, would a wider aft section AWL to gain deck area result in longer aft outer hulls to cary the additional load/orce/weight Aft ? So no accommodation in the Aft section , purely recreation area like seating/sunbathing, swimplatform.

    OK, so wider then 2.4 would severely limit the utility from your perspective, but would it be possible without increasing the necessary power to propel it ?
    (In the Netherlands, the standard design steel boats have 1:2.8 W/L setting.
  9. Guest625101138

    Guest625101138 Previous Member

    Going a little wider would improve the deck beside the cabin. The narrow deck is a compromise for the solar panel width, taper of the cabin sides and overall width. I would like a little wider.

    When you get very low wave drag the windage becomes a larger proportion of the total drag. Reducing the area of the stern lowers windage but I am only estimating the benefit. The bluff rear portion of the cabin is not the best.

    You could split the main cabin roof between enclosed and open. It is a large cabin for a boat of this length given that there is a separate cabin forward as well. Again I have it all enclosed to help with self-righting. I may yet adjust this so there is some shade above the rear deck. One problem is that I intend to have a flat aft deck over the central hull so I would have to elevate the cabin top to get head room over the aft deck.

    I keep iterating in an effort to reduce the size while still providing good room for two people. The performance possibility from one of the Mars motors I have is quite impressive. It should be capable of 14kts in calm conditions at continuous rated power.

    I have been targeting 8kts cruise as I believe this speed is enough to comfortably coastal hop from port to port on our eastern coastline.

    I think your requirements are somewhat different. If you are prepared to reduce cruising speed then you can add significant weight without having to increase power requirements.

    Without shopping around too much I can get 4kWh of lithium batteries for AUD3500. These would give 3 to 4 hours at 8kts or 9 to 10 at 6kts. The solar panels are AUD2000 each and 4 give the ability to actually charge in good light while doing 8kts. I have the motors and controllers. These set me back AUD1630. I am yet to test the wind turbine using the Mars motor as a generator. It is probably bigger than I need.

    Point of all this is that it is easy enough to provide the space for solar panels but it also costs power to provide that space. Solar panels are expensive.

    Rick W
  10. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Interesting to see you've chosen the Mars motor, Rick. The Mars PMSM is fairly similar in architecture to modern solar car motors (thus very efficient) but higher current / lower voltage. I think they'll be a good match for what you're looking at.

    The hull reminds me of the US Navy's new LCS ships for some reason....

    ASM, I think that Larry Graf's Aspen proa configuration does have some potential for a smaller, slower boat than that company is currently working on. Jerry Stansfield wrote an article in April's PassageMaker magazine about this boat, and his sea trial of the prototype seemed to indicate the design peformed quite well.

    At eight metres, though, I think the hulls would be too narrow to have much useable space inside. You might end up having to put all the accommodations in the bridgedeck, leading to something that might look a bit too much like a Winnebago perched on a pontoon boat. Trimarans do seem to have a bit of an advantage over cats, as far as living space goes, until the boat's big enough to put proper berths in the hulls.
  11. jamez
    Joined: Feb 2007
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    jamez Senior Member

    Jeff Gilbert did publish some studies for a larger version of Hot Chill called Alley Kat. If you do a search on Duckworks you may find them or join his Yahoo group there are pics in the files. He also recently put up an 8.5 powercat based on his Gumboots design.

    NZ designer Tim Clissold has been doing a lot of work recently on electric tri's and cats.
  12. Guest625101138

    Guest625101138 Previous Member

    If you want speed at low power, good ride quality, plenty of room, self-righting ability and easily developable lines it looks like this. Maybe the US Navy has the same objectives.

    Rick w
  13. Alan M.
    Joined: Jan 2006
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    Location: Queensland

    Alan M. Senior Member

  14. ASM
    Joined: Sep 2005
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    Location: The Netherlands

    ASM Senior Member

    Yes I did see the proa style powercat, I mentioned the link myself in the first post. The power needed is however quite big, I do not think this is a displacement Cta, more semi or even planing. The idea is good however, but buying one is a NONO from budget point of view.

    As for TC design, I have been there a few times as well and teh Elotri is actually build here in The Netherlands, looks good, though the speed seems a bit dissapointing, albeit the say cruising speed 8 km/hr = 5 kts, so tops might be higher.

    I do agree with Rick , the (faux) trimaran is the way forward for this size, although TC design has also got one other interesting option, the Bi maran...
    I could see this in a power version too, with the living area in the main hull, 2 small single beds in the outer hull for the kids, once docked and 'connected' to the main hull, ans a very large outside terras in the middle while cruising or achored somewhere remote. The power is still single, so cheaper then cat, solar panel could be fitted on top of outer hull.... even a small sail as a power option for simple fwd sailing when possible (for a non sailor). Mast top could hold windgenerator.... my brain is doing over time again..... and I wanted something simple....

    Back to square one.

  15. Guest625101138

    Guest625101138 Previous Member

    If you lock in on a hull design you could get on the water in a basic configuration. Operate with limited range just off a battery charge.

    You do not need a full set of batteries to do this. Likewise you do not need any solar cells. Just somewhere to charge it up. The solar cells are currently the expensive bit.

    I slowly fitted out the interior of a sailing boat while using it on weekends. You get an idea of how performance drops as you fill it with all the essential junk.

    The thing about the faux-tri is that it will not be slamming into waves like a planing hull. Similarly it does not have to carry large loads from sails that any sailing boat must contend with. The version sketched above requires only 16kgf on the prop to do 8kts. So the loads are very low and conducive to very light construction. Only risk is that it could blow away.

    I was going to buy VRLA batteries first off but I have now decided to jump straight into lithium. I have also been looking around for a small lithium battery for testing on my Mars motor. Something I can get maybe 100A out of for a few seconds on one of my slender hulls. It should be fun.

    My pedal boats were always intended as tests beds for bigger things and I find them useful for this. Maybe something you could get into so you can start experimenting hands on rather than going round in circles and arriving back at square one. You gradually accumulate enough bits and pieces to put things together as required.

    I am making my last pedal boat right now. Total weight target is 15kg. Once out of the way I will move into more serious work on the faux-tri.

    Rick W
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