How to Find a Leak When Water Gets Into a Pontoon Tube

Signs of water in a tube:

• One tube or one corner sits noticeably lower than the others at rest.
• The boat lists or plows, is slow to get up to speed or burns more fuel than it used to.
• You hear water sloshing when someone rocks the boat on the trailer or lift, or when you stop suddenly.

A slight lean can be normal. Avalon notes that a full fuel tank on one side can make that tube ride a little lower. Uneven seating, a heavy battery bank or a cooler can do the same. Also, lifting strakes (the fins welded along some tubes) and some under-deck spaces can hold water that drains out when the boat comes out of the water; that is not a tube leak. Even out the load and compare again.

Put the pontoon on its trailer or lift, level side to side and front to back. Water inside a tube runs to the low end, so a level boat lets you drain and test each chamber properly.

This is the most useful step, and it is free. With the water still inside, walk around each tube with a flashlight and mirror. A leak that lets water in also lets it out, so look for drips, wet streaks or rust-colored trails on the underside, especially at welds, brackets, the nose cone and dents. Circle anything suspicious with a grease pencil.

Put a bucket under each drain plug and open them one at a time. Note which chamber the water comes from and roughly how much. A cup or two after years of use can be condensation; gallons mean a real leak. Replace the plug O-ring when you reinstall it, and use thread sealant only if your builder says so.

If a chamber has no drain plug, some owners siphon water out through a top plug or vent with thin tubing. Do not drill your own drain hole until you know where the bulkheads are and what plug the builder uses. A hole in the wrong spot, or one without a proper threaded fitting, creates a new leak. Your dealer can add a correct drain if needed.

With the tube drained and dry, go over it closely:

• Welds along the length and around the nose cone
• Where each bracket or leg joins the tube
• Dents, gouges and scrapes from docks, rocks and trailers
• Any earlier repair or patch
• Small pits or white powdery spots, which point to corrosion
• The drain plug threads and seat

Soapy water only shows a leak when air is pushing out through the hole. Shops find pinholes by putting a very low, regulated air pressure into one sealed chamber and soaping every weld. That is effective but risky: tubes are thin and too much pressure can bulge or split them. If you want to try it, ask the builder for the maximum test pressure for your tubes, use a regulator and gauge (never a compressor straight into the tube), pressurize one chamber at a time, and stand clear of plugs and end caps. Otherwise, let the dealer or a welding shop do this step.

• Bad drain plug or O-ring: replace it. Done.
• Pinhole or crack at a weld, bracket or dent: the proper fix is welding by a shop experienced with aluminum pontoons. The tube must be drained, dried and vented before welding, because heated air trapped inside can blow the weld out. Tube walls are thin and the alloy matters, so this is not a job for a hobby welder; ask your dealer which aluminum welder they use. A torn tube (from a storm or a dock strike, for example) needs a patch of matching aluminum formed to the tube's curve, not a flat piece of angle stock welded over the hole.
• Small hole above the waterline: a flexible marine epoxy made for aluminum can serve as a temporary patch until you can get it welded. Clean to bright metal first and follow the product instructions.
• Many pinholes, heavy corrosion or a badly damaged tube: ask about replacing the tube.

Avoid filling a leaking tube with expanding foam. It can trap water against the aluminum, hide the leak and make a future weld repair much harder.

After the repair, launch the boat and compare how it sits. Then check it again after a few outings: open the drain plug of the repaired chamber, or rock the boat and listen. Note the date and what was found in your BoatMend log.

• Inspect the tubes for dents and scrapes every time the boat comes out of the water, and after any hard bump.
• Rinse salt and brackish water off the tubes, and keep the anodes on the motor (and on the tubes, if your builder fits them) in good shape.
• At a marina with shore power, have the boat's shore power and galvanic protection checked. Stray current can eat holes in aluminum quickly.
• Keep the drain plugs snug and replace their O-rings when they look flat or cracked.
• Clean the tubes with a cleaner made for aluminum, not harsh acids. Discover Boating warns that muriatic acid can streak and weaken aluminum, and points to weld seams and brackets as the spots where grime collects and corrosion starts; brush them clean and dry them when you wash the tubes.