We've been using standard rubber/brass drain plugs on our boats (6+, all in the 16-21' range). For the second time in about 2 months we had a catastropic failure of the boat drain plug (2 separate boats). Plugs were still "in" but the brass threaded bolts/lock down mechanishms had fallen out and left a nice 1/8" hole and round brass plate on the inside. Of course, the water (salt) came in. One boat swamped, the other we caught mid fill. One plug had been in 4 months, one 6; we change them when we put antifouling paint on. Have now resorted to plugs with nuts on the threaded end. <br /><br />These boats stay in the water, any helpful hints??? Or suggestions on tracking down the problem. Both were mounted exterior, new ones are now on interior of bilge. <br /><br />Please don't tell me to get Whalers - have 2. Thanks for any input..... It's exasperating to "sink" an expensive boat due to a $4.95 part..... 
