New Cabin Top- Steel or wood?

Discussion in 'Boat Design' started by JohnP, Mar 20, 2019.

  1. JohnP
    Joined: Oct 2017
    Posts: 4
    Likes: 1, Points: 3
    Location: Beaufort, NC

    JohnP New Member

    Hi All- I am working on a small steel Colvin designed trawler. The existing forward cabin top is plywood, and needs to be replaced. It is 3/4 with polyester and glass. The cabin sides are steel. I am trying to decide whether to replace with plywood again- would probably do 2 layers of 1/4, with glass which should provide plenty of strength, especially arched. Or... skip the wood and do steel sheet to avoid the wood to steel issues. If I did that, I would probably go 1/8 or 3/16 with bracing underneath as needed.

    Thoughts or guidance?

    Thanks-

    JP
     

    Attached Files:

  2. Barry
    Joined: Mar 2002
    Posts: 1,081
    Likes: 61, Points: 48, Legacy Rep: 158

    Barry Senior Member

    1/8 inch steel sheet weighs about 5.1 pounds per square foot, compared to the 3/4 inch ply with fibreglass that you are considering which would weigh about 2.5 lbs per foot. (an estimate only due to the fact that the fibreglass laminate weight is not known.

    3/16 inch plate would be weigh (sic) too heavy for your application. With the 1/8 inch, you would need minimal bracing if you get a camber rolled into it as the spans are minimal. If you went to say a 12 gauge sheet, .105 inches thick, you would need more bracing which would add more weight.

    For the ease of attaching the roof to the sides of the cabin with steel, welding, and the
    additional strength and the fact that you would not need a bolted joint, steel would be the way to go
     
  3. JamesG123
    Joined: Mar 2015
    Posts: 650
    Likes: 73, Points: 28, Legacy Rep: 10
    Location: Columbus, GA

    JamesG123 Senior Member

    Also need to worry about insulating the underside of a metal roof.
     
  4. JohnP
    Joined: Oct 2017
    Posts: 4
    Likes: 1, Points: 3
    Location: Beaufort, NC

    JohnP New Member

    Thanks- the cabin currently has an overhang, which is nice looking, but is also one more maintenance item. I am thinking with steel I would just go flush to the cabin or do an overhang with some round stock welded to the edge for looks/safety. Am I overthinking this?
     
  5. JamesG123
    Joined: Mar 2015
    Posts: 650
    Likes: 73, Points: 28, Legacy Rep: 10
    Location: Columbus, GA

    JamesG123 Senior Member

    Your boat is the way it is because of literal centuries of experience building and using boats.
     
  6. JohnP
    Joined: Oct 2017
    Posts: 4
    Likes: 1, Points: 3
    Location: Beaufort, NC

    JohnP New Member

    Not sure what you mean- are you saying I should go wood? Or are you saying I should keep the overhang either way?
     
  7. Barry
    Joined: Mar 2002
    Posts: 1,081
    Likes: 61, Points: 48, Legacy Rep: 158

    Barry Senior Member

    the overhang with round stock would look nice or even a flat bar style ridge to channel the water from rain to where ever you want it to go.
     

  8. JSL
    Joined: Nov 2012
    Posts: 709
    Likes: 35, Points: 28, Legacy Rep: 41
    Location: Delta BC

    JSL Senior Member

    stay with what you had- it was probably plywood for a good reason. Steel (sheet, stiffening, beams, etc) will likely weigh more and 1/8" can be prone to weld distortion and need fairing (more weight) compound.
     
Loading...
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.