Re: Drain plug
I can't say how much affect water pressure has on a drain plug, but I did have an incident with one boat that had an old waste water pump outlet which was below the water line. The old pipe was no longer used and had been plugged with one of those stamped steel 55 gallon drum bung hole plugs. It had rotted out and began taking on water, when I got there it had about a foot of water in the bilge. I imediately started both auxillarly bilge pumps and it began to keep up with the incoming water from what was about a 1 inch hole in the plug. I needed to find someway to stop the water flow while I dug out the rusted plug and reinstalled a new brass one in the pipe which extended about 8" up from the bottom of the hull and had a 90 degree elbow on it. What I did was take a sheet of heavy clear plastic that I found and slid it down the side and over the opening, the water pressure held the sheet of platic ther and stopped the water nearly 100% while I fixed the problem. I had tied two strings to each side of the plastic so I could retrieve it when I was done, a guy that was watching and who had called me to tell me of the problem watched and hollered to me that the sheet had fallen away at the same time I replugged the hole. I don't think the sheet of plastic would have stopped the boat from sinking, but it did slow the incoming water. I suppose that it would have fallen away once the pressure equalized or the water line inside equalled that on the outside?
I hadn't planned it to work that way, but my first attempt was to rummage through a nearby dumpster for some old plastic bags to stuff in the hole, when I saw how they were sucked to the hole, I got the idea of a larger, heavier sheet of plastic. The plastic sheet I used was a makeshift floor mat I had in the back of my van to protect the carpet, a piece of old greenhouse plastic.
I agree that there's probably not much pressure on a drain plug, but I would think that it's easier to seal the hole from the outside simply due the the shape and flare of most bilge drain tubes. If you have a garboard style threaded plug, they can only be installed from the outside as the threads are 1/2" NPT (Tapered). With the lever style, I believe they can be gotten tighter than the wingnut style expanding plugs, but I have always worried about the lever getting snagged and pulled open on grass or debris. My old bass boat had a welded on tab just above the drain plug, when you folded the handle of the plug, the tab protruded through the hole in the handle and a hair pin could be installed as a safety. I haven't ever seen that on any other boat, but it was good piece of mind. I always carry a spare plug or two, just in case. I've been boating for years and have never had a problem though.
Most of my boats now have little or no access to the inside of the drain tube, so installing the plug from the inside is impossible. I have also added threaded bronze garboard plugs and fittings to all of my boats. I like the idea of a tightened threaded plug better.Depending on how high the drain is from the bottem edge of the hull determines wether or not you can add the threaded style plug and plate.
