A Clear View: Replacing Perspex Boat Windows

Replacing perspex boat windows is a complex task that requires careful planning and execution. Perspex, also known as acrylic, is a popular choice for boat windows due to its strength, durability, and impact resistance. However, it is important to select the appropriate type of perspex and follow the correct installation procedures to ensure a successful replacement. The process typically involves creating templates for the windows, cutting the perspex sheets to size, painting and preparing the edges, and finally, installing the windows using silicone or two-sided tape. While it is possible to replace perspex boat windows as a DIY project, seeking professional assistance may be advisable to ensure a proper fit and seal.

Choosing the right material: Perspex, acrylic or polycarbonate

When choosing the right material for your boat windows, there are several factors to consider. All three materials—Perspex, acrylic, and polycarbonate—are types of plastic that offer greater resistance to forceful impacts than glass. However, there are some key differences between them that will help determine the best option for your needs.

Firstly, let's look at damage resistance. Polycarbonate is the strongest of the three, with over 30 times the impact resistance of glass. Acrylic, while still very strong, falls just short of polycarbonate's strength, offering between 10 to 24 times the resistance of glass. Perspex, a type of cast acrylic sheet, can resist impact 17 times more than glass. So, if strength and impact resistance are your primary concerns, polycarbonate may be the best choice.

Another factor to consider is colour. Acrylic offers a much wider range of colours than polycarbonate, which has a more limited selection. It is important to note that polycarbonate's colour clarity will diminish over time, and it will turn yellow with prolonged exposure to UV rays. Acrylic, on the other hand, can be polished to restore its clarity if needed.

The ease of cleaning is another important consideration. Both acrylic and polycarbonate are easily cleaned with soap and water, but they have different resistances to harsher chemicals. Acrylic is more susceptible to damage from harsh chemicals and should not be cleaned with glass cleaners or ammonia-based sprays. Polycarbonate, on the other hand, can withstand these types of cleaners without issue. However, once damaged, acrylic is easier to repair than polycarbonate, as it can recover from minor damages like light scratches with minimal effort and expense.

Transparency is another factor to consider. Acrylic is marginally clearer than polycarbonate, and this difference will become more pronounced if the polycarbonate is allowed to yellow due to sun exposure. Over time, both materials will lose some visual clarity, but acrylic can be polished to regain its clarity, while polycarbonate cannot.

Cost is also an important consideration. Polycarbonate can be significantly more expensive than acrylic, ranging from 35% to 300% higher in price.

Finally, workability differs between the materials. Acrylic is generally easier to cut and manage, especially when using electrical tools. However, polycarbonate is better suited for drilling, as it can be safely drilled anywhere on the sheet with a standard drill bit without suffering damage. Acrylic becomes more susceptible to breaking the closer you drill to the corners.

In summary, all three materials offer excellent impact resistance, but polycarbonate is the strongest and most expensive option. Acrylic offers a wider range of colours, better clarity, and is easier to cut, but it is more susceptible to chemical damage and drilling-related breakage. Perspex, a type of acrylic sheet, falls in the middle in terms of strength and is a good choice for those seeking a balance between strength and clarity.

Measuring and cutting the windows

To replace your boat windows with Perspex, you will first need to measure the window frames to determine the size and thickness of the Perspex sheets you will need to cut. You can bring your old windows to a Perspex supplier, who can cut the sheets to size for you. Alternatively, you can create a cardboard template of the window and bring that to the supplier.

When measuring the window frames, ensure you get the exact dimensions, as Perspex sheets can be cut to any size and shape. You can also choose from a variety of colours and finishes to suit your preferences.

If you are cutting the Perspex sheets yourself, it is important to use the right tools and techniques to ensure a straight and accurate cut. You can use state-of-the-art CNC machines or laser cutting to achieve a precise cut.

Perspex is a versatile and durable material that is a great alternative to glass. It is lightweight, impact-resistant, and offers excellent clarity, making it a popular choice for boat windows.

Removing the old windows

Removing the old perspex boat windows is a challenging task but can be done with the right tools and preparation. Here is a step-by-step guide on how to remove the old windows:

Prepare the Work Area:

Before starting the removal process, ensure you have all the necessary tools and materials, including safety gear such as gloves and eye protection. Cover the surrounding areas of the boat with drop sheets or plastic sheeting to protect them from any damage during the removal process.

Remove Old Sealant:

The first step in removing the old windows is to get rid of the old sealant. This can be a tedious and time-consuming task, but it is crucial to ensure a clean surface for the new windows. Use a sharp blade or a sealant removal tool to carefully scrape away the old sealant from around the window frame. Be careful not to scratch or damage the boat's surface.

Mark and Number the Windows:

Before removing the windows, it is essential to mark and number each window and its corresponding frame. This will ensure that you know exactly where each window goes when installing the new ones. Use a marker or tape to label each window and its frame, indicating their position on the boat.

Carefully Remove the Windows:

Once the old sealant is removed, you can start taking out the old windows. Gently pry or unscrew the windows from their frames, being careful not to damage the surrounding areas. If the windows are glued in place, you may need to use a heat gun or a hairdryer to soften the adhesive before removing them. Work slowly and carefully to avoid breaking the windows or damaging the boat.

Clean and Prepare the Frames:

With the old windows removed, clean the frames thoroughly to remove any remaining debris, sealant, or adhesive. You may need to use a solvent or a mild detergent to cut through any stubborn residue. Ensure the frames are completely dry before proceeding to the next step.

Inspect the Frames:

Once the frames are clean, carefully inspect them for any damage, corrosion, or weaknesses. Look for signs of rust, cracks, or warping. If the frames are severely damaged, you may need to replace them or have them repaired before installing the new windows.

By following these steps, you can successfully remove the old perspex boat windows, preparing the way for the installation of new, clear, and secure windows.

Sealing the new windows

Step 1: Prepare the Surface

Before installing the new Perspex windows, it is essential to prepare the surface by cleaning it thoroughly. Remove any old sealant or residue from the previous window using a scraper. Ensure that the surface is free of dust and debris. You may want to use a primer or paint on the surface to create an even base for the new window.

Step 2: Cut the Perspex to Size

Cut the Perspex sheet to the exact size and shape needed for your window. You can use a jig saw with a metal cutting blade to cut the Perspex. If you're not confident in your ability to cut the Perspex yourself, consider taking the measurements to a professional or using a company that offers a cut-to-size service.

Step 3: Choose the Right Sealant

Selecting an appropriate sealant is critical for a successful window installation. Avoid using black sealants, as they absorb heat and exacerbate the expansion and contraction of the plastic. Instead, opt for a neutral cure, non-acidic silicone sealant. GE's Silproof SCS 2000 and Dow 795 are recommended products that have been used successfully in similar projects.

Step 4: Apply the Sealant

Apply a generous amount of the chosen silicone sealant to the surface, creating a bed for the window to sit on. Work the sealant into any gaps or crevices, ensuring full coverage. You may want to use a caulking gun to apply the sealant for a more precise and controlled application.

Step 5: Install the Window

Place the new Perspex window into the aperture, pressing it firmly into the bed of sealant. Use gloves to protect your hands and smooth out any excess sealant. Ensure the window is positioned correctly, as you will not be able to adjust it once the sealant starts to cure.

Step 6: Masking and Finishing

Apply masking tape to the outside of the window, just beyond the edge of the Perspex, to create a clean line for the sealant. Then, apply a bead of sealant around the outside edge of the window, smoothing it out with your finger. Carefully remove the masking tape immediately, pulling it away from the silicone sealant. Allow the sealant to cure for at least 72 hours before exposing it to water or heavy use.

Tips and Tricks:

• When drilling holes for fasteners, make them substantially oversized to accommodate the material's expansion and flexing.
• Use rubber washers to cushion screws and prevent cracks.
• Always wear gloves when working with sealants and keep a bottle of methylated spirits and paper towels on hand to clean up any messes.
• If you're unsure about any part of the process, consult a professional or seek advice from a marine specialist.

By following these steps and taking your time, you can ensure that your new Perspex boat windows are properly sealed and will withstand the elements.

Fixing the windows in place

Prepare the Windows and Apertures:

Start by cutting the Perspex/acrylic sheet to size, allowing for a 40mm (1.5-inch) overlap around the window aperture for the tape and sealant. Use a metal cutting blade on a jigsaw for a straight cut. If you need curved windows, consider using a CNC router for a more professional look. Mark the inside of the window, about 5mm inside the edge, and paint this area with a high-temperature paint. This step will reduce UV exposure and improve the overall appearance.

Masking and Sealant Application:

Apply masking tape to the boat, just outside the window aperture, to create a neat edge for the sealant. Carefully cut along this line with a scalpel or fresh box knife blade. Prepare the window by masking or applying a protective film to the outside, except for the 5mm border you previously marked. Apply a bead of silicone sealant under where the window edge will be, ensuring it doesn't invade the tape area.

Installing the Windows:

Remove the protective covering from the two-sided tape. Carefully place the window, ensuring it is correctly positioned. Use your palm to firmly press and set the tape to the window. Apply a bead of silicone sealant around the outside edge of the window, working it under and smoothing it out. Use a gloved finger with detergent to form the edge and remove any excess sealant.

Post-Installation Care:

Remove all masking tape immediately after applying the sealant. Allow the silicone to skin for a couple of hours, but give it at least 72 hours before any rigorous use or testing. Expect some high-stress work during this process, but the project can be completed in a few hours.

Materials and Suppliers:

When selecting materials, opt for acrylic/Perspex windows instead of polycarbonate, as they are less vulnerable to UV light, resist scratches better, and are easier to seal. Dow Corning 791 black silicone is an excellent choice for sealant, offering a 50% movement rate. For two-sided tape, 3M VHB 4991 tape is highly recommended. Ensure you get the right thickness (2.3mm).

Frequently asked questions