Repairing Leaky Portlights

Posted by Practical Sailor at 12:24AM - Comments: (10)

Darrell Nicholson
Darrell Nicholson

Holes cut in your cabintop for windows—especially near genoa tracks—can lead to a loss of stiffness and more deck flexing.

Leaky portlights and hatches are one of the more frustrating projects to face on an old boat.

The best case scenarios are easiest to deal with, and these are usually the ones in which bedding has dried out and a simple removal, cleanup, and re-bed game plan is all it takes. When an acrylic (Plexiglas) or Lexan (polycarbonate) lens is removed, be very careful with solvents used to clean away old bedding because they can destroy the surface of once clear plastic.

To reattach the mechanically fastened lens, use a thick, adhesive butyl-rubber tape or equivalent bedding material instead of conventional tube-type sealants. (Practical Sailor testers have had good luck with Bomar hatch mounting tape.) Place the ¾-inch-wide bedding on the lens like thick tape, and squeeze in the mechanical joint between the lens and the cabin house. It acts like a compressed grommet as well as an adhesive seal. Fastener holes drilled into the lens should be slightly oversize, never chamfered, and the fasteners coated with a sealant when installed.

In all too many cases, the leak is a symptom rather than a problem. The underlying cause likely is that the holes in the monocoque structure create a loss of stiffness, resulting in excess cabin house flex. Rig loads carried to chainplates, mid-boom sheeting arrangements, and genoa track-induced flex can cause significant deflection. Such deformational loading creates energy hot spots that can change shapes or even fracture laminate. In situations where stiffness increases dramatically—like where mechanical fasteners attach a port lens to a lengthy opening in a cabin coaming—a bending moment can twist the fastener(s), cracking the surrounding acrylic or polycarbonate.

The rigid, much more heavily laminated hull, lacks large apertures, such as holes for hatches, ports, and lockers, but the less structurally substantial deck laminate is Swiss cheesed with such penetrations. Better builders add extra reinforcement commensurate with the size and location of these holes, and it lessens the tendency for a port lens to be deformed by sailing loads.

In some cases, the problem can be solved by reinforcing the inside perimeter of the aperture with a stiff metal surround or additional laminate. Without addressing the structural problems that led to the leak, the drip, drip, drip will no doubt start again.

Comments (10)

I have 2 cracked portlights in my Catalina 36 that I will be replacing this spring. I purchased the replacement acrylic panels already (I had a local plastics supplier cut and shape the new pieces for me using one of the old lenses). Catalina recommends Dow Corning 795 adhesive silicone for the job, which is the architectural stuff that they put skyscrapers windows on with mentioned in a previous post. Most of the professionals these days seem to use 3M VHB tape to adhere the portlight lens in, and then seal it in with the 795 sealant. There are several YouTube videos that show the process, and the tape seems to be a much less messier method than the adhesive sealant alone.

Posted by: DLincoln3 | March 25, 2017 9:49 AM    Report this comment

A brief search for the Bomar hatch tape leads me to believe it's been discontinued. I need to replace most of the portlights on my S2 9.2A and, while I've used butyl tape for many things and like it, it doubt it has enough adhesive grip to hold my S2's portlights in place (there are no fasteners involved). I seem to recall folks somewhere recommending an architectural adhesive such as they use on office building windows, but I also hear it's messy.

Posted by: Bugbitten | March 24, 2017 8:49 PM    Report this comment

Good info about mechanically-fastened lenses. How about your best info on non-mechanically fastened lights. For instance, my 2006 Beneteau 343 has a large light (nearly 1.5m x 0.5m) on the forward-sloping part of the cabin, and both forward corners leak. In fact, I need to put containers under those corners, inside, to catch the rapidly dripping water. I'd like to know the best way of removing the old sealant and the best sealant for re-doing the seal. Many thanks.

Posted by: jmkinsfbay | March 24, 2017 1:51 PM    Report this comment

Butyl tape absolutely rules in my opinion. It provides moderate sticktion, is flexible, relatively cheap, easy to work with and clean up and the butyled item can be removed later without the use of nuclear weapons. I basically use it for all sealing and bedding jobs on board the boat.

Posted by: Mike Cunningham | March 23, 2017 9:43 PM    Report this comment

Butyl tape absolutely rules in my opinion. It provides moderate sticktion, is flexible, relatively cheap, easy to work with and clean up and the butyled item can be removed later without the use of nuclear weapons. I basically use it for all sealing and bedding jobs on board the boat.

Posted by: Mike Cunningham | March 23, 2017 9:43 PM    Report this comment

"Spreading the Load" in August 2016 issue, starting on Page 17, illustrates the steps to take when replacing wet, damage or crushed core -- though the article focuses on horizontal deck fittings, the process is pretty much the same. We have described it in other articles as well, Gudgeon Brothers offers a good guide.

Posted by: sailordn | March 23, 2017 1:26 PM    Report this comment

Grizzly - We had a leak in the forward cabin hatch on our new-to-us 2004 Beneteau 471. Short term cure was to duct tape the hatch shut everytime we went offshore or inter-island where waves could slop on the deck. We finally determined that the fixed part of the aluminum hatch frame was slightly deformed by being well-bolted to a section of cabin top that was slightly dished. IE, the top edge was slightly curved in a vertical plane. Jackie figured out that she could locally thicken the hatch seal on the movable part of the hatch by putting a long cylinder of rubber (about the diameter of a pencil eraser) between the factory provided hatch seal and the hatch aluminum frame. In ten minutes she fixed a problem that had plagued us for a year, resulted in several bed-wettings, and consumed a couple rolls of duct tape! Not sure if this is your situation, but the fix required no hatch frame removal & reinstallation.

Posted by: Annapolis Sailor | March 23, 2017 12:37 PM    Report this comment

"In some cases, the problem can be solved by reinforcing the inside perimeter of the aperture with a stiff metal surround or additional laminate."
In our case we had Perko ports that clamped the outer fiberglass hull against the interior wood. Over time the wood degraded and no manner of increase in clamping pressure would stop the spongy wood from leaking.
The solution in our case was to remove the damaged perimeter wood and replace it with poured-in epoxy that is "formed" using clear box tape. Most importantly, the good wood can be coated with epoxy to seal the edge. In some cases a full thickness epoxy ring was used to completely replace the wood in the clamped region.
It is important to understand that the seal on these ports comes less from the hull-perpendicular surfaces than from the clamped hull-parallel surfaces. The caulk in the perpendicular region may degrade by temperature changes and hull flexing, but the caulk in the clamped hull-parallel surfaces is long lasting. The epoxy coating that soaks into the grain and seals any wood in the hull-perpendicular surface prevents water infiltration that eventually breaks through the caulk.

Posted by: Locquatious | March 23, 2017 9:32 AM    Report this comment

I understand that butyl, in addition to tape, is available as a paste in a can. Any idea where it can be purchased?

Posted by: Val | March 23, 2017 8:39 AM    Report this comment

Thanks for the tips on this. I have a water leak around the forward cabin hatch of my French-built J92S (2007). I think it is not coming from the light in the hatch, but instead is from the gap between the deck and the aluminum frame of the hatch where it meets the deck. Any tips on removing the frame from the deck? My plan is to remove, re-seal and reinstall the frame. What kind of sealant should I use?

Posted by: grizzly | March 23, 2017 8:19 AM    Report this comment

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