Part I: Leaking porthole and portlight short-cuts that never work

In a 40 year old boat, leaks are bound to spring up around portlights. Many newer boats even have this problem due to environmental exposure, heat expansion, and flexiblity properties of the material the portlight is constructed of and the fiberglass that it is adhered to.

The first thing I learned during my anti-leak crusade is what many of you maybe thinking, "What is a portlight?" According to http://www.seatalk.info/, a porthole is an opening in a boat that allows light and air to enter a boat. Often a clear glass portlight is attached to the porthole with hinges and can be closed with a gasket to make a waterproof seal. In land lubber terms, if the window opens it is a porthole and if it doesn't as on our Coronado 25 then it is a portlight. Now that we have our terms straight, let's get on to some things that most boat owners try and never work.

The biggest waste of time is slopping on a nice wide stripe of clear caulk over the gap in between window glass and its frame. Other than being a complete waste time, this also looks unsightly as the clear caulk often turns a chaulky, oxidized white with sun exposure. Leaks rarely come from this area because the flexibility and heat expansion of the window and it's frame are usually not that different and the glazing material is well hid from sun exposure making for a very long life and secure bond.

What sometimes works but usually doesn't is applying caulk over the gap between the portlight frame and the hull of the boat. This is where most leaks come from. However, applying caulk over the old caulk or other material used often doesn't work for a couple reasons. Once old caulk has dried, the new caulk doesn't adhere well to the old caulk. Another cause of leakage is that the caulk bridging the gap requires a much greater flexibility tolerance than caulk directly between the two surfaces. All it takes is microscopic gap to cause a capillary effect that will actually draw water into the boat.

The final short cut that rarely works is tightening down the screws or bolts that are securing the clam shell type portlights on most boats. And the reason this usually fails? You guessed it: the boat flexes. Tightening down the frame can sometimes lead to striping of the screws or bolts, but mostly reduces the elasticity of the caulk or other material used to create the seal. Even if it does provide some temporary relief, the first crew person to walk on the deck near the window will break the seal again because the caulk now has reduced tolerance to flexing of the hull.

What did I learn? As I have learned many times before, shortcuts have very little use in sailing and usually just cause more work. Specifically for the portlights, I learned the caulk used to make the water tight seals on the portlights has two main purposes: to adhere to the hull of the boat and portlight creating a water tight seal and to provide a buffer or flex point that allows the fiberglass hull and aluminum or steel frame of the portlight to move in different directions while still keeping the seal.

My next post will go through resealing the portlights the right way!