Bass boat outboard motors should be fail-safe impact tested

Most major outboard manufacturers conduct a log strike test on new outboard models to prove durability.

Manufacturers either test them on the water by actually running over a log of a given type, diameter, and length, or on a test stand they think simulates on water testing.

These impact tests are typically conducted at a speed based on the horsepower of the outboard. Testing tends to start at a lower speed, then build up to the maximum speed selected for the test. Some manufacturers conduct more that one test at the maximum speed tested.

In general, the outboard must still be operational (run) after the test, the cowl is to remain attached, and the outboard is to be capable of at least limping back to shore (capable of some steering and of some trim). The outboard is to have no major oil leaks. At least one manufacturer say no parts of the outboard are to enter the vessel during the testing.

Focusing our discussion on larger outboards, especially those targeting tournament bass boat applications, most manufacturers impact test them at maximum speeds of the nature of 30 to 40 mph.

The problem is tournament bass boats tend to run 70 mph or faster.

While it is wonderful the outboards can impact floating logs at those speeds and survive, it is even more important the same outboards can impact stumps and the operator survives.

The striking of very heavy or fixed submerged objects (dredge pipes, large logs, floating trees, piers, pilings, stumps) can result in at least some outboard motors breaking off at speeds below the maximum speed the outboard is log strike tested at. For example a specific outboard may be log strike tested at 35 mph, but can break off at 30 mph when striking a stump. If they will not break of at slower speeds, they most certainly can break off at speeds in excess of the log strike test speed when striking heavy or fixed submerged objects.

Some outboards that break off will enter the boat, typically with the engine still running and the propeller turning at a very high RPM.

It is quite obvious that outboards should be fail-safe tested to at least some speed higher than the current log strike test speeds. At this higher speed the outboard motor would pass the fail-safe test by not entering the passenger area of the vessel. The outboard might break off, might not be able to be restarted, might no longer have trim or steering capability, and its cowl my fly off. The test is merely to determine if the outboard enters the passenger area of the boat when striking fixed objects at a given speed. While cowls entering the boat can be dangerous, they are certainly less dangerous than a rotating propeller. Whether or not the cowl can enter the vessel and still pass a fail-safe test could be a point of discussion. There could theoretically be two fail-safe test speeds, one below which nothing enters the passenger area, the other below which small parts or the cowl may enter the passenger area.

Optimally the vessel would be fail-safe tested at its maximum speed. Some may argue it is not practical to design outboards to survive impacts at those speeds without sometimes breaking off and flipping into the boat.

Basic approaches to designing fail-safe large outboard motors in terms of the log strike system include (1) increasing capacity of the log strike system so it can handle faster and/or harder strikes without breaking off (includes the transom and jack plates), (2) designing the skeg and/or lower leg to break away during severe impacts, (3) using a tether to restrain the outboard and prevent it from entering the passenger area of the boat if it does break off, (4) limiting maximum speed of the vessel.

For more information on the design approach used, please see on our post titled, Design Chart for Preventing Outboard Motors From Entering Boats.

While we may all disagree on what speed the outboard should be fail-safe tested at, and whether or not the cowl should be allowed to enter the vessel, I would hope we can all agree large outboards designed for use on bass boats should be fail-safe tested at a speed higher than current log strike test speeds (30 to 40 mph).

The chart shows how those operating fail-safe outboard motors would not be exposed to risk at each step of the chart like they currently are. Currently bass tournament anglers are hoping they don’t hit something, hoping they did not hit it fast enough the outboard will break off, and hoping that if it does break off, it wont enter the boat. That is if they are among those that are actually aware of the hazard at all.

Fail-safe Outboard Design Chart: outboard broke off flipped into boat

Fail-safe Outboard Design Chart: outboard broke off flipped into boat

Click on the chart above to view a larger pdf version of the chart.

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