CNC Plans not Included

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

  1. jorgepease
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    jorgepease Senior Member

    Don't they present a solid wall like my plywood example?
     
  2. groper
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    groper Senior Member

    No, and neither does any other battery. The fuses are in the supply circuit, not between cells which are series- a short in a cell merely renders that cell useless and the total battery voltage will reduce by the cell voltage and otherwise keep working as per normal.

    Lifepo4 batteries are very safe. If youve heard scary stories about lithium- its almost always the lithium polymer type which are a completely different ballgame to this type.
     
  3. UpOnStands
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    UpOnStands Senior Member

    For Jorge
    They would if they were completely separated from the deck.
    The wind hits the hull side and spills over the coming. Since the coming in the current design is a hard sharp corner, the wind is forced to stream upward away from the deck. Given enough space to the windows, the wind may end up hitting the middle of the windows.
    If you had very rounded coming like Tek-50 and the window bottoms were real close to comings and the frame holding the window was strongly curved at the top, then window angle could make a difference.
     
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  4. jorgepease
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    jorgepease Senior Member

    Okay I see what you mean. Yeah Im not going that rounded route. Working on a flat roof, not inclined, with the lowered areas. Not sure if it's worth it but it does look a little less up in the air and I spaced the solar panels better. Another thing I might be able to do is drop bridgedeck 6 inches to 48" clearance. That is still more than most boats.

    For sure it's much better visibility but I will prob still put an inside helm with hyd.
    RNDR140.jpg
    RNDR141.jpg RNDR140.jpg
     
  5. jorgepease
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    jorgepease Senior Member

    Decided to get rid of all the space between bridgedeck upper and lower. Added some stiffeners along bottom and was able to drop the roof substantially. It's almost to the point that a person can see the tip of the bows, if I put a step up to the helm, it's a done deal.

    Also canned the sloped windbreak because UOS explanation makes sense, wind is tumbling up to right about the point over that slope. By making it straight I can take my bulkheads all the way up and cap them with a tie beam which the roof will sit on. That would be very strong and I eliminate the extra work of building mullions!

    It's already looking like a racer!! lol! ... except for the semi-flybridge :)
     
  6. jorgepease
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    jorgepease Senior Member

    don't know why photo didn't go through here it is

    RNDR150.jpg
     
  7. UpOnStands
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    UpOnStands Senior Member

    slammed and looking evil. :cool:
    How high above water are your winch bases?
     
  8. groper
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    groper Senior Member

    Next battery has arrived, another off grid lithium battery power system for a home in the rainforest next week :)

    20170714_145319.jpg
     
  9. jorgepease
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    jorgepease Senior Member

    What is the capacity, how much does it weigh? It doesn't look too big.

    UOS - 11 feet to base of winches, that is highest part of roof and 49 inches of BD clearance. I dropped the deck a total of 10 inches. Headroom under roof is 6.5 feet in the raised areas. I have another roof variation which is more extreme on the other computer which would drop it further, it's shown in a couple of posts above. That would drop it some more
     
  10. rob denney
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    rob denney Senior Member

    Sounds complicated to me. The worst case scenario is one rig lifting a hull. Does not make much difference to the mast strength if it is 60 knots and deep reefed or 25 knots and full sail. Each mast should be strong enough to tip the boat over as this is the max load it will see. We are often asked for masts that will break before this happens, but there are too many variables to guarantee this, so we don't. There are a lot of cats these days which will not capsize under likely conditions. For these, the mast size becomes colossal and your suggestion is the way to go.

    Stiffness is a different issue and this is another area that unstayed masts for cruisers are far superior. In an unexpected gust the mast bends and the sail depowers automatically. It is like having the first reef in or out depending on the wind strength. It results in higher performance than putting in a reef early and leaving it in too long, which is (rightly) cruising boat practice.
     
  11. jorgepease
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    jorgepease Senior Member

    Amen to that and peace of mind!!

    Ok do you want to see something ridiculous? The extreme roof can be extremely low!! Skip is probably saying, that's not low enough!!!! :)

    In this case you still have 6'6 headroom in walking areas but in sitting areas you only have like 3 feet above your head and not much window. Maybe this could be my sport version )) ... but I think the sweet spot is in between!

    RNDR151.jpg
     
  12. gonzo
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    gonzo Senior Member

    I work in battery research, my question is not about scary stories I heard. It is hard to tell by looking at the photo, but you are saying that there are no cells in parallel. In that case, the maximum current of the system is the maximum current of a single cell. Overheating can cause a runaway condition and out-gassing, which is what power management is supposed to prevent.
     
  13. Jim Caldwell
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    Jim Caldwell Senior Member

    That is the shipping container, they have not been configured yet.
    What area of battery research do you work in?
     
  14. groper
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    groper Senior Member

    Well if that were the case- you would also know about the very low internal resistance of lifepo4 cells? I have charged the entire pack at 150amp for a full charge in 1 hour and the cells are not even warm to the touch.... ie it is a non issue with lithium iron phosphate - even @ 2c or 300amp it would not be a problem. Lead acid cells would not fare so well...

    There is a BMS which takes care of cell balancing via current shunts at top of charge. There is also a NO and NC relay in the BMS which open circuits the coil of a large contactor inline on the main supply cable which isolates the battery when opened to protect it from over and under voltage situations. There is no need for any further complication... thre is over current protection in the form of fuses, and voltage protection in the form of voltage sensed contactor actuation. Perhaps that answers your question?

    edit - almost forgot - the inverter also has a thermistor which is embedded in the battery pack via a fly lead to monitor battery temperature - if it rises above set limits, the inverter shuts down and stops charging/discharging... it has never gotten remotely warm however so I forgot all about it. For a propulsion system on a boat however, I'm sure we could heat up the pack a little where you might want to begin current limitation. Again this is programmable in the inverter parameters which controls the load and ultimately the max current so there is temperature protection there also...
     
    Last edited: Jul 14, 2017

  15. groper
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    groper Senior Member

    This one is quite small for a small cabin type house in the rainforest with very modest energy requirements. It will be 51 volts @ 100amp hours (5.1kwh) and weighs 54kgs.
     
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