Nowadays, it’s the unusual boat that does not have charts of some type and an electronic depth sounder. But, there are other devices and even some clues that can help you estimate whether an area has enough depth for your boat. These devices and clues can complement and augment, even substitute when necessary, charts and sounders.
One of these devices, inexpensive and portable, too, is a lead line & a hunk of weight, lead, or some other metal, which is attached to a line marked at easy-to-remember intervals.
We find lead lines so useful that we carry two of them, both marked at 5-foot intervals which we find adequate for taking soundings. One of the lead lines, a forty-footer, is handily stored just inside our pilothouse, while the other, residing in our dinghy, is its rode which, being appropriately marked, can also be called upon to take soundings.
There are also small, hand-held, flashlight-like devices for taking soundings. Even though these devices require batteries and are pricier than a lead line, many folks find them useful.
There are also clues, many visual, which can provide information as to water depth or the lack thereof:
- Changes in current, water color, or the surface appearance of the water may indicate a change in depth.
- In turns and bends the deeper water generally follows the outside third of the channel, but in ‘S’ curves, the deeper water is often in the middle third of the channel.
- The presence of wading birds, poles of some sort, vegetation, or snags suggests shallow water¾when present, crucial clues when the shallows extend a considerable distance from the shoreline.
- Crab traps are usually set in depths of 10 feet or more; though in areas where shoal water predominates, this depth may be less.
- Water lilies seldom grow in depths greater than 6 feet, their edges often suggesting depths of 5 feet or less.
- Based on their draft, the presence of vessels can provide clues to the minimum depth in the immediate area: Small outboard-powered barges and push boats- 2 feet; large tugs- 10 feet; large barges empty- 2 feet; large barges full- 10 feet.
- Do not assume that the presence of another boat, especially a sailboat, suggests that the water is deep enough for your boat; even good-sized sail and powerboats might have relatively shoal drafts.
- It is possible to estimate where the edge of a shallow area begins by noting on a chart how many multiples of an adjacent structure’s length, such as a dock or jetty, would be required to reach this edge from the shoreline. Then using the actual adjacent structure as a measuring tool, imagine this ‘number of lengths’ as a guide to determine approximately where the edge of the shallow area begins.
- Be leery of using an aid to navigation for determining water depth; even adjacent depths revealed on a chart may not accurately show the depth where the ATON sits.
If you need to confirm depths, take soundings as your boat approaches the area of concern… slowly, remaining alert and ready to stop quickly; or, using your dinghy with a lead line or a portable electronic sounder, sound the area in question.
These rules-of-thumb are only some of the many tools available to a mariner; consider all available information, then apply it judiciously.
Rudy and Jill Sechez have been living aboard and cruising since 1997, first aboard a 37 foot, wood, cutter that they built, now aboard BRINEY BUG, a 34’, sail-assisted, wood trawler that they designed, built, then launched in 2005. Authors of ANCHORING-A Ground Tackler’s Apprentice. For other helpful information, go to trawlertrainingabc.com, click on pages.
