Cutting out my Bulkheads

Discussion in 'Boat Design' started by James Robinson, Nov 4, 2018.

  1. groper
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    groper Senior Member

    if you want to cut out the opening bigger just reinforce the cutout with unidirection glass fiber tape running around the opening. This is standard practice in composite construction and will restore the structure lost in the material removal. You will have to fair and paint it out tho after you been playing with the gooey stuff or cover up the mess by gluing on some lamainte of you dont wanna paint.
    For clarity - you wet out some 1000gsm x 100mm wide eglass tape and roll it up into a sausage or "glass rope". You then press this into a groove you make in the opening which has been buttered up with some thickened epoxy so its all sticky and doesnt fall out too easy. Use a router to make this groove btw. hold the wetout glass rope in place with peel ply strips or more wetout dbias glass tapes which wrap around the rope from 1 side to the other. This can all be done wet on wet but its a messy job and usually requires 2 people to hold everything in place as you go and stop it from falling out. Resin drips everywhere working overhead. Its a reasonably difficult laminating job working in a tight space. Easier if the bulkhead can come out to do this but that is probably an even bigger job.

    TANSL - i know what your saying but this is a tiny little 22ft lake boat - not a ship. The mast base doesnt even rest on a bulkhead the loads are so small they can be taken by the local deck structure! The ply wood bulkhead itself was probably chosen due to its low cost nature instead of fabricating it out of something else such as composites, and likely not even a fraction of its ultimate strength is required in the original design...
     
    Last edited: Nov 6, 2018
  2. TANSL
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    TANSL Senior Member

    @groper, with all due respect I must say that, among other things, the shear forces can produce deformations in the cross sections of the hull and the solution you propose will not be able to avoid them. Frankly, and it is only my opinion, without having made any estimate, some calculation, I would not give any advice. I still think that the designer did not put that bulkhead there, with that small opening, with the sole purpose of bothering. But, after all, the ship is not mine and I will never sail on it. Although we are not talking about a ship, a boat can also be subject to very compromised conditions.
    It is not my intention to annoy the party to anyone, I just wanted to recommend prudence.
     
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  3. fallguy
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    fallguy Senior Member

    Interesting. Where is the groove made? In the existing, but cut back BH or in an assumed hump between old BH fillets? Not the hull itself?
     
  4. SamSam
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    SamSam Senior Member

    On the Kestral, it looks like the shrouds attach to a yoke and so each shroud has two chainplates ( or sometimes 3 ) which I imagine are attached to the hull at the two bulkheads. So altering the bulkheads should probably take that into consideration, but as said earlier, it is a small boat and the loads are not that large.

    Also, the fact that you only use it in a force 5 doesn't mean a subsequent owner not might try and take the boat to extremes, such as the guy who was posting awhile ago who wanted to take the smallest possible boat into the largest possible storm for the excitement that might bring about. I would try and keep the boat as fit and sturdy as it was designed to be, but again, being small the loads are smaller and design factors for other things, such as the ability to smack into something without damage or to keep a persons foot from going through the hull or deck if they step in the wrong place, might make the construction over-built for the loads a sail might be putting on it.

    I had an O'Day 22 and that would have been much preferable with an open interior like you picture, less claustrophobic and warren-like with a much airier feeling. A curtain would suffice for privacy. Replacing the bulkheads with ring frames would entail a good bit of deconstruction and mess, it would be much easier to "open up" the bulkheads as shown in your last photo. That would be enough for me as it would probably eliminate the turning sideways down on your knees weaseling through I seem to remember from the O'Day. On mine, I would also have a slight wonderment as to what sort of critter might be lurking behind the bulkheads, but that was due more to the location than anything in reality.

    Here's a site with a bunch of interior and exterior photos for a Kestral 22...
    Seamaster Kestrel 22 - Topsail Marine Yacht Brokers (1869) https://www.topsail.co.uk/boat.php?refnum=1869#images

    [​IMG]
     
  5. James Robinson
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    James Robinson Junior Member

    Sounds to me like there's no definitive answers to this question but I feel fairly confident that it could work. I managed to get some more specific photos of the boat and the internal structure this weekend and it seems that the bhd aft of the mast doesn't really do a whole lot.

    I agree with the point about subsequent owners but I doubt that anyone would want to take this boat from Coniston and sail it off shore , there are probably many more suitable boats at a similar price that wouldn't need a new road trailer to get to the Coast. Also my mast stays are onto U bolts in re-inforced sections of the deck, slightly different design to the photo you have posted above.

    Looking at the outline of what I'm proposing below though I get the feeling that it would be a pretty bad idea. obviously I could cut less out but I think it might be a litte bit of a waste of time. Apologies about the awful job I did in paint marking that out.

    upload_2018-11-12_12-50-17.png
     

    Attached Files:

  6. groper
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    groper Senior Member

    i am more than confident it can be done- but im the kind of guy who goes and gets cracking, gets stuff done. Deisgned and Built my own boat and sailed over seas... Then i went to Turkey bought a yacht and sailed half way round the world... All my friends think im crazy and not normal... But i just think many people just mull things over too much and never make an attempt, living in fear of failure...

    what i would do;
    Take a router and run it around your intended cut line with an 8mm bit plunged to 95% depth of of the plywood.
    Wetout your unidirectional tape (1000gsm x 100mm or 33oz x 4in) the length of the routed groove (cutout circumference).
    Roll it up into a glass rope and stuff it into the groove and leave it cure.
    Cut the remaining ply away with a jigsaw after its cured leaving the UNI bonded to the ply edge.
    Wetout more dbias tape - 20oz or 450-600sgm tape and wrap it around the uni edge to consolidate the glass ring structure to the ply.
    Im not sure how its bonded to the hull but if it needs extra stiffness - you can lay uni on the hull - directly adjacent the bulkhead. Then run you tabbing from the bulkhead onto the uni- which is on the hull.
    With both ring structures in place you will have a very strong bulkhead.
    To be strict as per TANSL concerns - the thin ring structure can be stopped from buckling from hull shear (i dont think it will ever be a problem) but strictly speaking- the frame could be stiffened with further fore and aft gussets onto the ring frame in several places around the perimeter - incorporate them into the furniture (seats?) for a start. 2 either side of the companion way so you dont bang your head makes 4. With all that - it will likely be the strongest and stiffest thing in the entire boat! I wouldnt hessiate putting to sea in it with those mods ...
     
  7. James Robinson
    Joined: Nov 2018
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    James Robinson Junior Member


    Wasn't expecting such a profound answer there, I do agree that maybe I should just go ahead and do it.

    Not quite sure what you're getting at with the glass rope. Are you suggesting that I just need to do that to seal the edge of the existing bhd? do you think I will need to laminate the existing bulkhead to a new reinforcing bulkhead on the back?

    The current bulkheads are glassed to the hull with strip of glass approx 3inch on the hull and 3inch down the bulkhead.
     
  8. groper
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    groper Senior Member

    The glass "rope" is made from unidirectional glass fibers (warp). It is simply a rope or bundle of glass fibers that run around the perimeter of the opening which forms a ring once cured. Because of the unidirectional nature of the fibers and their orientation around the perimeter of the opening - it provides the strength in the way its required - to stop the new bulkheads shape (which is now like a ring frame) from collapsing. Wrapping the eglass dibias around the uni holds it all together and joins the rope to the bulkhead. The result is an Ibeam which if you can imagine has been turned full circle into a doughnut. The uni glass is the tension and compression caps and the remaining plywood forms the web.

    The method i described is simply a means of getting it done and being able to hold the rope in position as its not an easy task to get it where you need it - around that opening on its edge. This is where you use the groove from the router as it forms its own little mold to hold it in position whilst it cures.
    .
    This is standard practice around large openings in modern composite boat building using lightweight, high strength sandwich panel construction - late model racing yachts etc. The main difference being they use carbon whereas we will use glass however the engineering principles are the same. Then to complete the outer ring against the hull - you can simply laminate over the existing tabbing with some extra Uni - again this adds ring fibers around the outside of the doughnut to complete a giant I beam thats turned full circle - an extremely strong geometric shape (very efficient use of material)

    See this image of racing yacht that shows same structure;
    [​IMG]
     
  9. JamesG123
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    JamesG123 Senior Member

    The picture and concept you posit is an example of "black aluminum (iron?) thinking".
     
  10. groper
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    groper Senior Member

    No its a carbon fiber racing yacht
     
  11. JamesG123
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    JamesG123 Senior Member

    Yes I know that.

    [​IMG]
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    I can't see why it can't be opened up by just doubling or tripling the thickness of the ply around the perimeter, but still allowing say, at least 6 inches width of material, and no sharp corners. Added weight would be minimal. Just need ply, a jigsaw, some g-clamps and some glue.
     
  13. JamesG123
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    JamesG123 Senior Member

    That is the easiest and most effective solution.
     
  14. SamSam
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    SamSam Senior Member

    Adding layers of ply wouldn't allow you to get close to the hull in some areas unless the ends of the settees (and their cushions) and cabinets were cut back. Maybe if it was put in the small space between the two bulkheads you could do it without any problems, its hard telling if there's anything in there.
    Either way, with the ply (if possible) or with the fiberglass ring, it shouldn't be too hard to do and would open up the interior nicely and give a very different aspect to the boat.
     

  15. Barry
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    Barry Senior Member

    Mr E and JamesG have identified the easiest way to deal with the modification.

    SamSam says that you cannot get to the ply layers to reach the hull in all places and I don't see an issue here

    The underlying premise is that the current thickness of the wood at the joint AND the joint between the existing bulkhead and the hull have proven to carry the loads.

    When you cut out the wall, you will lose some stiffness meaning that when the loads are applied, the remaining ply frame could flex causing strength issues. So the goal then is to
    make the frame that is left stiff enough to restrict flex and strong enough to carry current loading.

    So I would do two layers of ply. The first layer, the plywood sheets would run horizontal with the joint being say half way down. Glue this with a strong epoxy and screw the sheets together
    316 stainless steel countersunk screws in a 4 inch x 4 inch pattern while the glue is wet. I would have the soon to applied sheets drilled and counter sunk prior to gluing, no need to pilot the underlying
    sheet, install all the screws part way into the soon to be applied sheet, apply the glue, push the sheet into position ( I would have done a dry test and had say 4 screws install through both sheets, the existing and the new sheet, and position the new sheet with these screws into existing holes. And then run them in with a cordless driver. I would also screw a couple of pieces of
    2 inch by 2 inch by 10 inch long "handles" screwed from the outside to help with a grab location to move the sheets around for positioning

    Then the same with the lower sheet.

    The second layer of sheest would then be installed with a vertical seam with the same process. As you are taking quite a bit of plywood out with the cut, your weight change should not be significant.

    The new sheets could easily be away from the hull side 1/2 an inch or so but it would be easy to fit them to within an 1/8 or less. Before installing the new sheets, I would seal the perimeter
    edges of the plywood.

    If you really like the smell of fibreglass resin in a confined space, you could fibreglass the new sheets into the hull but as stated earlier the existing joint has been proven and the additional
    ply layering will carry the load and provide stiffness to the web of your new frame to limit distortion.

    If the more full plywood bulkhead job was to take significant vertical or horizontal mast loads, then this bulkhead would have had stiffeners in horizontal and vertical directions to limit deflection of the bulkhead.
     
    Last edited: Dec 1, 2018
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