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-   -   Porthole Question (http://www.sailnet.com/forums/general-discussion-sailing-related/31875-porthole-question.html)

Alden68 04-28-2007 07:38 PM

Porthole Question
 
Prior to removal, my portholes were originally screwed into the fiberglass hull from the inside. My plan is to re-attach by bolting through the hulll from the outside with the bolt head and washer resting directly on the fiberglass (with the appropriate sealant).

Does anyone see any problems with this installation other than drilling 40 holes in my boat? Why were they secured from the inside with screws in the first place? That seems like a really weak installation as a force from the outside could (and did) easily push the porthole in.

Thanks.

Alden68 04-28-2007 07:40 PM

woops meant to post this under gear & maintenance......

sailingdog 04-28-2007 10:06 PM

I would put the port glazing material on the outside... that way the material's tensile strength is part of what is holding the water out and the seal between the glazing and the hull only increases as the water pressure against it goes up. Having the glazing material on the interior of the hull is rather stupid IMHO... since any pressure against the glazing will tend to open voids in the seals around the glazing. Many new boats have dead lights that are panes of plexiglass or polycarbonate that are thrubolted to the cabin top.

When you're dealing with liquids under pressure, you always want to design it such that any increase in pressure aids the sealing systems, rather than weakens it.

IIRC, you should drill the holes slightly oversize as polycarbonate and plexiglass both expand and contract at a different rate from the fiberglass, so the bolts will move slightly relative to the glazing material.


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