HELP! Hull is Sagging! I don't know what to do!

Discussion in 'Boatbuilding' started by CatBuilder, Mar 21, 2011.

  1. cthippo
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    cthippo Senior Member

    Keep in mind the height restrictions here, The truss is great, but it means things need to be lifted a foot further.
     
  2. rwatson
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    rwatson Senior Member

    It looks like he has plenty of room to the roof here, but the lifters may not go high enough.

    If things are tight, lay the truss right on the top of the temporary frames, and run the straps over the top of the truss, and pull them tight instead of hanging them underneath.
     
  3. hoytedow
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    hoytedow Wood Butcher

    The strongback could serve as the lifting bar/truss with the straps tightly wrapped around it and the hull and with the strongback firmly attached to nearest bulkheads to discourage distortion.
     

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  4. viking north
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    viking north VINLAND

    Looking at photos of the cranes and the set up, height restriction could be a problem due to the mechanical lifting distance of the cranes themselves. I feel the lifting problem has been solved, RE keeping the integtrety of the hull but now there is a real possibility of this new problem. Back in the beginning of the thread Catbuilder you enquired on how to cut away the outer frames of the mould in a manner that they could be accurately re installed. This could be one option but before jumping to it are there options RE the cranes themselves.
    (A) They look new so could they be traded back in for bigger units.
    (B) Could their lifting arms be extended to increase their lifting range(add a short piece)
    (C) Once fully raised is there some way to lock the lifting arm in place and re position
    the lifting jacks to the 0 position and resume jacking to increase the lift.
    (D) Hire a boom truck(if space restriction) rent one of those small powered working platform units used in the building trades.
    Hopefully it will not come to this but as with all projects one should not be surprised or discouraged by the Murphys Law Factor, we all experience it. My proceedure has always been, take a break, sit in the shop for a day with a bottle of El Dorado 12 yr. sip and ponder,(forum inputs)(modifying what you have in place)(rental options) the solution will evolve.---- Geo.

    P.S. Having read the entire post I must make a correction here and give credit where credit is due, the lifting beam idea was proposed prev. in the post by several others, and I apologize for having over posted the idea, consider my post as re ringing the bell. Tnx. Geo.
     
  5. rwatson
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    rwatson Senior Member

    Heeey - thats what boatbuilding is all about. Every now and then one gets finished and we have to think what to do with the bloody thing ( someone tells me they float ? )

    But for now, we have years of thinking and drinking ahead of us :p
     
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  6. AndrewK
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    AndrewK Senior Member

    CatBuilder; if you dont want to install permanent B/H's, shelving and landings then if this was my boat I would not be spending time and money making beams etc I would simply cut it into two.
     
  7. rwatson
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    rwatson Senior Member

    ... and then into four, then 8, then call the skip company ? ;)

    Andrew - dont get him to quit now, I have shares on the fibreglass company that he buys his stuff from.

    Seriously, if he cuts it into two lengthways, he still has the sag problem, if he cuts it into two halves - then all the longtitudinal stength of the inner fibre layup is gone.

    I can't see how a bit of scaffolding is more of problem than chopping the hull ???
     
  8. AndrewK
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    AndrewK Senior Member

    Thinking back when I lifted out the inboard half hull I did use 3 lifting points and attached a few 50 x 19mm battens between the B/H's in the cut away section.

    Another option is to make this a full outboard half as these are much more stiffer, then remove, flip and store. Then reverse the mold and make the inboard half that does not need to be taken out. Lower the full half over the one in the mold and join.

    This of course requires the mold to be set up 3 times rather than just twice. But it really does not take that much time the second time round. This option does not require any extra outlay in materials for beam construction etc.
     
  9. cthippo
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    cthippo Senior Member

    Updates, Cat!

    We're all dying to know how this turns out!
     
  10. AndrewK
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    AndrewK Senior Member

    Most home builders are paranoid about cutting and rejoining, race boats are often undergoing drastic modifications. Its not an issue.
    It will only be the inner laminate that will get secondary bonding and only a short section of the inboard half.
    The outer laminate is still to be done later.

    Also compare this to kit boats made from flat panels, the whole boats are put together with many secondary bonds.
     
  11. CatBuilder

    CatBuilder Previous Member

    Wow, this thread has really taken off. Thank you for all the input, guys.

    I was quite stressed yesterday, so sorry about the less than diplomatic response there, Herman. Caught a bit of a fever too, so not operating with a full contingent of sails. :)

    The update is that I have gone ahead and built an "L" shaped strongback or beam the length of the hull. I figure this will come in handy next time I have to move hulls around as well. It cost me $100 and took about 2 hours to build. Not a big deal. I used very large screws and glue... 36" scabs/gussets and it seems like it'll hold the hull up nicely.

    I am getting over this fever and giving myself some rest. I may pull the hull tomorrow if the fever breaks, or wait another day. It will be coming out quite soon.

    Andrew: Welcome back. Thank you for the input to the thread. Of course, you are again correct! :) I could have cut it. It is too late now though. It's ready to be pulled with the new beam.
     
  12. CatBuilder

    CatBuilder Previous Member

    I do plan to cut the mold as well.

    I already bought nuts, bolts and washers. I plan to put outer plywood scabs/gussets/cheeks on the mold and through bolt everything prior to cutting it.

    The problem with my engine hoist cranes is that I'm unable to lift the hull high enough (it is 1 meter, not .5 meters) to clear the mold without the arm making contact with the hull. For an illustration, imagine lifting a garbage can lid straight up with your arm, but with the handle held loosely in your hand so the lid stays level during your lift. At some point while you lift, the edge of the lid will contact your arm if it remains level to the ground. Same thing with my hull.

    I have to reduce my lift height requirement.
     
  13. CatBuilder

    CatBuilder Previous Member

    I do plan to do this, CtHippo. Definitely.

    Will take all the straps off and securely fasten them around that beam I made today.
     
  14. CatBuilder

    CatBuilder Previous Member

    This is answering both Andrew and War Whoop - two guys who have helped tremendously along the way:

    Andrew, the hull is quite clear of the mold. I could lift the sagging middle with one arm - easily. I just didn't want that kind of sag in it while I move it. Too risky... and some of you may remember my cylinder mold hulls fell apart when we moved them, so I have some baggage here. :)

    War Whoop: The plan is still in flux. One thing I could do is take the half hull out, set it up on a flat surface and glass it. This was suggested to me by someone as a way to keep it from getting damaged and to keep my balsa from getting too wet this summer in FL.

    However, I'm worried that if I do this, I may lock in a less than honest shape.

    The usually way to do this is to set this half aside, then make the other half it will be joined to. The other half will be sitting in the mold after it's made. I then bring this first half over and drop it on top of the one sitting in the mold... joining them perfectly.

    This seems like a safer way to go, but do you guys think it's a good idea to leave my hull around with core exposed through Florida's 98% humidity?

    Andrew: My laminate is cured well. It's a rock. It's already 86F here during the days. I am practically achieving post cure each day. ha ha

    I would much rather install the real bulkheads first, but I could not find a logical way to do so. If I installed half bulkheads, I worry they won't line up and how do I join them? Lining up a scarf joint on two half bulkheads that are made on different hull halves at different times? No way that's going to work.

    The other choice is full bulkheads. That would required me to lift the hull up to 1.5x the beam of the boat, plus the height of the mold. It can't be done in my building and certainly not with my engine hoists.

    So... the only logical way I could come up with to proceed was to install temporary half bulkheads on the first two hull halves to come out of the mold - just to support them. Then, i do as follows:

    1) Place real bulkheads in the mold, laying down, in the half hull in the mold.

    2) Grab one of the matching halves I have stored with temporary half bulkheads and place it over the mold/other half.

    3) Grind out my temporary bulkheads and rough up the hulls for real bulkhead installation.

    4) Tape the hull as necessary, lining up bilge and deck joints.

    5) Install real bulkheads, cove, etc...

    6) Remove full hull from mold, which I have cut, so that it opens up and allows me to slide the hull out by only lifting to hull beam plus height of mold, plus 6cm.

    That's the plan.... any input.?



     

  15. War Whoop
    Joined: Jun 2003
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    War Whoop Senior Member

    Cat I would glass the hull "Stacked" together, as you have found out these parts are subject to a lot of movement until the sandwich is completed and that would guarantee it all fits together properly in the end.


    I am real touchy in this stage and go to great lengths to assure accuracy before Laminating (I build from the outside IN)! Deck going on a One Off, Off-Shore"Race" Cat,I was building it on the second floor of a building in Secret.




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