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Old 01-11-2015, 06:12   #1
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Porthole replacement

Has anyone had any negative experience with increasing your porthole size. I have four I'm replacing and want to install slightly larger ones for more light and air flow. Will increasing the porthole size compromise the strength of the hull?
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Old 01-11-2015, 06:27   #2
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Re: Porthole replacement

They're in your coach... so slightly larger, I see no problem...

Others will chime in with the same I suspect...
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Old 01-11-2015, 06:53   #3
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Re: Porthole replacement

"Hull"?

I dunno, but just a SWAG, as I'm not an NA or certified anything....

Construction regs state that a load bearing member *may* be penetrated/cut/drilled to 1/3 of the beam/joist's web dimension before reducing the effective load carrying capabilities.
This is assuming ( the engineering "assume") a round hole; or one that the corners have been radius'd enuff to prevent stress cracking @corners.

I'd venture a guess that IF yer new port size is at least one diameter from the nearest "edge", you'd be OK, as long as there's no point load at the apex. Additionally; I'd consider the port to be non-structural and of no consequence in retaining "hull" integrity. IOW; IF there was no fixture in the hull, would a hole that size/place cause a lessening of integrity, not counting ingress of water? Think of it as a round-top window in a bearing wall and don't forget to calculate/consider wind (water pressure) loading.

I need to "grow" my cabin top ports by an inch or so to get new opening ports in. No worries,as there's still at least one width remaining top and bottom.
HTH,
Paul
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Old 01-11-2015, 07:15   #4
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Re: Porthole replacement

I guess it's not the hull, it's the deck really. It does have large radius' top and bottom and also a mid 70's era boat so it has way thicker fiberglass then necessary everywhere.

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Old 01-11-2015, 07:16   #5
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Re: Porthole replacement

A simple solution is to craft a "finishing ring" out of epoxied plywood (or even G10, if you're able to fabricate it or willing to accept the greater weight), larger than the hole itself. Secure it well with epoxy and you're done. I've installed a number of these this way.
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Old 01-11-2015, 07:22   #6
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Re: Porthole replacement

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Originally Posted by Roy M View Post
A simple solution is to craft a "finishing ring" out of epoxied plywood (or even G10, if you're able to fabricate it or willing to accept the greater weight), larger than the hole itself. Secure it well with epoxy and you're done. I've installed a number of these this way.
Thanks Roy. I'll look in to that. I will be needing to use a 3/8" to 1/2" spacer as it is already because the new Port hole will be sticking out a little further than I would like for my already tight walking space.
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Old 01-11-2015, 08:16   #7
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Re: Porthole replacement

Here are some pics of a couple hatches I did a couple years ago. One is a simple replacement, needing only slight enlargement. The other is a much larger foredeck hatch that had to fill a curved, cambered deck with a flat hatch. The last set shows the replacement technique I use for fixed ports, one using solid teak finishing rings on the interior, another is from my own boat where I simply replaced the plexiglass.
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Old 01-11-2015, 08:29   #8
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Re: Porthole replacement

Quote:
Originally Posted by Roy M View Post
Here are some pics of a couple hatches I did a couple years ago. One is a simple replacement, needing only slight enlargement. The other is a much larger foredeck hatch that had to fill a curved, cambered deck with a flat hatch. The last set shows the replacement technique I use for fixed ports, one using solid teak finishing rings on the interior, another is from my own boat where I simply replaced the plexiglass.
HAY!

Those are recycled pics... I've seen them before!

Roy has it goin' on here Echo... and ... Lots of other methods too ...
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Old 01-11-2015, 10:27   #9
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Re: Porthole replacement

Thanks for the pictures! I think I'm going to go that route and build mine up for strength.

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