Big windows - dangerous in an ocean-going yacht ?

Discussion in 'Boat Design' started by Boo2, Aug 11, 2009.

  1. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

    It's nothing wrong with pilot houses as a consept. Just the inadequate strength. ISO standards have "lesser" standards (pressure reduction 0,35 on higher pilot houses instead of 0,68 on decks ISO 12215-5 table 4) for higher superstructures and these just aren't allways enought when green water goes over or when capsizing..
     
  2. mark775

    mark775 Guest

    "~40' ship surfing in the tunnel of this massive, braking (sic) wave..."
    Sorry, there is just no way to be delicate here - surfing happens all the time. One wants to avoid it (in ways other than to "hunch in the saloon").
     
  3. apex1

    apex1 Guest

    I was´nt in doubt one will contradict.
    But first I said "CLASS" which means certified to valid classification standards (not RINA or BV).

    Then I mentioned "Top yard" in the megayacht range.
    The Other Woman was a cheap bargain after launch.

    And 9mm tempered glas would be the minimum for a vessel like "Windhorse" to pass class (absolutely insufficient), now we may guess what a vessel 5 times the size could probably require??? 10mm??

    Regards
    Richard

    Thanks Teddy for teaching Brent the basics!
     
  4. Brent Swain
    Joined: Mar 2002
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    Brent Swain Member


    I don't find the aesthetics a problem . I don't find the "Flimsey Yachtie " Look all that aestheticaly pleasing. Toughness has it's own aethetic appeal for the experienced, whom I'd far rather impress than the inexperienced. Some building my boats have built recesses welded into the cabinsides which make the outside of the plexi flush or slightly set in . A bit of extra work , but worthwhile if it is that important to you. I'd use stainless for these recessed frames ,as corosion behind the plexi would be hard to deal wit, and the extra corners could lead to more paint chipping, especially if the surface of the plexi is recessed, leaving the corner exposed.

    When you build your wheelhouse on a small yacht out of welded steel, strength is a non issue, and the safety factor of getting crew off the deck far outweighs any safety factor of not having a wheelhouse . I believe the use of steel flatbar in wheelhouses which are not built of steel can reduce drastically the odds of losing a wheelhouse. We dedicate a lot of concern to saving the boat , but too little to saving the crew from dying while the boat survives. The number of boats which survived the 79 Fastent, without their crews, is a good example of that.
     
  5. Bahama
    Joined: Jun 2010
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    Bahama Junior Member

    Stress is Greatest in the Corners and Along the Edges

    I watched a program of TV where these guys were testing all kinds of various glass type materials--everything that's been described in this thread. These were big 4' x 8' sheets of it too, that were held in place in welded steel frames.

    This was 30 minutes of total glass breakage, they drove hundreds of golf balls into them, sledge hammers, claw hammers, dropping bowling balls on them, firing pellet rounds into them, shot gun blasts.

    Out of all the glass, plexi, poly, lexan, etc. that was broken I noticed one common situation. The all broke easiest when struck in the corners. They also broke easier along the edges. And tempered glass, they showed was really strong until it gets struck from the side (downward onto the thin part). You can beat on it all day from the front, but they just tapped it with a hammer on top and the entire glass sheet shattered like a bomb of a million tiny pieces of glass.

    This was a few years ago when I saw the program, but I tucked it away in my head to know that design of the frame to protect against sheering, twisting, and pinching is vital. The glass, any glass will do good to have a strong frame that will not put stress on the glass, but will instead absorb stress instead where it connects to the pilothouse or superstructure and allow for some movement in the connection so that the connection moves and gives slightly rather than the frame. Obviously building everything strong is the way to go: the glass, the frame, the superstructure and everything that touches the frame. But I liked seeing that it will really add to strength to protect the corners and sides from being stressed.

    Nice thread, I've enjoyed reading it.
     
  6. jg451
    Joined: Jul 2010
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    jg451 Junior Member

    Having worked with plexyglas (oldetyme perspex) and the newer acrylics my take on it is forget plex. It's lifetime is dangerously short. A polycarbonate (such as Lexan, no ad just example) in appropriate thickness/span, with NO mounting holes please, is as strong and will last as long as the skin of most composite boats. 1/4"(6mm)x1mx1m @ 1m range will withstand repeated tosses of a 700gm hammer without even marring. the major cause in my view of failure is tortional twisting of substucture or frames/scantlings too light or mountings sub par because heavy enough or good enough usually ain't 'pretty' enough. Enough said.

    Jon
     
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  7. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Agree about plexi/lexan but those hammer tests are just idiotic.. anyway I've never seen raining anything so heavy:p and it's nothing more deceptive :(
     
  8. apex1

    apex1 Guest

    A window 1 by 1 meter with a 6mm glass / polycarbonate will be blown by the first wave in severe weather. Three times that thickness is just sufficient for a 60 cm by 70 cm window on a bluewater boat!

    The hammer test is senseless. A simple glass marble thrown hard, will destroy / crack even tempered glass, but not Lexan. But there are no hammers and marbles at sea. A 200 kg sandbag hitting the window at 30 knots will give another picture. (and test the framing as well)

    Regards
    Richard
     
  9. jg451
    Joined: Jul 2010
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    Location: portland,oregon,usa

    jg451 Junior Member

    Apologies. I certainly did not mean to suggest that one meter sq. windows should even be contemplated. I meerly refered to a filmed test of the material some 25 years ago. I have now struck a piece of 1/4" poly on the edge, out of curiosity, and saw no failure in the material, either a uniform blow or point load. Tortional loads of poly are still far superior to laminate glass, tempered glass, or plex. The point shold be made again that the larger a panel a commeasurate increase in thickness is appropriate. Tempered glass in the context of marine windows due to it's tortional weakness and edge weakness is, in my opinion, a dangerous material to use. All windows in maritime useage should have rounded off corners, frames and glazing. The hammer test, by the way, was in response to the comment that the glazing may not just have the enormous pressure of water, but may also be subject to debris in the form of loose deck equipment.


    IMHO,
    Jon
     
  10. apex1

    apex1 Guest

    Well, yes, the basics are the basics.

    But there is no severe difference in the material involved, the load per area is what we need. (and the ability to stand that). Neither the hammer, nor the marble are helpful.

    Frames are what is the most ignored issue (and sizes of course)

    But what was your original intention?

    Save a few pennies, or a few lives? Reinvent the wheel, or blame the industry.???
     
  11. Boston

    Boston Previous Member

    cant believe I missed this one

    a few years ago I was the primary consultant at a glass plant, I have a patent on Plasma insulated windows ( trying to sell it at the moment ) and I still work with glass regularly although not to the degree I used to.

    lets start at the beginning

    avoid weather that might damage your boat
    sounds good but there are times when your caught out and your in it now so what are you going to do

    storm shutters
    great idea which I plan on incorporating in my own build in such a way as they can be raised without to much trouble even in a rough patch

    glass or plastic
    there's a lot of prose and cons but for me its tempered laminated made up of 1/4 laminated panels
    given the size of the windows on the boat I want to build I want 4 laminations each 1/4 in front with a grid type shutter
    side and rear lites thinner but will have solid shutters

    I have some drawings but I'll save them for now

    IMHO plastic and annealed glass is worthless
    if laminated breaks its in a million pieces
    kinda hard to get hurt but its still posible
    if either of the above breaks its a fatal cut out at sea
    if you survive that then its green water in the pilot house
    with razors floating around in it

    glass has the same sheer qualities as plywood if applied correctly but most folks still apply it like it was a window rather than as a sheer panel
    thats another thread

    opacity is not really an issue with glass but it sure is an issue with plastics
    the stuff might start out slightly clearer but its not going to stay that way for more than a few seconds out in the sunshine

    refraction is also not much of an issue unless your in a submarine and most of us are specifically trying to avoid that

    impact strength
    laminated temp wins hands down specially if you use a blast resistant film and no not on outside, friend of mine has a sample in his show room of a piece of multi layer laminated glass with different caliber of bullets stuck in it
    the 45 usually convinces people that temp lami is better than polycarb any day. 1" Poly can only take one hit, the 3/4 temp lami can take multiple strikes as long as they are not all in the same spot

    no question that temp lami is more resistant than plastics of similar thicknesses

    edge vulnerability
    tempered anything looses this one
    the edges are the Achilles heel of the tempered world
    again proper installation is key

    anyway
    long story short I need to get my plans so I can do a proper weight budget but Im going to be spending weight on adequate frames glass and shutters, everything else is secondary.

    that and stay away from weather that might generate rogue waves
    as if thats possible

    no greater love
    no greater sacrifice

    not sure who's quote that is but its perfect for boating

    B
     
  12. jg451
    Joined: Jul 2010
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    Location: portland,oregon,usa

    jg451 Junior Member

    Hello Apex1,
    Thank You for your response. I;m hot sure about the 'Marble' reference- not mine. The original intent was simply to stress that the appropriate material used in an appropriate setting and you have a sub with a 'safe'(relatively) window. If you have experinced catastrofic failure, why? frames too light? Bad mounting? Inappropriate glazing material? Strike by loose deck furniture? Entire structure tortionally wracked? Some combination? By the sharing of mistakes found, problems should ease. Sizing of windows then at least can be better specified for a given application. Bostons last post says it better than I can.

    Regards.
    Jon
     
  13. u4ea32
    Joined: Nov 2005
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    Location: Los Angeles

    u4ea32 Senior Member

    Has anyone investigated frameless hatches?

    These seem to be gaining popularity in many custom yachts, as they are easily made and flush to decks or other surfaces. The builder makes a mould the size of the hatch that is essentially a scupper with a C cross section, with the inner edge being covered by a rubber gasket, the outer edge glassed to the deck, trunk, or topsides. Drains of course for horizontal deck hatches.

    Seems like it would win at sea:

    a) no frame, so the "glass" can move, avoiding the pressure point due to a frame.

    b) Hinges and dogs through bolted with holes about 50% larger than the fasteners, again prevent high pressure points.

    c) The rubber gasket spreads the load nicely

    d) Very easy to fabricate

    e) Very easy to replace panes.
     
  14. Northman
    Joined: Mar 2007
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    Location: Norway

    Northman Junior Member

    Boston, I would be very interested to see your drawings. Windows are a black art to me, still not sure which way to go.

    Walter
     

  15. Boston

    Boston Previous Member

    windows unfortunately are a black art in a way, specially if you want them to actually hold out water, which most do not.

    [​IMG]


    [​IMG]

    thing was clad in florpon coated steal over mullions and sealed with a product called chemcalk, which is unfortunately not available anymore as it was great stuff. Its an English design and was built at about 8,000' in the rocky mountains and redesigned for a snow load of 75lbs/ft. In spite of the increased loading its holding up beautifully.
     
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