Bilge pump as downwind siphon?
Prior to heading downwind this afternoon on my return trip to Santa Cruz, I was roaring along close hauled on a port tack. By my GPS I was making 5-9 to 6.2 knots with steady twenty knots of wind gusting higher.I had been below messing with my GPS and a chart while my self-steering lines did the work. All was dry below then.
I ran dead downwind for a while with the main up full and a class jib. I know that I was doing better than 8 knots with the swell and wind directly behind me, but I couldn't leave the tiller long enough to check my GPS. I eventually had to head for Santa Cruz. With a gusty 20+ mph wind on my port bow I was heeled over to 40 degrees. However when I finally slipped in behind the point where the water was calm, I once again went below to discover that the cabin sole and lots of other stuff was drenched. My deck shoes, which I had left below, looked like they had been swimming.
I lifted a hatch board, and the bilge was 3/4 full of murky water. When I had been heeled to 40 degrees, the water must have come out of the bilge and run up the hull to flood the locker beneath the starboard settee and even further up the hull to the opening at the forward end of the bench into the wet locker, which I suppose is intended to drain the settee bench. Unfortunately, this time it worked in reverse to drench the starboard cushion. The bottoms of the lifejackets in my closet were also soaked. Also drenched were my tools, fasteners and other goods stored in the locker underneath the settee. It was a mess.
With the manual bilge pump, which is mounted in my cabin beneath the companionway hatch, I quickly pumped the water out of the bilge. Satisfied that if I was sinking, I wasn't sinking very fast, I headed leisurely into the harbor.
After searching for a source, I concluded that the water must have come from something other than a deck hardware or hull-deck seam leak. There was too much water for one thing, and secondly the mess beneath the settee cushion looked a lot like bilge water and not so much like a fresh leak from above. The cowl vent on my bow was my first thought, but the anchor rode directly beneath the vent was dry as was the anchor locker as a whole. The V berth area and its raised floor were totally dry, as were all of the shelves in the V Berth and the shelves above the settees. The chainplates were dry. Only the teak main salon floor and starboard side of the boat up to the height of he settee cushion were wet. Even the pillows that sit against the hull on the settee cushion were dry.
Since the lazarette locker fills with water when running downwind and on a broad reach, and on a close reach under certain conditions, I checked the bulkhead separating that locker from the rest of the boat, but I could not find any openings in the bulkhead that could have leaked water into the bilge.
My suspicion is that the manual bilge pump is the culprit. The bilge pump pumps the bilge water overboard through the transom. The exit port is rather low on the port side of the transom, but above normal water level. I do not know whether that is standard or a modification. I do not see a specification or drawing for one in the manual, but the discussion about bilge pump installation in the manual makes me suspect that my bilge pump is other than original.
There could be a break in the line, or the system could be installed in such a manner that allows water to siphon from the sea through the transom into the bilge. My bilge pump outflow is mounted through the port side of the transom. Since the port side of the boat was dry, a break in the line is unlikely, but I will check the line. After pumping the bilge dry and letting the boat sit for a couple of hours the bilge remained dry. Of course the transom is above water when the boat is docked. My bilge is normally bone dry.
I would think that a manual bilge pump installation be made in such a way that even pressurized water will not flow from the opening in the transom into the bilge. Excuse the ignorance, but don't these things have a bult-in antu-siphon device? Tomorrow I am going to try to simulate this with a garden hose. Has anyone else experienced this phenomenon? Or does anyone out there have other suggestions as to how my bilge might have filled with seawater? I have read a few postings on bilge pumps on this site, but they did not answer my questions.