by Alan » Sat Sep 08, 2018 12:13 pm
For years I assumed that the bow flotation tank had some sort of wall that separated it from the bilge. Turns out that isn't the case. The flotation tank space forward of the forward bulkhead (inside the cuddy) is not separated from the bilge--the tank and the bilge are one continuous open space.
The biggest source of water in the bilge I know of is the centerboard trunk. In maybe two hours' sailing in choppy water, I've gone from a dry bilge to having several inches of water below the inspection ports in the cockpit, which means it was even deeper in the deepest part, around the mast. I left the boat overnight in a slip in that condition, and the water level hadn't changed at all in the morning. That tells me that the water in the bilge wasn't coming from some other source underwater, like a leak in the hull or from a drain plug.
Another source of water in the bilge is water in the cockpit (from rain, or maybe from water coming over the coaming during an interesting sailing experience), which seeps down through the inspection port threads.
I forgot something important in my previous post--there's a flotation tank in the bilge, sort of a fiberglass storage container, with styrofoam in it. It's installed forward of the mast and it runs crosswise for the full length of the bilge. It would block the fore-to-aft flow of water in the bilge, except that it has two narrow gaps on the underside, one port and one starboard, that allow the water to flow through, albeit slowly. I've posted photos of it elsewhere on the forum.
And finally, one more thing I forgot: Where's your transom drain plug (the bilge drain, not the cockpit drain)? I assumed it was offset to starboard, but someone has posted photos of a 1977 DSII where the transom drain plug is in the center. The hull molding and cockpit molding are very close together at that point and the self-bailer passes through both moldings in that area, so if your drain plug is in the center, that may account for the slow drainage.
Later DSIIs, including my 1980, had the drain plug moved to starboard so it opens into the space under the starboard seat. I assume that slow drainage from the center drain hole is the reason why.