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Striking A Submerged Object Claims Analysis

Our BoatUS Marine Insurance analysis of claims from boaters who've hit submerged objects offers good lessons for all of us.

Propeller and rudder damage

Striking a submerged object can damage propellers as well as rudders and any other underwater gear. (Photo: Ron Alcus)

It seems like if there's something lurking in the water — a log, sunken boat, engine block, crab pots — chances are a boater will hit it. That's the finding of an analysis of the BoatUS Marine Insurance claim files that looked at five years of striking a submerged object (SSO) claims.


If you have a depth sounder, know whether it's reading from the transducer to the bottom or from the boat's lowest point to the bottom. The difference could be up to a couple of feet depending on where the transducer is located.

Fractured hull damage

Struts are no match for a rock ledge, which can fracture a hull, causing the boat to take on water. (Photo: Ron Alcus)

Several years ago, when we analyzed the top 10 claims, SSO came in at No. 2 in frequency. There's a lot of junk in the water. For our purposes, SSO means hitting something that is floating or lurks underwater. Grounding, on the other hand (something we'll discuss in a future issue), is striking the bottom and getting stuck there.

Propeller shaft and stuffing box

Prop shafts and stuffing boxes are often victims of submerged objects. (Photo: Ron Alcus)

The good news is that if you know how, when, and where these SSO claims happen, you have a better chance of staying out of the statistics. In the article "What To Do If Your Vessel Strikes A Submerged Object", longtime marine surveyor and accident investigator Ron Alcus goes into detail about the kind of damage submerged objects can cause. He'll also give you tips for how to avoid them and what to do if they're unavoidable.

Damaged props

A rock ledge is not a friendly place for props. Keep a close eye on your depth sounder and charts. Make sure you know where your transducer is measuring from. (Photo: Ron Alcus)

Our analysis looked at boat length and type, propulsion type, speed, geography, and more. If we had to paint a picture of the most frequent SSO claim, it would be this: A fiberglass bass boat in Texas, sometime in July. One surprise from the study: The most experienced boat owners had slightly more claims than those with only a couple of years' experience. Seems like everyone can learn a little from this.

Frequency by years of experience chart

Lesson 1: Size Matters

Bigger boats tend to strike things in the water more frequently, as seen in the chart "Frequency By Boat Length" below. Once boats get over about 18 feet, these claims double in frequency. Little boats, of course, draw less and have less dangling in the water. Large boats will typically have two or more outboards or sterndrives, and the hulls tend to extend farther below the water.

Frequency by boat length chart

What to do: Be aware that your big boat draws a lot more than that little jon boat you're following. Keep a sharp eye for floating branches; they might be connected to a big tree trunk.

Lesson 2: Boat Type

Bass boats are the third most prevalent type of boat in the study. While their drafts are typically less than a foot, they hit submerged objects twice as often as other types of boats. That's because bass boats are typically used on inland lakes with lots of stumps, sandbars, and often extremely variable water levels. And they go fast, making it harder to avoid things in and under the water.

Frequency by boat type chart

What to do: The faster you go, the harder it is to avoid something in the water — and the harder you'll hit it. Especially after heavy rains, slow down so you can see what's in the water. Fishermen are often in a hurry to get to the best fishing areas and leave early, sometimes before daylight, when floating junk is invisible. Pay attention to the water when you first launch. If there's debris near the ramp, there's likely plenty more on the water. If the sun is in your eyes, slow down.

Lesson 3: Propulsion Type

Sterndrives are damaged more frequently than other types, with inboards a close second and outboards third. Unlike, say, waterjet drives in PWCs, these spinning propellers are 2 to 3 feet below the water ready to snag a wayward stump or rock.

Frequency by propulsion type chart

What to do: Be aware that expensive aluminum appendage behind you may extend down quite a bit farther than your hull.

Lesson 4: Time Of Year

July is the most common month for SSO claims, and not just in the SSO hotspot of Texas. While that's not earthshaking news given that the whole country is on the water then, it may also point to such things as lower water levels in summer and more frequent heavy rains with extra debris in rivers and bays.

Frequency by loss month chart

What to do: You're probably using your boat more, so you're more at risk of hitting something in the water. Take a little extra time to check water levels and consider what recent storms may have done to the water. In sunny areas, polarized sunglasses are a critical tool in helping you better see floating objects.

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Charles Fort

Contributing Editor, BoatUS Magazine

Charles Fort is BoatUS Magazine's West Coast Editor. He often writes local news items for BoatUS Magazine's Waypoints column and contributes to Reports, in-depth tech features in every issue written to help readers avoid accidental damage to their boats. He is a member of the National Association of Marine Surveyors, he's on ABYC tech committees, and has a 100-ton U.S. Coast Guard license. He lives in California.