Many in the recreational boating public are not aware of a serious type of accident that is neither rare nor without serious consequences. In these incidents the large outboard engine on a fast-moving boat strikes an underwater or floating object, breaks off the boat and flips into the passenger area while still running. The potential for disaster is obvious.
This accident has been occurring for several years. An on-line record of such accidents generated by the U.S. Coast Guard, the Boating Accident Report Database (BARD), provides details and shows incidents back to 2000. These accidents have continued into 2018 and in several U.S. states. A variety of injuries plus fatalities have occurred. Typically the boats involved are relatively large and are capable of high speeds. Outboard engines involved in the BARD are rated from 150 to 225 horsepower. The recorded incidents are not confined to any one boat or engine manufacturer but involve many manufacturers of both products.
These accidents most often take place on freshwater lakes and rivers that have shallow areas where trees and stumps are just below the waterline and floating wooden obstructions exist. Boats and large engines are often used at high speeds for activities such as bass fishing tournaments. In this application fishermen compete for cash awards in timed periods. The fishing is often done in shallow water areas where many underwater and floating obstructions exist. When fishing one such area the boat moves slowly using only an electric trolling motor. If that area is not productive the fisherman naturally desires to get to a new area quickly using his outboard. Often he makes the move at top speed so as to best use the limited time available in the tournament. The speed may be 50 to 70 miles per hour or more. Traveling at such speeds the boat operator may not see or be able to avoid barely submerged or floating objects before running over them. The results may be minor or catastrophic. This will depend on several variables including the boat's speed, the design of the boat and engine plus possible material defects present, the specific moveable position ("trim") of the outboard engine, the size and weight of the object that is struck and the angle of impact.
What is being done to avoid flipping accidents? Most engine manufacturers have provided warnings of this potential danger via written warnings in their engine operation manual. These include requirements to limit speed. The speed restrictions are often unrealistic relative to actual service use. Also it is uncertain whether boat owners read the literature they receive and if so do they abide by its warnings. Generally engine manufacturers have some type of hydraulic shock-absorbing piston, cylinder and valve protective system on their engines. This is intended to allow the engine to move a small distance on impact and thus absorb some of the energy that might otherwise cause failure of the engine's attachment to the boat's transom. This can be effective but the systems are limited by the energy they can absorb which relates directly to boat speed.
There are also some independently produced commercial products that have been patented and are available. One type of product wraps around the outboard engine and is attached to the transom of the boat. The idea is to stop engine rotation (flipping) due to impact. These products can be effective under certain conditions. However, it is unclear what type and conditions of prototype testing have been completed. For example, it may be that after impact at high speeds the device does not fail but the impact energy simply transfers to the boat's transom. Without design changes to boats to increase the strength of their transom areas the transferred energy could fracture or completly break off a normal transom and produce either minor damage or complete flooding in normal boats. Reinforcing a boat's transom through redesign could well be impractical based on the added cost, weight and other considerations.
Many other potentially useful means to address this overall problem have been proposed. Some engine manufactures have done the difficult development work and appear to be moving towards successful implementation of safe remedies. Other manufacturers seem to have paid much less attention to the problem. Boat manufacturers don't appear to have had a part of any corrective efforts. Solving the engine flipping problem presents several difficult engineering issues. In addition redesign will likely add cost to the revised products and may present potential difficulties in selling them at the desired profit levels. However, the boat and, especially, engine manufacturers face foreseeable legal liabilities until they develop effective solutions. More importantly the users of these products will suffer much more than monetary losses without more attention by all manufacturers.
Gerald O. Davis, PE, President and co-owner of DM&ME, has over 40 years experience in Materials Engineering and Business. Mr. Davis is a Forensic Expert in Materials Usage, Corrosion, Metallurgy, Mechanical Failure, & Root-Cause Failure Analysis. His recent background includes work as a corrosion researcher, senior engineer, and program manager for Battelle Memorial Institute, DNV, Inc., Henkels & McCoy, Inc., respectively and, since 2004, as president of DM&ME.
©Copyright - All Rights Reserved
DO NOT REPRODUCE WITHOUT WRITTEN PERMISSION BY AUTHOR.