Why can't I use film for heat and uv control?

[RKsailsolo]

The tropical sun is degrading my plexi cabin windows and hatches. Will an exerior application of solar/uv control film stop this or at least retard it to some degree?

[Ric Sheridan]

Only if it is designed for first surface application. Then you will have to get the 3M window sealer to seal the edges from wicking up water. If the windows are crazed just replace them. I read somewhere here that the only sealer to use on sailboat windows is the Dow Corning Commercial grade window caulking.

[tkeithlu]

Probably not. I was tempted to reach the same conclusion - that UV light was the cause, but Wikipedia says it's stress, not light, that causes crazing in acrylics (and other polymers).

"Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction. The effect is visibly distinguishable from other types of fine cracking because the crazing region has different refractive indices from surrounding material. Crazing occurs in regions of high hydrostatic tension, or in regions of very localized yielding, which leads to the formation of interpenetrating microvoids and small fibrils. If an applied tensile load is sufficient, these bridges elongate and break, causing the microvoids to grow and coalesce; as microvoids coalesce, cracks begin to form."

[Ric Sheridan]

Do not use Plexiglas for windows. Use Polycarbonate. If you use cheaper Plexiglas you will be sorry. Poly Carbonate is what they use on vending machine fornts.

[JPA Cate]

One thing you can do that will stop further degradation is to make (or have made) sunbrella or shade cloth covers for the hatches and port lights. It will depend on the actual hatch, for the design of such a cover, but one can usually work something out. If they are too far gone, then replace with fresh acrylic, and cover them. Use a dark color with the sunbrella: the darker colors have been shown to absorb more UV.

In our case, I've covered the mid hatch with Breezeway, so as to allow some light in, and that cover stays on full time. For our main hatch, we invented a dorade style cover that attaches around the bottom of the hatch (on the deck), and ties forward to the baby stay. It allows us to leave the hatch open a bit when it rains....but then we live on our boat full time. You may not want a hatch dodger at all. Ours was made from stamoid, a solid pvc cloth with a 10 yr. guarantee.

Ann

[RGN]

Originally Posted by Ric Sheridan

Do not use Plexiglas for windows. Use Polycarbonate. If you use cheaper Plexiglas you will be sorry. Poly Carbonate is what they use on vending machine fornts.

Poly-carbonate fares much worse with UV degradation than Acrylic does. You can buy treated Lexan and it will do a lot better but similarly treated Plexiglas will still be much better. Check the suppliers for info.

[sailorboy1]

There is an exterior film to saw last year. It was very expensive.

[Bycrick]

Polycarbonate will not stay clear in the tropics. It will gradually cloud and yellow. But you won’t break it.

Acrylic won’t cloud but it will "craze." I have 4 opening hatches and the companionway sliding hatch which has been under the dodger. All completely flat. The 4 that are in the sun have been changed twice since 1998, because of "crazing." I finally changed the companionway lens this time because it was cheaper to buy the bigger sheet. Some crazing, but it was almost 40 years old.

[contrail]

Originally Posted by Bycrick

Polycarbonate will not stay clear in the tropics. It will gradually cloud and yellow. But you won’t break it.

Acrylic won’t cloud but it will "craze." I have 4 opening hatches and the companionway sliding hatch which has been under the dodger. All completely flat. The 4 that are in the sun have been changed twice since 1998, because of "crazing." I finally changed the companionway lens this time because it was cheaper to buy the bigger sheet. Some crazing, but it was almost 40 years old.

My experience with Polycarbonate in the tropics is that it crazes very badly. In my case, in two years.

[wfetter]

We use this for heat on the hatches. It's made a huge difference. Now, it does nothing for crazing since, as mentioned, that's stress not U/V but it has cut down on the heat in the boat tremendously.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[stewy]

Use PERF on the portholes / hatches! Available in any sign making store. Inexpensive. You can see out. You can't see in. Some decent UV / heat protection.

[vpbarkley]

If tensile forces are a prime cause of crazing in acrylics, those forces are likely the result of different thermal expansion rates in the constituent materials - glazing, surround and cabin and a lack of compliance in the seal.

A solution would be a seal that can readily accommodate the differential expansion of the assembly. If a sealer is used, a thicker application will offer increased compliance. It's also important that the sealer doesn't harden over time.

Perhaps common marine sealers are not ideal for this application. Just a thought.

[Locquatious]

It's not tropical sun, more like tropical forest, but we have some plexiglass over the porch that has been in place for 45 years. There may be slight crazing but the surface is shiny hard.
We have some polycarbonate skylights that have been in place for 5 years. The surface seems to be more sensitive to mold growth and scratches. The surface is already not shiny hard like plexiglass.
Both have held up well against acorns and sticks dropping. Material scientists I have worked with indicate that polycarbonate has better impact resistance because it can pass a particular standard impact test with higher values. But a scratched polycarbonate may actually have lower impact resistance.

[Pauls]

VPBarkley's post about stress and bedding material/thickness is spot on.

Acrylic is a far better material for ports as regards scratch resistance and maintaining clarity over time. It is important to know that there are basically 2 different types of acrylic, extruded and cast. Extruded is softer, scratches easier and has a larger coefficient of thermal expansion, all undesireable for use on boats. Cast is harder and has a lower thermal expansion coefficient. It is the type to use. Cast is available in two types, cell cast and continuous cast. As far as I know there is little difference between these.

[Cliffhanger]

Crazing of clear plastics is due to internal stresses in the material. Those stresses are relieved over time, causing surface cracks (crazing). This process can be accelerated by some chemicals. Acrylic and polycarbonate are amorphous and so prone to chemical attack. The casting process creates less internal stress than extrusion and so cast acrylic is less prone to crazing.

Perhaps the most important thing to extend the life of clear plastics is to make sure you keep them clean (pollution can contain a variety of chemicals) but only clean them with soapy water or a cleaner specifically designed for clear plastics. Never, ever use an organic solvent to clean any clear plastic.

UV will make polycarbonate go yellow over time but UV stabilisers minimise this.

So, in my opinion, cast acrylic is a better option than polycarbonate for boat windows and hatches as it has better scratch, UV and chemical resistance. It also has slightly better clarity and is cheaper. Polycarbonate has superior impact strength though which might be an important consideration.

As for the original question about the UV film, I wouldn't use it. Depending on the adhesive it might actually do more damage than it prevents.