what to do with the deck.

Discussion in 'Boat Design' started by whitepointer23, Dec 30, 2014.

  1. whitepointer23

    whitepointer23 Previous Member

    Thanks fred. I have not heard of dolfinite. I will look it up.
     
  2. michael pierzga
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    michael pierzga Senior Member

    3m 5200 is a structural adhesive, not a bedding compound . Dont use it. Use 3m 4200 for bedding .
    Sika flex 291 is also low bond strength bedding.

    Dolphinte is old fashioned and prone to ozze out and dry out.

    curing compounds like 3m or sika are superior .

    For large surface area bedding use a break film , foam tape or contaminate one side of the bond before appling the compound to ease future disassembly
     
  3. Steve W
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    Steve W Senior Member

    Brendan, Im glad to see you are coming around to doing the job correctly. You have gotten a lot of good recommendations already so I don't have much to add except that while you can certainly apply a single layer of plywood with either a butt block between the beams or a scarf joint on the beam, 2 layers laminated over the camber will be a little stronger, but not really significantly enough to sway the decision that way. The biggest factor in making the decision will be how easily the thicker layer bends over the camber. My guess is that your planked deck will be around 3/4" to 1" or so but I don't see any reason to go any thicker than 3/4" so you may need to add spacers between the new deck and the bottom of the cabin side. Please don't be tempted to use anything less than BS1088 plywood and while you could just paint the plywood it would be much preferable to sheath it with epoxy/dynel first. Yep, the toerail needs to come off to be reinstalled later. Ive not done the scarf over the beam method but it makes perfect sense to me and as has been suggested it is quite easy.

    Steve.
     
  4. PAR
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    PAR Yacht Designer/Builder

    3M-5200 isn't a structural adhesive, it's an adhesive/sealant and there's a huge difference between the two. It can and commonly is used, as a bedding and performs this role well, though tends to yellow and cures much stiffer than most think.

    Dolfinite is a straight bedding, a traditional oil based product that works well. I've disassembled pieces bedded in it after 50 years and it's still gooey. It's main weakness is it has very limited elongation, particularly compared to the polyurethanes and polysulfides, which can distort over 300% before the bead breaks. It doesn't dry out unless exposed, which means you have fastener issues and the part need to be rebedded anyway.

    There's no need to contaminate a surface for easy future disassembly. If you're familiar with the bedding products, you can break them loose, when the time comes, without damage. 3M-5200 is notorious for tearing stuff up when it's removed, but these complaints are from folks that don't know how to remove it and take grinders and other absurd tools to it.

    Fred is correct, bedding needs to be renewed and it usually isn't until something leaks. This isn't the fault of the bedding product employed, just owner neglect.

    Typically, when replacing a solid wood deck with plywood, the same thickness plywood is used, as was used in the solid wood it replaces. I agree, the deck is probably designed an inch or more thick, so this is the thickness you'll need in plywood, which suggests, you'll have multiple layers at this scale.

    I disagree with the BS-1088 requirement. You can use AA marine or BS-6566 for a significant savings, without a lot of worry. You'll be double planking and entombing it in goo and fabric, so the usual issues are mitigated to a large degree. Just inspect each sheet well, looking for veneer issues. The 6566 I get, looks as good as the 1088, for 1/2 the price.
     
  5. Steve W
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    Steve W Senior Member

    If you were to replace a solid planked deck that is 1" or maybe 1 1/8" thick with an equal thickness of plywood you will probably be laminating 2 layers and it is just unnecessary to use more than 3/4" on a boat this size. Ok, you could use BS 6566 for this, but if I remember right in Australia and NZ they have a standard of their own which is supposedly equal or better than 1088 so i would probably use that, its not that many sheets so it really is not worth penny pinching on a job that if done right will last a very long time. I have no idea what AA marine is but if its a US standard it is pretty worthless, ive lived in the US for 35yrs and ive yet to see a piece of so called marine plywood i would use for anything crucial in a boat, we make the worst plywood in the world.

    Steve.
     
  6. waikikin
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    waikikin Senior Member

    WP,
    Here's a reference to USL Code, the tables at the bottom are easy to apply to make deck thickness choice if beam spacing etc match. Table M13.
    http://www.amsa.gov.au/domestic/standards/usl-code/documents/USL_Code_5M_ALL_2008.pdf

    The USLC was developed in 76-78 & followed proven practice , a little clunky to apply at times but durable vessels used in commercial fishing & hard service created to it.

    Regards from Jeff
     
  7. PAR
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    PAR Yacht Designer/Builder

    All the plywood standards are now voluntary, regardless of where it's made, so it's subject to what you can get a manufacture to make. A deck has modest crown and sweep, so not a lot of twist involved, so lesser grades can be acceptable, assuming you've a good stock source. I have to agree, most USA made plywood isn't very good, but it can be if you deal with big vendors (World Panel, for example).

    The 3/4" recommendation just doesn't make sense, as the deck will have to absorb and transmit rigging and hardware loads to the hull shell and it's framing. Unless the plywood is glued, this means it's fastening to the beams, carlins and clamps. A 1 or 1 1/8" solid wood deck is considerably stiffer longitudinally than 3/4" plywood, meaning now the beams, carlins and clamps have a relatively weak interconnection, keeping them in column. The general rule is the same size if plywood is the substitute, no matter what the eventual dimension might end up being.

    This said, it may well be that the decking on this 35' ketch may be only 3/4", which is possible with some structures, such as longitudinal stringers or closely spaced beams, but more often than not, a laid deck is over moderately wide beam spacing, often without longitudinals. Maybe Brendan can tell us the beam and frame spacing and if any longitudinals exist. Their spacing would determine the thickness of the decking.
     
  8. Steve W
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    Steve W Senior Member

    Of course the plywood would be glued to the deck frame, i guess i assumed this would be the case, ive never done it any other way with plywood. While a 1" thick planked deck may be stiffer longitudinally it is nowhere near as stiff transversely and a typical deck frame will have a king plank at the least and probably more longitudinal members contributing to longitudinal stiffness. A good, strong, reasonably priced BS1088 or 6566 panel readily available in the US and is Meranti. There are many more good selections available down under than we have here fortunately.

    Steve.
     
  9. waikikin
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    waikikin Senior Member

    Australian manufactured marine ply AS/NZS 2272 is a high quality product, some BS 1088 is, some is not, Aus manufactured exterior in some grades is better than some of the imported BS(BS can mean something else).The Table suggests 20mm as minimum for an 11m vessel, of course equal thickness to original deck would be fine.Availabilty of Aus marine ply is 12.5, 16, 19, 25, 32. The ply deck acts as a continuous lodging knee & effectively brackets the carlin to half beams & to sheerclamp & upper edge of sheer plank, it serves some of the function of the tie bolts along the side decks although I'd leave them in or replace if dodgy regardless.
    There's usually plenty of longtitudinal in the deck edge, clamp+sheer strake, sometimes a beam shelf, sometimes a sponson & crusher but you can discount them as consumables.
    Jeff
     
  10. whitepointer23

    whitepointer23 Previous Member

    I will measure the spacings next weekend. And I can take some photos from underneath as well.
     
  11. FAST FRED
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    FAST FRED Senior Member

    >I will measure the spacings next weekend. And I can take some photos from underneath as well.<

    The spacing will only matter if the beams are rebuilt enough to add to the structure, otherwise they are simply decoration.
     
  12. whitepointer23

    whitepointer23 Previous Member

    you have lost me, par asked for the deck beam spacings. why would I have to rebuild deck beams that are in good condition.
     
  13. PAR
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    PAR Yacht Designer/Builder

    Beam spacing and dimensions are directly scaled to the decking thickness. Of course, the beams are part of the structure. Do you think they put a laid softwood deck over faux beams?
     
  14. Steve W
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    Steve W Senior Member

    I don't get it either, the only way you can eliminate the deck frame is to laminate multiple layers of thinner plys. I have done a 45ft motorsailer with 4 x 1/4" over temporary beams for the entire deck with just bulkhead doublers and carlines and many frameless cabintops with 3 x 1/4".

    Steve.
     

  15. waikikin
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    waikikin Senior Member

    I guess Fred is just saying that the deck framing should be repaired to good condition, I'm sure Brendan will find the opportunity to do this.
    Jeff
     
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