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Thread: Wood - Plywood - Epoxy bond, re-building my ketch Tonga

  1. #701
    Join Date
    Apr 2010
    Location
    South Australia and Tasmania
    Posts
    18,063

    Default

    In the original configuration maybe they were not notched because the didn't need to be, if they were just there as a belt and braces reinforcement for any aftward forces transmitted from the Samson post. Now you have a 30mm deck I don't reckon you need them at all.

    Sent from my CPH1851 using Tapatalk

  2. #702
    Join Date
    Jun 2017
    Location
    Nazaré, Portugal
    Posts
    645

    Default Re: Wood - Plywood - Epoxy bond, re-building my ketch Tonga

    Hmmmm, all of you, John, Rumars and Phil, good thoughts ...

    Could that have been installed later? In Theory yes - if I don't take into account that before the changes I made access was next to impossible from below. Unless of course they did that the moment when they changed the stern. Some of you might remember that the "negative" stern Tonga had originally was actually something that was added to the "positive" stern Tonga had when she was launched. At that moment they would have had to open the last part of the deck which would have given them access to the whole area, depending on how far further forwards they were cutting the deck open.

    At the Samson-Post the distance across is 132 cm. All my deckbeams and frames are between 49 and 51 cm apart.

    When taking the deck off I did have tiny nails going from the bottom-sheet of ply down to these stringers.

    Just wondering ... could it have been that these were kind of an afterthought just before closing the deck just in case something ugly should hit the outer bottom of the added stern? Right now I don't remember where exactly the joint between sheets was which might give a hint. I've got to have a look at the photos I took when I dismantled the deck. Unfortunately I've got to get up early tomorrow and these photos are on the computer downstairs in the Caravan. I've got to make a note and check on that when I come back from Vila do Conde!!!
    fair winds, Dody

    "They did not know it was impossible so they did it" - Mark Twain, my own project: http://forum.woodenboat.com/showthre...h-Tonga/page12

  3. #703
    Join Date
    Dec 2016
    Location
    EU
    Posts
    499

    Default Re: Wood - Plywood - Epoxy bond, re-building my ketch Tonga

    I don't think you need any stiffeners at your spacing and deck thickness.

  4. #704
    Join Date
    Jan 2004
    Location
    Norwich,United Kingdom
    Posts
    6,321

    Default Re: Wood - Plywood - Epoxy bond, re-building my ketch Tonga

    Quote Originally Posted by Dody View Post

    When taking the deck off I did have tiny nails going from the bottom-sheet of ply down to these stringers.
    Thats conclusive evidence that the stringers went in before the deck was laid.Which makes me suspect that the ply may have flattened out between the beams had they not been present and this might have caused additional problems with additional layers.

  5. #705
    Join Date
    Jul 2011
    Location
    Lindstrom, MN
    Posts
    2,608

    Default Re: Wood - Plywood - Epoxy bond, re-building my ketch Tonga

    Quote Originally Posted by Rumars View Post
    If the deck flexes or not depends on the unsuported area of the plywood and it's thickness. Basicly how wide the boat is and what distance there is between the deckbeams.
    Quote Originally Posted by Rumars View Post
    I don't think you need any stiffeners at your spacing and deck thickness.
    I don't think that you need to understand the purpose of the stringers as much as you need to design the new deck properly. There are span tables for plywood that might be of some help. They do give you loads and deflections that are instructive, if not intended directly for boats.
    http://www.pacificwoodlaminates.com/...SpanTables.pdf
    For a boat, I suppose you design around the depth of water that you might see on deck in a storm and impact from dropped anchors or even people jumping or falling.

    If I understand it correctly (please correct me as needed) in table with your 50 cm (~19.2") span, it would take 120 pounds per square foot to deflect a 1/2" panel by .14 cm with the face grain running across the deck beams(fore and aft). (L/360 = 50/360 = 0.13889).
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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