Hard Dodger Window Material

[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

[pcmm]

before you get to the windows...1 layer of 1708? Really? 1 layer of 1708 is only 0.044" thick not much for structure or impact resistance. I cant really see any less than 3 layers being reasonable for skin thickness.

For the glass, I would just use plexiglass as its relatively easy to machine, mouldable with heat if needed and readily available. 0.25" thickness minimum

[more]

3M Safety and Security Window Film for glass

[JPA Cate]

I would say that 1/4" is NOT thick enough. We had some 6mm plexiglass that shattered in a knockdown. It was supposed to have been 8 mm. That hard dodger had been built up from laminated door skin , and the plexiglass anchored by screws with adequately large expansion holes and glazing for acrylic sheeting.

As to using glass, armoured glass is wonderful, but it IS heavy; and it is clear. I've seen it used on dodgers on steel boats.

I don't know enough to comment on the lightness of construction, whether it is too light or not. Someone else will give an opinion on that, I bet, one way or the other.

Ann

[nuku34]

To the OP:
Re your window question:
For the sizes of windows indicated (which are fairly large), I'd go at least 8mm and maybe 10mm of acrylic. The forces in a knock down or from a large breaking wave are immense (I speak from personal experience). I like to put the windows on the outside of the dodger material with a least a 15mm overlap and through bolted with 6mm bolts in oversized holes to allow for expansion. Use a flexible non-adhesive sealer (not 5200).

Laminated or hardened glass would be ok as long as the structure is solid and doesn't flex, but it is expensive and holes for bolts would be a problem.
Yes, acrylic will scratch/craze over time, but its relatively cheap and easy to replace (if you don't use an adhesive sealer!).
Your dodger structure sounds very weak. Airex foam doesn't have much resistance to bending, and the epoxy layup sounds very thin. Again, unless you have been out there in very bad conditions, you will have no idea of the forces that the structure will have to resist. And the flat surfaces you show will cop more stress than a rounded form (which looks better) The upside is if a wave wipes it off your boat, you won't have a huge hole in the cabin top!

[SailingHarmonie]

Our hard dodger has 10mm acrylic windows. They last 8 to 10 years depending on care and amount of uv exposure. I would not go thinner for an offshore boat.

On a fleet of over 400 very actively sailed sister ships, I’ve never heard of a window failure. “Nothing too strong ever broke.”

On the op’s post, the dodger really needs to be rigid. If it flexes, any method of fitting windows will fail. And by “rigid” I mean during a wave strike with tons of water washing the deck.

[scherzoja]

Hey ya'll,

Thanks for the input on window material and structure. I received the quotes from the window makers and have inputted the data into a spreadsheet to compare the costs of pre-fab windows with acrylic/polycarbonate panels I put in place. The price difference between prefab glass windows, when accounting for the hardware and installation materials needed for plastic panels, and plastic panels that I install is roughly twice that of the plastic panel installation (or 3X depending on which vendor). That includes the hardware needed to make the forward opening window (hinges, latches, stainless gas struts).

Once I get the dodger finished, I will know how rigid it ends up being, then I can review the window cost spreadsheet (and my bank account). I'll be able to make a better decision at that point. Thanks again for your help and I hope y'all have a great weekend.

[thinwater]

If the consensus is 8-10 mm windows, then 2-3 layers of 1708 is the minimum. That was the layup on many parts of my pretty darn light PDQ, including the hard top. On layer on the inside might be OK, but I'd go 2.


The window mounting descriptions puzeled me. Practically all plastic glazing is mounted with thick VHB tape and DOW 795. You do NOT want to use polyurethane sealant; the bond is not UV resistant and will fail after some number of years unless an opaque primer is used (this is in Sikas instructions).

[Matt Johnson]

If you recess the edges, you can bond glass to the hard dodger without needing the aluminum frames. Bonding is the same as acrylic, but they do need their edges protected from impact.

The easiest comparison for the glazing thickness is to look at production deck hatches from companies like Bomar, Lewmar and Vetus. For similar size opening hatches, the manufactures typically use 10-12mm acrylic.

[s/v Jedi]

Build a rebate into the openings so that the outside is flush after window installation. This protects the edges of the windows against impact and/or UV damage. It also aids window installation.

Use 10mm acrylic (Perspex) for the front facing windows. The side windows 8mm acrylic.

Mount with VHB tape that is set back 6mm on the windows. Get a thick VHB tape and account for that thickness when preparing the rebate. Also, the window must leave a 6mm gap all around the edge.

You can use foam tape for the inside edge, to fill the space between window and flange so that no dust etc.can get in later.

After sticking the window in with the VHB tape, use a glazing silicone (like Dow 795) to fill the 6mm gap around the window, with the nozzle all the way down to get the silicone into the 6mm setback against the VHB tape as well as filling the 6mm gap around the window. You need that much space to cope with thermal expansion.

For an opening window, I recommend to open a center section of the window so that you have a ringof acrylic mounted all around like a fixed window. With a router and a couple of templates, create the opening as well as the piece that was cut out, a couple mm smaller due to the kerf of the blade used and the cleaning of the edges with router and template.

Now make an acrylic ring that you can mount on the inside functioning as a flange for the opening part. You need to route a dado or channel around it for the gasket. This leaves the hinge. You can buy an acrylic hinge as a replacement part for golf cart windows. I’ve seen them on Amazon. It’s all acrylic. The flange and hinge are glued, so you have zero metal hardware but you still need two latches for securing it as well as something to hold it open. A gas spring is okay but a dowel works too. You can buy fiberglass sticks with reflectors that people stick in the ground along driveways etc. that make excellent material for these kind of applications. For latches you could use acrylic cogs that turn around a machine screw that taps into the flange.

Do not use mechanical fasteners for the windows. It’s a path of hurt that isn’t needed now that we have VHB take.

[s/v Jedi]

Here’s the hinge I mean… it’s waterproof: https://www.amazon.com/Source-Premiu.../dp/B06Y1V4GDX

[thinwater]

Thermal Expansion. If you do the math on the difference in growth between fiberglass and plastic glazing, you'll see that somewhere around 3-4 feet the differential becomes quite a strain on the tape and the sealant. My experience, across several boats, and the experiences of others, seems to be that somewhere between 30" and 40", the frequency of leaks after 5-10 years goes way up. Properly installed, almost never on the smaller windows. Practically always as windows approach 5 feet.


My suggestion is to break them up with structural sashes every 30 inches or so. If the windows butt within ~ 3/8" with black sealant, it will look like one piece from the outside. On the inside, comfort yourself that it is stronger and will last.


Making the window from thicker plastic does not help with the thermal expansion problem.


This is less of an issue with glass, because it expands 10x less.

[Knotical]

Originally Posted by s/v Jedi

Build a rebate into the openings so that the outside is flush after window installation. This protects the edges of the windows against impact and/or UV damage. It also aids window installation.

Use 10mm acrylic (Perspex) for the front facing windows. The side windows 8mm acrylic.

Mount with VHB tape that is set back 6mm on the windows. Get a thick VHB tape and account for that thickness when preparing the rebate. Also, the window must leave a 6mm gap all around the edge.

You can use foam tape for the inside edge, to fill the space between window and flange so that no dust etc.can get in later.

After sticking the window in with the VHB tape, use a glazing silicone (like Dow 795) to fill the 6mm gap around the window, with the nozzle all the way down to get the silicone into the 6mm setback against the VHB tape as well as filling the 6mm gap around the window. You need that much space to cope with thermal expansion.

For an opening window, I recommend to open a center section of the window so that you have a ringof acrylic mounted all around like a fixed window. With a router and a couple of templates, create the opening as well as the piece that was cut out, a couple mm smaller due to the kerf of the blade used and the cleaning of the edges with router and template.

Now make an acrylic ring that you can mount on the inside functioning as a flange for the opening part. You need to route a dado or channel around it for the gasket. This leaves the hinge. You can buy an acrylic hinge as a replacement part for golf cart windows. I’ve seen them on Amazon. It’s all acrylic. The flange and hinge are glued, so you have zero metal hardware but you still need two latches for securing it as well as something to hold it open. A gas spring is okay but a dowel works too. You can buy fiberglass sticks with reflectors that people stick in the ground along driveways etc. that make excellent material for these kind of applications. For latches you could use acrylic cogs that turn around a machine screw that taps into the flange.

Do not use mechanical fasteners for the windows. It’s a path of hurt that isn’t needed now that we have VHB take.

Jedi, that is an excellent write up, visualizing the process I imagine it not being that easy to inject silicone under the plastic with the rebate that you are talking about. Do you suggest making a wide rebate, or maybe use a small and curved nozzle?

[Bowdrie]

Originally Posted by scherzoja

Once I get the dodger finished, I will know how rigid it ends up being

How "rigid" it is has little to do with strength.
Others have posted some good info about sealing/mounting, etc.
But your lay-up schedule is woefully lacking.
A much heavier lay-up should be used.
Add a goodly amount of camber to the top.
Don't stint on the interior lay-up either.
Hard dodgers are one of the "add-on" structures that benefit from being overbuilt to a degree.

[JPA Cate]

Hard dodgers are one of the "add-on" structures that benefit from being overbuilt to a degree.

Yes, I remember Jim telling the man who made ours, "It has to be strong enough that I could fall on it, and not damage it."

Ann