Hull steel - superstructure fiberglass

Discussion in 'Fiberglass and Composite Boat Building' started by Renato Dias, Aug 21, 2013.

  1. Renato Dias
    Joined: Aug 2013
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: South Africa

    Renato Dias New Member

    Dear fellows,

    I am working in a project where it will be required the installation of a fiberglass deck and superstructure on a steel hull.

    For the connection between these two different materials I am considering to fit a (horizontal) flat bar all around the bulwark where it can be laid the fiberglass panels on and then a bolted joint will complete the connection.

    Although using a flexible gasket in between the fiberglass and steel to reduce the effects of the different expansion properties of these materials I am still fearing that the fiberglass panels can crack around the bolts.

    Could you guys give me some feedback about this idea please?
     

    Attached Files:

  2. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    A rubber gasket would only work if the mating surfaces were perfectly true...one hundred percent surface contact along the entire joint..

    Mechanical fasteners need to be made one hundred percent waterproof for the life of the vessel or corrosion will form under the sheer clamp.

    I would investigate an adhisive bond.

    You may be able to fabricate the steel part of the sheer clamp out of Stainless steel to eliminate corrosion problems if you decide mechanical fasteners are needed.

    I find fastenerers tapped into steel are easier to keep watertight than fasteners bored thru with a nut and washer
     
  3. Renato Dias
    Joined: Aug 2013
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: South Africa

    Renato Dias New Member

    Thank you Michael Pierzga for your opinion.

    In fact the watertightness of the connection is also a issue I will have to sort out. But I reckon if the gap between the bolt and the fiberglass panel is filled up with Sika or another silicone of this kind and by using a proper washer it will be prevented the infiltration of water through the connection.

    My main concern rests on the mechanical side of the problem: will the hotspots around the bolts be enough to crack the fiberglass panel?

    The adhesives will for sure eliminate this problem. Thanks for the tip.
     
  4. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Stress concentration at the fasteners. I dont know.

    Whenever you have a long line of fasteners on a flexible structure like a boat some will be loaded, some will be slack.

    The only fiberglass to metal joints that I come across are superstructure components on metal yachts. These were bonded with a Sika type product.

    Ive never seen a sheer clamp , metal to fiberglass, joint

    Perhaps others have more info
     
  5. jonr
    Joined: Sep 2008
    Posts: 721
    Likes: 11, Points: 0, Legacy Rep: 57
    Location: Great Lakes

    jonr Senior Member

    I would look at the coefficients of linear thermal expansion for both and calculate how much differential movement (or stress) you need to accommodate. You could have a .25" difference that might very well cause cracks.

    I would guess that a steel bar on top of the fiberglass would better distribute the force. Ie, steel bar, fiberglass, steel instead of just washers.

    If a rubber gasket is compressed, it provides a good seal, even on imperfect surfaces. Thin lines of glue or caulk can't move very far before they break.
     

  6. brian eiland
    Joined: Jun 2002
    Posts: 4,882
    Likes: 168, Points: 73, Legacy Rep: 1903
    Location: St Augustine Fl, Thailand

    brian eiland Senior Member

Loading...
Similar Threads
  1. Tygafan
    Replies:
    5
    Views:
    2,156
  2. cy fishburn
    Replies:
    5
    Views:
    125
  3. Gianf1041
    Replies:
    0
    Views:
    308
  4. E350
    Replies:
    17
    Views:
    633
  5. fallguy
    Replies:
    14
    Views:
    547
  6. SeaWeavers
    Replies:
    4
    Views:
    360
  7. Mattskii89
    Replies:
    23
    Views:
    1,160
  8. fleix
    Replies:
    13
    Views:
    1,158
  9. E350
    Replies:
    38
    Views:
    1,739
  10. Joey2682
    Replies:
    0
    Views:
    365
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.