Portlight Replacement

By Don Casey
Illustrations by Paul Mirto

Over time, plastic portlights lose clarity. Polishing can't correct issues like crazing and discoloration. Sometimes pane replacement is the only solution.

Photo of an illuminated portlightPhoto: Billy Black

Once you've established that your portlights need replacing, the first thing you need to do is find new ones. If your portlights are round, oval, or rectangular, chances are they're a catalog item originally supplied by a hatch-and-portlight manufacturer such as Beckson, Bomar, Gebo, Lewmar, Taylor, or Vetus. Even irregular portlights are often shared across a number of boat models and become available as off-the-shelf items. If your boat's manufacturer is still in business, their customer-service department can probably tell you who manufactured the original windows. Where an exact match isn't a requirement, locating the appropriate replacement can be as easy as taking a couple of measurements and surfing the Web.

If you find that your particular portlights aren't available as a standard item, the easiest and surely the least expensive option will be to select a standard portlight that requires a slightly larger opening in one or both dimensions. Enlarging an opening is typically just a matter of minor grinding or sawing, while reducing the size of the opening is a major glasswork project. Don't think you can make up the difference with extra sealant.

If you're intent on a perfect fit for an existing opening, and you're unable to locate a suitable catalog-item window, custom manufacture is an option. Check around for small manufacturers in your area or contact one of the big players in this market such as Bomon or Vetus. It's worth noting that many standard-size fixed portlights are also available in an opening version, often at a surprisingly small additional cost. If much of your boating happens in a hot climate, replacing fixed windows with portlights that open will deliver the additional benefit of improved cabin ventilation.

Ins And Outs Of Removal

Old portlights may be screwed, bolted, clamped, or glued in place. Where the flange and/or trim ring exhibits fastener heads (sometimes hidden under a flexible insert), remove these. Anticipate that the fasteners will be corroded in place, so be sure you use the largest available driver that mates perfectly with the fastener. A hand impact tool can be helpful in freeing old marine fasteners. Where the flange is sealed with a gasket, you should be able to separate it from the boat by gently prying with a stiff putty knife, using a second wedge behind to maintain the separation you gain as you work your way around the window. If sealant was used for the installation, you'll likely need to combine cutting with your prying. The best tool is a single-edge razor blade — in a holder initially, then not in a holder to allow deeper penetration. A carpet knife is a good and arguably safer option. The safest way to cut sealant is with leader wire or braided fishing line. Attach dowel handles to a 15-inch length of thin braided wire or line and saw this back and forth in your initial knife cut. Use shallow wedges behind the wire to allow deeper penetration. If, (and hopefully not), the seal is with polyurethane — 3M 5200 — you may need the chemical assistance of DeBond Marine Formula.

It's All In The Prep

With the old window out, you'll need to prepare the opening for the replacement. This is also the time to trace a pattern if you're having the replacement custom fabricated. Be aware that there are often substantial differences in port and starboard cutouts on the same boat, so don't assume that a single pattern will suffice for two or more seemingly identical portlights. Trace out and identify a pattern for each opening.

Start your preparation for the new portlight by removing every trace of gasket or sealant material. Scrape with a sharp plastic blade, then buff with a Scotchbrite pad, and finally block-sand with 180-grit paper. If the old sealant was silicone, you have an extra challenge because silicone leaves behind a residue that prevents new sealant, even new silicone, from adhering. With the silicone scraped away, but before sanding, wet contaminated surfaces with a xylene-saturated rag, then blot-wipe clean with paper towels, using lots of fresh paper towels to pick up rather than spread the contamination. Sand only after water misted onto the cleaned surface sheets rather than beads.

Examine the edge of the cutout for damage to a wood core, or to an interior wood liner, and make appropriate repairs. Fill unused fastener holes with a stiff epoxy paste. Don't be surprised to discover that the corner radii are crude or inaccurate. You can improve them with the same epoxy paste. Fair your filled holes and corner adjustments and you should be ready to install the portlights.

Easy Install

Your specific installation should be guided by the instructions provided by the supplier of your new windows, so here you're going to find only supplemental guidance. Many modern portlights are sealed by a rubber gasket under the outside flange and clamped in place by screws through the inside flange. If the gasket has a seam, place it at the bottom of the window. The primary concern for gasket-sealed portlights is to make sure the mounting surface is flat. When you dry-fit the window (without the gasket), any gap around the perimeter of the flange must be less than 1/16-inch. You also want the window to slide into the opening without binding. Hole clearance all around of about 1/16-inch is ideal. Paying attention to these two requirements, follow the manufacturer's instruction for installation.

Some manufacturers will instruct you to seat the outside flange onto a bed of marine sealant, either to seal, or to bond, or both. You still need a flat mounting surface and a slip fit. For mechanically fastened portlights, the best bedding choice is butyl tape, a solid sealant that will not be ejected when you compress the flange against the boat.

Portlights to be bonded in place require the adhesive strength of a curing liquid sealant. To avoid squeezing out most of the sealant when you clamp or press the window in place, glue small spacers to the underside of the flange, one at each corner and additional ones as necessary to keep the span between them under 10 inches. Spacers should be 1/8-inch thick and perhaps 1/4-inch across, cut from any plastic or hard rubber and fixed in place with the sealant you're using to bed the flange.

Just before applying the sealant, always wipe both flange and boat with alcohol to remove oily contamination. You'll avoid the potential mess of bad aim if you apply your sealant only to the flange. A suction handle is a useful tool for positioning sealant-coated portlights.

Solid-sealant squeeze-out is easily trimmed away with a plastic blade, but you'll get a neater job with liquid sealant if you first mask both boat and flange edge. Masking the boat 1/8-inch beyond the flange trace line will allow you to shape the sealant into an attractive fillet with your finger (wetted in turpentine for the best effect). This permits removal of the tape before the sealant cures, which avoids problems that occur when the sealant cures to the tape.

If the window clamps in place with internal fasteners, tighten them evenly. Sealant must ooze out the entire perimeter of the portlight, so be sure you apply it liberally. You can wipe away excess, but if you apply too little, you must start all over. The spacers assure a uniform gasket. In addition to your clear view, your boat gets a facelift from this project. That makes it a buy-one-get-one-free deal. No coupon required. 

Don Casey has written eight books on boat repair and maintenance including This Old Boat, a comprehensive guide to refitting an older fiberglass boat.

— Published: February/March 2015


Nothing But Pane

Surface-mounted acrylic windows are common on sailboats and can be an economical option for any boat. This is simply a piece of clear acrylic larger than the opening and fastened directly to the cabin side. Overlap all around should be at least an inch, but if the acrylic has a dark tint, its size and shape can be dictated by appearance. No frame is used, but the outside edges of the plastic are typically rounded and polished. Closely spaced fasteners through oversize finishing washers around the perimeter used to make surface-mounted windows unattractive, and prone to cracking, but today's modern adhesives have given surface mounting a fresh lease.

Using black poster board to make patterns will provide a preview of the end appearance. You can have the plastic supplier cut the windows or fabricate them yourself. After appropriate cleaning, de-glossing, and masking or unmasking, the installation process is to apply double-sided VHB (very high bond) acrylic tape 1/2-inch wide by .091 thick (3M 4991) around the entire perimeter 1/2-inch in from the edge, then, taking great care with your alignment — there's no adjusting after the tape touches — press the window to the boat. Mask the pane edge and the boat 1/8-inch beyond the plastic and use a caulking gun to overfill the perimeter gap with Dow Corning 795 architectural-grade silicone sealant. Create a fillet with your fingertip, peel the mask, and your new window is installed.

 

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