Acrylic portlight thickness.

[Rumrace]

A good frame has an expansion area. Where window manufactures used a rubber on your homes boats are using TPU gaskets. Like running shoe soul UV chemical resistant to take up movement of lens.

[JPA Cate]

Data points: Our portlights that open are 6 mm; our deck hatches (~ 2 x 2 ft) are 12 mm. Deck hatches are smoky acrylic. "Lexan" IS stronger, but gets cloudy from salt water, and requires polishing to keep it clear. Polish for the lenses over automobile headlamps works well.

Ann

[GILow]

Originally Posted by JPA Cate

Data points: Our portlights that open are 6 mm; our deck hatches (~ 2 x 2 ft) are 12 mm. Deck hatches are smoky acrylic. "Lexan" IS stronger, but gets cloudy from salt water, and requires polishing to keep it clear. Polish for the lenses over automobile headlamps works well.

Ann

I'll be very interested to see how those numbers stack up against the great post by ItDepends.

The glass in the old portlights on the KP seems to be a little under 6mm. Another point for comparison.

[Cheechako]

Originally Posted by tkeithlu

QUOTE: "Glass portlights don't need frames but can be glued into position just as a car windscreen is."

Whoa. I used to run a 25 ft. work boat with a tempered glass windshield mounted that way. Another user crossed a wake, took it on the bow, and spread the windshield all over the floor of the wheelhouse. I think clamping strips or an overlap are called for.

While testing an experimental boat with Tempered Glass spray shield mounted in an aluminum enclosure, a wave remnant plowed through hit the windshield, shattered, and it sliced up the driver big time. Pretty surprising, not like a green water full wave. Major damage to tendons in his wrist and hand.

It was a fairly big shield though, thinking... 32-36 x 24 high? It was rubber mounted, but not sealant mounted as mentioned.

Good small portlites seem to be 3/8" plexi or lexan.
IIRC my glass ones were at least 1/4" glass.. But these were only maybe 10 x 5 portlites.
For large-ish side windows I would want 1/2" like decent hatches.

[noelex 77]

Originally Posted by Cheechako

While testing an experimental boat with Tempered Glass spray shield mounted in an aluminum enclosure, a wave remnant plowed through hit the windshield, shattered, and it sliced up the driver big time. Pretty surprising, not like a green water full wave. Major damage to tendons in his wrist and hand.

Tempered glass should not fracture in this fashion. The tempering process is designed so that even if a breakage occurs the glass crumbles. Fragments should be benign and unlikely to cause injury. Very high speed small missiles can occasionally cause sharp fragments to form but this type of breakage is very rare on boats.

It is possible that in this case the hardening process was not correctly performed, or that untempered (ordinary) glass was used.

Visually, tempered and untempered (or incorrectly tempered) glass appear identical, although it is possible using polarising filters to identify glass that has received this heat treatment.

One of the few advantages of plastics is that the properties are intrinsic to the material and it does not require any subsequent (hard to verify) treatment to be safe to use on a boat . Tempered glass requires an expensive heat or chemical process to increase its strength and improve its shatter pattern.

[coopec43]

Originally Posted by tkeithlu

QUOTE: "Glass portlights don't need frames but can be glued into position just as a car windscreen is."

Whoa. I used to run a 25 ft. work boat with a tempered glass windshield mounted that way. Another user crossed a wake, took it on the bow, and spread the windshield all over the floor of the wheelhouse. I think clamping strips or an overlap are called for.

ABSOLUTELY!!

Toughened glass glued in place is NOT safe (That is why it has been banned in motor cars)

"Since 2014 Lewmar has invested heavily in the machinery and talent required to launch an entirely new range of glass & glazing products. From flat to curved, monolithic to laminated, fixed to opening and clear to full-colour frit printed;"

https://www.lewmar.com/Glass%20Products

[Nekton73]

Hope the OP doesn't mind me asking a sort of related question here...



Anyone have, or ever seen or considered, a non-opening portlight (porthole?) in the forward facing portion of the cabin top in the v-berth? When I am below I have good visibility in all directions, and in all parts of the cabin, except straight ahead in the v-berth. Of course there's no substitute for keeping watch from above deck but I would find it reassuring to be able to look forward when I am below when under way, and also when at anchor.



I recently replaced my saloon windows and v-berth hatch cover, and upsized as I felt the originals were a bit thin. Old saloon were 1/4" smoked acrylic and hatch was 3/8", bedded on butyl, both heavily crazed and cracked at many of the through holes where they were through bolted. For the new install I went the VHB tape and polyurethane sealant route and upsized to 3/8" for the saloon and 1/2" for the hatch, and am very happy with the result. The 1/2" on the hatch was mainly for extra support if accidentally stepped on as the old 3/8" had quite a bit of flex. The 3/8" on the cabin sides seems almost overkill compared to the old 1/4" (although no regrets, it looks great and is reassuring to have the extra thickness) and I was thinking it would be sufficient for the front facing as well.



The cabin top sides are 3/16" thick fiberglass with no core. The front facing section of the v-berth is roughly 24" high by 30" wide. I was thinking maybe just a round opening of about 8" diameter, or an oval about 6"x10".


Thoughts appreciated.

[GILow]

Originally Posted by ItDepends

With the caveat that "nothing too strong ever broke", this is the only calculation for this I have seen. It is specifically for wheelhouse windows, and should work for smaller openings as well:

From Lloyd's Special Service Craft P3, Ch 4, sec 7.8

Thickness calculations for toughened safety glass, not less then 6 mm.

Calculate thickness with:

t = .005b*sqrt(B*p) [mm]

b = length of shorter side of window, in mm
p = design pressure (take 70 kN/m^2).
B = -.17 + .54*A-.078*A^2 for A<=3
= .75 for A > 3

A = aspect ratio of window, a/b
a = length longer side of window

Multiply the calculated thickness by 1.3 for polycarbonate and by 1.5 for acrylic.

Llloyds does not allow Plastic as wheelhouse windows, but you probably aren't building to their standards.

The design standards a a gold mine of design information, and if you are building boats, you should have them. They are free.

So crunching the numbers for an opening 340mm x 170mm gives me 7.1mm acrylic. In practice this means 8 mm acrylic.

Bugger.

Real trouble finding 8 mm acrylic in anything with a tint. Some ok choices in 6 mm but I think I'd rather trust Loyds on this one.

10 mm has some tints available but I suspect it will look a bit odd.

Hmmmm.....

[GILow]

Originally Posted by Nekton73

Hope the OP doesn't mind me asking a sort of related question here...



Anyone have, or ever seen or considered, a non-opening portlight (porthole?) in the forward facing portion of the cabin top in the v-berth? When I am below I have good visibility in all directions, and in all parts of the cabin, except straight ahead in the v-berth. Of course there's no substitute for keeping watch from above deck but I would find it reassuring to be able to look forward when I am below when under way, and also when at anchor.



I recently replaced my saloon windows and v-berth hatch cover, and upsized as I felt the originals were a bit thin. Old saloon were 1/4" smoked acrylic and hatch was 3/8", bedded on butyl, both heavily crazed and cracked at many of the through holes where they were through bolted. For the new install I went the VHB tape and polyurethane sealant route and upsized to 3/8" for the saloon and 1/2" for the hatch, and am very happy with the result. The 1/2" on the hatch was mainly for extra support if accidentally stepped on as the old 3/8" had quite a bit of flex. The 3/8" on the cabin sides seems almost overkill compared to the old 1/4" (although no regrets, it looks great and is reassuring to have the extra thickness) and I was thinking it would be sufficient for the front facing as well.



The cabin top sides are 3/16" thick fiberglass with no core. The front facing section of the v-berth is roughly 24" high by 30" wide. I was thinking maybe just a round opening of about 8" diameter, or an oval about 6"x10".


Thoughts appreciated.

Really worth starting a new thread. It's an interesting topic.

[GILow]

Originally Posted by GILow

So crunching the numbers for an opening 340mm x 170mm gives me 7.1mm acrylic. In practice this means 8 mm acrylic.

Bugger.

Real trouble finding 8 mm acrylic in anything with a tint. Some ok choices in 6 mm but I think I'd rather trust Loyds on this one.

10 mm has some tints available but I suspect it will look a bit odd.

Hmmmm.....

Oops, make that 8.1 mm, multiplied by 1.3 not 1.5.

[Nekton73]

Thanks for crunching those numbers. Coincidentally that is just about the size I was considering for my front facing port, so 3/8" should be more than sufficient. Still interested in opinions on actually doing it.



Not sure if it helps you in Australia as they only ship to the continental US, but if you know someone who can ship them on to you afterwards this is where I bought my replacement pieces from:


https://www.estreetplastics.com/Tran...heets-s/55.htm


I chose #2064 smoked grey, looks great. It took about 2 weeks from placing the order to actually shipping. Packaging was very good, no worries about damage in transport.

[JAFO]

Originally Posted by Nekton73

Not sure if it helps you in Australia as they only ship to the continental US, but if you know someone who can ship them on to you afterwards this is where I bought my replacement pieces from:


https://www.estreetplastics.com/Tran...heets-s/55.htm

For getting items forwarded to Australia from the US, when I needed to get some hardware from McMaster-Carr, I had good results with Shipito.

[noelex 77]

Originally Posted by coopec43

ABSOLUTELY!!

Toughened glass glued in place is NOT safe (That is why it has been banned in motor cars)

A mechanical retaining system for boat windows (in addition to glue/sealant) is a nice, but increasingly a rare system for both plastic and glass glazing.

My understanding is modern car windows are simply glued in place (there is not much chance of a car sinking if the window integrity is compromised ). I am not sure why you think this has been banned.

[skenn_ie]

A word of caution here. I recently glued acrylic panels into wooden frames. The panels have been on the boat for several years, but just pressed against rubber window seals. Since glueing them in, several of then have developed substantial cracks starting at the edges. How or why, I haven't yet worked out. I do know that extruded acrylic is likely to have internal stressed due to uneven cooling, so nicks along the edge can be the start of stress fractures. Factories use a hydrogen flame to melt the edges to smooth out the cut marks and reduce fracturing. I wonder if heating the whole panel to vacuum-forming temperature after cutting could relieve those stresses. Cast acrylic doesn't have those stresses anyway, but is not optically correct (varying thickness across the panel).
Polycarbonate is very strong, but is almost impossible to remove scratches. It is also hard on cutting tools. Vivak (a brand name) is almost as strong, but easier to work/hot-form.

[Cpt Mark]

Borrowing this thread for my own selfish purposes

My cat has the truly sexy wraparound compound curve windows, one of which cracked as they all will. Finally found a thermoforming company that for $1,000-$1,500 will form what I need if I supply the mold and plastic. They don't stock what I would prefer to match. The plastic I have wraps all the way around the boat.

Current acryllic is 1/2" thick. My plan is to eliminate the wrap around feature. This greatly simplifies the bending process to the point where with a steam box I should be able to make the small required gentle bends.

Where I'm really having a hard time is finding the Acryllic! I'm in Portland Oregon so choices are small. Anyone have a line on a manufacturer or distributor that works in the PNW or West coast of the U.S.?

Color choice, bronze 2307.

Thanks