SJ23 Tech Tip B05 - Window Leaks

SJ23 Tech Tip B05, (2020-03-02) Bob Schimmel, Rick Bensyl & Brian King

Window Leak - A Trick to Seal the Frame to the Hull.
INDEX - Reseal a Window, Vinyl Moulding, Rebuild A Window, Tempered Glass.

The windows of a San Juan 23 were top of the line at the time of manufacture. They consist of 1/4" thick clear acrylic (Plexiglas) glazing housed in a two piece exterior aluminum extrusion equipped with an internal locking ring and a decorative inside vinyl trim. The top and bottom halves of the external aluminum frame are held together at the joints (fore & aft ends) with a short internal steel strap and two steel screws. While you shouldn't have dissimilar metals touching each other, my straps were coated in very light grease and not rusted so I left them as is. This might still be OK in salt water. I'm not sure. The acrylic glazing is sealed to the external aluminum frame with what looks like silicon sealant. The aluminum frame that houses the acrylic, forms the outside half of the window assembly that keeps the water out. This frame is sealed to the outside of the hull with a liberal application of adhesive under the overlapping flange. The external assembly is clamped to an internal locking ring at the edge of the window hole. The screws through the locking ring are visible in the photo below. Finally a grey vinyl trim is pressed inside the locking ring to cover the gap and create a finished look inside the cabin. In time, this window will leak in accordance with some obscure but universal law of nature. This is due to the fact that a sailboat hull flexes under load and the acrylic expands and contracts more than fibreglass. For this reason the rigid window frame has to "float" over the flexible sealant sticking to the edge of the rigid fibreglass hole. One of the best things you can do for your boat is to spend time onboard to look for leaks while it is raining! The heavier the rain the better.

If the acrylic is not scratched or milky, the minimum repair will likely involve resealing the aluminum frame to the hull. Trying to reseal the window by smearing sealant on the outside edges of the frame is not only incredibly messy and ugly, but almost certainly doomed to failure. Acrylic has a higher coefficient of thermal expansion than metal or fibreglass, which is why this window design leaks so often. This is especially true if the window frames are not sealed to the hull with the glazing version of polymer sealants designed to deal with large expansion and contraction. Some people rid themselves of this problem by replacing the acrylic with tempered glass. The clarity is far superior, they don't scratch, the window is easy to clean, and the ultimate strength is far superior to acrylic. The bonus is that tempering glass is fairly inexpensive.

If there is a leak between the aluminum frame and the hull, then the entire window assembly should be removed and re-bedded. Leaks such as these can cause horrible rot problems in a boat with balsa core or plywood sandwich construction, not to mention cushions and fabric. (This is why it is so important to seal the balsa or plywood core with epoxy before you install a fitting through the deck). Luckily, the cabin sides of a SJ23 are 1/8" solid glass. The core of the cabin roof, deck, cockpit floor and seats are all edge grain balsa. This procedure requires delicate "surgery" with trim knives and anything else you may have that is sharp and flat. See Tech Tip G08.

Shown at right is the metal locking ring on the inside of the window. To remove the window from the hull, remove the screws to reveal the frame to hull sealant. The factory likely used Boat Life, a similar flexible lightweight off-white caulking or sealant. If the sealant has turned to a rubbery consistency that crumbles under the push of a finger then it has deteriorated a long time ago.

It may be difficult to duplicate the original manufacturer seal between the acrylic and the aluminum frame. If it is bad it might be better to replace the whole window, frame included. I'm told that superior windows are available today but I don't know at what price. Rick Bensyl bought some from Minney's Yacht Surplus in Irvine, California for about $59 each (2008). They are slightly bigger so he simply cut the hole a bit larger. On the other hand, you could replace the acrylic with tempered glass bedded in glazing polymer. See "Rebuild a Window" at the bottom of this Tech Tip.

BEFORE you REMOVE the WINDOW - Apply masking tape around the window keeping no more than 1/8" away from the frame. This leaves space for a fillet to stick to the hull. Apply a pull of tape overlapping each corner of the window frame to the hull. Draw a reference line down the center of each tape, from hull to window. Use a razor knife to cut the tape along the perimeter of the frame. These lines will be used to position the window in the same place. Without these reference lines you cannot place the window in the center of the hole with equal overlap on all sides. Temporarily tape 2 wood blocks to the cabin side, along the bottom of the window frame. These will be used to support the frame on the edge of the opening during installation. As an alternative to wood blocks you could use 1/8" guide pins temporarily set though the hull and the aluminum frame to support the window. It would also be possible to place 3/16" long tubes over each pin to act as a spacer. Remove the grey vinyl trim from inside the frame and remove the mounting screws in the locking ring. The old sealant between the aluminum frame and the hull may have to be cut in places with a razor knife or sharpened putty knife. Be gentle in this procedure so you don't bend or break the window. Move around the window in small steps so you don't gouge the gel coat. Once free pull the window frame out gently so you don't bend it. Remove all remnants of old adhesive from the hull and the aluminum frame. If silicon sealant was used, apply a liberal amount of silicon seal remover to clean the surface down to bare gel coat. (NOTE - Acetone dissolves acrylic, so don't let it contact the window). If you have to take the window home, cover the window hole with heavy duty poly taped to the hull with duct tape. It will stay stuck in the rain provided it was applied dry.

INSTALL AND SEAL THE WINDOW - Now is the time to make a decision on which sealant, and the accompanying procedure, you want to use to install your window. The procedure for slippery glazing sealant is more complex and messy than for butyl rubber tape.

NOTE - To maintain a water tight seal the metal components used for the windows MUST NOT be installed rigidly against the hull. Rigid metal frame bends less than the hull that jiggles and flexes while under way. In addition, metal, and especially acrylic, have a larger thermal expansion than fibreglass. To maintain a water tight seal between the two requires a thick enough sealant that is flexible enough to allow for shear movement so the sealant is not torn loose.

Regardless of the sealant, just prior to installing the window, sanitize the gel coat and inside of the frame with acetone so the sealant can stick to its max.
When you install the window have an assistant hold it from the outside, lining it up to the reference lines, while you are on the inside to check your reference lines to install the screws. It helps to do a dry run first. It is difficult to yell instructions through a closed window so have patience with each other.

Glazing Sealants - A windows that is lathered up with slippery glazing sealant is very difficult to hold and keep your hands clean. Without support it easily slips to the bottom of the window hole creating a holy mess and leave an air gap along the top! Exactly what you are trying to prevent. The 2 wood blocks temporarily taped to the outside of the cabin under the window frame can support it to keep it centered over the hole. This did a great job of holding Panache's window in position with equal overlap all around the window hole. Later I applied a bead of sealant on the inside between the frame and the edge of the hole for more strength.
Use a marine grade glazing adhesive like Sikaflex 295UV with Sika-Primer 209, Silpruf (GE), methacrylates urethane, or DOW 795 to seal the window frame to the hull. All these adhesives cure to a flexible consistency of + or - 50% which is required to match the expansion/contraction of an acrylic window relative to the fibreglass hull. Apply a minimum 1/8" thick sealant all around the aluminum frame. Read on and you'll learn the trick to ensure permanent adhesion.
When installing the window you'll discover that the frame does not match the curved cabin wall. This is OK since the window is flexible enough to conform to the curve. I prebent my aluminum frame a bit to more closely to match the hull curvature and ease fitting the frame. However, it was still too straight when I realized the soft sealant in the middle of the frame would be squeezed out as it was pressed against the hull. To prevent this I placed 3/16" thick rubber spacers against the outside of the cabin where the aluminum frame touches.
Use some creativity here. I used 1/4" square pieces of adhesive backed bicycle inner tube patching material. The 3/16" thick pieces were placed about 2" apart around the hole. Then I applied a thick bead of Sikaflex, circling and covering each rubber spacer. They stayed in place and maintained a 3/16" thick gap of sealant as the ring was tightened.
Install the locking ring and tighten the screws to just snug. If you over tighten you will just squeeze out sealant rendering the job useless.
A fair amount of sealant should have oozed out over the masking tape. Drag a rubber spatula around the outside edge of the frame to create a smooth, tapered the fillet. The taper helps to shed water.
Remove the masking tape while the sealant is still flexible and don't touch anything for the next 24 hours till it cures. Although if you have splotches of sealant on the cabin side now is the time to clean them with a rag soaked in acetone. Just don't get the acetone on the acrylic or the fresh sealant.
After 24 hours the sealant will have hardened and now is the time to tighten the locking ring screws to final setting.

If one of Panache's windows leaks again I will seal it with butyl tape using the following sequence.

Butyl Rubber or Glazing Tape - Neither butyl rubber, 1/8" thick butyl tape, 3M double sided VHB 4991 tape (2.3mm thick), or weather sealing foam tape are as messy or difficult to handle than a sticky glazing sealant. For this reason you might dispense with the masking tape to protect the cabin wall, but it will keep the cabin wall clean. Your choice. You still require tape to mark the four reference lines at the corners. One of these tapes will be my choice for resealing Panache's windows. While the following steps state butyl rubber, the instructions work for any of these tapes.
Roll out the butyl tape on the inside of the window frame letting about 1/16" stick out from the edge. Apply it using the paper backing. Try not to touch it with your skin as it reduces adhesion. If the tape is too wide for the window frame, run the excess up the inside of the frame that sticks into the window hole. This will help to keep the frame centered in the hole. Start the tape on a vertical side of the window to minimize the chance of a leak.
(This step is for butyl tape) If the curvature of your window does not match the hull apply 1/4" square pieces of adhesive backed bicycle inner tube patching material around the hole to prevent sealant squeeze out. Space them 4" apart. You may have to space them closer together at the middle of the window if your frame is pushed real tight against the hull here. If the curvature of the window frame matches the hull then spacers are not required.
With the outside frame lined up to the reference marks (on tape) and centered in the hole, push the frame against the hull. Treat this as a one time action. It is very difficult, if not impossible, to remove if you place it wrong.
Tighten the inside locking ring screws to final setting, permitting the excess butyl rubber to ooze out.
Let the window sit for about an hour. "It's OK to have a beer now. Time to relax." The exposed butyl will skin over making it possible to handle without sticking to your skin.
Use a very sharp razor knife to cut off the excess butyl at about a 30 degree angle to the frame. This angle helps to shed water. Just kiss the gel coat with the knife point.
For a job like this I usually run the tip of the blade over a stone to remove the very sharp point, thereby protecting the gel coat. If the butyl doesn't cut easily its OK to wait till it does.
8' of tape should do a window.

If you've done this job correctly, you can forget about window leaks for the next ten years, or more! Ironically the 3 front windows have never leaked. Only the side windows have. TOP

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INSIDE VINYL MOULDING: The vinyl moulding inside the locking ring creates a decorative finish for the inside of the window. The moulding is 7/16" wide with ribs on the sides to grip the inside of the locking ring. The ring is 7/16" deep. Problem is, the moulding has a nasty habit of shrinking lengthwise that creates an ever-widening gap between the ends. After many years it finally stops shrinking. Besides looking tacky, the 2" gap on Panache's windows collect a lot of dead bugs that are difficult to remove. yech.

Scuttlebutt has it that the length of this moulding can be restored by heating and stretching it. So I tested this by soaking it in hot tap water and washed it with a nail brush while I was at it. It was left in very hot soapy tap water for about 30 minutes till it became soft. Then it was dried and moved to the "rack" which consists of a long (1x2)" stick marked at 78" to create a target to stretch to. The moulding was first clamped at the end of the stick with a paint stir stick and a C clamp. Then stretched past the 78" mark to offset shrinkage and clamped similarly. I kept it on the "rack" for a day to cool in the stretched position, hoping it would acquire a new memory. By the way, removing the moulding from the window makes this job a lot easier than putting the whole boat in the sink!!! See results below.
- Unfortunately this vinyl moulding is no longer available. The best source might be a glass shop. So be very careful with handling it. If you find a source, please let me know. (Insert update here)

AFTER NOTE: Stretching this moulding does not work. It shrinks back to its shrunken length since it has memory. Too bad. For this reason I will plug the gap with a reasonable facsimile, this time at the top of the window frame where it can't be seen unless you look up from the berth. I'll cut the length of the plug so it pushes and holds the grey moulding into the ends of the window frame. This will look a whole lot better than the ugly gap with the moulding drooping out of the frame ends.

This bug screen roller is the perfect installation tool. I decided to install the moulding at about 5 C⁰ thinking that it will only get tighter when it expands during the warm summer months.

The photo below shows the washed moulding reinstalled with a spacer at the top. What an improvement. Washed and repaired curtains don't hurt either!

TOP

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REBUILD A WINDOW (Brian King): I replaced the vinyl glazing on both main windows in 2009. They have been in place for a couple of weeks now and experienced some pretty heavy Seattle winter rains. There have been no leaks so I'm pronouncing this a qualified success. Now it is only a matter of a test of time. It should be noted that I have tempered glass in my windows, not acrylic. See Glass below.

The new vinyl moulding between the glass and the aluminum frame is for a 3/16" thick glass that fits in a 3/8" deep channel that is 11/32" wide. It is part number GC727C from C.R. Lawrence. While not an exact replacement the dimensions are very close and as such it fits snug. The actual measurements of the glass channel on my boat are 27/64" depth and 21/64" metal opening. Minimum order is a 100' roll and only about 20' are needed for the SJ23. Ordered on line, it cost about $72 with shipping to Seattle. Here are the photos showing the installation:

fig 1 - REMOVE the WINDOW - The window frame is clamped from the inside. First remove the rectangular vinyl cosmetic trim from inside the frame. Then unscrew the clamp inside frame ends to remove the frame.

fig 2 - DISASSEMBLE THE WINDOW - Disassemble the split frame from around the glass by unscrewing the two straps that hold both ends together. After the straps are moved, simply pull the upper and lower sections of frame apart.

fig 3 - OLD GLAZING - The old vinyl glazing was stiff and brittle from years of UV exposure. No wonder it leaked.

fig 4 - GLASS REMOVED - The glass needs cleaning before it can accept a new seal.

fig 5 - CLEAN GLASS - Clean the glass with a razor blade scraper, Windex and water. It must be perfectly clean in order to seal.

fig 6 - CLEAN FRAME - Clean the frame, inside and outside. Remove old sealant from the outside. Be sure to remove any grime that may prevent the vinyl from forming a seal inside the window channel.

fig 7 - READY TO ASSEMBLE - With everything clean, the window glass and frame are ready for assembly.

fig 8 - NEW GLAZING SEAL - The vinyl glazing was slipped over the edge of the glass. It was easier to do this with the vinyl softened with hot tap water. The butt ends of the vinyl were placed at the top center of the glass to prevent a leak. It also seemed better to cut the vinyl just slightly short (1/4") and stretch it together around the window edge. It will stretch even more when squeezed into the slightly too small groove of the window frame.

fig 9 - GLASS AND SEAL IN FRAME - With the frame halves pressed over the glass and vinyl glazing, you will find it isn't easy to close. There will be a gap between the two frame pieces. It sure helped to heat it under the hot water tap to soften and lubricate things.

fig 10 - CLOSE THE FRAME GAP - I used bar clamps to push the two frame halves together. A bit of a nervous time as it does take some force. Close one end and then screw the little plate in place to secure that end then move to the other end. Once this step was complete, I used silicon sealant to cover the screw heads and seam where the two ends of the frame meet. When the sealant cured I laid the window frame flat and filled the inside with water to check for leaks.

fig 11 - FRAME WEATHER SEAL - The seal is used to seal the frame to the hull.

Instead of using sealant to seal the window frame to the boat side as was originally done, I used closed cell weather sealing foam tape. It is self adhesive (double sided) and applied it to the window frame flange as show at right.

fig 12 - WEATHER SEAL INSTALLED ON FRAME -

You can barely see the 3/16" thick tape on the inside of the frame. As an alternative you can use 3M VHB 4991 tape. It is 2.3MM thick.

fig 13 - HOUSE CUT OUT READY - Before installing the window frame to the outside of the cabin side be sure the surface area around the cut out is nappy clean. I used a putty knife to scrape all the old sealant off and then finished with a Scotchbrite pad. A wipe with acetone will sanitize the surface for best adhesion. Be sure the window is centered in the hole so the weather seal gets contact and compression all the way around. Clamp the window on the inside and you're done. TOP

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TEMPERED GLASS WINDOWS - Several of my SJ28 buddies replaced their acrylic windows with tempered glass. SJ28 and SJ23 windows are identical in construction. Disassemble the windows using Brian's instructions listed above and verify they fit perfect in the frame. Lay the port acrylic on the starboard side to determine if the two are symmetrical. You might be surprised. Give your acrylic to the glass shop as a template to cut the glass and temper it. Use the services of a glass shop for this as polishing the rounded edges are beyond the abilities or tools that most people have. Install and seal the tempered glass as per the steps shown above. The vision through tempered glass is clearly superior!

Glass has less expansion and contraction which is a major factor to prevent future leaks.
Glass has greater clarity than acrylic and can be cleaned without fear of scratching it.
Tempered glass is much stronger than acrylic but it is heavier.
Glass cannot yellow due to UV. TOP

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