How are hullside windows engineered in frp boats?

Discussion in 'Boat Design' started by Mamaboo, Apr 30, 2009.

  1. Mamaboo
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    Mamaboo Junior Member

    More and more small boats seem to have rather large fixed windows in the hull. I've seen some, like Intrepid, putting them rather far forward in the boat where they would be subject to some pretty intense loads when running into a head see. Does anyone know how these windows are engineered? I'm particularly curious as to how they are secured to the frp hull to keep them from popping out, and if there is any additional structure required in the hull to prevent flexing at the joint between the two materials.
     
  2. marshmat
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    marshmat Senior Member

    In many cases, they aren't.

    Good builders will calculate appropriate scantlings for windows and frames; there is a wide assortment of standards from all over the world dealing with windows, frames and the reinforcing that must occur around them. It's more reading than I care for, or need to deal with, at present. But if you're building something that's going to go into heavy weather, you'd better enjoy reading technical standards.

    But there are also builders who are quite happy to cut gaping holes in the hull and superstructure, then glue in whatever Plexiglas sheet happens to be on sale that month, using whatever adhesive they have lying around. I have seen production sailboats with an uninterrupted, 5' long by 1' high window on either side of the superstructure- with the mast stepped right in between. Virtually no structure to transfer the loads. Or production powerboats that sell hundreds of units a year, where a fibreglass deck is completely unsupported because of huge cutouts in the sides for windows. Then the owners wonder why, as soon as the one-year warranty is out, they have water gushing in every time it rains.
     
  3. apex1

    apex1 Guest

    I have to agree with Matt (as usual), many of my dear competitors do´nt engineer that sort of stuff, they use common (non) sense and "skills" to calculate. I use the same regulations as postulated for front windows Class A.
    Tempered and laminated glass only! For the 72´ Lobster boat (see my Gallery) we used 19mm which is about 4mm over the GL or LLoyds rules. But what do we win if we skimp on weight there? Maybe two KG each side. Is it worth? All the sampan is 3 M €, so, why take a risk for some 40€.
    But that is unfortunately not common anymore, saving some penny, hunting for "shareholder value" and f...king the customer became too popular in the past ten years.
    Sorry was a bit besides topic, the last statement.
    Regards
    Richard
     
  4. marshmat
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    marshmat Senior Member

    I seem to recall a good Steve Dashew article on this issue.... http://www.dashewoffshore.com/glazing_decision.asp
    Richard's not the only one who goes a bit over the requirements of the rules.
    But then again, who wants to go out and hang 10 square metres of storm shutters as a Force 8 approaches? And who wants to come off a wave to find an anchor or a paravane coming right through the window (a la Perfect Storm)?
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    "...I'm particularly curious as to how they are secured to the frp hull to keep them from popping out,..."

    As already noted, so would we!
     
  6. rwatson
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    rwatson Senior Member

    From my limited experience, the 'small' FRP boats have a substantial (say 1.5 - 3" ) "ledge" moulded around the "cutout", for the individual windows to be well supported.

    Others have a one or two piece length of plexiglass or whatever that cover the entire cabin side, so that the pressure is distributed over a really wide area.

    But, for an in depth sensible discussion, perhaps you should define "small frp boats' a bit more, and give some specific examples. The manufacturer 'Intrepid' covers a lot of models as well.

    To my mind a 'small' frp boat has a lot more to worry about than forward facing ports when they strike seas big enough to break in even the cheapest plexiglass.
     
  7. apex1

    apex1 Guest

    Yes, for shure, all of us! Thanks Ad Hoc.

    Matt, yahh not only a bit, I nearly doubled the scantling! I do three layer tempered glass laminated! Dashews use a single glass!
    Shutters are nt a good idea, if you have to carry the weight for shutters, you can make the glass rigid to the same weight and have a win win situation, but these idiots in the industry do´nt tell the people that shutters are needed IF. So they may buy some or not.
    Outriggers braking the front (or side) windows. ja, ja, nice movie...............
    If there is any equipment (like anchors) stored in front of the wheelhouse windows, possible to break loose and to be moved into these windows, these windows have to stand the test of failure with a 200% overload, otherwise are not out of my door!
    BTW: the frames are more of a problem than the glass itself! We tested a 120 kg steel anchor to go through a 16mm laminated, tempered glass window of 45x65cm, the glass broke on the INSIDE, the frame was completely destroyed (8mm marine bronze).
    Edited: we found that a perfect laminated wooden frame stands at least twice the load of any metal!!! bearing in mind that a bended metal frame is a failure.
    And thank you for the Dashew hint. You know, that we know these articles, but it is always a good idea to send the novices to the right address.

    Regards
    Richard
     
  8. TollyWally
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    TollyWally Senior Member

    Back in the day we blew a front window out of the wheelhouse halibut fishing in the western Gulf of Alaska. We patched it with plywood and the next year put in tin bulworks to break the force of the waves against the glass. The glass did not break but was blown out of a rubber seal that held it in place. We added an inner flange of fiberglass on the inside of the wheelhouse to try and keep it penned in. The exact details escape me. Good times.
     
  9. apex1

    apex1 Guest

    Thanks,
    I very much appreciate the input of the mature ones here. Not the "boaters", "yachties", or even my breed, "builders", no, those who earn a living out there can tell us what the "real" world demands!
    Thanks again.
    Regards
    Richard
     
  10. rwatson
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    rwatson Senior Member

    The discussion started out at a much lower size than commercial fisshing boats.

    Like I said - the "small FRP boats" would have more to worry about in the big seas than just windows being blown in.

    I doubt they would even have survived long enough to get a big impact over the bow.
     
  11. mydauphin
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    mydauphin Senior Member

    I made molds from fiberglass for my windows, I still have them. After reading this thread, I am making shutters for my windows from them. Seriously, I can believe the new yachts with windows everywhere and now every boat has a electric sunroof, balcony that opens, etc... I can not believe that these things are not going fail miserably in a storm especially after some ware and tear of marine abuse.
     
  12. apex1

    apex1 Guest

    Mydauphin
    Just get some proper sized laminated windows with at least one layer of tempered (like carglass) glass in it and you can leave the shutters at home. Look at the "Dashew" link Matt posted above. They made the same decision, and they are right. Although I call the glass they have choosen insufficient its just single layer tempered.
    Regards
    Richard
     
  13. mark775

    mark775 Guest

    rwatson, The racking a boat is subjected to is enormous and the problem the man's trying to address is the thing popping out - not getting blown in. I've experimented with "frameless" (glued in place) windows but never in a hull side (nor will I).
    The rubber framed ones Tolly mentioned have been known to be blown in if not fitted and sealed well (I've been there) but others have a problem with just racking and leaking...sometimes badly. I think these hullside windows are asking for it. Builders are using 'em but not in water I need to be in... It's houseboat stuff, IMO, and looks derivative, not innovative.
    Tolly, you were in the Western Gulf in a glass boat with rubber sealed windows? What boat? Where? You mean area "M"? I guess, to most people, that's west. Anyway, you've got big ones.
     

  14. rwatson
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    rwatson Senior Member

    Yeah, I know he say "popping out", but he must mean "popping in", because he is talking about "head seas".

    You cant "pop out" a window in a head sea, technically, unless it turns around and comes in from behind.

    Except for a gas explosion, or a good head butt, I dnot know how you would "pop out" a window ( from the inside)

    I have never heard of a "small frp boat" having one of the forward windows getting "popped in" by a big head sea. Like I said - that is the least of their worries. All the points about big seas in comercial boats is nowhere what he was asking, interesting as it may be.

    The whole argument is probably just a physics one - take a say, square metre of window, calculated the weights and velocity of water, then get the specs for the laminate or perspex etc etc

    My bet is that most windows in small boats are way overengineered for the odd "tall" wave that might get encountered.
     
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