Electronics
An accidental grounding reminds the author to utilize the rich assortment of navigation tools available, even in familiar waters.
Hitting an unmarked mound of sand in a familiar harbor sends an electronics guru searching for answers.
Last year’s cruising with the family started with a trip up Lake Michigan’s Wisconsin coast bound for Manistique, a small town on Michigan’s Upper Peninsula aboard our Carver Voyager 570 Have Another Day. We had something very rare—three consecutive days of flat water on Lake Michigan—so we made the most of the conditions and ran all three days for a total of 300 nautical miles at 9 knots. We made it to Manistique without incident, but our luck changed on the cusp of entering its port.
I’ve been into Manistique’s little harbor a handful of times before and never had the slightest issue getting in or out; in fact, I had tracks on my MFD from a previous visit. Moreover, several years ago a big deal was made of rebuilding a long breakwall so the channel was large enough for Great Lakes cruise ships, and the approach had been dredged. On top of that, last year Lake Michigan was running north of 3 feet over chart datum.
So imagine my surprise pulling in only to hear the sickening sound of props striking bottom, and, immediately after, the sound of the starboard engine shutting down.
I quickly used the bow thruster to spin her out toward the lake and then used both thrusters to move the boat farther south still. I engaged the engines and moved several hundred feet southwest to where I’d previously seen deeper water and dropped anchor. It was time to think.
We called the marina and quickly realized the gentleman on the other end of the line wasn’t equipped to help us after he asked us what a prop is. He then called his boss who said to stay west for the deepest water. In the meantime, we’d asked an outgoing fishing boat about the deepest water and they in- dicated it was to the east (our starboard side).
With this contradictory information, and having already hit bottom once, I decided to deploy our dinghy and do some sounding of my own. I had installed a Garmin echoMAP 44dv on the dinghy about three years ago, a decision I am frequently proud of. I made several passes back and forth from the anchored boat to the marina. It eventually became clear that if we hugged the far eastern edge of the channel, we’d be afforded 7 or 8 feet of depth, plenty for Have Another Day’s 5-foot draft.
Even so, we felt the best bet was an escort into the harbor, so with my wife Laura in the dinghy and me at the helm of Have Another Day, we inched toward the marina. Laura led and called out depths as she saw them, and I’m pleased to say we made it in without further incident.
Once tied up and with an adult beverage in hand, it was time to figure out what had gone wrong. I had been in and out of here before, in years of lower water no less, so I had been complacent. It turns out that wasn’t the only factor that contributed to our trouble.
This was our maiden voyage cruising with Aqua Map as our primary planning tool, and I realized in hindsight that I just didn’t understand how it displays depth boundaries. When I glanced at the charts I saw something my brain couldn’t reconcile. Instead of investigating further, I shrugged it off.
It wasn’t that I didn’t have the tools to investigate: I had several sources of cartography for cross-reference but didn’t use them all, and some were even out of date. The NOAA RNC (raster charts) sat unused in the chart drawer. If I had further researched the harbor, I’m certain I would’ve been more vigi-
lant and possibly avoided this entire bit of unpleasantness.
In the past, I’ve relied on current and some older cartography. I also used the Navionics app with current soundings, about 12-month-old Navionics data on my MFD and BlueChart Mobile with year-and-a-half old data. Nearly every source showed different depths.
With these varying depths in mind, I assumed that with more than 3 feet of water over datum, we’d have wiggle room even in potentially dicey patches. What I didn’t realize is how quickly this river mouth, exposed to the fetch of Lake Michigan, can silt in.
There were also no ActiveCaptain reviews with any guidance about depth or approach (I left one afterwards). I subsequently found out from the city marina manager that they were aware of the hump we hit and that it was still here because the sand is considered contaminated. Contaminated sand requires special disposal methods not covered by the city’s dredging funds, so they left it. The marina manager did mention that they could possibly put a float on it. I concurred that would be wise.
Not long after our incident, I shared my experience with Power & Motoryacht’s Senior Electronics Editor Ben Ellison. He tactfully sent me a clipping of the NOAA RNC chart that shows a clearly defined 4-foot area on the chart. It was time to admit I’d seen similar small numbers on Aqua Map but that while quickly scanning the charts I didn’t figure out what they meant. He reminded me that the benefit of raster charts is that a cartographer has made decisions about what should be displayed in each location. This avoids confusing areas that are sometimes the result of software rendering vector chart data.
That day in Manistique I failed to understand how data was displayed in Aqua Map, but because I’d been there before and thought I knew the depth, my brain just discarded the discordant information without even thinking about it. That complacency extended to not calling the marina beforehand to ask if any instruction would be needed for our approach. In this case, I don’t think that phone call would have been productive, but I’m amazed at what I’ve learned at times by just asking.
I’m not 100 percent certain of what we should have done differently, which is concerning. I’m contemplating the installation of forward-looking sonar. I know we won’t get enough range to be able to cruise with it and attempt to avoid problems, but for approaching known shallows it will give us another tool in the arsenal.
I pride myself on running the boat safely and in a considered manner. I failed to make use of all the tools available to me that day and it bit me. But it also reinstituted a healthy resolve to be more meticulous in reviewing the available data. The good news is the only thing that seems to be damaged is my ego.