Big windows - dangerous in an ocean-going yacht ?

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

  1. Boo2
    Joined: Jul 2009
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    Boo2 Junior Member

    Hi,

    I'm interested to know what people here think about the current fashion for big windows in yachts with eg pilothouses ? Most cats like eg Fusion 40 and Schionning designs seem to have huge areas of glasswork as do monohulls with big pilot houses. I just wondered what opinions are about the seaworthiness of these types of designs in terms of withstanding extreme weather conditions in ocean passages ? Could green water smash large windows and swamp the boats as a result ? Anyone heard of this ever actually happening to such a yacht design ? (I've heard of big ships having glass broken by green water but am specifically interested in the situation wrt small (40-50 ft ) yachts).

    What do people here think of acrylic or perspex domes/hemispheres as an alternative to pilothouses ? Anyone tried one and care to relate their experiences ?

    Thanks,

    Boo
     
    Last edited: Aug 11, 2009
  2. Submarine Tom

    Submarine Tom Previous Member

    It Happens

    "Could green water smash large windows and swamp the boats as a result ?" Yes.

    "Anyone heard of this ever actually happening to such a yacht design ? (I've heard of big ships having glass broken by green water but am specifically interested in the situation wrt small (40-50 ft ) yachts)." Yes, I've experienced it. Things go from bad to worse in a hurry. We didn't swamp and lose the boat but we did lose all our electronics and took on an uncomfortable amount of water, got really wet and mild hypothermia.

    I'm guessing you've never had this happen. It's not pretty. The risk is real
    and it's scary. Avoid it at all costs.

    Why do you ask?

    Tom
     
  3. PAR
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    PAR Yacht Designer/Builder

    Storm shutters should be on all off shore craft, though most don't carry them. Serious cruisers usually do, because they've had their butts kicked before and know how easy it is to pick up damage in a rough slosh.

    To directly answer you questions, yep, I've had ports stove in from boarding seas. I had a cabin crushed and literally shifted sideways on it's carlins from a boarding sea, ports, vents, companionway and all. I barely made it to port on that run, so yes, you can have a personal relationship with Neptune, if your ports aren't properly protected in a storm.

    You don't really need shutters but a few times a decade, but you might install them on several more occasions, just being safe.
     
  4. FAST FRED
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    FAST FRED Senior Member

    Boats are like belly buttons , there are innies and outies.

    The innies sit IN the water and will have scantlings to be hammered by breaking waves.

    The multihulls are Outies , hopeing to sit ON the water not be in it.

    The light weight big windows may survive , but in the ocean , I would be very cautious , storm shutters , course change , and really good weather window .

    FF
     
  5. alan white
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    alan white Senior Member

    Bearing in mind that most boats you see at the boat show are for selling and not sailing... the big ports have always been put on big power boats obviously not intended for offshore or even rough near shore cruising.
    Few boats indeed are built for actual "caught out" conditions.
    It's always been up to the buyer to know what makes for offshore readiness.
    PAR was right that shutters are the right approach. A pilothouse boat otherwise built for offshore use has large windows by necessity. The placement of the sailor in under cover is itself a big safety bonus if fatigue and warmth are factors, which they are. Windows around the pilothouse should be very beefy because you can't lose visibility. Even they should have a means to be shuttered as a last resort when an emergency tiller helm is available.
    The bottom line is "buyer beware". Big ports are found on every fishing boat working offshore, so size isn't as importasnt as construction--- thickness, material, frame scantlings, and so forth. The bigger the port, the stronger it ought to be.
     
  6. Boatpride
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    Boatpride Boatpride

    My pennies worth suggests that having a hemisphere dome is a good idea. The dome shape is much stronger than the flat surface.

    Further to that the hemisphere would not cause an obstruction - unlike a pilot house window. The green water would wash over, rather than potentially through.
     
  7. Fanie
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    Fanie Fanie

    Gee whiz FF :eek:

    Perspex is much lighter, 10 x stronger than glass and also clearer. There is a proportion to the perspex thickness to size. If you install a decent thickness perspex it is going to be hard to break. Expensive though, but probably worth it. I did a couple of break tests with perspex. The thicker becomes impressive, although not to underestimate the power of water.

    Just pulling your leg there Fred :D Kinky bugger, for a second there I thought you were referring to boats with your innies and outies :rolleyes:
     
  8. marshmat
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    marshmat Senior Member

    It looks like the important points have been made and reiterated: Yes, big windows are a potential hazard. No, the huge expanses of glass and patio door found on many boats are not intended for offshore passagemaking. Yes, storm shutters are a good idea.

    Designing a window to survive a certain water pressure is fairly straightforward. Figuring out exactly what that water pressure should be is a bit harder, and for this we have guidelines in the various classification society rules. The nasty part, I think, is when you have something break loose from the deck and hit the window- whether it's an anchor, or a paravane, or any other piece of equipment, the concentrated stress of a mechanical impact is what will probably break your window.

    Acrylic domes are used on tourist submarines and can be made to withstand enormous pressure. I suspect the main reasons you rarely see them on surface ships are (a) scratch resistance, and (b) styling.
     
  9. apex1

    apex1 Guest

    Think you´re right Matt. Moitessier used a dome and that looked like "milkglass" after a while.

    Breaking windows are not uncommon in the fishing fleet in high latitudes (sometimes just cracked by tension, stress, not green water or equipment only). And I think not all classification societies are on the safe side here with their rules (ABS in this special case is a joke). When stability is not endangered (glass is heavy) you can build your shutters in by using laminated and tempered glass in combination. "Pilkington".
    You have to double the thickness ABS recommends, even in this case! We even double the (more conservative) GL sizes. When using laminated glass you MUST prepare the edges to withstand water (humidity) ingress into the plastic film. We use a "gummed" Epoxy resin, which stays flexible when fully cured (not really as rubber, but not brittle).

    Regards
    Richard
     
  10. Landlubber
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    Landlubber Senior Member

    Good point there Apex, many boats built in China today use tempered glass, the stuff that shatters into tiny pieces, but large open spaces when the glass fragments. Laminated glass, made from tempered sections is definately the best of both worlds, but very often neglected.
    Unfortunately the mullions of these boats are also scant, so they fracture easily when the **** hits the fan, I have seen many examples of so called offshore boats with cracked window sections and shattered glass as a result of just twisting forces.
     
  11. Fanie
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    Fanie Fanie

    Wineglass ?

    http://www.hydrosight.com/article/worlds_biggest_window.php

    http://www.travelblog.org/North-America/United-States/Georgia/Atlanta/blog-162460.html

    Perspex are used for a reason. No, it's not because it is lighter than glass or cheaper, not because it simply is much stronger, neither because it lasts forever, and not even because it can be repaired, the ONLY reason is because it doesn't take the milkglass shape after a while :D

    On a smaller scale, I have replaced glass doors and windows in my house with perspex ones because the glass ones break when the ol witch wead eater the lawn ends. I won't consider anything else on the boat either.

    Easy to test. Get a few perspex offcuts and break them. Also, the manufacturers can give you specific force per size and thickness.
     
  12. apex1

    apex1 Guest

    Right Lubs, the main failure reason I guess. And PROPER ship windows (frames) are almost as rare as real gold in the toilet bowl.

    Fanie

    you are right! It does not need a while, it needs a few days only under the "right" conditions. (sunny days and "salty" sprays are good on that).
    Perspex is just a name, it is acrylic "glass" (Polymethylmethacrylat) and known since the 30ies of the last century. On a true ocean going vessel a nono. It is not UV resistant (in fact it absorbs UV rays), and yellows. It is extremely susceptible for tension cracking!!! It gets extremely brittle when it had contact with alcohol, aceton, benzol.
    Buy a good single malt (Glenmorangie) and sip it down (you feel better doing the next step), throw the last glass over your Terrace door, close the door under light tension. When your hangover is gone, your door is too! If not, snip it with your finger nail!

    Read: No party onboard Fanies boat! (maybe Muslim fete)

    Regards
    Richard
     
  13. marshmat
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    marshmat Senior Member

    Part of the appeal of acrylic for a submarine is that its refractive index is very close to that of water, thus there is very little distortion or reflected glare when looking through acrylic into water. (Incidentally, its neutron absorption cross-section is also very close to that of water, but most of us don't care about that....)

    I'm not sure I'd want plain old acrylic, ie. poly(methyl methacrylate) for windows, though, for exactly the reasons Richard mentions- cracking problems around edges and fasteners, chemical attack, and UV degradation. Perhaps some of the manufacturers have figured out how to blend additives into the mix to improve these problems, I wouldn't be the one to ask though.

    Of course, it should be obvious that a strong, rigid frame is essential, or ANY window will fail.
     
  14. Brent Swain
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    Brent Swain Member

    You are unlikely to break heavy perspex. Make sure your windows are not so large it leaves little material in the corners and between them to hold the works together. If that is the case , then beef up the corners and material between the windows.
    Brent
     

  15. apex1

    apex1 Guest

    Strong and rigid are many Matt, but I (and the whole megayacht industry) know of only ONE who makes them so sophisicated that they do not brake the glass even when the superstructure twists (to a certain extend).
    (when you are in building process I´ll let you have the name)


    Brent
    you can brake perspex with ease as mentioned above
     
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