Stateroom port lights low to waterline

Discussion in 'Boat Design' started by makobuilders, Jan 5, 2016.

  1. makobuilders
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    makobuilders Member

    I am in design stage for my trawler which has relatively low freeboard. The forward cabins are designed with oval portholes 16"x9" are are about 22 inches above DWL. Specs call for aluminum frame with 10mm toughened (tempered) glass glazing.

    I'm concerned about low portholes this far forward in an ocean-going boat. One of my previous boats had portholes like this amidships in the engine room and they took on plenty of water (horrible plastic frames never sealed tight) during rough weather.

    I'm thinking that the best way to make these work would be if outswing with internal metal gasketed deadlights. Basically a double seal in rough conditions.

    Should I be considering double laminated glass, reducing the size of the port lights, etc.?

    Feedback is appreciated.
     
  2. TANSL
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    TANSL Senior Member

    Here you have a solution adopted by me in several boats, for underwater windows.
    In addition I calculate the thickness of the glass so that the deflection does not exceed thickness. Polycarbonate, in several layers, is what I usually use.
    This solution has been approved by the Administration of my country.
    I hope that works for you guidance.
     

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  3. FAST FRED
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    FAST FRED Senior Member

    The only safe solution is to have a closing cover on in the ports.

    Bronze ports with aluminum covers are fine .

    Even above deck plastic ports have a short life , go bronze .

    http://www.dovermfg.com/pdf/dovercatalog.pdf

    Page 9 has covers.
     
  4. TANSL
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    TANSL Senior Member

    Closing covers inside the hull because, otherwise, how do you close them?
    Who has suggested plastic?. They should be FRP with a metal frame and bolted. The FRP is a material of great strength and durability. You can check if you study this material and see how many boats are built today.
    Bronze is a material too soft for ports, like aluminum, and the combination bronze/aluminum does not seem the most appropriate, imo.
     
  5. PAR
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    PAR Yacht Designer/Builder

    It depends on the bronze alloy for ductility, but generally is considered a fine port frame material. The same would be true of plastic, which is purely dependant on the composition, for its application as a port frame.

    The real issue is their location on the hull (assuming sufficient strength and stiffness material is selected). Ever since I stove in a port, that was mounted fairly low on a bow, I've never placed a port in this relative position in any of my designs. The boats general operational envelop, also has considerable bearing on the choices. A harbor queen could live with PVC frames, while and passage maker would require a much tougher arrangement.
     
  6. gonzo
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    gonzo Senior Member

    Marelon would be an appropriate material if you choose plastic for the portlights. However, if the frames are aluminum, it would make sense to make everything of the same material.
     
  7. TANSL
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    TANSL Senior Member

  8. makobuilders
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    makobuilders Member

    I appreciate the feedback.

    One of my minor concerns is material. My past experience with plastic frames was bad but it was an existing boat and I didn't have the money to change them out.

    This vessel is a new construction, steel hull, so I'll speak to the shipyard to see if they can affordably provide stainless frames, otherwise we'll have to stick with aluminum and then hassle with the galvanic isolation issues. I don't doubt that there exists some space-age composites that work well in normal conditions, but high latitudes extreme cold generally challenges plastic/frp/composites. I don't want to experiment.

    My biggest concern is how low they are to the water. The two that are amidships are about 2ft off DWL. Perhaps can raise them 2 inches more. But I've gone and redrawn the foremost port lights to be about 3ft off the water. They're not exactly in the forepeak but still a concern.

    Will stick with outswing design (so they seal tight against outside pressure) like all the windows (I don't have any sliders). And then will look into gasketed deadlights that bolt on from the interior. Glazing is spec'd at 10mm tempered.

    Of course the obvious comment would be to make them smaller. Tiny little circles, but that would compromise the enjoyability of the boat during the 99.99% of the cruising days, when the skies are blue, the air warm and the breeze a perfect summer day :p
     

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  9. FAST FRED
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    FAST FRED Senior Member

    "Bronze is a material too soft for ports, like aluminum, and the combination bronze/aluminum does not seem the most appropriate, imo."

    The past 500- 800 years of naval and commercial ship construction might disagree .

    As the aluminum port cover is inside the cabin it should seldom be immersed in sea water for extended periods of time.

    Even under 11 ft of water the pressure is about 5psi , so opening inward is preferred.

    Think of the fun an out opening port would offer to vandals!

    Internal opening & Ventilating , with a screen , would make the cabin more comfortable , climbing over the side to close a port as it begins to rain? Much unfun!
     
  10. TANSL
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    TANSL Senior Member

    "The past 500 to 800 years of civil and commercial ship construction Might disagree" in relation to the construction of steel ships. Carbon steel, steel grade "A",or SS, did not exist a few years ago (not to mention GRP, CRP, ARP, etc.).
    Today there are more suitable materials for hull openings frames, cheaper and more resistant than bronze. I'm not saying you can not use bronze, I'm just saying that I do not find bronze to be the right one, in the XXI century. I'm not talking about the ships of Columbus.
    I do not see the need, in the twenty-first century, of placing metalic covers, even inside the hull. I prefer to adopt modern solutions, whether or not those used 500 or 800 years ago. But it is only an opinion and, like all others, is rebuttable.
    Fortunately, imo, no one does anything just because it was 500 or 800 years ago.
    makobuilders, I guess that you want to build your boat in accordance with the regulations of any Classification Society. In these regulations you will find detailed information on how they should be the port holes and the thickness of the glass. This information is much more valuable than any of us can contribute.
     
  11. waikikin
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    waikikin Senior Member

    I'd be taking a lesson from the cruise ships.... use a screen for the scenery outside...
    Make all side lights/scuttles/windows etc FIXED & bring your ventilation from above...
    Jeff
     
  12. FAST FRED
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    FAST FRED Senior Member

    "In these regulations you will find detailed information on how they should be the port holes and the thickness of the glass."

    For inspected vessels that have an incline test , only half the freeboard can be used as the vessel goes over.

    A port with no dead light is counted as deck level , and only 2 ft up from the water would allow almost no heeling, very little load or passengers.

    While the rules are for inspected vessels ,a yacht should not be put at risk when the knowledge base exists . The holes in the hull rules are for a reason.
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Never compromise safety.

    The frames must be steel, same as hull, (ally may be acceptable but so low in the water..i would not recommend it. On the deckhouse is fine, but not the hull).

    Also the must be fitted with storm shutters/dead lights.

    The frames of the windows must be able to withstand 4 times the hull design pressure.

    Anything less, and you're asking for trouble.
     
  14. TANSL
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    TANSL Senior Member

    Ad Hoc, appear reasonable some of the things you say. I wanted to ask, what is the hull design pressure? and, where does it come the figure is 4 times the pressure on the hull?
    Thanks.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    You'll have to ask the designer.

    Typical value used by most Classification societies.
     
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