How to find leak in old Sears jon boat

[senkosam]

Way back when Sears sold aluminum boats, 11.5' to be exact, the drain was welded to the bottom of the boat. Pretty dumb if you ask me considering the amount of dragging to launch or put the boat in the back of the truck (no trailer). What's happened is a split in the metal cylinder that hold the plug and for awhile I could seal it, but even after sealing it there's still a slow leak. Any ideas how to find where?

(BTW the rivets are fine.)

 

[1960 yellowboat]

From what I remember about those. The cylinder goes about 3 inches or so. Is the boat empty? Tape the end shut that is in the boat or glue a tight fitting cork into it. With the boat upside down, Make a plug out of an old bicycle inner tube to fit over the transom end. Coat the tube with dish washing soap and using the inner tube air valve, force air in and watch for bubbles. This is assuming you have an air compressor.

 

[senkosam]

Sounds like a plan. Thanks.