Bulkhead Tabbing at Chines

Discussion in 'Fiberglass and Composite Boat Building' started by weldandglass, Aug 6, 2017.

  1. weldandglass
    Joined: May 2010
    Posts: 23
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Gulf Coast of Texas

    weldandglass Junior Member

    I'm building an 18ft cored skiff in a mold. I've tapered my 1/2" divinycell core so that the laminate transitions to solid laminate at the chines, as shown below. I'm about to start tabbing in bulkheads and have thought about several different ways to deal with the residual space between the bulkhead and the core, shown in the sketch below.

    I was planning on ripping divinycell fillets on the table saw and tabbing over them along the hull planels but this will create a larger void at the chine. If I use a full size bulkhead that lays flush against the hull panel and build an epoxy fillet I can use small divinycell strips to fill in the void and tab over them. Or I could just not tab at the chine and leave the space open.

    I was wondering what other builders were doing. Any input would be appreciated.

    upload_2017-8-6_22-24-44.png
     

    Attached Files:

  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,005
    Likes: 356, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Bulkheads in a small skiff ? where ?
     
  3. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,005
    Likes: 356, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'd say if you trowel in a generous fillet of lightweight filler ( Q-cell should do it) to fill your space, and spanning across from where your inside skins taper from the full sandwich thickness, you won't need much in the way of bulkheads cluttering things, you'd just need to glass across the filler on to the inner skins.
     
  4. Ad Hoc
    Joined: Oct 2008
    Posts: 6,201
    Likes: 415, Points: 83, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    In your image above, you need to extend the "solid laminate" some distance past the joint so it is ovetr the core, at least 100mm.
    Then you should have an angle (triangular shape) foam section to take away the hard spot that sits on top of the solid laminate that must also be on the inboard side. Then laminate as the exterior, some 100mm past this triangular foam section joint.
     
  5. TANSL
    Joined: Sep 2011
    Posts: 5,856
    Likes: 215, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    A bulkhead should be seated on a transverse frame, an omega profile, to better distribute the loads that the bulkhead transmits to the shell. This way, in addition, the problem that you raise would be solved.
     
  6. gonzo
    Joined: Aug 2002
    Posts: 13,769
    Likes: 431, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The bulkhead is the frame.
     
  7. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,005
    Likes: 356, Points: 83, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Whack a nice fillet into the corner, as I mentioned above, and the need for bulkheads and frames is vastly reduced, if not eliminated in a small, lightweight boat
    corner.png
     
  8. jorgepease
    Joined: Feb 2012
    Posts: 1,614
    Likes: 46, Points: 48, Legacy Rep: 75
    Location: Florida

    jorgepease Senior Member

    That is the way I did mine, pic above, but I only infused one side at a time on a jig. In a mold you would probably have to pack that void with glass. I have no bulkheads on my 22' skiff just big fillets and it's entirely flat decked with a low sheer so not a great example.
     
  9. TANSL
    Joined: Sep 2011
    Posts: 5,856
    Likes: 215, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    A bulkhead is not a transverse frame. That is a very common mistake but, however common it may be, it is still a mistake. The way of working of each of these two elements is totally different. The method of calculating a bulkhead has nothing to do with that of a frame, the loads applied on each one of these elements are totally different. A very different thing is that a bulkhead can be used as a transverse resistant element, of course you can.
    Back to the OP's question, as always happens in a structure, there may be several solutions, as long as they are applied correctly. The solution that I propose, in my opinion, is the most correct but perhaps, given the special circumstances of this boat (which I do not know), can not be applied.
     
  10. weldandglass
    Joined: May 2010
    Posts: 23
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Gulf Coast of Texas

    weldandglass Junior Member

    Thank you for the replies everyone.

    The attached graphic shows the best approach, I think.

    Ad Hoc:
    Yes, I've added additional laminate plies at the solid glass area and extended those significantly over the tapered core.

    Thanks.

    upload_2017-8-7_10-51-33.png
     
  11. TANSL
    Joined: Sep 2011
    Posts: 5,856
    Likes: 215, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    It should be noted that this solution serves to reinforce the entire length chine but that does not, in my opinion, serve the case of the bulkhead proposed in your post # 1.
     

    Attached Files:

  12. weldandglass
    Joined: May 2010
    Posts: 23
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Gulf Coast of Texas

    weldandglass Junior Member

    TANSL,
    Right, but the bulkhead could still be added and tabbed to the inboard side of the laminate/triangular foam fillet. It would therefore serve two purposes, reinforcing the chine and removing the residual space at the chine for easier bulkhead tabbing.
     
  13. TANSL
    Joined: Sep 2011
    Posts: 5,856
    Likes: 215, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Reinforcing chine is a different problem. If that was not necessary (there are other means of reinforcing it) or the bulkhead was not watertight, that hole or gap could be left, without having to close it.
    (I have added a sheet of Lloyds SSC Rules, July 2016 to my previous post)
     
  14. weldandglass
    Joined: May 2010
    Posts: 23
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Gulf Coast of Texas

    weldandglass Junior Member

    TANSL,
    Roger that. I appreciate the input.
     

  15. fallguy
    Joined: Dec 2016
    Posts: 2,390
    Likes: 187, Points: 63, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Newb question....

    What is the purpose of using solid laminate at the chines?

    Is it just a requirement of 'special service craft'? Or is it that much stronger? Or is it just to comply with Lloyd's standards?

    It is with good reason I ask as I am building a catamaran with about 9 hard chines, but the specs are different and I am running laminated corecell right to the chines and taping them all.

    Thanks.
     
Loading...
Similar Threads
  1. robwilk37
    Replies:
    9
    Views:
    5,354
  2. gregbe
    Replies:
    6
    Views:
    3,582
  3. Martin Upton
    Replies:
    51
    Views:
    450
  4. Ralph Aloha
    Replies:
    23
    Views:
    497
  5. chowdan
    Replies:
    7
    Views:
    623
  6. rpdwyer
    Replies:
    5
    Views:
    1,818
  7. Skua
    Replies:
    6
    Views:
    1,318
  8. FishStretcher
    Replies:
    2
    Views:
    1,665
  9. hyboats
    Replies:
    6
    Views:
    3,684
  10. groper
    Replies:
    66
    Views:
    13,928
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.