There are photos at the bottom of this article, you can skip to them if the technical stuff is not your cup of tea (we won’t be offended).
We used to pilot the boat using only a lead line. A lead line is exactly what it sounds like…a rope with a piece of lead attached, you use it to physically measure the depth of the water. We’ve been through some hairy places with only a lead line (like Oliver Inlet, near Juneau, AK)…and certainly appreciate the skillset we have refined, but this refit provided the opportunity to upgrade to modern conveniences. It’s been a long project that has taken about 2 years to complete. Most everything else had to be in place before it could be connected. Today, the transducer cable was routed through three watertight bulkheads, connected to the chartplotter, and tested. We used a commercial transducer with a Garmin chart plotter, that was listed as compatible way down in the small print in an online manual. It looks like it works just fine!
We installed the transducer to electronically measure the depth. It’ll read to 1200 feet (366m). Of course, we didn’t just drill a hole in the boat and stick it in, nope, we went “overboard“ and fitted it into a standpipe. The standpipe is a watertight enclosure that houses the transducer. Since the boat is aluminum, we used a plastic transducer to avoid an interaction with the hull. Just in case we accidently shear-off the plastic transducer on ice, rocks, or whatever we hit in the middle of the night…it’s protected. It’s installed in a streamlined solid aluminum fairing block to align it straight down when the boat is trimmed level, positioned so the keel won’t reflect, and in the least vulnerable location while still being near the bow. We can still careen (beach the boat on its side, on a falling tide) without damaging the transducer.
We designed the standpipe to be 4 inches (101mm) above the waterline when the boat is level and engineered it to withstand freezing water. The standpipe is fitted onto a 1/2 inch (12.7mm) thick aluminum doubling plate which makes the hull 3/4 inch (19mm) thick at the standpipe. The bow is 3/4inch (19mm) thick anyway, just ahead of the transducer. The pipe wall is 5/8 inch (15.8mm) thick and is fitted with a flanged lid with a viewport that unbolts for access. If the lid wasn’t bolted on (or leaked for some reason) it would keep water out up to a 15 degree heel. As we know from physics class…or simply handling ice cube trays from the freezer…water expands when it freezes. The expansion of freezing water inside a standpipe could possibly cause it to rupture which could result in the loss of the vessel if it was unattended. Many vessels with standpipes have been lost when their standpipes burst. So we designed ours with these thoughts in mind. Technically, we could replace the transducer while boat is sitting in the water, without water coming in, but I don’t think we’ll try it