How to find elusive leaks

[T-Schwan]

One of the most common questions in 20+ years of this forum is how to chase down the elusive leak. Because anyone who has done it knows, the water you see at the stern could be coming from the bow, the mast boot, a hatch, a winch, a window, a stanchion, or a partridge in a pear tree.

What methods have you used to find those mystery leaks? And once found, how did you repair it?

 

[MIGuy]

I luckily have been successful in finding and fixing many surface water leaks on our 1994 sailboat. I am proud to say that as a result, my bilge has been bone dry now for years. Don't accept statements from old sailors that boats are always wet.

Most of the time, it has been easiest to be on/in your boat during a rain event and be able to directly see the leak source or track it back to the actual problem spot when a puddle winds up in an unexpected area. "Seeing" the source may require sticking your head into really strange and uncomfortable areas though. It may also take some interior disassembly (compartments, shelves, etc.) to see the problem.

Leak sources don't have to always be complicated to resolve. Also, many are caused just by ignoring to do simple maintenance. For instance, window leaks may be due simple to the latches. Disassembling and doing maintenance on the latches for some types/brands of opening ports/windows is simple. Latches may contain very small o-rings that seat against the window lens and are the things that keep water out. These o-rings dry out and crack over time, but an annual removal and replacement of these very inexpensive items, or cleaning and lubricating with a proper grease does wonders. Also, don't tighten the latches during reassembly too much. Let the o-ring have room to do its job. Flattening the o-ring due to overtightening will only result in early leaks and marring of your acrylic lenses. Then you will ultimately need to replace the lens too.

A leak in an original/old potable water line from my water tank to my head sink on the opposite side of the boat caused water to build up slowly in my bilge. Initially I was worried that I had a keel bolt leak. However, when my potable water pump kept cycling on/off, that was the key. I depressurized the water lines and gradually dried out the bilge helping to confirm my diagnosis. I ultimately had to replace the water lines. I was not able to remove the old lines because they were essentially held in permanently within a structural fiberglass floor/hull grid in my boat. Thus, I had to get creative to install/redirect new lines.

 

[stickinthemud57]

Depends on the boat. You might want to include that in your profile.

 

[rgranger]

I had a leak on my H26 that took me several years to track down. I would get old nasty water leaking out of the headliner in the head area and it would pool up in the head's sink. The water would find its way into the boat about two days after a rain. So I started by removing all of the stanchions, cleats, clutches etc and re-bedded them. No JOY!. Next I got a canvas companionway cover and that seemed to help... so somehow the leak is associated with the companionway. Did all of the normal things but that did not help.

Then a year later the rubber grommets that act as bumpers for the cockpit locker's hatch gave up the ghost and I purchsed some new ones and replaced them... they came in a pack of six...

The slide track in the companionway also used these same grommets and they were getting a little dry rotted so... I took them off only to find that the screw had gotten into some unwetted fiberglass unded the gelcoat... Yep! That was the source of my leak. Water would sit in the companionway's hatch track and eventually find its way around that screw... then into the headliner and eventually into my head area of the boat.

 

[Benny17441]

I luckily have been successful in finding and fixing many surface water leaks on our 1994 sailboat. I am proud to say that as a result, my bilge has been bone dry now for years. Don't accept statements from old sailors that boats are always wet.

Give me a boat that does not have gallons of water trapped bellow the sole in the stringers and It would be a boat that has not been frequently used. The source of this trapped water is varied, wash downs, wet bathing suits, liquid spills, condensation, fridge drains, galley spills, Sea spray, rain leaks, plumbing leaks, etc. There is likely to be a mix of fresh and salt water, some diesel fuel, oil, food crumbs, some dirt and of course bacteria which has turned that mix into a fouled concoction. Having a little water in the bilge serves as a trap to help keep the foul odors away from the cabin and does not make for a wet boat.

 

[Davidasailor26]

Dusty dry bilge here. Water does get trapped under the pan after things like winterizing, but after bouncing around for a sail or two it drains to the sump where it can be sponged out.

We did have an anchor locker leak because the gap between the anchor locker liner and the hull wasn’t well sealed from the factory. Trying to find the source just looking at the bilge was impossible. The only way to find the cause was to be on the boat during a rainstorm and look around the inside of the topsides, before the water could get to the bilge.

Having a little water in the bilge serves as a trap to help keep the foul odors away from the cabin and does not make for a wet boat.

Sorry, but I don’t see how having water in a low spot would have any beneficial effect on odors from water trapped elsewhere. The idea of a trap in home plumbing is that the water fills a section of pipe to block noxious sewage gasses from passing. Water in the bottom of a sump isn’t going to block anything from remote places.

 

[Orbweaver]

See my thread for finding a rainwater leak, using a method that Crazy Dave recommended. Works like a charm: I thought I had one leak (located roughly where I suspected) but also found 4 others. Repairs depend on the location/connections.
Here's a link to that thread.

 

[Crazy Dave Condon]

Old truck. Close up boat. Put a large piece of plastic over the companionway taping it down. Put a small slit in plastic and insert leaf blower nozzle taping the plastic aroound the nozzle. Have another person ready with a brush and bucket of water. When you start the blower, you are pressuring the cabin. Brush all fittings and everything else for air bubbling out. That generally finding leaks

 

[WayneH]

The dorades on my Tartan are sealed at the factory but after 40 years of flexing the sealant (thin glass? paint?) had cracked. And I had water that was coming into the headliner through the overhead glass and running over to starboard to ruin the paneling over the galley.

We thought that was the problem and so we used Great Stuff Sealer in the dorades. BAH!!!! It just sucks up the water and slowly releases it into the boat. Creating a much longer duration problem.

So we dug out 99% of it. There are some places you can't get back to with your hand and flat head screwdrivers only get so much of it. Then the Admiral suggested we use Flex Seal. We bought a can of white for two reasons. First, the original seal material was a hard gray product. Second, the Great Stuff was yellow so we would know we covered everything while painting the inside of the dorades. When we finished the aft dorades, we still had most of the can left over so we did the forward dorades which we thought were not leaking. So now everything looks factory fresh. And later that day, we had a tremendous storm roll through. Nearly 3 inches of rain fell. And the boat was dry when we checked her the next morning. And we found out that the leaking head port was actually one of the forward dorades leaking to the headliner before dribbling out at the port.

 

[capta]

From the water line up, I've used different color food coloring in water at any likely place. It worked most of the time.

 

[Project_Mayhem]

From the water line up, I've used different color food coloring in water at any likely place. It worked most of the time.

Does it stain any materials?

 

[Captain Larry-DH]

I’m surprised nobody mentioned using a moisture meter, such as this one I use https://www.amazon.com/gp/product/B00HARYVUQ/. I move it around along the overhead liner and inside cabin walls, and it can help identify leak paths, even when you can’t feel wetness with your sense of touch. It also can help determine if stained areas are still wet.

 

[stickinthemud57]

I’m surprised nobody mentioned using a moisture meter, such as this one I use https://www.amazon.com/gp/product/B00HARYVUQ/. I move it around along the overhead liner and inside cabin walls, and it can help identify leak paths, even when you can’t feel wetness with your sense of touch. It also can help determine if stained areas are still wet.

I'm a home inspector by trade and have three different moisture detectors. My go-to is a cheap pin-type unit, great for testing sheetrock and wood. It measures the conductivity of the material, which can be highly affected by the presence of moisture. The non-pin type use radio waves to determine the density of the material they are reading. These can reveal moisture, but they might also indicate moisture when in fact they have simply encountered an area of higher density due to varying material thickness. Not saying they are not useful, one just needs to be aware of how they work and their potential for giving erroneous readings.

Another potentially useful tool is an infrared camera, but it will only read temperature from the surface. They can't see through walls like on CIS. So, either evaporation or significant temperature difference between the water and the material affected has to be present. Again, potentially useful, but not sure-fire.

I used the pressure and soap method on my Hunter 170 back when I owned one. That was a very effective method.

 

[capta]

Does it stain any materials?

I've never had food coloring stain anything permanently.