CNC Plans not Included

Discussion in 'Multihulls' started by jorgepease, Sep 19, 2016.

  1. gonzo
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    gonzo Senior Member


    What kind of power management do you have to prevent runaway/explosions? It is difficult to tell by the photo.
     
  2. groper
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    groper Senior Member

    The system was not finished at the time of the photo. Not shown is s pair of 200amp HRC fuses on the battery cables. The inverter feeds the switchboard on the left, and MCB RCD combos protect all final sub circuits from there.
     
  3. rob denney
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    rob denney Senior Member

    I am not suggesting a proa. Merely pointing out that a biplane rig costs more, weighs more and takes up more space than a single mast in one hull with the same sail area. Actually, it can have a fair bit less area if the top part is only for light air as there is a lot more wind up high in light winds.
    And to look at problems from the end use angle rather than from replacing what is already there.

    UOS,
    Why not use capsize/hull lifting as the criterioa for mast strength? What are the alternatives?

    Groper,
    The Schionning biplane rig apparently cost $AUS70,000 all up (sails, strings, freight, painting, fittings, etc), all pro built. He chopped 14' off each mast. Not far off the same final sail area as ditching one of the rigs. So, maybe $35-40,000. If he had built the mast himself (he could have, his workmanship is excellent and it is a pretty easy exercise), it would have been a small fraction of the cost.

    When you work out the vision from the helm, include the headsail. The majority of boats that are going to hit you will come from your lee bow. Almost no boats have visibilty on this sector with the headsail up.
     
  4. jorgepease
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    jorgepease Senior Member

    One mast in one hull sounds interesting but I can build the masts so if it costs me 40K and I don't have to add all that rigging I am a happy camper.

    On the runaway explosions, Tesla uses a Goo which surrounds each battery. If one goes south the goo prevents a chain reaction. So far it's never been needed but as volumes increase ...

    I think I might add the troughs to the flat roof for strength and aesthetics but keep the helm down in front where I had it originally. From there you see all four corners of the boat, are protected and don't have to peer under sails. The angle is not great for seeing submerged objects but I have taken every possible other precaution by not having appendages in the water.

    I will leave the dingy/platform socializing area (scaled down a bit) it's mostly behind the beam anyway so shouldn't cause much extra drag. Speaking of drag, how much drag are we actually talking about. I know there is form drag and induced, from a form perspective I am pretty good, from an induced I have that huge flat surface but how much drag does that actually equal at these low speeds.
     
  5. groper
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    groper Senior Member

    The air drag you will end up with is propotional to the cross sectional area of the boat at an angle of approx 30 degress off the bow ie the apparent wind angle.

    Other wind angles are less important, almost irrlevant when sailing off the wind so its really only an upwind problem worth discussing. You may not understand it fully but the air drag when going upwind has a significant effect on the boats VMG upwind. This is why so many condomarans have to motor sail to make any decent VMG upwind- its not the weight of the boat- as a heavy mono will still go upwind just fine - its the windage and leeway which kills your performance. That and having a good rig which achives good amount of lift (power) with a minimum amount of induced drag (drag due to lift). Achieving all of these goals is going to be difficult with such a huge solar array... this is why not many boats have been built like this with 100% reliance on electric propulsion- its a very tall order. Last thing you want is a half million dollar white elephant which sucks the last 5 of your best years from you and leaves you wishing for something else...
     
  6. UpOnStands
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    UpOnStands Senior Member

    for Rob. tough question. biplane rig with rotating masts. How about mast should withstand max operating wind loading with safety factor of 4.
    Strictly a question of sail area, sail area distribution (square top pin top) and max operating wind loading (design speed of the boat plus wind speed that yields that speed). This means that if boat is designed to achieve max speed of 14 knots at wind speed of 25 knots then 35 knots is the max operating wind speed. This "wind" is treated as normal to the sail.
    I'd be happy with the biplane rig knowing that the masts will bend off and spill wind and the sails will weathercock if the main sheets are fused.
     
  7. jorgepease
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    jorgepease Senior Member

    If you hold a sheet of plywood up flat to a stiff breeze it will blow you over, if you angle it horizontal or parallel to the flow of wind ... the wind the force is gone. I have hauled a lot of sheets of plywood to know this lol ... So I don't see why a horizontal roof is going to cause that much windage? And the drag from a low aspect ratio roof at such low speeds?? How much drag can that be?
     
  8. UpOnStands
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    UpOnStands Senior Member

    Trouble is the roof is not adequately isolated/separated from the hull. You may see a lot space under the roof but the wind sees more of long tunnel and like the surface wave interference effects you get between the hulls, the wind gets stuffed up and so it basically sees a solid object in its path
    at 10 knots, 30 degree wind direction, the drag loads are not less than 186 lbf (I have assumed roof top is 14 feet above water surface, if more scale the load up). At 15 knots the load is 418 lbf. Wind speed is squared in calculating loads.
    this wind speed is apparent so boat speed is a factor.
     
  9. groper
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    groper Senior Member

    Its the CSarea of not just the roof, but the cross section of everything beneath it too! The breeze wont just flow through the cabin like it wasn't there, theres turbulence and eddies and the wind changes direction with changes im pressure as it flows around things... it ends up all over the place, you cant just think in 2D man!
     
  10. jorgepease
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    jorgepease Senior Member

    I will have to chew on that a bit but if that is the case then having a roof without sides is counter productive. The wind is going to create more drag than the extra weight, I might as well glass the whole darn thing in.
     
  11. UpOnStands
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    UpOnStands Senior Member

  12. groper
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    groper Senior Member

    A boat is like the mountain in this pic;
    [​IMG]

    The roof presents an area to the wind not just in the horizontal plane- there is a vertical component to it. In reality there are many more conponents to it.

    At the end of the day, the more of anything you have means more drag. You have to decide whats important and what the compromises will be - and there will be many... this is why designer's have degrees- theres alot in this stuff and what your trying to do requires more skill and calculation than most other boats. It requires collaboration of skills in electrical design, yacht design and energy calculation. If you dont have all these things properly designed, theres a high probability that this wont fly as well as you think it will. Many have tried, none have succeeded to a level that can compete with fossil fuel propulsion in a complete package that will perform as an equal on all fronts such as speed, upwind abilty, endurance/range, cost, etc etc
     
  13. jorgepease
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    jorgepease Senior Member

    Ok but it has to get done so it seems this problem occurs mostly when sailing into the wind. If that is the case then my roll down windows should be long enough to extend forward at a good angle so as to present a nice leading edge into the wind.
     
  14. UpOnStands
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    UpOnStands Senior Member

    umm, if your windows are well inboard of the comings their angle is not so critical.
     

  15. gonzo
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    gonzo Senior Member

    If one cell shorts out, how do you prevent it from discharging the other cells at a high C rate and possibly making them explode or ignite? Is there some kind of power management or fuses between cells?
     
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