Wooden Boat Building... Steel Deck to a Wooden boat

Discussion in 'Boat Design' started by Nirman, Sep 20, 2011.

  1. Nirman
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    Nirman Naval Architect

    Can anyone please advise me the method of connecting a Steel Deck to a Wooden boat.. Length of the boat is around 50m.
    My worry is when the vessel is in water, behavior of wood and steel is completely different and the steel deck may not be possible to withstand contractions and expansions which wood will undergo.:confused:

    Your valuable comments are expected with thanks in advance.:idea:
     
  2. Landlubber
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    Landlubber Senior Member

    Hi mate,

    It is a bit difficult to answer your question without more details, such as is it ocean going or a river boat, but either way, the steel deck is fastened to the wooden hull by mechanical fasteners, bolted in fact, to the carline beams or the top shelf if there is no deck. Many old ships were constructed this way in days long gone, but commercial vessels are still made this way if for river barges etc etc.

    Being in the UAE I assume it is for local conditions as a working barge, either dumb or powered does not matter much. As long as your hull is sound it will work.

    No, there is really no big deal regarding expansion and contraction of the different materials as they are moving as one body anyhow, the steel deck beams if epoxy coated after extensive sandblasting to SA1 1/2 (white metal blasted) are going to be there for a long time to come with minimal maintenance, as long as they are done right in the first place....like everything, do it right at the start and the results will be more than fulfilled in the future.
     
  3. Nirman
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    Nirman Naval Architect

    Hi,
    Thanks for the quick reply. If I go in to detail this is a old dhow boat which is using for pleasure, it may go in to deep sea but it will not cross sea. They want to have steel frames fixed on the transverse direction and fill the spacing between frames with wood. Transverse Steel Frames needs to take the load due to vessel panting. My worry is the connection between steel and wood. Will it crack? Or else is there any other material which we can use between the connection to absorb the effect.. (May be hard rubber)
    Please comment.
    Thanks again.
     
  4. Ilan Voyager
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    Ilan Voyager Senior Member

    What is the interest of a steel (rather heavy) deck on a wooden boat? A good plywood epoxy deck will be more rigid and lighter. Also it won't need all the insulation work coming on a steel deck, and that's also heavy and costly.

    Really I do not see the interest. It's adding engineering complications. Generally it pays to do not mix materials...
     
  5. Nirman
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    Nirman Naval Architect

    Hi Ilan,
    Yeah I agree with your point. Main issue is the owner thought to do like that and they already started the work.
     
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    It would be more interesting to use in this case aluminum 6061 T5 or T6 rather than steel. Easier to work, no corrosion. No costly painting. It's better to insulate the metal from the wood with a rubbery/gluing polyurethane compound like a 3M520 or sikaflex 241. That cuts off a lot of corrosion problems.(and also noise...)
    If using aluminum do not use bronze screws; 316 SS works very well with the usual precautions

    Wood building over metal frames is known since more than 150 years. Aluminum frames and wood planking was used on fast boats.

    The connection between the metal beams and the wooden sheer is at the same time simple and complicated. Simple because it's an easy calculation to get the number of bolts, screws, etc for connecting, but it's complicated to ensure a good repartition of the connecting bolts. The simplest system is to connect the metal beam to the ribs with plates, so the main stresses are taken by the ribs. All that can be done bolted with no need of welding. Another way to relieve the stresses is to make a monolithic plywood deck (at least 2 plyes) well screwed on the sheer, so the function of the beams is to "rigidify" the plywood deck. The plywood deck acts also as connection between the beams and the hull.
     
  7. Nirman
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    Nirman Naval Architect

    Hi Ilan,
    Your suggestions are valuable. Al may be a good solution. Is Sika241 is stronger after curing may be like hard rubber and what may be the advisable thickness?
    Please suggest.
     
  8. michael pierzga
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    michael pierzga Senior Member

    The interface between the steel and wood will be problematic from a corrosion perspective. . On a metal boat the frames and sheer clamp are easy to sandblast and barrier coat before the wood deck is laid. With a steel deck, the structure will be large and difficult to handle as a component. How will you apply the protective barrier coat on the underside of the deck in the area of frames and sheer clamp ? Also consider the fastener details. It will be challenging to waterproof and isolated these fasteners. It would seem logical to fabricate a separate steel to wooden sheer clamp and separate steel to wood frame component then fasten or weld the deck plating to these components.
     
  9. Nirman
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    Nirman Naval Architect

    Thanks a lot for suggestions.
     
  10. Petros
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    Petros Senior Member

    I think your worry about the steel to wood connection is perhaps a bit unnecessary. As an engineer I design these kind of connections all the time, a few precaustions are all that is necessary.

    Consider first however that the more rigid steel frames will dictate the shape of the hull, the wood will flex and expand/contract around the more stable length of the steel. As long as the hull will tolerate that condition (with a hull this large I suspect there will be no issues), the only other concern is keeping trapped moisture out of the connection, as with any connection. Use of flexible sealant aheasives on all surfaces and install the fasteners "wet" with sealant should work well. Use large area washers where the bolt heads bear on the wood (also with sealant).

    It is far more common to build boat hulls from similar materials, but in most other types of construction very different materials have always been combined for many centruies without issues if done with care. There is no reason to think this will not work out just fine.

    What is the reason to deviate from the original design of wood deck beams? Steel is not the most desirable material to use, but it has its benefits.
     
  11. Poida
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    Poida Senior Member

    Although a previous post mentioned wood and steel have been used around 150 years wharfs, jetties, roof trusses the list is probably endless.

    I don't understand the reason being, it's because you want to paint the boat.
     
  12. BATAAN
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    BATAAN Senior Member

    CUTTY SARK is wood on steel I believe, and many other sailing ships were steel frame and wood plank. A complete steel deck is something else again. Needs to be thoroughly bolted both beams and skin to plank sheer and clamps. I suppose it's being built in place due to size. Weird way to do things. Steel beams and ply/plank deck over would be better.
     
  13. gonzo
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    gonzo Senior Member

    It is a really straightforward thing to do. However, the method depends on the structure it will be attached to. The poster claims to be a Naval Architect, but is not giving enough specifics for an answer.
     
  14. Nirman
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    Nirman Naval Architect

    Dear Mr. Petros, Mr. Poida and Mr. Bataan,
    Thanks for your comments and suggestions.

    Since the case is not clear to Mr. Gonzo, I am attaching a sketch which gives more detail for understanding the issue. If I repeat the issue,, When the 50m vessel is on Dock we will fix the Steel Deck transverse. But when the vessel put in to water, wood will behave in different way and it will try to stress the steel deck transverse. Therefore crack formation is possible at the joints.

    My question, is there any material which we can use in between wood and steel connection to damp the stress formation. (as an ex. we are using bi-metalic strips between steel and Aluminium to avoid corrosion, but here the issue is stress, so something like rubber)
     

    Attached Files:


  15. Landlubber
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    Landlubber Senior Member

    ...as stated above, the steel is going to control the shape, do not worry about expansion/contraction, as the steel will be the controlling factor and the wood will adjust to suit. No big deal.
     
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