Hard Dodger Window Material

[Cavalier MK2]

The acrylic plexiglass in either form won't craze but cast expands less. Lexan/polycarbonate will yellow and craze over time, coatings slow this down. Acrylic is 10 times stronger than glass, polycarbonate is stronger yet. For a multihull glass is so much heavier you shouldn't use it on that alone. I use thick grey VHB 3M tape which gives you the gap you need for the adhesive sealant. I use Dow products with the large expansion rate. 1 1/2 overlap has been plenty, the sealant also covers the edge, the inside of the overlap is painted with appropriate plastic adhering paint to protect the joint from UV and tidy up appearances.

[s/v Jedi]

Originally Posted by Tupaia

Got to disagree.

Try wearing sunglasses at night. It's not because it's dark outside.

This a hard dodger, I assume to replace a soft dodger with PVC clears. If you have ever piloted a powerboat from inside a cabin you will understand. They invariably have clear forward windows. Pretty much the same applies to tinted windows on motor vehicles. Most countries strictly regulate of prohibit tinted windscreens because it cuts down night time vision. Even clear glass/plastic reduces clarity over nothing at all.

Sure there are lots of modern aids but they are just that aids.

But so is a window. Of course I agree that when you would try to see a dark object in the night then a clear window is better. But we’re trying to see lights at night and this works fine with tinted windows.
Of course there are many levels of tint, you don’t need to go all blacked out. I have the 2nd lightest tint where they often sell 4 levels and it is fine, not overly hot during the day and still good enough to see all the ships around you at night. Been looking through these windows for 21 years now.

[coopec43]

Why wouldn't you use toughened (tempered glass) like yacht constructors do? Glue it in place like our car windows are!

[coopec43]

Advanced marine glass products for new build & refit yachts

"Chemically toughened glass is five to eight times stronger than toughened glass. It retains its colour and light transmission properties after treatment."

https://www.berthglaze.com/marine-glass

[Cavalier MK2]

Still not as strong as plastics and way to heavy for multihulls. Heavy boats may like it. For dodgers you would be adding weight up high, bad for the center of gravity so increasing roll moment for monohulls.

[coopec43]

Originally Posted by Cavalier MK2

Still not as strong as plastics and way to heavy for multihulls. Heavy boats may like it. For dodgers you would be adding weight up high, bad for the center of gravity so increasing roll moment for monohulls.

Sorry! (I wasn't aware the yacht the dodger was going on was a catamaran)
Yes weight is terribly important with a cat.

[scherzoja]

Thank you for the link to tempered glass. I haven't ruled out glass completely, but have excluded prefab windows because of cost. From what I understand, the two plastic choices are still stronger than glass. However, glass does have the scratch resistant advantage over plastic. My concern is that if there is any flex or twist, the glass will break. This might be a unfounded fear; nonetheless, the concern is still present. Once I get the dodger fiberglassed, I'll know how flexible it is.

Regarding weight, for my largest window (32 x 12"), the weight difference between glass and acrylic is about 2 lbs (5lbs vs 7 lbs). The total weight difference for all windows is only about 7 1/4 lbs. This is for a 37' monohull and I think this weight difference is not that much.

My primary concern with glass is its inflexibility. I do concede that I don't know how much twisting or bending glass can take before it breaks. A reservation I have with tempered glass specifically is that, unless coated with film like what "More" mentioned in post #3, if it breaks, I have a hole. It won't sink the boat, but will introduce considerable discomfort. Laminated glass solves this, but it's not as strong. There is no perfect solution (light, non-scratch, stick together when breaks, wont' break with twisting, low cost, replacements easily sourced, UV resistant, least complication.), but acrylic seems to meet many of these criteria.

I did a quick check on that onedayglass.com site posted the other day and the price difference between a piece of glass and acrylic of the same dimensions (1/4" thick) is about $20 more for glass. However, If I use price out 1/4" glass with 3/8" acrylic, the price is the same. It's possible that a local shop can match or beat the prices. It's interesting that the sister company to OneDayGlass quoted me for glass/aluminum framed windows and was among the highest priced quotes.

I've still got some time to mull this over because the fiberglassing is not comp and won't be for at least another week. The are not as warm as they were this summer, still workable with a swing from 50s to 80s in 24 hours. The two exterior layers are on and I now have to test fit and layout the wire runs through the core and lighting placement before the interior layers can go in.

Again, thank y'all for the advice and information. This formerly daunting project is becoming easier as I gain greater understanding of the material and forces involved.

[Cavalier MK2]

For the same thickness acrylic weighs 50% less than glass, it also doesn't require a frame structure which saves more weight. Obviously weight is less important for a cruising monohull, the rubber style of insert window seal for glass does allow for structure flex. They are heavy too however.

Acrylic cuts well with a jigsaw using a plexiglass blade, a belt sander dresses the edges if you like doing your own projects.

[coopec43]

scherzoja

As far as glass being flexible. If you lean against a large pane of glass it will bend All our cars would flex a little and I wonder if the adhesive allows for that?


https://www.reddit.com/r/HomeImprove...ass/?rdt=64415


I worry about plexiglass/Lexan crazing.

[Bowdrie]

I don't think any of us have to keep harping about weight, the OP has already said that the difference between selected thicknesses of plastic vs. glass is only ~7>8 lbs.
That's nothing on a monohull, and d**m little on a multi.
Rigidity? a shoe box without a lid has very little rigidity, add a well fastened top and the structure becomes quite rigid.
A strong structural top, well integrated to the front/sides, (with goodly camber,) is the key to keeping the front/side panels rigid, (assuming they have structural integrity with WELL joined corners).
The OPs lay-up schedule, (a couple layers,) still seems weak to me, and such a lay-up is much too thin to receive or hold any fasteners.
Glass panes can be fitted with thick rubber gaskets on both sides of the edges of the panes and secured by simple retainers.
But the rabbets/recesses in the panels have to have sufficient structure to hold fastenings.
Or, simply not use recesses in the fiberglass structure and mount the panes externally, overlapping the openings.
That has much to recommend it, everything becomes far easier, whether glass or plastic.

[Cavalier MK2]

Yeah back to the crazing, acrylic doesn't, lexan does, I've run the same plexiglass windows for over 10 years without issue. Planes from WW2 with plexiglass windows that weren't shot up are still clear. Weight wise replacing my glass back when saved 100 pounds but that included those seals.

The thick VHB tape and appropriate sealant should accommodate some flex for glass.

[Cavalier MK2]

So for those numbers, biggish multi here uses 1.5 sheets of 8x4 window material . 105 pounds per sheet, say 158 total on 1/4 glass plus 100 the seals.

258= pounds

Plexiglass 50 pounds a sheet x 1.5= 75 pounds total, weight of tape and sealant less than 10 pounds.

Obviously a mono shouldn't have this much glass area but a for a cat or tri it is worth it.

[SV__Grace]

I'm a fan of Boatwindows.com and they make a "heavy duty" version that might be a good choice for your application.

Having replaced the windows in the salon of our Nauticat I learned the importance of having a flat mounting surface, and on a boat surfaces are rarely flat even if they appear so. You shouldn't have that problem for new construction but being able to "float" a new epoxy bedding for a window, hatch, or port is a good skill to have for anyone replacing windows. (it's not hard to do, even for an amateur like me)

Boats do flex and it seems to me that if your dodger panels are strong, stiff and rigid, with strong window frames such as mentioned above you will be fine and the worst that happens is the bedding gives way and starts leaking, which can be easily fixed (flexible sealant would be preferred for this application). Why not fiberglass the core? Even better, why not marine plywood, you need the strength more than the weight savings.

Originally Posted by scherzoja

I am building a hard dodger and am at the point of deciding on window material.

My two choices are between one of the two plastics (acrylic/polycarbonate) that I install and manufactured framed glass windows (boatwindows.com, wynneinc.com, bomon.com, etc...)

The dodger is 1" Airex T92.100 foam core with 1 layers of 1708/Epoxy with 2 or 3 layers in corners and unsupported edges. It will be bolted to a G10 cleat glassed to the coach roof.

Window at forward end of the dodger will open, hinge up. The two windows per side will be fixed windows . I've attached a drawing of the windows.

I am leaning toward glass because of the scratch/crazing issues with the plastics, but I am concerned that the glass might break from bending/twisting. The dodger panels are straight, no curves, but it's not finished yet, just tacked together the core, so I don't know how rigid it will be (see picture).

For those of you who have aluminum-framed glass windows with a cored fiberglass hard dodger, is breaking from twisting/bending an issue?


Thanks

[Mark Johnson]

3/16" coated both sides polycarbonate. Leave 1/16" min all around for expansion.

[quartersplash]

There is a type of plexiglass that you can get that has an actual glass coating. I don't remember what it is called but I used to use it in my race cars on the windshield and side windows and I made hundreds of runs at 270 mph without failure. The glass coating keeps the windows from scratching. Without the coating, in a couple years of washing, the windows are all scratched up and getting hard to see through.