[Rhodes22-list] Fixed Ports

Wed May 27 11:28:15 EDT 2015

Curtis:
For what it is worth, regular silicone did not work well for me last time
around. The recommended silicone for this purpose is Dow Corning brand,
silicone # 791. It is a specialized sealant used for glazing that adheres
well and is able to expand and shrink by 50%. In my first attempt, thermal
expansion with lexan was enough to break the lexan around the screw holes.
That is a pretty serious force as lexan is very strong. 

If you use screws, oversize the holes in the acrylic. 

There are two reasons to use the tape - whether with screws or not - one is
adhesion and the other is to leave an even space between the glass and the
cabin sides for a thick layer of sealant. You need that space to give enough
thickness to the sealant to allow it to expand and shrink. If the sealant is
squeezed too thin the seal will break as the glass expands and shrinks. The
recommended tape is 3M brand tape VHB 4991 which, very importantly, is 2.3
mm thick. I would be very doubtful about the quality of the seal letting
silicone cure or partially cure before fastening it down. I would worry that
it would not be an even seal or might leave the sealant too thin. If I were
not going to use the tape I would use spacers to make the space even and
allow me to tighten the screws before the sealant cures.  I had thought that
thin flat faucet washers might do the trick if I could find the right size.
I was thinking I might drill the holes bigger and place the washers under
the screw head. In the end, the tape just seemed like a better idea. This
stuff is used a s the sole means to hold large glass panels on high raise
buildings so its adhesive qualities are very significant.

While there is significant and compound curve to the cabin size it does not
appear to take a lot of pressure to bend the acrylic and I have not seen
much difference in that respect between acrylic and lexan. The reason I
chose acrylic is because it is more resistant to scratches. Acrylic is not
as strong as lexan - it won't stop a bullet if that is an important
consideration - but it is plenty strong for the purpose. 

I would be very interested to hear from you if you use heat to form the
plastic to the shape of the cabin side. In my case the size of the piece of
acrylic meant building a rather large oven of some sort and I wasn't sure if
I softened the plastic whether any clamping in place might leave impressions
in it. If you try using heat, please let us know how it works.

Graham 

-----Original Message-----
From: rhodes22-list-bounces at rhodes22.org
[mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of The Rhodes 22 Email
List
Sent: May-26-15 9:13 PM
To: The Rhodes 22 Email List
Subject: Re: [Rhodes22-list] Fixed Ports

So my four fore ports have already been replaced, so i'm trying to get out
with the minimal work necessary, though I love the size of your deadlights.
I also didn't realize the curve in the fiberglass until seeing your photos.

I believe i'm going to try 3/16" or 1/8" plexiglass (not lexan) as it should
flex better for the hull curve.  I might also try heating the plexiglass to
match the hull curve, depending on pressure required for holding in place
for the cure time.

I'm seeing other posts about doing the double sided tape with silicon, but
i'm hesitant, seems to me making a silicon gasket, then using screws to pull
the plexiglass in tight after 24 hours of curing would improve the seal
drastically.  Based on my understanding of thermal expansion, on individual
deadlights the worst case thermal expansion for me would be 0.06" difference
between the acrylic and fiberglass, so I wouldn't think that would be a
problem.

-- Curtis

On Mon, May 25, 2015 at 7:04 PM The Rhodes 22 Email List <
rhodes22-list at rhodes22.org> wrote:

> Curtis:
>
> I am planning to do as you suggest - apply smoked Plexiglas with 
> special double-sided tape and glazers sealant. I have done the 
> research and made the window pieces, figured out a clamping system and 
> obtained the materials. I hope to be installing the windows in a few 
> weeks once other repairs are finished - and I get up the nerve. The 
> best set of instructions for this that I have found on line is here:
> http://www.thecoastalpassage.com/windows.html .
>
> Total material costs for Plexiglas, tape and sealant is about $300 
> Canadian which probably means about half that in the US.
>
> This is my second try. First time was about in about 1993 when I did 
> everything wrong. Those were the pre-internet days for me. I used the 
> wrong sealant (silicone), attached the glass snug with screws, and 
> used Lexan rather than acrylic Plexiglas, to name only a few mistakes. 
> Thermal expansion eventually resulted in the Lexan breaking at the 
> screw holes and the silicone leaked. I also used clear Lexan that I 
> painted black on the inside. The paint peeled. Even so, it lasted 
> about 10 years without serious issues.
>
> I chose to make one window for each side rather than three. Three 
> windows reduces the expansion factor and might make installation 
> easier but I like the looks of the single piece.
>
> This time I will try it without using any hardware. The adhesive tape 
> is supposed to be as strong as the hardware and allows for thermal
expansion.
> The problem is that the sides of the cabin is a complex curve. While 
> the tape is tenacious I want have a system to clamp the panels in 
> place while the tape and sealant cure. I have experimented with 
> clamping systems both complex and simple and settled on the simple 
> one. It works in dry runs but whether it will work once the tape and 
> sealant is applied is something to be learned from experience - and I 
> hate learning from experience as it is almost always bad experience. I 
> have attached some pictures of the clamping system I intend to use. If 
> you want more information just ask. I also attached a picture of the 
> boat with the previous Lexan windows just so you can get an idea of 
> what it looks like.
>
> If you are wondering what the ring is that the clamp is attached to, 
> that is the new chainplate I have installed to replace the old ones. I 
> assume something similar could be rigged using the original 
> chainplates.
>
> If you are interested, I will let you know what happens - when I get 
> up the nerve.
>
> Graham
>
>
>
> -----Original Message-----
> From: rhodes22-list-bounces at rhodes22.org
> [mailto:rhodes22-list-bounces at rhodes22.org] On Behalf Of The Rhodes 22 
> Email List
> Sent: May-25-15 2:20 PM
> To: The Rhodes 22 Email List
> Subject: [Rhodes22-list] Fixed Ports
>
> Has anyone replaced the 4 fixed portlights recently?  I'm at the point 
> where its necessary (all four leak, and the black plastic is 
> cracking).
>
> I'm having issues finding replacements of the same size.  Cutout hole 
> size measures 5" x 11.75".  I saw the post from two years ago 
> mentioning Beckson, but they don't offer my size.
>
> Based on the cost i'm seeing if I had to enlarge the existing holes, 
> i'm tempted to just replace the outside trim/window and gluing on some 
> smoked plexiglass or lexan.
>
> Any suggestions?
>
> --
> Curtis
> Havre de Grace, MD
> s/v "Ruck It"
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