extending the boat deck

Discussion in 'Boat Design' started by expedition, Jun 16, 2009.

  1. expedition
    Joined: Jun 2007
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    Location: Panama

    expedition Thorwald Westmaas

    Hi everybody,

    We have a boat deck that could use a little extra space. Yes, I know, we already have 132 ft. to play - it should be enough right ? - with but still. We want our tenders to be a little longer and 2 extra feet of tip clearance for the heli isn't a bad idea either.

    The image attached shows the current design in the center. Any thoughts?

    Thorwald
     

    Attached Files:

  2. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    The question is where are you going to find a pilot that can land or take-off on that pad... Perhaps pictures don't show the reality of the space. That mast looks real close.

    Seriously, what is more important looks or function. I never like putting tenders up high. It makes for a rocky boat, keep CG low... You know.

    or I would leave tenders in front deck since that is where you have big crane and most stable.

    Or get ride of Crow's Nest up front and put helipad there. You can make Crow's nest with controls, telescope hydraulic very easy so it doesn't have block helipad.
    I guess you have that front crane for submarine. A knuckle crane will also lift sub without taking up vertical space. It will be more expensive and heavy.

    I would have gone with a flat back area an A Frame crane.

    How big a sub are you looking to place on deck?
     
  3. expedition
    Joined: Jun 2007
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    expedition Thorwald Westmaas

    Hi MD,

    Well, I've landed on smaller heli ports like this one and consulted with several pilots. But see my post on helipads at http://www.expeditionyacht.org/helicopter/helipad-issues and you'll see our helipad is huge. We have 2 m. of blade tip clearance. That's more than enough under normal circumstances with an experienced pilot. If circumstances are not normal, we don't fly.

    With the extended deck, we'd have 2.5 m. of clearance. If a pilot cannot land a helicopter with that much space, he should not be flying helicopters to yachts.

    Ahhh, and check out the lower middle picture in this post:

    http://www.expeditionyacht.org/picture-gallery-alumb1extend/helipads-helicopters

    Now, there's some scary stuff!

    The tenders that high is not the most practical place but you have to make some compromises with a conversion. The CG with this boat is not an issue. It's almost too low. We took of a 13ton mast and 22 ton winches from the main deck. A few extra tenders won't be a problem.

    But we can also place the tenders up front when needed and use the big crane. After all, towing a helicopter is not very practical :).

    butting the helipad on the bow doesn't give that much more space and a voyage with the heli on the bow is not a good idea either. Besides, the rear is the most stable platform as the mainengine and prop. damp any up/down movement. And finally I think landing on top of accommodations is not allowed.

    I looked at the knuckle crane too. But boy, they are ugly. And more expensive too. This crane setup actually looks good, has all the capacity we need and is more affordable.

    We planned for the SeaMagine but we now plan to go for a 4-pax VAS (kind of extended 3-person version).

    It will go on the main deck, just in front of the lounge, under a removable deck piece behind the crane.

    Putting an 8-ton sub on the already heavy rear is not great either. And it's a lot higher out there. Even if I would not have the boat deck, it's one deck higher. And less space.

    You know, I've spent some time thinking this over :)

    But please keep trying shooting holes in it !! :).
     
  4. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Not trying shoot holes in it but give you ideas. I have my own conversion, and I understand that you are stuck with many design points. I also use boat design to get second opinion on issues. I like your conversion it is a big boat. I kind of like boats the other way around, bridge in front, deck open in rear, like OSV.
    Anyway you can get a used knuckle crane for about $5000 and then rebuild it, add you own hydraulics. I went away from idea because of weight. My boat is only 72 feet and every pound is more important, same for CG.
     
  5. expedition
    Joined: Jun 2007
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    Location: Panama

    expedition Thorwald Westmaas

    I don't mean this as a negative. Maybe better wording is 'challenge my ideas and decisions'.

    This post shows the knuckle crane option: http://www.expeditionyacht.org/submarine/new-crane-solution .

    I'm a fan of form follows function but this was ugly and expensive. We plan to do this conversion under class rules so rebuilts from scrap yards are not really an option.

    Thorwald
     
    Last edited: Jun 16, 2009

  6. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    I've just finished designing a 53m crew boat boat with a heli-deck and the clearance you have is a dream, we have to design the pad to CAP 437!
     
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