Jamal Kazi snapped this photo of an aid to navigation in Ha Long Bay,Vietnam, a UNESCO World Heritage Site. Jamal wrote, “The fisherman here rows with his arms, perhaps because in transit. Otherwise, we most often saw them oaring with their feet while trolling for fish. Weather was overcast and cool in January, but it made for an eerie atmosphere with the fantastic karstic islands in the background.” Send michael_r@goodoldboat.com your favorite hi-res photo of an aid to navigation, be creative. If we use your pic in Good Old Boat magazine, we’ll send you a Good Old Boat cap or shirt.


Last month we put it to the readers about a contraption aboard a 1970s-vintage 36-foot Swedish ketch that reader Dave Cook encountered and was puzzled by. He didn’t have a photo, but described it for us: “In the main cabin there was a small tube that came up through the floor and ran up the main mast support, to about 1/3 of the way to the ceiling, where it stopped. It appeared to have a fluid inside it, green in color and not labeled in any manner. However, on the mast support post there were numbers that started near the floor and continued nearly to the top of the tube. I did not write down the numbers. But, they were something like 2,4,7,10,14,18. Also there was nothing to indicate what the unit of measure was.” Dave went on to include his best guess, that the tube was somehow a gauge of heeling moment.

We got a few responses, unfortunately nothing that is definitively correct. This one might remain unsolved. –Eds.

Several readers echoed Dave Croy’s thought: “Look at the gauge, then fill the fresh water tank and see if the gauge moves up. My first assumption is that it is to see how much water is in the fresh water tank and the unit of measure is gallons. That would explain why the numbers go up as the head pressure is higher. The green is possibly stagnant water because of the difficulty in cleaning out the tube.”

Brian Corbett offered that it could be a water tank vent, but that doesn’t address the numbers.

Even though Dave Cook opined it wasn’t a draft indicator, Al Penn voiced his assurance that it probably is. John Barry, who also owns a Swedish-built boat, a 1949 wooden sailboat just under 10 meters, guesses that this tube is a, “load or boat mass indicator. As the boat becomes loaded and heavier in the water it will sink lower in the water and can be measured on the scale. It can be measured while at sail and heeled as it is in a tube. I bet the lines for the number gradients were on the front and or rear and not the sides much like a measuring cup.”

Two readers, David Watson and Tom Alley, suspect it’s a knot meter working under the same principal as a pitot tube, with water flow increasing pressure and rising the column in the tube. But 18 knots?