Carbon fiber davit design.

Discussion in 'Multihulls' started by svquintana, Jun 28, 2016.

  1. svquintana
    Joined: Mar 2012
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    svquintana Junior Member

    Thanks for those numbers. Lots of force there...

    I'm not sure what you mean about "slinging the dingy vertical along it's width". If I take your meaning correctly, the dinghy will empty itself of all it's contents.

    It is common practice to leave the drain plug out of the dinghy while it's on the davits. This usually works fine, unless something else, like a baggy, plugs the hole.

    We cruised full-time from 1995 to 2009, when we started the cat build, so consider ourselves to have ample experience in this regard.

    Your suggestion is not without merit; but it might be difficult to raise the dinghy in such a manner, as the attachment points would be on the inflatable parts of the dinghy, which are it's weakest areas. If not, there would have to be other attachment points to "tip" the dinghy on it's side, while it's weight is supported by the main hull. There are "payload" considerations, and outboard motor considerations as well. Dinghies are like the family car, and are not emptied every evening.

    Thanks again for your thoughts, and calculations.

    Paul.
     
  2. UpOnStands
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    UpOnStands Senior Member

    [​IMG]

    not really user friendly, of course
    original description should have said "across its width"
     
  3. svquintana
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    svquintana Junior Member

    Yes, and that wouldn't be very convenient to do every night. That dinghy is not a RIB, it's a fair bit lighter and easier to manhandle than a RIB.

    If I could do that, I wouldn't need davits. ;)
    Cheers.
    Paul.
     
  4. UpOnStands
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    UpOnStands Senior Member

    leave no baggies in the dingy then :D
    would love to see design - build log
    look forward to the davit installation.
     
  5. svquintana
    Joined: Mar 2012
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    svquintana Junior Member

    The original Design was a Kurt Hughes 45.

    With the designer's help, we:
    1) Stretched the hulls 10%, by changing the form spacing on the mould.
    2) Deleted the forward berths on the bridgedeck, thereby shortening the bridgedeck by 1.5m
    3) Built a carbon fibre forebeam, and eliminated the need for the "A" frame and wires to counter the forestay loads.
    4) Installed a forward working cockpit (1.2mx1.5m)
    5) Moved the Bridgedeck roof aft 1.2m
    6) Moved the engines forward 2.5m, to help centre the weight in the boat.
    7) Changed the rudders to external kick-up carbon fiber rudders, and surrounded them with the hull and back step.
    8) Increased the size of the Bridgedeck windows by nearly 20%
    9) Increased the size of the aft cockpit by 15%
    10) Lengthened the roof to cover part of the aft cockpit.

    There are no build logs to share, and the boat looks nothing like the original KH45 from which it is based. It does, however, share many design elements of Kurt's "Outsider 48"

    [​IMG]

    and of his new 49' "performance cruiser"

    [​IMG]

    Cheers.
    Paul.
     
  6. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Nice design but, how is the davit and how it is attached to the hull ?. What is the configuration that you want to calculate ?. Will you attache it to the deck or ...?. How is the deck/beam/transom at this area?
     
  7. svquintana
    Joined: Mar 2012
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    svquintana Junior Member

    The davit installation is covered in Post #9

    It is not yet finalized, but I'm pretty sure it'll be very close to what's described there.

    Cheers.
    Paul.
     
  8. TANSL
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    TANSL Senior Member

    Okay, all you can explain is in post # 9. I am unable to discover there the necessary details and you are unable to attach a picture of your davit so, regretfully, for my part only wish you good luck. I am not able to do anything else.
     
  9. svquintana
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    svquintana Junior Member

    That's ok, thanks for your consideration. My original reason for starting this thread was to understand which parts of a beam carry the load; vertical or horizontal. And, perhaps, with luck, discover if my intended layup was thick enough to carry the load.


    Cheers.
    Paul.
     
  10. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Perhaps the following scheme, very simplistic, help you see the most critical areas of a traditional davit.
     

    Attached Files:

  11. svquintana
    Joined: Mar 2012
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    svquintana Junior Member

    Thanks for that, but I'd need more formal training than I have, to fully understand that sequence of photos.

    I drew the davits on a plan sheet, Ignore what looks like a large 45 degree gusset at the bottom of the davits. Although I plan on putting gussets on the aft bulkhead, it wouldn't be nearly as large as what's shown. That line actually represents a part of the original cockpit coaming, which is far outboard of the area where the Davits will be located.

    Cheers.
    Paul.
     

    Attached Files:

  12. Moewaka
    Joined: Jun 2016
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    Moewaka Junior Member

    Hi Paul, this sounds like an interesting project and is similar to what I'm trying to do. I'm also looking at modifying a current design to better suit my needs with changes to the layout and the addition of a forward cockpit as you mention below. I'd be interested in photos or info on what you've done with the turret shape and protection for the forward cockpit.
    Cheers
    John

     
  13. svquintana
    Joined: Mar 2012
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    svquintana Junior Member

    Hello Moewaka, thanks for your response.

    I'm not sure what you mean by "what you've done with the turret shape". What Turret? Do you mean the pilot house on top of the bridgedeck? If so, we just moved the whole thing back 1.2m, so the forward cockpit has not "roof".

    The front cockpit doesn't have any protection, as yet, but we do plan on building a bimini which will fold back to the window frames on either side of the cockpit. This will help protect from rain or sun, but do little for wind and waves coming from forward. The cockpit is only intended to be used for sail handling, and does not have seating.

    Whose design are you building? Some of the Oram's have forward cockpits.

    Cheers.
    Paul.
     
  14. Moewaka
    Joined: Jun 2016
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    Moewaka Junior Member

    Hi Paul, yes the turret is the roof. Im not building yet but have been playing around with the Waller 1480. I've had advice from the designer and so Im trying to do what I want within existing bulkhead positions etc. This is what I have so far. I should note that Im not making any changes below the waterline.
    http://www.boatdesign.net/forums/attachment.php?attachmentid=108692&stc=1&d=1468160744

    http://www.boatdesign.net/forums/attachment.php?attachmentid=108693&stc=1&d=1468161048

    The red line is the turret shape which has wings that taper down to the bridgedeck forward, so cant simply be moved back. Also one of the big areas of concern for the designer was keeping enough weight in the front half of the boat to keep it balanced as he intended.
    The galley to starboard and the stateroom to port are only one step down from the bridgedeck keeping all the living space for one couple pretty much on the same level.
    The wings that extend past the front cockpit will offer some protection from rough weather but I quite like the 'windscreen' in you 2nd photo so I'll have a look to see if I can adopt it in front of the mast without getting in the way the jib sheets etc.

    I'd be interested to see photos of you build.

    Cheers
    John
     

    Attached Files:


  15. svquintana
    Joined: Mar 2012
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    svquintana Junior Member

    Yes, balance is always an issue. We moved the engines foward to help compensate for changes further forward.

    Our build is done within a purpose built garage, which, unfortunately, is only 600mm wider than the boat, and 1000mm longer than the bridgedeck. This means that we cannot get good photos of the boat from any angle. Even the joists of the garage are only 150mm above the roof of the the boat. It's very tight.

    Your design of choice looks like a treat, I hope you decide to build.

    Stay well.
    Paul.
     
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